SRS Labs Home Theater System SR554 User Manual

Model SR554

Transformer Preamplifier

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Model SR554

Transformer Preamplifier

1290-D Reamwood Avenue

Sunnyvale, California 94089

Phone: (408) 744-9040 • Fax: (408) 744-9049

email: [email protected] • www.thinkSRS.com

Revision 1.2 (07/2004)

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SR554 SPECIFICATIONS

Inputs

Single ended or differential

Input Impedance

Maximum Inputs

0.5 Ω

Transformer and Buffer:

Transformer only:

14.0 mV RMS (±20 mV peak)

350 mV RMS (±0.5 V peak)

Common Mode

Isolation

Range:

Rejection:

± 100 VDC

140 dB @ 100 Hz

> 40dB

DC to 500 MHz

Input Noise

(Transformer and Buffer)

120 pV/√Hz @ 10 Hz

100 pV/√Hz @ 100 Hz

100 pV/√Hz @ 1000 Hz

(see noise contours, pg. 5)

(typical)

Gain

Transformer and Buffer:

Transformer only:

500

100

(nominal)

See Amplitude-Frequency Response Curve (pg 6).

5% (with fixed source resistance)

100 ppm/ °C

Gain Accuracy

Gain Stability

Outputs

Single ended or differential

Output Impedance

Transformer and Buffer:

Transformer only:

< 1.0 Ω

> 5000 Ω

Maximum Output

Power

Transformer and Buffer:

Transformer only:

7.1 V RMS (10 Volts peak)

35.3 V RMS (50 Volts peak)

Provided by any SRS lock-in amplifier via the supplied

connector cable or from a ± 20 volts DC @ 100 mA source.

Mechanical

Warranty

2.9" X 3.8" X 7.5" (HxWxL), 4 lb.

One year parts and labor on materials and workmanship.

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OPERATION

The SR554 Transformer Preamplifier is

indicator on the SR554 will light.

designed to be used with all SRS Lock-in

amplifiers. It can reduce input noise of a

lock-in amplifier dramatically (as low as

100 pV/√Hz) and extends the lock-in’s full

scale sensitivity (without expand). It also

nearly eliminates noise radiated back from

the lock-in amplifier to the users

experiment. When used as a remote

preamplifier, the SR554 can eliminate the

effects of noise pickup on long signal

The SR554 output switch selects between

buffered mode with a gain of 500,

(transformer and buffer) or bypassed

mode with a gain of 100 (transformer

alone).

In the buffered mode, the

transformer secondary goes into a low

noise buffer which drives the output cable.

This is to reduce loading due to the

transformer output impedance (about 5

kΩ) and cable capacitance (10's of pf). If

the user prefers not to use the buffer or if

power isn’t available for the preamp, then

the SR554 can be used in the bypassed

mode. In the bypassed mode, the output

impedance of the pre-amp is 5 kΩ and

care must be taken to avoid loading the

output with too much cable capacitance.

Power should not be connected to the

SR554 when used in the bypass mode.

cables.

The SR554 transformer is

designed to be used with its internal

buffer, but the buffer may be bypassed for

transformer only operation. When used

as a simple transformer, no power

connection is required.

CONNECTING THE SR554

When the transformer and buffer are used

together, power is supplied to the SR554

via the 9 pin connector and cable. This

cable mates with all SRS lock-in amplifiers

through the rear panel connector. To use

the SR554 without an SRS lock-in, the

user must provide their own ±20 VDC

(100 mA) source. Always connect the

power cable to the SR554 while the lock-

in power is off. Attach one end of the

cable to the connector on the rear of the

SR554, and connect the other end to the

PRE-AMP connector on the rear of the

lock-in. If a longer cable is required, any

standard 9 pin cable will suffice since all

connections are straight through. When

the lock-in power is on, the POWER

INPUT CONNECTION

Signals into the SR554 can be connected

either single ended through the (A) input,

or differentially through the (A-B) inputs.

In the single ended configuration the

shield and center conductor of the (A)

input are connected to the transformer.

For differential connection, the shields of

the input BNC’s are connected to the

SR554 case and the (A) and (B) center

conductors connect to the transformer.

