Crate Amplifiers Musical Instrument Amplifier BT 350 User Manual

Owners Manual  
for the  
BT-350  
Bass Amplifier  
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BT-350 ThunderBass Amplifier  
Introduction:  
The Crate BT-350 ThunderBass amp is a high-quality bass guitar amplification system that combines  
extremely high power with very desirable features. Each feature and control is discussed in detail in the sec-  
tions entitled “The Front Panel,” “The Rear Panel” and “Using the Biamp Capabilities.”  
Crate offers a heavy-duty three rack space enclosure (Crate model #CR-3) which will house the BT-350  
perfectly, providing the extra protection and convenience needed when you take your Crate on the road.  
Also available is a five rack space enclosure (Crate model #CR-5) which is ideal for use when the BT-350 is  
combined with a second amplifier for biamping.  
The BT-350 is equally suited for use in the club, the studio or on the stage. When combined with Crate’s  
line of superior bass cabinets, the results are nothing less than phenomenal. (But then, what else would you  
expect from Crate?)  
Features:  
Additional information can be found on the pages indicated.  
Tube Preamp: Adjustable Drive control. Low, Mid and High frequency controls. Low and High Boost  
switches. Normal (0dB) and padded (-15dB) input jacks. (page 4)  
Graphic EQ: 7 bands. 40Hz to 10kHz. 12dB cut or boost. Master Level control. Footswitch control-  
lable. LED Indicator. (pages 4 and 5)  
Master Level: Peak (overdrive) LED indicator. Switchable Limiter circuit with LED indicator. (page 4)  
Chorus: Adjustable Depth and Rate controls. Variable cut-off (“Spectrum”) control. (page 5)  
Biamp: Adjustable crossover frequency control. Low-to-high balance control. Independent Line Out  
level control. Balanced (XLR) and unbalanced (1/4”) outputs. (pages 5 and 6)  
Internal Amplifier: 350 watts into 4 ohms. 1/4” mono speaker output jacks. Extensive heatsinking.  
Detachable AC power cord. (page 6)  
Effects Loop: 1/4” Send and Return jacks. Allows use of external signal processors. Return jack  
doubles as input for power amp in Biamp mode. (page 6)  
Musician made in the U.S.A.  
Crate’s exclusive 5-year warranty (U.S. only, – see your dealer in other areas for warranty informa-  
tion)  
3
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BT-350 ThunderBass Amplifier  
The Front Panel:  
INPUTS:  
1. 0dB INPUT: Connect your bass the impressive 8dB of gain added at seek a more traditional sound.  
here using a shielded instrument cable. 20Hz, increasing the deep, “floor-shak-  
8. HIGH BOOST: Turning on the High  
Boost greatly enhances the upper-har-  
5. LOW: Adjust the output level of your monic overtones of your bass, increasing  
low-bass tones with this control: the cen- such subtleties as the sounds of your fin-  
The output signal of your bass will run ing” sounds of your instrument.  
full-strength into the amplifier, which is  
fine for most basses having passive elec-  
tronics and/or low-output pickups. If  
ter position is “flat” (no boost or cut). gers on the strings or the strings striking  
your bass has active on-board electron-  
Turning the control to the left reduces the the fretboard. High Boost produces an  
ics and/or active pickups, use the -15dB  
low frequency output; turning to the additional 10dB of gain at 10kHz, mak-  
input jack (#2) to avoid overloading the  
right increases the low frequency output. ing the “crisp” characteristics of your  
amp’s input stage.  
The Low control primarily affects the bass even more pronounced.  
2. -15dB INPUT: Connect your bass notes you feel, providing up to 13dB of  
here if it has active on-board electronics boost or cut at 40Hz.  
MASTER LEVEL SECTION:  
9. PEAK LED: This LED indicator will  
and/or active pickups. The bass’s output  
signal will be attenuated by 15dB to keep  
6. MID: Adjust the output level of your light when you’re nearing the highest  
upper-bass tones with this control: the desirable level for your input signal and  
it from overloading the amplifier’s input  
center position is “flat” (no boost or cut). are in danger of overdriving the pre-  
stage.  
