Alesis POWER AMPLIFIER RA150 User Manual

REFERENCE SERIES  
POWER AMPLIFIERS  
REFERENCE MANUAL  
©2000 Alesis Corporation  
CONTENTS  
Introduction......................................................2  
How to Use This Manual...........................2  
Connectors..............................................18  
Speaker Cables........................................18  
Connecting Speaker Cables to Binding  
IMPORTANT SAFETY INSTRUCTIONS.... 3  
Posts.......................................................19  
The Importance of Speaker Polarity..........20  
Output Connections for Bridged  
Instructions de Sécurité Importantes (French)......4  
Beim Benutzen dieses Produktes beachten Sie  
bitte die folgenden Sicherheitshinweise:  
(German) ..........................................................5  
CE Declaration of Conformity.............................6  
Operation ...............................................20  
OPERATION......................................21  
Front Panel Controls.........................................21  
Volume Controls.....................................21  
On-Off Switch.........................................21  
Mute Switch............................................21  
Protect/Clip Indicators............................22  
Meters (RA300 and RA500 only)...............22  
Back Panel Controls..........................................22  
AC Voltage Switch ..................................22  
Stereo/Bridged Mono Switch...................22  
Checking For Proper Polarity............................22  
Using the RA150 as a Headphone Amplifier.......23  
Choosing the Correct Speakers..........................23  
About Ground Loops........................................24  
System Setup and Testing .................................25  
Setting the Gain Properly.........................25  
Output Relays/Thermal Cycling ..............26  
ABOUT THE RA150/300/500............. 7  
Principal Features..............................................7  
The Chassis..............................................7  
Inputs and Outputs...................................7  
Amplifier topology ...................................7  
Protection Circuitry ..................................7  
About this manual.............................................8  
CONNECTIONS ...................................9  
Unpacking and Inspection..................................9  
Power Considerations........................................9  
The AC Cord and Grounding ....................9  
120 Volt/230 Volt Operation.................... 10  
Fuse....................................................... 10  
Electrical Service to the RA150/300/500... 10  
Operating Environment ................................... 11  
Temperature Considerations in Rack  
TROUBLESHOOTING.......................... 27  
Troubleshooting Index......................................27  
Care and Maintenance......................................28  
Cleaning.................................................28  
Refer All Servicing to Alesis.....................28  
Obtaining Repair Service .........................29  
Customers outside the USA and  
Mounting............................................... 11  
Other Rack Mounting Tips ...................... 11  
Mounting on a Shelf or in a Non-Rack  
Enclosure ............................................... 12  
Avoiding Electromagnetic Interference .... 12  
Inputs ............................................................. 13  
Input Jack Characteristics........................ 13  
Cables.................................................... 15  
Cable Wiring Tips................................... 15  
Balanced or Unbalanced? ........................ 16  
Outputs .......................................................... 18  
What's the Load Impedance?................... 18  
Canada: ..................................................29  
SPECIFICATIONS...............................30  
INDEX.............................................34  
ALESIS LIMITED WARRANTY ............ 35  
RA150/300/500 Reference Manual  
1
Introduction/Safety Instructions  
HOW TO USE THIS MANUAL  
INTRODUCTION  
This manual is divided into the following  
sections describing the various functions and  
applications for the RA series amplifier. Though  
we recommend you take time to read through  
the entire manual once carefully, those having  
general knowledge about amplifiers should use  
the table of contents to look up specific  
functions.  
Thank you for purchasing this Alesis RA150, RA300,  
or RA500™ Reference Series power amplifier. To  
take full advantage of this amplifier’s functions, and  
to enjoy long and trouble-free use, please read this  
user’s manual carefully.  
Chapter 1: Introduction. If you want to start  
using the RA150/300/500 right away, here’s a  
one-page guide to hooking it up and trying it  
out.  
Chapter 2: Connections. This chapter gives  
detailed instructions for connecting the  
RA150/300/500 to a variety of typical sound  
systems.  
Chapter 3: Operation. This section explains  
how to run the Reference Series Amplifier  
properly.  
Chapter 4: Troubleshooting. This chapter  
contains troubleshooting tips and service  
information should problems occur.  
When something important appears in  
the manual, an icon (like the one on  
the left) will appear in the left margin.  
This symbol indicates that this  
information is vital when operating  
the RA150/300/500.  
2
RA150/300/500 Reference Manual  
Introduction/Safety Instructions  
IMPORTANT SAFETY INSTRUCTIONS  
11. Unplug this apparatus during lightning storms  
SAFETY SYMBOLS USED IN THIS PRODUCT  
or when unused for long periods of time.  
This symbol alerts the user that there  
are important operating and maintenance  
instructions in the literature accompanying this  
the polarized or grounding-type plug. A  
unit.  
12. Do not defeat the safety purpose of  
polarized plug has two blades with one  
wider than the other. A grounding-type  
plug has two blades and a third  
This symbol warns the user of  
uninsulated voltage within the unit that can cause  
dangerous electric shocks.  
grounding prong. The wide blade or the  
third prong are provided for your safety.  
When the provided plug does not fit into  
your outlet, consult an electrician for  
replacement of the obsolete outlet.  
This symbol warns the user that output  
connectors contain voltages that can cause  
dangerous electrical shock.  
13. Use only with a cart, stand, bracket, or table  
designed for use with professional audio or  
music equipment. In any installation,  
make sure that injury or damage will not  
result from cables pulling on the apparatus  
and its mounting. If a cart is used, use  
caution when moving the cart/apparatus  
combination to avoid injury from tip-over.  
PLEASE FOLLOW THESE PRECAUTIONS  
WHEN USING THIS PRODUCT:  
1. Read these instructions.  
2. Keep these instructions.  
3. Heed all warnings.  
4. Follow all instructions.  
14. Refer all servicing to qualified service  
personnel. Servicing is required when the  
apparatus has been damaged in any way, such  
as when the power-supply cord or plug is  
damaged, liquid has been spilled or objects  
have fallen into the apparatus, the apparatus  
has been exposed to rain or moisture, does not  
operate normally, or has been dropped.  
5. Do not use this apparatus near water.  
6. Clean only with a damp cloth. Do not spray  
any liquid cleaner onto the faceplate, as this  
may damage the front panel controls or cause a  
dangerous condition.  
7. Do not block any of the ventilation openings.  
Install in accordance with the manufacturer's  
instructions.  
15. This unit produces heat when operated  
normally. Operate in a well-ventilated area  
with at least six inches of clearance from  
peripheral equipment.  
8. Do not install near any heat sources such as  
radiators, heat registers, stoves, or other  
apparatus (including amplifiers) that produce  
heat.  
16. This product, in combination with an amplifier  
and headphones or speakers, may be capable of  
producing sound levels that could cause  
permanent hearing loss. Do not operate for a  
long period of time at a high volume level or at  
a level that is uncomfortable. If you experience  
any hearing loss or ringing in the ears, you  
should consult an audiologist.  
9. Protect the power cord from being walked on or  
pinched, particularly at plugs, convenience  
receptacles, and the point where they exit from  
the apparatus.  
10. Use only attachments or accessories specified by  
the manufacturer.  
RA150/300/500 Reference Manual  
3
Introduction/Safety Instructions  
INSTRUCTIONS DE SÉCURITÉ IMPORTANTES (FRENCH)  
8. Ne pas installer à proximilé de sources de chaleur  
SYMBOLES UTILISÉS DANS CE PRODUIT  
comme radiateurs, cuisinière ou autre appareils  
(don’t les amplificateurs) produisant de la  
chaleur.  
Ce symbole alèrte l’utilisateur qu’il  
existe des instructions de fonctionnement et de  
maintenance dans la documentation jointe avec ce  
produit.  
9. Ne pas enlever la prise de terre du cordon  
secteur. Une prise murale avec terre deux  
broches et une troisièrme reliée à la terre. Cette  
dernière est présente pour votre sécurité. Si le  
cordon secteur ne rentre pas dans la prise de  
courant, demandez à un électricien qualifié de  
remplacer la prise.  
Ce symbole avertit l’utilisateur de la  
présence d’une tension non isolée à l’intérieur de  
l’appareil pouvant engendrer des chocs électriques.  
10. Evitez de marcher sur le cordon secteur ou de le  
pincer, en particulier au niveau de la prise, et aux  
endroits où il sor de l’appareil.  
11. N’utilisez que des accessoires spécifiés par le  
constructeur.  
Ce symbole prévient l'utilisateur de la  
présence de tensions sur les raccordements de  
sorties, représentant un risque d'électrocution.  
12. N’utilisez qu’avec un stand, ou table conçus pour  
l’utilisation d’audio professionnel ou instruments  
de musique. Dans toute installation, veillez de ne  
rien endommager à cause de câbles qui tirent sur  
des appareils et leur support.  
VEUILLEZ SUIVRE CES PRÉCAUTIONS LORS  
DE LUTILISATION DE LAPPAREIL:  
13. Débranchez l’appareil lors d’un orage ou lorsqu’il  
n’est pas utilisé pendant longtemps.  
1. Lisez ces instructions.  
2. Gardez ces instructions.  
14. Faites réparer par un personnel qualifié. Une  
réparation est nécessaire lorsque l’appareil a été  
endommagé de quelque sorte que ce soit, par  
exemple losrque le cordon secteur ou la prise  
sont endommagés, si du liquide a coulé ou des  
objets se sont introduits dans l’appareil, si celui-ci  
a été exposé à la pluie ou à l’humidité, ne  
fonctionne pas normalement ou est tombé.  
3. Tenez compte de tous les avertissements.  
4. Suivez toutes les instructions.  
15. Puisque son fonctionement normale génère de la  
chaleur, placez cet appareil au moins 15cm. des  
équipments péripheriques et assurez que  
l’emplacement permet la circulation de l’air.  
5. N’utilisez pas cet allareil à proximité de l’eau.  
6. Ne nettoyez qu’avec un chiffon humide. Il est  
potentiellement dangereux d'utiliser des  
pulvérisateurs ou nettoyants liquides sur cet appareil.  