The input impedance is a combination of

0.5 Ω and 0.5 H (in series) in parallel with

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functional when the unit is in the buffered

mode. If the unit is operated in the

bypassed mode and power is applied, the

overload LED may light even when the

unit is not overloaded. This does not

indicate an overload, but is due to leakage

current of the buffer amplifier and its

protection circuitry. To avoid this, power

should not be connected when the unit is

used in the bypassed mode.

1.6 µF. The real portion of the input

impedance (0.5 Ω) determines the noise

performance. See page 7 for detailed

information on input impedance.

The input can be floated up to ±100 VDC

with respect to the chassis.

The

maximum AC input before overload is 14

mV RMS (±20 mV peak) when the unit is

in the buffered mode. In either mode, the

input is clamped at about 350 mV RMS

(±0.5 V peak). Care should be taken when

the unit is used in the bypassed mode,

since a ±0.5 V peak input becomes ±50 V

at the output.

OUTPUT CONNECTION

For single ended operation the (A) Output

of the SR554 should be connected to the

(A) Input of the lock-in amplifier. The

center conductor carries the signal and

the shield is ground.

applications, this single connection will be

adequate.

For most

In the buffered mode, the OVERLOAD

indicator will light when the preamplifier

overloads. An overload that occur after

the preamplifier will be indicated by the

lock-in amplifier’s overload indicator. The

SR554’s overload indicator is only

For situations with potential noise pick-up

on the cable, it may be better to operate in

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the differential mode. In differential

operation the (A) and (B) center

conductors carry the signal and shielded

preamp ground, and the shields are tied to

the SR554 chassis. The (A) and (B)

cables should be twisted together to

prevent inductive pick-up.

significant cable capacitance will create a

low-pass filter with this output resistance

as well, so short cables should always be

used.

GAIN OF SR554

The actual gain of the SR554 is a function

of the source impedance, frequency and

the set gain. In the bypass mode (x100),

the gain will be affected by loading on the

output. The gain is fairly flat over a range

of input impedances (<10 Ω) and

frequencies (5 Hz-10 kHz). The actual

gain can be determined from the

amplitude-frequency response curves on

page 4. The plot assumes operating the

SR554 in the buffered mode or with no

loading on the output in the bypassed

mode.

For most experiments it is preferable to

use the SR554 in the buffered mode. If

the preamplifier is used in the bypass

mode, care must be taken to not load the

output. The output resistance of the

transformer is at least 5 kΩ (for a 0 Ω

source) and is typically 10,000 times the

input resistance.

Therefore, a 50 Ω

source impedance will become 500 kΩ. If

the instrument that the SR554 is

connected to has an input impedance of 1

MΩ, 1/3 of the signal is lost.

Any

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EXTRA LOW NOISE MEASUREMENTS

When making extremely low noise

measurements, it is a good practice to

connect the grounding plug of the SR554

to a ground point near the experiment. If a

good ground is not available near the

experiment, connect a wire from the lock-

in chassis (using a lug under one of the

chassis screws) to the grounding lug of

the SR554.

USING THE SR554 WITH SRS LOCK-

INS

The SR554 is not sensed through the 9

pin cable by SRS lock-in amplifiers.

Therefore the lock-in does NOT

compensate for the gain of the preamp.

Measurements made using the preamp

must be divided by the gain of the SR554.

The actual gain can be obtained from the

amplitude response curves on page 4.

NOISE FIGURE

The noise figure describes the noise

USING THE SR554 WITH THE

SR810/830/850

contribution of an amplifier in

measurement when compared to an ideal

amplifier.

For typical measurements the lock-in input

should be set to AC coupled, with the

shield grounded.

For low frequency

measurements (<1Hz), set the lock-in to

DC coupled, with the shield grounded,

since the SR554 can sense signals below

the lock-in’s AC coupling frequency

(0.16 Hz).

The expression:

USING THE SR554 WITH THE

SR510/530

The SR510/530 is AC coupled from 0.5

Hz to 100 kHz. Measurements below 0.5

Hz are not recommended with the

SR510/530.

where N is the measured noise, A is the

pre-amp gain and enrs is the Johnson

noise of the source impedance, describes

the noise figure contours shown below.

The optimum operating frequency can be

determined from this graph.

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USING THE SR554 WITHOUT AN SRS

LOCK-IN

The SR554 can be powered with an

external power supply. Power is applied

through the 9 pin connector as described

below.

ground point. If a ground is not available

near the experiment, connect a wire to the

lock-in using a lug under one of the

chassis screws.