Turning the control to the left reduces the amp’s solid state circuitry. (This can  
NOTE: Even if your bass has passive upper-bass output; turning to the right cause the output of the amplifier to  
electronics, if the Peak LED (#9) flashes increases the upper-bass output. The sound distorted.) To get the maximum  
at seemingly low levels when you’re Mid control provides up to 11dB of benefit from the BT-350’s tube preamp  
plugged into the 0dB input, try using the boost or cut at 260Hz, which changes section (good, clean sound with the  
-15dB jack instead.  
the “voice” of your instrument’s sound. “feel” of natural tube compression),  
By boosting the Mid control you can adjust the Tube Drive control (#3) until  
make the sound of your bass cut through this LED begins to flash when you’re hit-  
the rest of the band, without getting a ting your strings pretty hard.  
TUBE PRE-AMP section:  
3. TUBE DRIVE: This serves as the gain  
control for the BT-350’s tube preamp  
section, which gives you the natural  
whole lot louder.  
10. MASTER LEVEL: This is the BT-350’s  
compression of a tube amplifier. For the 7. HIGH: Adjust the amount of high-fre- master volume control. The output level  
best compression. adjust the Tube Drive quency overtones with this control: the of the amplifier through your main  
control as you strike your strings (hard). center position is “flat” (no boost or cut). speakers, the Biamp Outputs and the  
Watch the Peak LED (#9): when the Turning the control to the left reduces the Effects Loop Send are simultaneously  
LED starts to flash, you’ve reached a high-frequency output; turning to the adjusted by this control: at the full-left  
choice setting for the best signal-to-noise right increases the high-frequency out- position there will be no output; rotating  
ratio and “tube feel.”  
put. The High control allows up to 15dB the control to the right increases the vol-  
of boost or cut at 5kHz, which allows you ume level.  
to adjust the “crispness” of the sound of  
your bass. Players looking for a sharp,  
slapping sound may tend to want this  
4. LOW BOOST: Switch on the Low  
Boost and you’ll feel a large increase in  
the very lowest bass notes, especially  
noticeable when you hit the low B string  
of a five or six-string bass. This is due to  
control turned up farther than those who  
4
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BT-350 ThunderBass Amplifier  
The Front Panel (con’t):  
11. LIMIT LED: The BT-350 offers a the Line Out Level control to the right control up from center boosts the output  
special limiting circuit which helps to increases the output level; to the left at its given frequency; pulling it down  
keep the output of the amplifier “clean” decreases it.  
when played at extreme volume levels.  
reduces that frequency. The 40Hz and  
100Hz controls affect the lower notes of  
your bass, changing how much bass is  
felt. 250Hz through 1.6kHz affect the  
upper notes, modifying the amount of  
“punch” that comes across. 4kHz and  
10kHz affect the upper harmonic over-  
tones of your bass, such as the sounds of  
your fingers in the strings or the strings  
striking the fretboard.  
NOTE: The Line Level signal is pre-  
When the Limiter is engaged, the Limit  
LED will come on as the power amp is  
being driven to full output.  
Effects Loop and therefore will not be  
affected by any external signal proces-  
sors connected to the Loop (see #33  
12. LIMITER: When a power amplifier and 34).  
reaches maximum output levels, it may  
16. POWER: This heavy-duty rocker-  
begin to “clip” its output signal, which  
generates potentially speaker-damaging  
distortion. The BT-350 has a special  
APM (Automatic Power Maximizer) limit-  
ing circuit which helps minimize this  
problem by monitoring the power amp’s  
output signal, keeping it below clipping.  
This feature insures you that even as you  
push your amplifier to its full 350-watt  
output, the sound will remain clean and  
pure. To activate the limiter circuit, press  
the Limiter switch in until it locks in  
place. The limit LED (#11) lights up  
when the APM circuit is actually limiting  
the signal.  
type switch is used to turn the amp on in  
the “up” position, off when “down.” The  
switch lights up when the power is on.  
20. ON: When this switch is in, the EQ is  
active, and the settings of the controls  
affect the sound of your bass.  
17. FOOTSWITCH: A two-button  
footswitch (such as Crate’s CFP-2) can  
be plugged in here to give you remote  
on/off control of the graphic eq and the  
chorus. When connected, the footswitch  
overrides the front panel on/off switches  
for these features.  