16. Ce produit, utilisé avec un amplificateur et un  
casque ou des enceintes, est capable de produite  
des niveaux sonores pouvant engendrer une  
perte permanente de l’ouïe. Ne l’utilisez pas  
pendant longtemps à un niveau sonore élevé ou à  
un niveau non confortable. Si vous remarquez  
une perte de l’ouïe ou un bourdonnement dans  
les oreilles, consultez un spécialiste.  
7. Installez selon les recommandations du constructeur.  
4
RA150/300/500 Reference Manual  
Introduction/Safety Instructions  
BEIM BENUTZEN DIESES PRODUKTES BEACHTEN SIE BITTE DIE  
FOLGENDEN SICHERHEITSHINWEISE: (GERMAN)  
1. Lesen Sie die Hinweise.  
2. Halten Sie sich an die Anleitung.  
3. Beachten Sie alle Warnungen.  
4. Beachten Sie alle Hinweise.  
und deshalb nicht mehr normal arbeitet  
oder heruntergefallen ist.  
14. Dieses Gerät produziert auch im  
normalen Betrieb Wärme. Achten Sie  
deshalb auf ausreichende Lüftung mit  
mindestens 15 cm Abstand von anderen  
Geräten.  
5. Bringen Sie das Gerät nie mit Wasser in  
Berührung.  
6. Verwenden Sie zur Reinigung nur ein  
weiches Tuch. Verwenden Sie keine  
flüssigen Reinigungsmittel. Dies kann  
gefährliche Folgen haben.  
15. Dieses Produkt kann in Verbindung mit  
einem Verstärker und Kopfhörern oder  
Lautsprechern  
Lautstärkepegel  
erzeugen, die anhaltende Gehörschäden  
verursachen. Betreiben Sie es nicht über  
längere Zeit mit hoher Lautstärke oder  
einem Pegel, der Ihnen unangenehm is.  
Wenn Sie ein Nachlassen des Gehörs  
oder ein Klingeln in den Ohren  
feststellen, sollten Sie einen Ohrenarzt  
aufsuchen.  
7. Halten Sie sich beim Aufbau des Gerätes an  
die Angaben des Herstellers.  
8. Stellen Sie das Gerät nich in der Nähe von  
Heizkörpern, Heizungsklappen oder  
anderen Wärmequellen (einschließlich  
Verstärkern) auf.  
9. Verlegen Sie das Netzkabel des Gerätes  
niemals so, daß man darüber stolpern kann  
oder daß es gequetscht wird.  
10. Benutzen Sie nur das vom Hersteller  
empfohlene Zubehör.  
11. Verwenden Sie ausschließlich Wagen,  
Ständer, oder Tische, die speziell für  
p r o f e s s i o n e l l e  
A u d i o -  
u n d  
Musikinstrumente geeignet sind. Achten  
Sie immer darauf, daß die jeweiligen Geräte  
sicher installiert sind, um Schäden und  
Verletzungen zu vermeiden. Wenn Sie  
einen Rollwagen benutzen, achten Sie  
darauf, das dieser nicht umkippt, um  
Verletzungen auszuschließen.  
12. Ziehen Sie während eines Gewitters oder  
wenn Sie das Gerät über einen längeren  
Zeitraum nicht benutzen den Netzstecher  
aus der Steckdose.  
13. Die Wartung sollte nur durch qualifiziertes  
Fachpersonal erfolgen. Die Wartung wird  
notwendig, wenn das Gerät beschädigt  
wurde oder aber das Stromkabel oder der  
Stecker, Gegenstände oder Flüssigkeit in  
das Gerät gelangt sind, das Gerät dem  
Regen oder Feuchtigkeit ausgesetzt war  
RA150/300/500 Reference Manual  
5
Introduction/Safety Instructions  
CE DECLARATION OF CONFORMITY  
Manufacturer’s Name:  
Alesis Corporation  
Manufacturer’s Address:  
1633 26th Street  
Santa Monica, CA 90404  
USA  
declares, that the product:  
Product Name:  
RA150/300/500  
Audio amplifier  
Model Type:  
conforms to the following Standards:  
Safety:  
EMC:  
EN60065  
EN55103:1997 Class B  
(all tests were performed with fully- shielded cabling.)  
European Contact:  
Sound Technology  
17 Letchworth Point, Letchworth,  
Hertfordshire, SG6 1ND, England.  
Phone: +44.1462.480000  
Fax: +44.1462.480800  
October 2000  
6
RA150/300/500 Reference Manual  
Chapter 1: Introduction  
CHAPTER 1  
ABOUT THE RA150/300/500  
plugs. A recessed rear panel switch allows easy  
PRINCIPAL FEATURES  
selection of stereo or bridged monaural operating  
modes. AC power entry is via a detachable,  
grounded IEC connector cable.  
Please remember that a power amplifier  
is a high-current, high-power device and  
should be treated with respect and care.  
Even if you are an audio veteran, we  
urge you to read the entire manual to  
make the best use of the RA150/300/500.  
AMPLIFIER TOPOLOGY  
The amplifier sections of the Reference Series utilize  
a direct coupled, fully complementary circuit  
topology. The input stages are a dual differential  
type with active current sources. Output from the  
differential amplifiers are coupled to balanced level  
shifters operating on isolated boost rails for  
improved efficiency and higher performance. These  
stages then drive discrete, high current, triple  
darlington output stages, fully rated for continuous  
4 ohm operation with 2 ohm dynamic stability  
(stereo mode only). The output stages are biased for  
class AB operation. Emphasis is placed on  
maintaining wide bandwidth, linearity and stability  
under all operating conditions. An active DC servo  
circuit is employed to automatically null DC output  
voltage offsets. All models feature bridged mono  
operation.  
Thank you for purchasing an Alesis Reference  
Series power amplifier, one of the most advanced  
and highest value amplifiers available.  
The Alesis models RA150, RA300, and RA500  
provide extremely accurate sonic quality as well as  
measured specifications, but their conservative  
design and careful attention to electronic protection  
means they will continue to operate at top condition  
without special attention, year after year.  
THE CHASSIS  
The Alesis Reference Series amplifiers are  
constructed on rugged, heavy gauge steel chassis.  
All units feature rack mount faceplates. For  
maximum reliability and low-noise operation the  
amplifiers use convection cooling with massive  
extruded aluminum heat-sinks for reliable  
operation under all ambient and load conditions.  
The design of the external chassis protects rear  
panel connectors (except RA 150). All models  
feature detented front panel input level controls,  
and overload/protect indicators. The RA300 and  
RA500 amplifiers incorporate bar graph LED power  
metering.  
PROTECTION CIRCUITRY  
Protection for the amplifier consists of active  
circuitry that continuously monitors the output  
stage for excessive DC offset, short circuits and  
thermal overload. In the event of an output fault,  
the protection circuitry will activate the output relay  
and disconnect the loudspeaker load. This circuitry  
will also mute the amplifier during power on/off  
transitions.  
The power supplies of the amplifiers utilize heavy-  
duty stacked steel EI laminated transformers for  
maximum performance and reliability. High current  
bridge rectifiers, massive secondary capacitors and  
current in-rush limiters are used in all models. All  
models are designed for 120/230-volt operation  
with an external voltage selection switch.  
INPUTS AND OUTPUTS  
The input sections of the amplifiers utilize precision  
electronically-balanced input circuitry for low noise  
balanced input operation. All units have 1/4”  
balanced TRS input connectors. The RA300 and  
RA500 also have XLR connectors. Unbalanced RCA  
(phono) style input connectors are also used. The  
output connectors are industry-standard, heavy-  
duty dual binding posts, which can accept large  
diameter wire or 3/4" (19 mm) spaced dual banana  
All components are of high quality and mechanical  
construction and are optimized for high reliability  
under adverse physical and electrical conditions.  
RA150/300/500 Reference Manual  
7
Introduction: Chapter 1  
Reference Series Features-  
ABOUT THIS MANUAL  
DC coupled, fully complementary discrete  
amplifier topology  
In most respects, the three different amplifiers  
covered by this manual are similar except for their  
power ratings. Operational differences will be  
noted individually.  
Actively biased, dual differential input  
stages  
Wide bandwidth, low distortion design  
Fully protected from all fault conditions  
LED output level metering (RA 300, RA  
500)  
Front panel level controls  
Overload/Fault indicators  
Bridged mono operation  
Balanced 1/4” & RCA single-ended input  
connectors  
XLR input connectors (RA 300, RA 500)  
Heavy-duty, dual binding post output  
connectors  
Relay-controlled turn on/off  
Silent, convection-cooled design  
Heavy-duty steel chassis  
8
RA150/300/500 Reference Manual  
Chapter 2: Connections  
CHAPTER 2  
CONNECTIONS  
UNPACKING AND INSPECTION  
POWER CONSIDERATIONS  
Your Alesis RA150/300/500 was carefully packed  
at the factory, and the shipping carton was designed  
to protect the unit during shipping. Do not discard  
the packing materials; they may be helpful in the  
unlikely event that you need to return your  
RA150/300/500 for servicing, or for transporting  
the amplifier when it is not mounted in a rack or  
other enclosure.  
THE AC CORD AND GROUNDING  
The RA150/300/500’s IEC-spec AC cord (do not  
substitute any other type of AC cord) is designed to  
connect to an outlet that includes three pins, with  
the third, round pin connected to ground ("earth").  
The ground connection is an important safety  
feature designed to keep the chassis of electronic  
devices such as the RA150/300/500 at ground  
potential. Unfortunately, the presence of a ground  
contact in an AC socket does not always indicate  
that an outlet is properly grounded. Use an AC line  
tester to determine this. If the outlet is not  
grounded, consult with a licensed electrician.  
The shipping carton should contain the following  
items:  
RA150/300/500 amplifier  
This instruction manual  
Power cable  
The audio ground (pin 1 of the XLR, the sleeve of  
the 1/4" jack) is not isolated from the chassis.  