INPUT IMPEDANCE

The input impedance of the SR554

appears as a combination of 0.5 Ω and

0.5 H (in series) in parallel with 1.6 µF and

VOLTAGE

+20 V

-20 V

Ground

CURRENT

100 mA

several parasitic impedances.

The

7,8

transformer primary has a DC resistance

of 0.2 Ω and a primary inductance of 0.5

H. The secondary has a DC resistance of

3 kΩ and a capacitance of about 160 pF.

When the secondary impedance is

converted over to the primary side of the

transformer by the turns ratio (1:100), the

0.5 Ω, 0.5 H and 1.6 µF values are

Both voltages are required. Pins 7 and 8

should be tied together and grounded. All

other pins should be left open.

COMMON MODE REJECTION RATIO

The SR554 has an extremely high CMRR

at low frequencies (up to 160 dB below 10

Hz). It drops off at higher frequencies due

to capacitive coupling between the

primary and secondary windings and

reduced signal gain. See the graph below

for the relationship between CMRR and

frequency.

obtained.

The actual values of the

magnitude and phase of the input

impedance is shown in the graph below.

RADIATED NOISE

The SR554 reduces radiated noise from

the lock- in amplifier’s input by 40 dB

(100x) over most frequencies (DC to 500

MHz). To minimize radiated noise, a thick

(low impedance) wire should be

connected from the ground plug to a quiet

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PERFORMANCE TESTS

Performance tests are designed to verify

that the unit is performing within the

specifications.

4) For each frequency, the following

amplitude should be observed, ± 5%.

Necessary Equipment:

Frequency

1.0 Hz

10 Hz

100 Hz

200 Hz

500 Hz

1 kHz

10 kHz

100 kHz

Amplitude

31 mV

252 mV

438 mV

442 mV

439 mV

414 mV

96 mV

1. Lock-In Amplifier

Freq Range

Output Ampl

Output Z

0.1 Hz - 100 kHz

4 mV rms - 1 Vrms

50 Ω

Recommended SRS SR850/830/810

11 mV

2. 50 ΩTerminator

5) Disconnect the lock-in reference from

the SR554 input. Connect the 50 Ω

terminator to the SR554 (A) input.

3. 50 Ω, 20 dB Attenuator

The instructions here apply to SRS DSP

lock-ins (SR850/830/810). Other lock-in

amplifiers may be used. However they will

require substantially longer time constants

to arrive at accurate measurements.

6) Set the lock-in to measure noise.

7) For each frequency and time constant,

the following rms noise voltage should

be observed (±10%). Set the lock-in

sensitivity to about 5 times the

expected reading and allow it to settle

(10-20 time constants) before making

readings.

1) Connect the 9-pin power cable from

the rear of the lock-in amplifier to the

SR554. Connect the 20 dB attenuator

to the lock-in reference output and a

BNC cable from that to the SR554

(A) input. Connect another BNC cable

from the SR554's (A) output to the

lock-in’s (A) input. Set SR554 to

Frequency Time Constant Noise Voltage

1.0 Hz

10 Hz

100 Hz

200 Hz

500 Hz

1 kHz

3.0 s

1.0 s

0.1 s

0.03 s

480 nV

260 nV

460 nV

420 nV

120 nV

60 nV

buffered mode (X500), (A) input.

2) Power on the lock-in in the default

condition. (SR810/830 Power on

Setup, SR850 Power on Bksp) This

places the lock-in in a known state.

The power LED of the SR554 should

light.

10 kHz

100 kHz

3) Set the input to DC coupled, grounded

shield. Set the time constant to 300

ms (1 s for 1 Hz measurement), 12

dB/oct filter and turn on synchronous

filtering (if available). Set the display

type to magnitude (R) and the

reference sinewave amplitude to 10

mV rms.

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Part List

Ref.