21. ENABLED LED: This LED will only  
light when the EQ is activated, showing  
you that the signal will be affected by the  
settings of the EQ controls.  
CHORUS section:  
NOTE: This is a stereo 1/4” jack: “ring”  
controls the chorus, “tip” controls the  
eq, and the “sleeve” is ground. Use only  
a footswitch equipped with a stereo plug  
(such as Crate’s CFP-2).  
22. ON: When pushed in, the on-board  
Chorus is activated and the signal pro-  
duced by your bass will have the Chorus  
effect applied to it.  
NOTE: The limiter may be defeated,  
which allows higher power output, but  
there may be more distortion than the  
.2% shown in the specifications chart.  
23. ENABLED LED: This LED will light  
when the Chorus is activated, giving you  
a visual sign that the Chorus is function-  
ing.  
EQUALIZATION section:  
The graphic equalizer can be used in  
two different ways: 1: To fine-tune  
your sound, make small adjustments  
at the desired frequencies and leave  
the EQ on for the entire performance;  
2: For a completely different sound,  
make larger adjustments and only  
switch the EQ on when you want the  
radical change (such as during bass  
solos).  
BIAMP section:  
13. FREQUENCY: This sets the  
crossover point when using the BT-350  
in the biamp mode (using two power  
amplifiers, one for the low frequencies,  
one for the highs). Please see the section  
entitled “Using the Biamp Capabilities”  
on pages 8 and 9 for more details about  
biamping.  
24. SPECTRUM: (or “crossover:”) This  
unique feature allows you to adjust  
which frequencies – either the entire  
range or only the upper bass tones – are  
enhanced by the Chorus effect. In the  
fully counter-clockwise position the  
entire range (or “spectrum”) will have  
the chorus effect. As you rotate the con-  
trol clockwise you change the roll-off fre-  
quency for the Chorus, which allows the  
lowest tones to come through “dry”  
(without chorus applied). This is  
extremely useful for maintaining full low-  
end impact and definition during live  
performances.  
18. LEVEL: This serves as the overall  
volume control for the BT-350’s on-  
board 7-band graphic equalizer, and  
only affects the signal when the EQ is on  
(see #20). Use this control to adjust the  
volume of the equalized signal: pulling  
the Level control down from the center  
position reduces the volume, pushing it  
up from center increases it. The center  
detent is “flat” (no increase or decrease  
in level).  
14. BALANCE: This adjusts the relative  
level between the low frequency and the  
high frequency biamp output signals.  
Please see the section entitled “Using the  
Biamp Capabilities” for more details  
15. LINE OUT LEVEL: This adjusts the  
output level for the Line Outputs jacks  
on the rear panel (#31, 32), separately  
and independently from the amplifier’s  
Master level control (#10). The line out  
feature can be used to send a low-level  
(pre-amplified) signal to a mixing board,  
recorder or external power amp. The  
Line Out signal will have the same tone  
and Chorus information as the Master  
Level (speaker output) signal. Turning  
25. DEPTH: Adjust the overall amount  
of the Chorus effect with this control: to  
the left for a little, to the right for a lot.  
26. RATE: Adjust the speed of the cho-  
rus effect with this control: to the left for  
slow, smooth “phasing” sounds, to the  
right for faster, “vibrato” sounds.  
19. 40Hz – 10kHz: These slide controls  
allow you to vary the output at the fre-  
quencies shown under each control by  
12dB. The center position of each con-  
trol is “flat” (no boost or cut): pushing a  
5
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BT-350 ThunderBass Amplifier  
The Rear Panel:  
27. SPEAKER OUTPUT jacks: Using a high-frequency power amplifier. See the NOTE: The Balanced Output jack is  
1/4” mono phone plug, connect the out- section entitled “Using the Biamp wired as follows:  
put of the BT-350 to your speaker cabi- Capabilities” on pages 8 and 9 for  
PIN 1: GROUND  
net(s) via these jacks. Be sure to use details.  
heavy gauge speaker cable – not instru-  
PIN 2: POSITIVE (+)  
30. LOW OUT: When used in the biamp  
ment patch cords – for these connec-  
PIN 3: NEGATIVE (–)  
mode, this output connects to the low-  
tions. These jacks are wired in parallel:  
frequency power amplifier. See the sec-  
when connecting your speakers, keep  
tion entitled “Using the Biamp  
Capabilities” on pages 8 and 9 for  
details.  