Alesis Warranty card  
Tip: You don' t have to use the provided 6-foot long  
AC cord. Many electronic stores carry the  
standard "NEMA-to-CEE" cable in lengths  
from 6 inches to 20 feet. This is better than  
wrapping the cord in a coil if it is too long, or  
using extension cords if it is too short.  
It is important to register your purchase;  
if you have not already filled out your  
warranty card and mailed it back to  
Alesis, please take the time to do so now.  
Carefully unpack the amplifier and inspect it for  
physical damage originating in shipping. If damage  
is discovered and the amplifier was shipped to you,  
immediately contact the transportation carrier and  
make certain that the packing materials are  
preserved for inspection. You as the consignee  
must make any shipping claims; neither your dealer  
nor Alesis can do this for you. If the amplifier was  
not shipped to you, i.e. you picked it up from your  
dealer, contact the dealer as soon as possible for  
assistance.  
DO NOT OPERATE ANY ELECTRICAL  
EQUIPMENT WITH UNGROUNDED  
OUTLETS. PLUGGING THE RA150/300/500  
INTO AN UNGROUNDED OUTLET, OR  
“LIFTING” THE UNIT OFF GROUND WITH A  
THREE-TO-TWO WIRE ADAPTER, CREATES  
A HAZARDOUS CONDITION. ALESIS  
CANNOT BE RESPONSIBLE FOR PROBLEMS  
CAUSED BY USING THE RA150/300/500  
OR ANY ASSOCIATED EQUIPMENT WITH  
IMPROPER AC WIRING.  
RA150/300/500 Reference Manual  
9
Connections: Chapter 2  
120 VOLT/230 VOLT OPERATION  
ELECTRICAL SERVICE TO THE  
RA150/300/500  
The Alesis Reference Series amplifiers feature dual-  
voltage operation. The AC input voltage is selected  
by a recessed switch on the back panel. The tab is  
recessed and a tool (small screw driver, pencil, pen,  
etc.) is required to shift from 120-volt to 230-volt  
operation. Units sold in areas with 120V power (as  
in the United States) should come with the switch  
already set to that position.  
One of the most important considerations for  
proper installation and operation of a power  
amplifier is the capacity of the circuit feeding the  
AC mains voltage to the amplifier. If the line does  
not have sufficient current and voltage capacity, the  
amplifier may not be able to deliver its full rated  
output, both steady state and peak, with the result  
that the sound character can dramatically suffer. In  
short, any amplifier will only sound good when  
connected to adequate AC power.  
Before connecting the amplifier to AC  
power for the first time, make sure that  
this switch is set correctly for the country  
you're using the amp in.  
The maximum audio output rating of each amp (200  
watts bridged for the RA150 to 1000 watts bridged  
for the RA500) does not represent the total AC  
power consumption by the unit. The following  
table shows the power consumption at rated output:  
If you change the voltage when  
travelling, you must also replace the  
power fuse with the proper amperage  
(see page 10) and obtain the proper  
detachable IEC power cable for the  
country.  
Model  
Rated AC  
consumption  
Maximum  
(peak)  
RA150  
RA300  
RA500  
270 watts  
500 watts  
840 watts  
390 watts  
650 watts  
1080 watts  
FUSE  
Note that in typical studio applications the  
average power consumption will be much less.  
When not being driven, current consumption is 30  
watts or less. Under most circumstances, normal  
household or commercial power outlets will be  
adequate. (A standard 15-amp circuit is capable of  
supplying 1800 watts.) However, peak power  
consumption may momentarily be 100 to 200 watts  
higher on transient peaks; if you're connecting a lot  
of other equipment to the same circuit you should  
plan for an extra 20% headroom to avoid blowing a  
circuit breaker. Note that when multiple devices  
are plugged into a single AC outlet, the possibility  
of overheated connections can exist. Long AC  
extension cables may also degrade the supply  
power.  
If the fuse blows, replace with a fuse of the correct  
type only; use of any higher amperage value will  
void the warranty. FUSES ARE FOR YOUR  
PROTECTION—NEVER SUBSTITUTE A FUSE  
OF A HIGHER RATING, OR BYPASS IT.  
All fuses are the "Slo-Blo" type, sized at 5mm  
diameter x 20mm:  
Model  
RA150  
100-120 volt  
T3.15AL250V  
T6.3AL250V  
T10AL250V  
220-240 volt  
T1.6AL250V  
T3.15AL250V  
T5AL250V  
RA300  
RA500  
The fuse will not blow unless the unit is  
overstressed. Before replacing the fuse, correct the  
condition that caused it to blow in the first place.  
Electrical standards have taken enormous strides  
toward increased safety over the past few decades  
thanks to circuit breakers, ground fault interrupters,  
and improved wiring and insulation materials.  
Unfortunately, some clubs are situated in older  
buildings whose wiring may not meet current safety  
standards, or have wiring that has deteriorated over  
the years. Make sure the circuit supplying power to  
the RA150/300/500 can supply enough current to  
run it properly. If the circuit has to supply other  
high-powered consumption units such as  
10  
RA150/300/500 Reference Manual  
Chapter 2: Connections  
refrigerators, coffee pots, toasters, air conditioning,  
or stage lighting, plug the RA150/300/500 into a  
different circuit with a lesser load.  
You may wish to leave an empty rack space  
above or below the amp to promote good air  
flow. If multiple amplifiers are mounted in the  
same rack, there should be at least one rack  
space left between them; solid blank panels may  
be used to fill the spaces, but perforated grilles  
used as fillers will help exhaust the hot air from  
within the rack.  
OPERATING ENVIRONMENT  
TEMPERATURE CONSIDERATIONS  
IN RACK MOUNTING  
OTHER RACK MOUNTING TIPS  
The RA150/300/500 can be mounted in an  
equipment rack (taking up 2 rack spaces or 3 spaces  
for the RA500), placed on a shelf, tucked away in a  
vocal booth, etc. When you install it, keep in mind  
that heat is the major enemy of electronic equipment.  
Fortunately, the RA150/300/500’s protection  
circuitry will not allow the unit to run hot enough to  
damage any of the circuitry. However, sustained  
high-temperature operation sufficient to cause  
limiting will adversely affect the sound quality, and  
eventually the amplifier will shut itself off for as  
long as the excessive temperature conditions exists.  
Due to the RA150/300/500’s weight (from 15 to  
28.5 lbs.), it’s a good idea to mount it in the  
bottom of the rack frame. Support of the back  
of the unit may be necessary for portable or  
road use.  
Alesis Reference amplifiers are well shielded;  
however, mounting low-level electronics some  
distance away from power amplifiers is  
common practice to reduce the possibility of  
electromagnetic interference into the low level  
units, which may sometimes be unusually  
susceptible to picking up such radiation.  
The RA150/300/500 has extensive heat sinking to  
minimize overheating, as well as eliminate the need  
for a ventilating fan. The latter feature is crucial for  
the cramped control rooms typically found in  
smaller studios; any fan noise would interfere with  
the mixing or monitoring process.  
When wiring a rack, it is good installation practice to  
route all AC wiring along one side of the rack  
and all audio wiring along the other side to avoid  
coupling AC-borne interference into the audio.  
But the RA150/300/500 must be installed so that  
its heat sinking is allowed to do its job.  
Please observe the following:  
The RA150/300/500 is designed to perform  
properly over a range of ambient temperatures  
from 0° C to +50° C (32° F to 122° F), in up to  
80% non-condensing humidity. These are not  
absolute limits, but Alesis cannot guarantee that  
the RA150/300/500 will meet its published  
specs if operated outside of these ranges. If  
necessary, use a fan to blow air over the  
RA150/300/500 and promote cooler operation.  
Prevent the side heat sink fins from becoming  
obstructed. There should be enough airspace  
around the amplifier for it to “breathe.”  
Always allow adequate ventilation behind the  
RA150/300/500. Do not seal any enclosure that  
holds the RA150/300/500.  
Never throw a coat or other flexible fabric or  
covering over the top of the amp when it’s in  
use.  
RA150/300/500 Reference Manual  
11  
Connections: Chapter 2  
MOUNTING ON A SHELF OR IN A  
NON-RACK ENCLOSURE  
AVOIDING ELECTROMAGNETIC  
INTERFERENCE  
To mount the amplifier on a shelf or other flat  
surface, Alesis recommends using the enclosed  
stick-on feet to avoid scratching the shelf’s surface  
with the amplifier bottom. To properly mount the  
stick-on feet:  
Because the RA150/300/500 contains a large power  
transformer, we recommend that you do not:  
Place the RA150/300/500 next to an unshielded  
video monitor, as the magnetic fields may  
distort the image.  
1
Place the amplifier upside down on a clean  
cloth or piece of cardboard so the amp top does  
not scratch your work surface.  
Place tapes, disks, or other magnetic media  
close to the RA150/300/500.  
2
Clean the bottom of the amp where you plan to  
stick the feet. Isopropyl alcohol is recommended  
as a cleaning agent. This step insures that no  
small amounts of oil or other substances will  
inhibit proper adhesion of the feet.  
Play guitar, bass, or any other instrument with  
magnetic pickups near the RA150/300/500. No  
damage will occur but AC fields may enter the  
pickups, causing hum.  
3
When the surface has dried, attach the feet.  
Please observe the comments on thermal  
considerations given under “Temperature  
Considerations in Rack Mounting” no matter where  
or how the amp is mounted.  
12  
RA150/300/500 Reference Manual  
Chapter 2: Connections  
INPUTS  
INPUT JACK CHARACTERISTICS  
The RA150/300/500 include two balanced, 1/4"  
TRS (tip-ring-sleeve, 3-conductor) phone jack  
inputs, and unbalanced RCA/phono inputs. The  
RA300 and RA500 feature combination XLR input  
jacks as well. The inputs are wired according to IEC  
standards, as shown in the table below.  
These are compatible with the low-impedance,  
unbalanced or balanced, line-level outputs typically  
emanating from equipment such as mixers,  
synthesizers, samplers, direct boxes, crossovers, etc.  
Electric guitars, microphones, and other low-  
level/high-impedance output devices require a  
preamp.  