SRS part

Value

130P

Description

C 101 5-00254-501

C 102 5-00023-529

C 103 5-00023-529

C 104 5-00005-501

C 105 5-00023-529

C 106 5-00312-503

C 107 5-00016-501

C 108 5-00044-509

C 109 5-00100-517

C 110 5-00100-517

C 111 5-00023-529

C 112 5-00312-503

C 113 5-00016-501

C 114 5-00044-509

C 115 5-00100-517

C 116 5-00281-521

C 117 5-00281-521

D 101 3-00226-301

D 102 3-00226-301

D 103 3-00403-301

D 104 3-00403-301

D 105 3-00011-303

D 106 3-00010-303

Capacitor, Ceramic Disc, 50V, 10%, SL

Cap, Monolythic Ceramic, 50V, 20%, Z5U

Capacitor, Ceramic Disc, 50V, 10%, SL

Cap, Monolythic Ceramic, 50V, 20%, Z5U

Capacitor, Ceramic Disc, 50V, 20%, Z5U

Capacitor, Ceramic Disc, 50V, 10%, SL

Capacitor, Electrolytic, 50V, 20%, Rad

Capacitor, Tantalum, 35V, 20%, Rad

Cap, Monolythic Ceramic, 50V, 20%, Z5U

Capacitor, Ceramic Disc, 50V, 20%, Z5U

Capacitor, Ceramic Disc, 50V, 10%, SL

Capacitor, Electrolytic, 50V, 20%, Rad

Capacitor, Tantalum, 35V, 20%, Rad

Capacitor, Electrolytic, 25V, 20%, Rad

Diode

LED, T1 Package

Connector, BNC

.1U

150P

.1U

.005U

470P

47U

2.2U

.1U

.005U

470P

47U

2.2U

220U

1N5822

1N459A

RED

GREEN

BNC

J 101

J 102

J 103

J 104

J 109

L 101

L 102

PC1

1-00003-120

1-00014-160

1-00229-102

6-00174-630

7-00613-701

BNC

Connector, BNC

Connector, D-Sub, Right Angle PC, Female

Binding Post

Ferrite Beads

9 PIN D

BINDING

6611 TYPE 43

SR554 PREAMP

100

4.99K

1.24K

10.0K

100K

200K

100K

3.0K

2.0K

DPDT

SR554

T68-17

AD743

LM339

78L15

79L15

3/8"

Printed Circuit Board

R 101 4-00141-407

R 102 4-00188-407

R 103 4-00134-407

R 104 4-00138-407

R 105 4-00142-407

R 106 4-00166-407

R 107 4-00166-407

R 108 4-00142-407

R 110 4-00063-401

R 111 4-00045-401

R 112 4-00056-401

R 113 4-00056-401

R 114 4-00056-401

SW101 2-00022-217

SW102 2-00027-214

T 101 6-00169-610

T 102 6-00173-614

T 103 6-00173-614

U 101 3-00535-340

U 102 3-00193-340

U 103 3-00118-325

U 104 3-00124-325

Resistor, Metal Film, 1/8W, 1%, 50PPM

Resistor, Carbon Film, 1/4W, 5%

Switch, On-None-On, Toggle, Right Angle

Switch, Miniature Bat Toggle

Transformer

Iron Powder Core

Integrated Circuit (Thru-hole Pkg)

Transistor, TO-92 Package

Lugs

Z 0

0-00025-005

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Part List

Ref.

Z 0

SRS part

Value

Description

Nut, Kep

Standoff

Tie

Wire #24 UL1007 Strip 1/4x1/4 Tin

Screw, Black, All Types

Screw, Panhead Phillips

Screw, Flathead Phillips

Screw, Panhead Phillips

Hardware, Misc.

Wire #22 UL1007

BLK Wire #22 UL1007

Washer, nylon

0-00043-011

0-00079-031

0-00089-033

0-00128-053

0-00150-026

0-00187-021

0-00208-020

0-00209-021

0-00221-000

0-00263-052

0-00266-052

0-00304-043

0-00386-003

0-00440-052

7-00604-720

7-00605-720

7-00606-720

7-00607-709

9-00267-917

4-40 KEP

4-40X3/16 M/F

4" #24

4-40X1/4PF

4-40X1/4PP

4-40X3/8PF

4-40X3/8PP

SR440FOOT

3" #22

8-1/2" #22

7/8X3/8X1/16

SOLDR SLV RG174 Termination

2-1/2" #22 RED

SR554-1

SR554-2

SR554-3

SR554

Wire #22 UL1007

Fabricated Part

Lexan Overlay

Product Labels

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