EFFECTS LOOP:  
the total impedance at or above 4 ohms.  
The chart below can help you determine  
the total impedance load when connect-  
ing various combinations of speakers in  
parallel.  
33. SEND: When using an external sig-  
nal processor with the BT-350, connect  
a shielded cable between the Send jack  
of the amplifier and the input of the  
effects unit. This “sends” the pre-ampli-  
fied bass signal to the device for process-  
ing.  
NOTE: You may access the BT-350’s  
internal power amp through the Effect  
Return jack (#34), for either the high or  
low signal. This is covered in the section  
entitled “Using the Biamp Capabilities”  
on pages 8 and 9.  
SPEAKER  
IMPEDANCE  
NUMBER OF  
SPEAKERS  
TOTAL  
IMPEDANCE  
4 OHMS  
8 OHMS  
8 OHMS  
16 OHMS  
16 OHMS  
1
1
2
2
4
4 OHMS  
8 OHMS  
4 OHMS  
8 OHMS  
4 OHMS  
34. RETURN: When using an external  
signal processor, connect a shielded  
cable between the output of the effects  
unit and the Return jack of the amplifier.  
This “returns” the processed bass signal  
to the BT-350’s internal amplifier.  
LINE OUTPUTS:  
31. UNBALANCED: This 1/4” mono  
phone jack supplies an unbalanced out-  
put signal for connecting to an external  
power amplifier. Very short runs (under  
20’) to a mixer or recorder having unbal-  
anced inputs can also be made from this  
jack; for longer runs use the Balanced  
output (#32). The output level at this  
jack is adjusted by the Line Out Level  
control (#15) on the front panel.  
28. AC Line cord: Firmly plug the sup-  
plied, heavy-duty grounded power cord  
into this receptacle. When in use, be sure  
this cord is properly plugged into a safe-  
ly-wired, grounded 120 volt, 60Hz AC  
power outlet. Do not attempt to defeat  
the ground connection on this cable!  
32. BALANCED: This XLR-type con-  
nector supplies a balanced signal for con-  
necting to an external mixer, recorder or  
power amp which has balanced inputs.  
The output is adjusted by the Line Out  
Level control (#15). Use the Balanced  
output when the distance between the  
BT-350 and the mixing console or  
recorder is over 20’.  
If your BT-350 was purchased outside of  
the United States, see the unit’s rear  
panel for its power rating and follow the  
above guidelines.  
BIAMP OUTPUTS:  
29. HIGH OUT: When used in the  
biamp mode, this output connects to the  
6
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BT-350 ThunderBass Amplifier  
System Block Diagram:  
7
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BT-350 ThunderBass Amplifier  
Using the Biamp Capabilities:  
Your BT-350 can be used along with an additional power amplifier, to “biamp” your system: that is, using two ampli-  
fier/speaker combinations to share the task of reproducing the full range of your bass. Due to increased efficiencies, the  
combined output may sound cleaner and more powerful than that of a single-amped system, especially during high-vol-  
ume, live performances.  
Using the BT-350 as the low-frequency power amplifier:  
In the biamp configuration shown below, the BT-350 serves as the system preamp, biamp crossover, and low-fre-  
quency power amplifier. A second power amp of 75 to 200 watts (such as the Crate model SPA-200) may be used to  
amplify the upper frequencies. The crossover frequency (that point where one amplifier ends and the other amp takes  
over) is set by adjusting the BT-350’s Biamp Frequency control (#13).  
To connect the unit for biamp operation using the BT-350 as the low-frequency power amp, refer to the diagram below:  
1
Connect a shielded cable from the BT-350’s Biamp HIGH OUT jack and the input of the amplifier which  
will be used for the upper frequencies.  
2
3
Connect a shielded cable from the BT-350’s Biamp LOW OUT jack and its Effects Loop RETURN jack.  
Connect the Speaker Outputs of your high-frequency power amp to the speaker cabinet(s) that will be  
used to reproduce the upper frequencies. (10” or 12” drivers work well for this.)  