Connection  
Audio Ground  
High (+)  
XLR  
Pin 1  
Pin 2  
Pin 3  
Phone Jack  
Sleeve  
Tip  
RCA/phono jack  
Shell  
Pin  
--  
Low (–)  
Ring  
RA150 Back Panel  
RA300 Back Panel  
RA500 Back Panel  
RA150/300/500 Reference Manual  
13  
Connections: Chapter 2  
To use an unbalanced source with an  
Alesis amplifier:  
Warning: Be sure that the AC power is off prior  
to connecting or disconnecting any signal  
wiring.  
Connect the High (+) signal wire as shown in Table  
1 and connect the shield wire to both the Low (–)  
and Audio Ground input connections. See Figures  
4 and 6. If a two-wire (tip and sleeve only) phone  
plug is used for an unbalanced input, the sleeve of  
the plug will automatically connect the Low and  
Audio Ground connections together inside the  
amplifier.  
The input circuits of the Alesis amplifiers are  
electronically balanced. They may be fed from  
either symmetrical (“balanced”) or unbalanced  
sources. On the RA300 and RA 500, there are two  
combination XLR/1/4” (6.3 mm) jacks provided,  
one for each channel.  
Long input cable runs, particularly in areas with  
high electrical interference, should be done with  
symmetrical (“balanced”) configuration, if possible,  
to lessen the possibility of interference being picked  
up by the cables.  
Only one input jack of a channel should be used at a  
time: don't use the 1/4"/XLR input jack and phono  
input jack simultaneously. Do not plug two  
different sources into the same amplifier channel.  
While this will not harm the amplifier, the sources  
may interfere with each other causing distortion.  
Figure 3. Balanced wiring of an XLR input  
connector.  
Figure 4. Unbalanced wiring of an XLR input  
connector.  
Figure 5. Balanced wiring of a 1/4” (6.3 mm) three-  
wire phone plug.  
Figure 6. Unbalanced wiring of a 1/4” (6.3 mm)  
three-wire phone plug  
All input wiring should be done with shielded  
cable.  
14  
RA150/300/500 Reference Manual  
Chapter 2: Connections  
CABLES  
CABLE WIRING TIPS  
Use only high quality cables when interfacing  
equipment with the RA150/300/500. These should  
be good quality shielded cables with a stranded (not  
solid) internal conductor. Although quality cables  
cost more, they do make a difference. Route cables  
to the RA150/300/500 correctly by observing the  
following precautions.  
If you decide to wire your own cables, Alesis  
recommends that you use three-conductor shielded  
cable (even in an installation that uses unbalanced  
wiring) with either a braided or foil-type shield.  
Connect one conductor to the phone jack tip  
connection to carry the hot signal, and the shield  
connection to the sleeve. The other conductor  
should also connect to the shield since it is not good  
practice to depend on the shield wire itself to  
complete the signal connection. This is because the  
shield wires are more subject to breakage, especially  
in portable installations, than the more protected  
internal insulated wires. By using a second “safety”  
conductor for ground, the worst that could happen  
with a broken shield would be a rise in noise or  
hum due to the lack of shielding. If the ground  
connection were completely lost, there would be  
either extremely loud hum or major loss of audio.  
Do not bundle audio cables with AC power  
cords.  
Avoid running audio cables near sources of  
electromagnetic interference such as  
transformers, monitors, computers, etc.  
Do not place cables where they can be stepped  
on. Although stepping on a cable may not cause  
immediate damage, it can compress the  
insulation between the center conductor and  
shield (thus degrading performance) or reduce  
the cable’s reliability.  
Avoid twisting the cable or having it make  
sharp, right angle turns.  
Never unplug a cable by pulling on the wire  
itself. Always unplug by firmly grasping the  
body of the plug and pulling directly outward.  
If you experience difficulty in removing the  
plug, sometimes a slight rotating motion while  
unplugging will solve the problem.  
Keep the cable contacts clean at all time.  
Oxidation may lead to intermittent contacts,  
degraded sound quality, or even distortion. DO  
NOT USE AN ABRASIVE TO CLEAN A DIRTY  
PLUG. This may remove some of the plug’s  
conductive plating. Instead, spray contact  
cleaner on a clean, lint-free cloth and vigorously  
rub the plug until the oxidation is removed.  
Although Alesis does not endorse any specific  
product, chemicals such as Tweek and  
Cramolin, when applied to electrical connectors,  
are claimed to improve the electrical contact  
between connectors.  
NEVER PLUG OR UNPLUG INPUT CABLES  
UNLESS THE RA150/300/500 IS TURNED  
OFF, UNPLUGGED FROM THE AC LINE, OR  
HAS THE CHANNEL 1 AND CHANNEL 2  
LEVEL CONTROLS TURNED TO MINIMUM  
LEVEL. Failure to observe these precautions  
may result in damage to your speakers if the  
cable being plugged into the RA150/300/500 is  
carrying a signal, and the level is turned up.  
RA150/300/500 Reference Manual  
15  
Connections: Chapter 2  
BALANCED OR UNBALANCED?  
If you have the RA150, which doesn' t have an XLR  
input, you may use an XLR-F to TRS-M cable  
or adapter. The 1/4" input jack of the RA150 is  
balanced. (See Figure 5 on page 17.)  
With long cable runs (e.g., over 6 meters/20 feet) in  
noisy electrical environments, the cable itself can act  
as an “antenna” and pick up RF fields, AC hum, or  
other types of interference. To avoid these  
problems, many professional studios and live sound  
companies use balanced line connections. The  
average application will probably not require  
balanced lines, but using balanced connectors  
between the mixer and the RA150/300/500 means  
one less possibility for ground loops and hum  
elsewhere in the system.  
To connect an unbalanced source to  
the amplifier input:  
Unbalanced cable  
Simply use a standard, shielded 1/4" patch cord.  
Or, if the source has an RCA/phono output, use a  
shielded phono-to-phono cable.  
Balanced lines carry a pair of signals, each out of  
phase with respect to the other but otherwise  
identical. To be converted back into a single,  
unbalanced line, both balanced lines feed a  
differential amplifier input or transformer that  
responds to the difference in levels between signals.  
Thus, the out-of-phase signals are recombined into  
an unbalanced signal, but interference induced into  
the cable will not be out of phase. Since there is no  
difference between these signals, the differential  
amplifier or transformer will reject the interference  
to a great degree. This tendency to ignore  
interference is called Common Mode Rejection.  
Unbalanced-to-balanced cable with  
telescoping shield  
In some installations, you may be able to eliminate a  
ground loop even though the source is unbalanced  
by wiring a cable or adapter that has the shield  
connected at only the unbalanced end, using the  
inner conductor wires to carry the "hot" signal to  
pin  
2
and the ground to pin  
3
of the  
RA150/300/500. This may keep any ground  
potential difference between the source and the  
amplifier out of the signal path. The following  
diagram shows an adapter that assumes pin 2 of the  
XLR connector is “hot”; note that the shield of the  
phone jack is NOT connected to pin 1 (the ground of  
the amplifier), but is left floating (disconnected).  
To connect a balanced line output to  
feed the RA150/300/500:  
You have two options:  
Male XLR  
Connector  
1/4 "  
phone  
jack  
TRS-to-TRS cable  
Most modern mixing consoles, such as the Alesis  
Studio 32, feature balanced outputs on 1/4" TRS  
jacks. This is the same balancing connector used by  
the RA150/300/500. Get a 3-conductor cable with a  
1/4" male TRS connector at each end.  
1 (float)  
2 (hot)  
3 (cold)  
XLR-to-XLR cable  
If you have an RA150 without an XLR input, then  
make a 1/4" mono to 1/4" TRS adapter. Wire the  
"hot" of the input signal to the tip, the  
shield/ground to the ring, and leave the sleeve  
disconnected at the RA150.  
A slightly more expensive balanced connector is the  
XLR type, most commonly sold as a "microphone  
cable". The main advantage of this is that the  
connector locks in place, making it more resistant to  
accidental disconnection. If your mixing console  
has XLR outputs, and you have the RA300 or RA500  
amplifier, you may connect it with an XLR female to  
XLR male cable. (The mixer will have an XLR male  
jack, the amp has an XLR female jack.)  
16  
RA150/300/500 Reference Manual  
Chapter 2: Connections  
Isolation transformer or direct box  
To feed the same source to several  
different amplifiers:  
If your mixer or other sound source doesn't have a  
balanced output, you may turn it into a balanced  
signal with an external device, either active  
(electronic, powered) or passive (a transformer).  
These commonly available audio accessories have a  
balanced line output, usually in the form of an XLR  
connector, and an unbalanced line input, usually in  
the form of a 1/4" phone jack.  
The input impedance of the Alesis amplifiers is 20  
kin balanced and 10 kin unbalanced  
configuration. Thus, the inputs of several amplifiers  
may be connected in parallel if desired. The  
maximum number of amplifier channels will  
depend on the minimum output load impedance of  
the device feeding the amplifiers. For example, if  
the minimum output load impedance of the source  
device is 600 , up to 30 amplifier channels may be  
connected to it in parallel without overloading the  
source device’s output.  
A line transformer can also convert balanced  
signals to unbalanced signals. Advantage of a  
transformer: High signal carrying capacity, no power  
required, generates no hiss. Disadvantages:  
Inexpensive transformers may color the sound due  
to frequency response irregularities and can pick up  
hum due to inductive nature of transformers. Very  
high-fidelity models are expensive.  
However, use of a distribution amplifier is  
recommended in large systems.  
To use the amplifier in Bridged Mono  
mode:  
Active direct boxes use an active electronic circuit  
to drive a balanced line, but does not work in the  
other direction. Advantages: Good frequency  
response specs, no inherent hum pickup, less  
expensive than transformers. D isadvan t ages:  
Requires power, generates some noise.  
Connect the input signal to Channel A/Left only.  
Move the recessed slide switch under the right  
input connectors to the Bridged Mono position. Do  
not connect any signal to the Channel B/Right  
input jack. Leave the input level control for  
Channel B down. See page 20 for output wiring in  
Bridged Mono configuration.  
RA150/300/500 Reference Manual  
17  
Connections: Chapter 2  
SPEAKER CABLES  
OUTPUTS  
The cables you use between the RA150/300/500  
and its speakers are very important. Speaker cables  
must deliver large amounts of peak current to a  
speaker. To complicate matters further, a speaker  
represents an inductive load, and is more difficult to  
drive than a purely resistive load. Speakers are also  
very low impedance devices. Any resistance  
between the amp output and speakers will degrade  
the damping factor, efficiency and ultimately, the  
sound quality.  
Warning: Be sure that the AC power is off prior  
to connecting or disconnecting any signal  
wiring.  
WHAT'S THE LOAD IMPEDANCE?  
Alesis amplifiers can reliably drive 4 loads in  
Stereo mode and 8 loads in Bridged Mono mode.  
However, the impedance of a loudspeaker varies  
with frequency, and its nominal rated impedance is  
not necessarily its minimum impedance. Some  
loudspeakers carry both nominal and minimum  
impedance specifications, and some are supplied  
with impedance curves. When connecting multiple  
loudspeakers or systems to any amplifier, care  
should be taken that the actual load impedance does  
not drop below the amplifier’s rated output load.  
The RA150/300/500 amplifiers will not be damaged  
by excessively low output load impedances, but  
they will not be able to provide full output power  
and their protection circuits may automatically cut  
off their outputs until the low load condition is  
removed.  
Alesis recommends stranded, rather than solid,  
cables for flexibility and ease of installation.  
However, solid cables are equally usable.  
Never use shielded guitar cords as speaker cables.  
Because they lack sufficient current-carrying  
capacity, the amp and speakers will not perform  
properly and the sound may be degraded.  
If you make your own cables, use electrical zip cord,  
which is designed to handle several amps of  
current, or heavy-gauge speaker cables if possible.  
In any event, the thicker the cable, the lower the  
resistance and the better the current-carrying  
capability. Thin hookup wire is not acceptable; the  
minimum acceptable wire type is the common “zip  
cord” used to connect AC to appliances. The table  
below relates the wire gauge to the how many feet  
of cable will lead to a 1 dB power loss at different  
impedances. The lower the resistance, the better.  
For cables run up to about 25 feet, 16 to 18 gauge  
wire is satisfactory.  
CONNECTORS  
Each channel features a standard binding post  
connector (red = “hot” output, black = ground).  
The binding post or "banana" connectors are the  
preferred choice for permanent installations. There  
is greater surface area contact than with phone  
connectors, thus promoting a better electrical  
connection between the speaker wire and amplifier.  
Cable length that produces 1 dB of power loss  
wire gauge  
at 4Ω  
meters  
at 8Ω  
meters  
feet  
1200  
feet  
2425  
6
8
366  
244  
145  
91  
58  
37  
23  
15  
9
740  
488  
290  
183  
114  
73  
46  
30  
18  
800  
475  
300  
190  
120  
75  
1600  
950  
600  
375  
240  
150  
100  
60  
10  
12  
14  
16  
18  
20  
22  
50  
30  
18  
RA150/300/500 Reference Manual  
Chapter 2: Connections  
In recent years, expensive audiophile cables of high  
current capacity have appeared. These have been  
somewhat controversial; some feel the extra expense  
produces an audible improvement in sound quality,  
while others find no sonic difference between  
audiophile cables and other heavy-duty wiring.  
While Alesis does not endorse any particular brand  
of cable, we suggest that you investigate different  
cable types for yourself to discover if they improve  
the sound of your particular setup.  
Using a banana plug:  
Standard "dual banana plugs" (such as Pomona type  
MDP) should be used if the speaker cable will be  
removed from the amplifier often (for example,  
when used in a portable PA system).  
In this case, simply:  
1. Loosen the setscrews in the shaft of the plug  
until there is enough room to insert the wires in  
each side of the connector. (But be careful that  
the setscrew doesn't fall out.)  
CONNECTING SPEAKER CABLES  
TO BINDING POSTS  
The RA150/300/500 connectors are perfect for  
studio installations, especially near field monitor  
usage, where an effective and reliable connector is  
required. In addition, these connectors are very  
easy to set up in several different ways.  
2. Remove approximately 1/4" of insulation from  
the ends of the wires, being careful not to nick  
any of the strands.  
3. Determine the + and – conductors of the cable  
(by markings or moldings on the wire, or by the  
color of wire or insulation). Push the "-" side  
into the opening in the side of the connector  
marked "GND" or with a ridge sticking out the  
side.  
To connect speaker cable to the  
connectors:  
4. Using a small screwdriver, tighten the setscrew  
against the wire.  
1. Remove approximately 1/4" of insulation from  
the ends of the wires, being careful not to nick  
any of the strands.  
2 . Twist the strands together. Unscrew the  
speaker terminals on the amplifier.  
5. Push the other "+" wire through the strain relief  
and into the other opening, and tighten it as  
well.  
3. Feed the strands through the exposed hole in  
the binding posts, with the negative connected  
to the black terminal and the positive to the red  
terminal. Be careful that:  
When plugging the banana plug into the amplifier,  
make sure that:  
The red and black wire nuts in the amplifier  
have been screwed down first.  
The connector clamps down on the strands,  
not the insulation  
The side of the banana connector with the  
ridge or nub is plugged into the black  
connector.  
No stray strands contact any part of the  
chassis other than the connector.  
Using a crimp-on connector:  
4. Tighten down the binding posts and check that  
the wires can't be pulled out.  
If a crimp lug terminal is used on the speaker wire  
and the lug is too small to fit onto the threaded post,  
one leg of the terminal may be inserted in the hole  
in the post. As with wire connections, make certain  
that the terminal is snugly attached by tightening  
the plastic insulator nut.  
Tip: It may be easier to attach the speaker wires  
before the amplifier is mounted into a rack.  
RA150/300/500 Reference Manual  
19  
Connections: Chapter 2  
THE IMPORTANCE OF SPEAKER  
POLARITY  
OUTPUT CONNECTIONS FOR  
BRIDGED OPERATION  
The speaker cone’s motion should mimic the  
instrument it’s reproducing. For example, a kick  
drum pushes air toward you on the initial transient,  
so a speaker reproducing a kick drum should have  
its cone push air toward you. If the polarity is  
reversed, the cone will suck air away from you.  
Even though the same amount of air is moved in  
either case, many listeners report superior sound  
with proper polarity as opposed to reversed  
polarity.  
Instead of using the RA150/300/500 as a stereo 2-  
channel amplifier, it is possible to use it as a mono  
amplifier with twice the power. This uses both  
sides of the amplifier in a push-pull configuration,  
so the speaker must be wired to the amp differently.  
However, note that the minimum load impedance is  
8 ohms, instead of the 4 ohms in stereo operation.  
To connect a speaker in bridged mono  
mode:  
An additional problem occurs if the polarity of one  
speaker is reversed with respect to the other. This  
can cause phase-related problems such as thin bass,  
poor stereo imaging and frequency response  
anomalies.  
Following the instructions on the previous page for  
binding post or crimp-on connection, connect the  
"+" wire to the red binding post for the Channel  
1/Left and the "-" wire to the red binding post for  
Channel 2/Right.  
With the RA150/300/500, polarity is a function of  
correctly hooking up the output cables. Usually, for  
proper polarity, the tip of the output phone plug or  
the red terminal of the output connector must  
connect to the speaker’s positive (+) terminal. This  
will ensure that polarity from the RA150/300/500  
input to speaker cone motion will be consistent.  
Check your speakers' polarity, however, because  
not all brands follow this wiring convention.  
You may use a dual banana plug in this situation. If  
present, remove the protective caps from the top of  
the binding posts for the two red terminals. Plug  
the banana connector into the two center red  
terminals with the ridged/GND side on Channel  
2/Right.  
The single input is connected ONLY to the Channel  
1/Left input jack, and the stereo/mono switch  
under the right input connector should be set to  
BRIDGED MONO. Don't plug any input into the  
Channel 2/Right input jack, and leave the Channel  
2 volume control all the way down.  
Please note that polarity reversal can occur in  
devices (such as mixers or effects units) “upstream”  
of the RA150/300/500. To test for proper speaker  
and system polarity, see page 22.  
Should you use bridged mode?  
In a typical PA system with two speakers, in most  
cases you'll be better off running the  
RA150/300/500 in stereo mode, because most  
speakers are 8 ohms and if they were wired in  
parallel the total load would be 4 ohms, too low for  
bridged mode. In any case, the total system volume  
doesn't rise if you were to connect 2 speakers to a  
single 500-watt amp instead of to two 250-watt  
amps.  
But if you are connecting to a single speaker (such  
as a subwoofer) in a biamped or triamped setup,  
bridged mono mode will give you the chest-  
thumping headroom you need.  
20  
RA150/300/500 Reference Manual  
Chapter 3: Operation  
CHAPTER 3  
OPERATION  
ON-OFF SWITCH  
FRONT PANEL CONTROLS  
Press the switch to turn the amplifier on, and  
again to turn the amplifier off.  
The following diagram shows the various front  
panel controls, as described next.  
Upon turning on the amplifier, the power  
indicator LED will light. Note that in direct  
sunlight, this light may not be easily visible.  
RA150  
When powering a system on or off, it is  
usually advisable to turn on the power  
amplifiers last and to turn them off  
first, so that any turn on or turn off  
transient signals generated by other  
equipment in the system are not  
amplified and sent to the loudspeakers.  
RA300  
RA500  
However, the RA150/300/500’s output  
protection relays have a 4.5 second turn-on delay  
which keeps the loudspeakers disconnected  
while the system is powering up. These relays  
also disconnect the load very quickly when  
power is removed from the amplifiers, thus  
minimizing the chance that turn-off transients  
originating elsewhere in the system will be sent  
to the speakers. So, if the RA150/300/500 power  
switch is left on and the entire system is powered  
up on a single master AC switch, transient  
"thumps" should not be a problem.  