4
Connect the Speaker Outputs of the BT-350 to the speaker cabinet(s) that will be used to reproduce the  
low bass notes. (Woofers in the 15” to 18” range work well for these low notes.)  
Use the BT-350’s Balance control (#14) to adjust the relative level of lows to highs: to increase the level of low fre-  
quencies in the mix, rotate the Balance control to the left (towards “LOW”). To increase the amount of highs in the mix,  
rotate the control to the right (towards “HIGH”).  
8
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BT-350 ThunderBass Amplifier  
Using the Biamp Capabilities (con’t):  
Using the BT-350 as the high-frequency power amplifier:  
In the biamp configuration shown below, the BT-350 serves as the system preamp, biamp crossover, and high-fre-  
quency power amplifier. A second power amp of 200 to 500 watts may be used to amplify the low frequencies. The  
crossover frequency (that point where one amplifier ends and the other amp takes over) is set by adjusting the BT-350’s  
Biamp Frequency control (#13).  
To connect the unit for biamp operation using the BT-350 as the high-frequency power amp, refer to the diagram below:  
5
Connect a shielded cable from the BT-350’s Biamp LOW OUT jack and the input of the amplifier which  
will be used for the low frequencies.  
6
7
Connect a shielded cable from the BT-350’s Biamp HIGH OUT jack and its Effects Loop RETURN jack.  
Connect the Speaker Outputs of your low-frequency power amp to the speaker cabinet(s) that will be  
used to reproduce the low bass notes. (Woofers in the 15” to 18” range work well for these low notes.)  
8
Connect the Speaker Outputs of the BT-350 to the speaker cabinet(s) that will be used to reproduce the  
upper bass notes. (10” or 12” drivers work well for this.)  
Use the BT-350’s Balance control (#14) to adjust the relative level of lows to highs: to increase the level of low fre-  
quencies in the mix, rotate the Balance control to the left (towards “LOW”). To increase the amount of highs in the mix,  
rotate the control to the right (towards “HIGH”).  
9
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BT-350 ThunderBass Amplifier  
Some Suggested Settings:  
ROCK:  
Biamp and Chorus controls optional. You can crank the Tube Drive even more for distortion; if you do, back off the  
EQ level.  
JAZZ:  
This will produce a very smooth sound with a minimum of percussive tones.  
10  
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BT-350 ThunderBass Amplifier  
Some Suggested Settings:  
COUNTRY:  
Increasing the EQ Level produces more clean volume. Set the Master Level to taste.  
FUNK “POPPING”:  
Chorus is a great effect with this setting.  
11  
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BT-350 ThunderBass Amplifier  
Technical Specifications:  
Output Power Rating  
350 watts @ 0.2% THD, 4 ohm load – 120VAC  
200 watts @ 0.2% THD, 8 ohm load – 120VAC  
Gain @ 1kHz  
61dB, tones at “5”  
Tone Control Range  
Low Boost  
Low  
+8dB @ 20Hz  
13dB @ 40Hz  
11dB @ 260Hz  
15dB @ 5kHz  
+10dB @ 10kHz  
Mid  
High  
High Boost  
Graphic EQ Level  
Graphic EQ Range  
Signal to Noise Ratio  
Input Impedance  
+8dB, -10dB  
12dB @ 40Hz, 100Hz, 250Hz, 625Hz, 1.6kHz, 4kHz, 10kHz  
84dB typical  
0dB input: 1M ohm  
-15dB input: 122k ohm  
Maximum Signal Level Accepted  
0dB input: 2.5V peak to peak  
-15dB input: 14V peak to peak  
Tube Type:  
12AX7 (preamp)  
Effects Loop Level  
1V RMS for full power output  
Power Requirements  
Domestic  
Export  
120VAC, 60 Hz, 10A  
240VAC, 50 Hz, 5A  
Size and Weight  
5.25”H x 19”W x 15.75”D, 36 lbs.  
CRATE continually develops new products, as well as improves existing ones. For this reason,  
specifications and information in this manual are subject to change without notice.  
CRATE/SLM ELECTRONICS, A DIVISION OF ST. LOUIS MUSIC, 1400 FERGUSON AVENUE, ST. LOUIS, MO 63133  
47-599-02 • 02-96  
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