VOLUME CONTROLS  
Detented level controls are on the front panel,  
where they can be easily adjusted if necessary.  
These regulate the input signal going into the  
RA150/300/500. Always turn the volume controls  
all the way down (counterclockwise) when making  
input or output connections to the RA150/300/500.  
Power should be off as well. It’s also good practice  
to turn the volume controls all the way down when  
turning on power just in case a signal source  
feeding the RA150/300/500 is “live.”  
MUTE SWITCH  
Because turning the RA150/300/500 on and off  
generates no spikes within the amplifier, the  
power switch doubles as a mute switch or “panic  
button.” For example, if there is a serious  
feedback problem, you can simply turn off the  
RA150/300/500, then chase down the source of  
the problem.  
RA150/300/500 Reference Manual  
21  
Operation: Chapter 3  
PROTECT/CLIP INDICATORS  
BACK PANEL CONTROLS  
Clip lights for each channel indicate the onset of  
actual clipping. Even if the problem occurs for only  
a few microseconds, a pulse-stretching circuit will  
allow the LED to light long enough for you to see  
that a problem is occurring.  
AC VOLTAGE SWITCH  
Located near the power inlet is a recessed switch  
that allows voltage conversion from 120 volt to  
230 volt operation. Use a small tool or pen to  
change the setting of this switch only if it is set to  
the wrong value for the country the amplifier will  
be used in.  
Because of the RA150/300/500’s ability to enter  
and exit clipping with as few audible artifacts as  
possible, you may not hear any distortion even if  
the indicator flashes. In general, a few flashes every  
now and then will not be a problem. However, if  
the LEDs flash often or remain on for any extended  
period of time, then turn down the volume controls  
to reduce the signal level going to the  
RA150/300/500. If this doesn’t solve the problem,  
check your output cables and speakers.  
When changing voltages the fuse must be  
changed to the correct rating as shown  
on page 10.  
STEREO/BRIDGED MONO SWITCH  
Underneath the right input jack, this switch  
converts the RA150/300/500 from its normal  
operation as a two-channel amplifier to operation  
as a single-channel amplifier with approximately  
twice the power. Make sure this switch is set  
properly for your application. See page 20.  
METERS (RA300 AND RA500  
ONLY)  
In the center of the front panel are two meters that  
show the total power output of each channel. The  
highest (red) LED indicates the unit is at maximum  
output, at the onset of clipping. The orange  
PROTECT LEDs come on when the unit is 6 dB  
below rated output. Operation with the PROTECT  
LED on continuously will lead to amplifier  
overheating and eventual thermal shutdown to  
protect the circuitry. The two green LEDs closest to  
the PROTECT LED will actually light at higher  
levels than –6 dB, but before clipping. Lower green  
LEDs indicate signal in a normal operating range.  
No LEDs will light if the amplifier is operating 33  
dB or less below maximum rated output.  
If this switch is accidentally switched to Mono  
while wired for stereo, you will hear  
out-of-phase audio as the Channel  
2/Right control is turned up.  
CHECKING FOR PROPER  
POLARITY  
To check for correct speaker polarity, briefly  
connect the + terminal of a 1.5V battery to the  
speaker cable’s “hot” or + lead, and the battery’s  
- terminal to the speaker cable’s “cold,” ground,  
or - lead. You will hear a “pop” from the  
loudspeaker as you connect the battery, and  
another as you disconnect it. Observe the  
direction of the speaker cone movement. If the  
speaker cables are wired in the common manner  
(and the speakers themselves are not  
mislabelled), the speaker cone will move forward  
(toward you) when you connect the battery and  
away from you when the battery is disconnected.  
The PROTECT LEDs will light in two other cases:  
For 4.5 seconds at initial turn-on while the  
output relay is connected.  
When the thermal protection circuitry is  
activated because the amplifier is  
overheating. Thermal protection will stop  
automatically when the amplifier cools  
down.  
If the speaker cone moves in the opposite  
direction, reverse the wires going to the speaker  
and re-test for proper polarity. Always check  
your speakers' polarity as not all manufacturers  
follow the same wiring convention.  
22  
RA150/300/500 Reference Manual  
Chapter 3: Operation  
USING THE RA150 AS A  
HEADPHONE AMPLIFIER  
CHOOSING THE CORRECT  
SPEAKERS  
The RA150 is particularly suited for use driving  
high-impedance headphones in studio applica-  
tions. However, the power is considerably greater  
than that provided by most "headphone  
amplifiers", which are often rated at 1 watt or  
below.  
Near-field monitoring through “reference”  
speakers has become the preferred way to  
monitor and mix music. With near-field  
monitoring, small speakers are placed so that  
they are a few feet from the engineer’s ears. As a  
result, room acoustics become less important  
since the primary acoustic interaction involves  
direct sound from the speakers rather than  
reflected sounds from the room. Since few home  
and project studios have good acoustics, near-  
field monitors can provide realistic monitoring in  
a small space at relatively low levels.  
Due to the high efficiency of headphones  
and the power of the amplifier, serious  
hearing damage may result from misuse  
of this product. Exercise caution  
regarding sound levels.  
Near-field monitors offer other advantages  
compared to large studio speakers, including  
smaller size, lower cost, and easier  
transportability to other studios for reference  
purpose.  
Keep the following in mind:  
Many studio-quality headphones feature  
impedances of 600 ohms or greater. This  
means that many headphones of the same  
type may be plugged in parallel to the  
output of the RA150/300/500 before the 4-  
ohm limit is reached.  
Because of its moderate power rating, excellent  
fidelity, and lack of a noise-generating fan, the  
RA150/300/500 “Reference Amplifier” excels in  
driving reference near-field monitor speakers in  
smaller studios. However, you should choose  
speakers that can handle the power the  
RA150/300/500 can generate. Speaker wattage  
ratings are often confusing, and standards by  
which ratings are obtained vary from  
manufacturer to manufacturer. If a speaker can  
handle 100 watts RMS continuous power, it  
should be able to handle the RA150/300/500.  
However, under conditions of clipping or other  
abuse of the RA150/300/500, damage to speakers  
is possible. For best results, use speakers  
designed for medium- to high-power  
applications.  
If you plug in a headphone with a lower 8-  
ohm impedance, it will be dramatically  
higher in level than the others, and the  
high-impedance headphones may drop to  
inaudibility.  
The TRS 1/4" jack used in headphones will  
tie together the grounds of the left and  
right amplifier channels. Use caution and  
only connect or disconnect head-phones  
when the amplifier is powered off.  
Keep the RA150's front panel volume  
controls at a very low level and the controls  
of the headphone send near maximum.  
This will prevent accidental "blasting"  
during a session.  
RA150/300/500 Reference Manual  
23  
Operation: Chapter 3  
ABOUT GROUND LOOPS  
A hum or buzz may be introduced into some audio systems by a phenomenon known as a ground loop. This can  
occur if a piece of equipment “sees” two or more different paths to ground, as shown below.  
shielded  
cable  
Device B  
Device A  
path 1  
path 2  
To AC power  
service  
One path goes from device A to ground via the  
ground terminal of the three-conductor AC power  
cord, but A also sees a path to ground through the  
shielded cable and AC ground of device B.  
Because ground wires have a small amount of  
resistance, small amounts of current can flow  
through ground and generate a voltage along the  
cable shield. This signal may end up getting  
induced into the hot conductor.  
because it sacrifices the safety factor the AC  
ground wire provides. In the previous diagram,  
a better option would be to interrupt the cable  
shield. There are two ways to do this: one is to  
simply break the shield at some point, usually by  
disconnecting it from ground at one jack. (The  
other end should remain connected so that the  
shielding properties are retained, even if there is  
no direct path for ground.)  
The loop can also act like an antenna into which  
hum is induced, or can even pick up radio  
frequencies. Furthermore, many components in a  
circuit connect to ground. If that ground is “dirty”  
and contains noise, it might get picked up by the  
circuit. Ground loops cause the most problems  
with high-gain circuits, since massive amplification  
of even a couple millivolts of noise can give an  
audible signal.  
The other is to use a balancing transformer or  
direct box as mentioned on page 16 “Adapting  
the RA150/300/500 to Balanced Lines,” to  
provide isolation in the audio line between the  
two pieces of gear. Transformers generally have  
no ground connection between the input and  
output connections.  
Most ground loop problems can be solved by  
plugging all equipment into the same grounded  
AC source. However, it is important to make sure  
that the AC source is not overloaded and is  
properly rated to handle the gear plugged into it.  
For really tough cases, you may need to break the  
connection that causes the loop condition.  
Although some do this by using a ground lifter and  
breaking the AC ground, THIS IS A DANGEROUS  
OPTION WHICH YOU SHOULD NOT USE  
24  
RA150/300/500 Reference Manual  
Chapter 3: Operation  
SETTING THE GAIN PROPERLY  
SYSTEM SETUP AND TESTING  
Setting the system gain is fairly straightforward,  
but if it is not properly adjusted, the system’s  
distortion and noise characteristics may be less  
than optimum.  
Before applying power for the first time, double  
check the wiring to insure that everything is firmly  
connected and that the proper signals are being fed  
to the proper places. If a low frequency signal in a  
multi-amplified system is applied to a high  
frequency transducer, the transducer can be  
damaged, and a loose connection can cause noise  
which can damage any transducer.  
The most common cause of noisy operation,  
especially in studio use, is that the amplifier' s  
gain controls are left all the way up, while the  
mixer' s output is turned down. This can lead  
to blown speakers if the mixer is accidentally  
turned up, but more importantly, it amplifies  
the noise floor of the mixer output stage or  
wiring unnecessarily. Keeping the source  
level as high as possible and lowering the  
amplifier input gain will keep the noise level  
at a minimum.  
Be certain that the amplifier front panel gain  
controls are set to minimum when the system  
under test is first powered up. After the power is  
applied, slowly advance each gain control to  
confirm that there are no driver-destroying hums  
or buzzes present—if there are, turn the power off  
and locate the source of the difficulty.  
When first applying program material to the  
system, it is also advisable to keep the gain controls  
turned down to confirm, once again, that the  
wiring is correct. Once the system wiring is  
determined to be correct, the gain controls can then  
be set to an appropriate level for the system gain  
structure.  
The input sensitivity of the RA150/300/500  
amplifiers at the 1/4" input or XLR input is  
1.23 volts (+4 dBu) for rated output with the  
amplifier gain controls at maximum. If you're  
plugged into the phono jacks, the sensitivity is  
–10 dBV (.316 volts). If the signal at the amplifier  
input is higher than this, the input gain controls  
of the RA150/300/500 must be turned down to  
avoid amplifier clipping. Most mixers output +4  
dBu at nominal level/0 VU; that means if you go  
"into the yellow" on the meter of most mixers, the  
amp will be clipping its outputs or distorting the  
speakers unless you turn down the input gain  
controls.  
It is generally best to try to keep the gain of the  
source device set for best signal-to-noise ratio  
consistent with distortion, and to then set the  
amplifier inputs for the desired SPL level.  
A good way to set levels is to use a test tone or  
pink noise with a sound level meter. Set the  
mixer' s controls at nominal levels, increase  
the test tone until the mixer is exercising its  
dynamic range without clipping itself. The  
mixer' s meter should read from +10 to +15.  
Then slowly raise the RA150/300/500' s input  
level controls until the desired peak sound  
pressure level is achieved.  
RA150/300/500 Reference Manual  
25  
Operation: Chapter 3  
Amplifier input clipping  
OUTPUT RELAYS/THERMAL  
CYCLING  
On the other hand, the maximum level at the  
amplifier’s input terminals is +26 dBu, regardless  
of the setting of the channel input level controls. It  
is possible that the output signal from the source  
may be too high and, thus, distorted before it  
reaches the amplifier gain control, either because  
the source device is clipping or the amplifier input  
stage is overloaded. In either case, no amount of  
level control adjustment at the amplifier can  
remove this distortion, and you should lower the  
output level of the device feeding the amplifier  
until the distortion stops.  
Reference Series amplifiers have high-current  
output protection relays which disconnect the  
output in the event of overheating, DC offset,  
audio signals below 5 Hz on the output terminals  
or excessively low line voltage. When this  
happens in the RA300/500, the PROTECT  
indicators of both channels will glow. Additional  
protection circuitry keeps RFI out of the audio  
circuits, assuring clean, stable operation in  
difficult environmental conditions.  
If the unit shuts off, turn off the power and check  
for problems with the wiring, input level, or  
ventilation of the amplifier.  
Continued high-temperature operation may also  
trigger an internal thermal fuse, which will shut  
the unit off entirely until it has cooled off. In this  
case, the PROTECT indicators and POWER  
indicators will turn off as well.  
Overheating is the most common cause of  
amplifier shutdown. You must ensure that  
the heat sinks of the amplifier are not blocked  
and can receive a supply of cooler air.  
26  
RA150/300/500 Reference Manual  
Chapter 4: Troubleshooting  
CHAPTER 4  
TROUBLESHOOTING  
TROUBLESHOOTING INDEX  
Once all gain adjustments are made and proper operation is confirmed, no special considerations are required for  
Alesis Reference Series amplifiers. Aside from the front panel gain controls, there are no user adjustments or  
routine maintenance operations necessary (or available). If you experience problems while operating your  
RA150/300/500, please use the following table to locate possible causes and solutions before contacting Alesis  
Product Support for assistance.  
Symptom  
Cause  
No input audio  
Bad cables  
Solution  
Hook up inputs  
No audio from outputs  
Replace the cables.  
Amplifier is turned  
down  
Set levels to "12:00" or above  
Is the amplifier very hot? Normal operation will resume  
Is the ambient  
when its internal temperature  
has dropped to reliable levels.  
temperature and/or the  
air flow in the rack high?  
If so, the amplifier may  
be in thermal protect  
mode (PROTECT LEDs  
on)  
Power is not connected  
Time for a coffee break.  
Low output power  
Line voltage set  
improperly  
Set the switch on the back panel  
to the "120 V" position  
Bass disappears, speakers  
sound out of phase  
Amplifier accidentally  
set to "Bridge Mono"  
mode when wired for  
stereo  
Set the switch on the back panel  
to the "stereo" position  
Buzz from outputs  
Input cables are crossing Make sure that the  
a power cable or near a  
transformer  
RA150/300/500 and its audio  
cables are kept away from  
power cables, other power  
transformers and wall warts.  
Use balanced inputs instead of  
unbalanced  
Bad cables  
Replace the cable with a new,  
high-quality cable.  
Problem with the source Try plugging a known line-level  
source to the amplifier inputs to  
see if the problem remains.  
Noise induced from a  
Connect to a different electrical  
bad AC ground or noisy circuit; use balanced inputs or  
AC circuit  
plug amp and source into the  
same AC circuit  
RA150/300/500 Reference Manual  
27  
Troubleshooting: Chapter 4  
Symptom  
Cause  
Solution  
Audio cuts in and out  
Intermittent amplifier  
input signal  
Clean input connectors,  
check wiring  
If the sound cuts out for Check for short circuits in  
a minute or two and then the output wiring or  
returns, the amplifier  
excessive ambient  
may be overheating and temperature  
cycling through thermal  
protect mode  
Dirty volume pot  
Move volume pot up and  
down several times  
Unit shuts down, all lamps Blown fuse  
are off  
Obtain the proper size fuse  
(see page 10) and replace it  
Internal thermal fuse  
activated  
Shut off power and let  
amplifier cool down  
Thin or Muffled Sound  
Defective loudspeaker  
drivers  
Replace drivers  
In a multi-amplified  
system with a low level  
crossover network, bad  
outputs from the  
Check crossover and  
connections. Check  
speaker connections.  
network, or improperly  
connected loudspeakers  
Balanced connector with Make sure input cables are  
one side disconnected, or connected to ground as  
no ground with an  
unbalanced input  
required  
CARE AND MAINTENANCE  
CLEANING  
REFER ALL SERVICING TO  
ALESIS  
Disconnect the AC cord, then use a damp cloth to  
clean the RA150/300/500’s metal and plastic  
surfaces. For heavy dirt, use a non-abrasive  
household cleaner such as Formula 409™ or  
Fantastik™. DO NOT SPRAY THE CLEANER  
DIRECTLY ONTO THE FRONT OF THE UNIT AS  
IT MAY DESTROY THE LUBRICANTS USED IN  
THE SWITCHES AND CONTROLS! Spray onto a  
cloth, then use cloth to clean the unit.  
We believe that the RA150/300/500 is one of the  
best amplifiers that can be made using current  
technology, and should provide years of trouble-  
free use. However, should problems occur, DO  
NOT attempt to service the unit yourself. Service  
on this product should be performed only by  
qualified technicians. NO USER-SERVICEABLE  
PARTS INSIDE.  
28  
RA150/300/500 Reference Manual  
Chapter 4: Troubleshooting  
OBTAINING REPAIR SERVICE  
Before contacting Alesis, check over all your  
connections, and make sure you’ve read the  
manual.  
CUSTOMERS OUTSIDE THE USA  
AND CANADA:  
Contact your local Alesis distributor for any  
warranty assistance.  
The Alesis Limited  
Warranty applies only to products sold to users  
in the USA and Canada. Customers outside of  
the USA and Canada are not covered by this  
Limited Warranty and may or may not be  
covered by an independent distributor warranty  
in the country of sale. Do not return products to  
the factory unless you have been given specific  
instructions to do so.  
Customers in the USA and Canada: If the problem  
find the Product Support web page. Make  
sure you have the unit’s serial number with you.  
If necessary contact one of our technicians;  
if appropriate, you will be given a return order (RO)  
number and instructions on how to return the unit.  
All units must be shipped prepaid and COD  
shipments will not be accepted.  
Internet Address: Important information and  
advice is available on our web site:  
For prompt service, indicate the RO number on the  
shipping label. Units without an RO will not be  
accepted. If you do not have the original packing,  
ship the unit in a sturdy carton, with shock-  
absorbing materials such as Styrofoam pellets (the  
kind without CFCs, please) or “bubble-pack”  
surrounding the unit. Shipping damage caused by  
inadequate packing is not covered by the Alesis  
warranty.  
Email may be addressed to:  
Tape a note to the top of the unit describing the  
problem, include your name and a phone number  
where Alesis can contact you if necessary, as well  
as instructions on where you want the product  
returned. Alesis will pay for standard one-way  
shipping back to you on any repair covered under  
the terms of this warranty. Next day service is  
available for a surcharge. Field repairs are not  
authorized during the warranty period, and repair  
attempts by unqualified personnel may invalidate  
the warranty.  
RA150/300/500 Reference Manual  
29  
Specifications  
SPECIFICATIONS  
Reference 150  
Size  
18.9" W x 3.9" H x 10.25" D  
(480mm x 99 mm x 260 mm)  
2RU height  
15lbs = 6.8Kg  
Rack units  
Weight  
Rated output, per channel  
4 ohms @ 1kHz, .02% THD+N 75 watts RMS per channel  
8 ohms @ 1kHz, .05% THD+N 45 watts RMS per channel  
8 ohms, bridged mono mode  
150 watts RMS  
Signal to Noise Ratio  
Frequency Response  
Damping Factor  
Slew Rate  
Input Sensitivity  
Maximum input level  
Input impedance  
Crosstalk  
>105dB, 22Hz-22kHz bandwidth referenced to rated output  
10Hz – 70kHz +0, -3dB  
200  
60 V/µs (two channel), 120 V/µs (bridged mono)  
+4dBu (1.23 V) for rated output with input control at maximum  
+26 dBu  
20k , balanced, 10 kunbalanced  
-85dB, 1kHz  
Output offset  
+/- 50 mV, Servo controlled  
Reference 300  
Size  
18.9" W x 3.9" H x 10.63" D  
(480mm x 99 mm x 270 mm)  
2RU height  
Rack units  
Weight  
Rated output, per channel  
19lbs = 8.6Kg  
4 ohms @ 1kHz, .02% THD+N 150 watts RMS per channel  
8 ohms @ 1kHz, .05% THD+N 90 watts RMS per channel  
8 ohms, bridged mono mode  
Signal to Noise Ratio  
Frequency Response  
Damping Factor  
300 watts RMS  
>105dB, 22Hz-22kHz bandwidth referenced to rated output  
10Hz – 70kHz +0, -3dB  
200  
Slew Rate  
60 V/µs (two channel), 120 V/µs (bridged mono)  
+4dBu (1.23 V) for rated output with input control at maximum  
+26 dBu  
20k , balanced, 10 kunbalanced  
-85dB, 1kHz  
Input Sensitivity  
Maximum input level  
Input impedance  
Crosstalk  
Output offset  
+/- 50 mV, Servo controlled  
30  
RA150/300/500 Reference Manual  
Specifications  
Reference 500  
Size  
18.9" W x 5.63" H x 10.71" D  
(480mm x 143 mm x 272 mm)  
3 RU height  
Rack units  
Weight  
Rated output, per channel  
28.5lbs = 13.0Kg  
4 ohms @ 1kHz, .02% THD+N 250 watts RMS per channel  
8 ohms @ 1kHz, .05% THD+N 150 watts RMS per channel  
8 ohms, bridged mono mode  
Signal to Noise Ratio  
Frequency Response  
Damping Factor  
500 watts RMS  
105dB, 22Hz-22kHz bandwidth referenced to rated output  
10Hz – 70kHz +0, -3dB  
200  
Slew Rate  
60 V/µs (two channel), 120 V/µs (bridged mono)  
+4dBu (1.23 V) for rated output with input control at maximum  
+26 dBu  
20k , balanced, 10 kunbalanced  
-85dB, 1kHz  
Input Sensitivity  
Maximum input level  
Input impedance  
Crosstalk  
All measurements done over a 20Hz-22,000Hz range with 1KHz sine wave at Full Scale, except for the dynamic  
range which was done with a -60dBFS 1KHz sine wave.  
Dimensioned drawings  
RA150  
RA150/300/500 Reference Manual  
31  
Specifications  
RA300  
RA500  
32  
RA150/300/500 Reference Manual  
Specifications  
Architect's and Engineer's Specifications  
The power amplifier shall be a two-channel unit  
capable of being switched to single-channel  
bridged mode operation. All components shall be  
of high quality and mechanical construction and  
optimized for high reliability under adverse  
physical and electrical conditions. Cooling shall be  
convection-type only, with no fan mounted inside  
the amplifier.  
The chassis shall be rack mountable in a standard  
19" EIA equipment rack. Output connectors shall  
be two-way binding posts capable of accepting  
heavy gauge wire or banana-type connectors.  
The power output of the amplifier shall be 75  
watts per channel (RA150), 150 watts per channel  
(RA300) or 250 watts per channel (RA500) into a  
4-ohm load, with no more than .02% total  
harmonic distortion. The units shall be capable of  
150 watts (RA150), 300 watts (RA300), or 500  
watts (RA500) into an 8-ohm load when operated  
in bridged mono mode with no more than .05%  
total harmonic distortion.  
The inputs shall be differentially balanced with  
active current sources for rejection of electro-  
magnetic interference. The input connectors shall  
be 3-conductor 1/4" TRS jacks mounted on the back  
panel. Additional unbalanced RCA/ phono inputs  
shall also be mounted on the back panel. [RA300  
and RA500: There shall also be provision for  
female XLR input jacks on each channel.]  
The amplifier shall be an Alesis RA150/300/500  
Reference Series power amplifier.  
The output stages of the amplifier shall be a high  
current, triple darlington type biased for class AB  
operation, fully rated for continuous 4 ohm  
operation with 2 ohm dynamic stability (stereo  
mode only). An active DC servo circuit is to be  
employed to automatically null DC output voltage  
offsets. The amplifier shall feature active circuitry  
that continuously monitors the output stage for  
excessive DC offset, short circuits and thermal  
overload. In the event of an output fault, the  
protection circuitry will activate the output relay  
and disconnect the loudspeaker load. This circuitry  
will also mute the amplifier during power on/off  
transitions.  
The power supplies of the amplifier shall utilize  
heavy-duty stacked steel EI laminated transformers  
for maximum performance and reliability, with  
high current bridge rectifiers, massive secondary  
capacitors and current in-rush limiters. An external  
voltage selection switch on the back panel shall  
allow the user to switch between 120-volt and 230-  
volt AC power input. A power switch shall be  
provided on the front panel with an on/off  
indicator lamp.  
The front panel of the amplifier shall feature two  
detented volume controls capable of delivering full  
rated power at full clockwise rotation with a +4  
dBu input, and turning the amplifier down at least  
70 dB or to silence at full counterclockwise rotation.  
RA150/300/500 Reference Manual  
33  
Index  
INDEX  
120-volt to 230-volt conversion, 10, 22  
AC cord, 9  
AC power, 10  
phase. See polarity  
phone plug inputs, 14  
polarity, 20  
balanced inputs, 14  
balanced lines, 16  
banana plugs, 19  
Bridged Mono mode, 17, 20  
cables  
how to test, 22  
power  
output, 30  
Power cable, 3  
power loss  
in speaker cable, 18  
protection, 7  
shielded input, 15  
speaker, 18  
class AB, 7, 33  
cooling, 7, 11  
direct box, 17  
Fuse, 10  
Rack Mounting, 11  
RCA/phono input jacks. See  
Repair Service, 29  
Safety, 3, 24  
gain setting, 25  
ground  
shield  
telescoping, 24  
audio, 9, 14  
sound level meter, 25  
Specifications, 30  
thermal protect mode, 27  
transformer  
ground lifter, 24  
ground loop, 24  
grounding, 3  
headphone amplifiers, 23  
heat sink, 11  
high-temperature operation, 11  
impedance  
input, 17  
speaker, 18  
input clipping, 26  
Inputs, 13  
magnetic fields, 12  
Maintenance, 28  
Meters, 22  
input, 17  
transformers  
power, 7, 33  
TRS jacks, 14, 16  
turn-on delay, 21  
unbalanced input, 14, 16  
Unbalanced-to-balanced cable, 16  
ungrounded outlets, 9  
volume controls, 21  
XLR input, 16  
XLR input jacks, 13  
Mono. See Bridged Mono  
noise, 25  
Output Relays, 26  
Outputs, 18  
34  
RA150/300/500 Reference Manual  
ALESIS LIMITED WARRANTY  
ALESIS ("ALESIS") warrants this product to be free of defects in material and workmanship for a  
period of one (1) year for parts and for a period of one (1) year for labor from the date of original retail purchase. This  
warranty is enforceable only by the original retail purchaser and cannot be transferred or assigned.  
During the warranty period ALESIS shall, at its sole and absolute option, either repair or replace free of charge any  
product that proves to be defective on inspection by ALESIS or its authorized service representative. In all cases disputes  
concerning this warranty shall be resolved as prescribed by law.  
To obtain warranty service, the purchaser must first call or write ALESIS at the address and telephone number printed  
below to obtain a Return Authorization Number and instructions concerning where to return the unit for service. All  
inquiries must be accompanied by a description of the problem. All authorized returns must be sent to ALESIS or an  
authorized ALESIS repair facility postage prepaid, insured and properly packaged. Proof of purchase must be presented in  
the form of a bill of sale, canceled check or some other positive proof that the product is within the warranty period.  
ALESIS reserves the right to update any unit returned for repair. ALESIS reserves the right to change or improve design of  
the product at any time without prior notice.  
This warranty does not cover claims for damage due to abuse, neglect, alteration or attempted repair by unauthorized  
personnel, and is limited to failures arising during normal use that are due to defects in material or workmanship in the  
product.  
THE ABOVE WARRANTIES ARE IN LIEU OF ANY OTHER WARRANTIES OR REPRESENTATIONS WHETHER  
EXPRESS OR IMPLIED OR OTHERWISE, WITH RESPECT TO THE PRODUCT, AND SPECIFICALLY EXCLUDE ANY  
IMPLIED WARRANTIES OF FITNESS FOR A PARTICULAR PURPOSE OR MERCHANTABILITY OR OTHER IMPLIED  
WARRANTIES. Some states do not allow limitations on how long an implied warranty lasts, so the above limitation may  
not apply to you.  
IN NO EVENT WILL ALESIS BE LIABLE FOR INCIDENTAL, CONSEQUENTIAL, INDIRECT OR OTHER DAMAGES  
RESULTING FROM THE BREACH OF ANY EXPRESS OR IMPLIED WARRANTY, INCLUDING, AMONG OTHER  
THINGS, DAMAGE TO PROPERTY, DAMAGE BASED ON INCONVENIENCE OR ON LOSS OF USE OF THE  
PRODUCT, AND, TO THE EXTENT PERMITTED BY LAW, DAMAGES FOR PERSONAL INJURY. Some states do not  
allow the exclusion or limitation of incidental or consequential damages, so the above limitation or exclusion may not apply  
to you.  
THIS CONTRACT SHALL BE GOVERNED BY THE INTERNAL LAWS OF THE STATE OF CALIFORNIA WITHOUT  
REFERENCE TO CONFLICTS OF LAWS. This warranty gives you specific legal rights, and you may also have other rights  
required by law which vary from state to state.  
This warranty only applies to products sold to purchasers in the United States of America or Canada. The terms of this  
warranty and any obligations of Alesis under this warranty shall apply only within the country of sale. Without limiting  
the foregoing, repairs under this warranty shall be made only by a duly authorized Alesis service representative in the  
country of sale. For warranty information in all other countries please refer to your local distributor.  
ALESIS  
Los Angeles, California USA  
PLEASE REGISTER YOUR PRODUCT ONLINE:  
WWW.ALESIS.COM  
Alesis, Los Angeles, CA USA  
© 2000 Alesis Specifications Subject To Change Without Notice  
7-51-0097 11/00  
RA150/300/500 Reference Manual  
35  
Warranty  
36  
RA150/300/500 Reference Manual  

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