SRS Labs SR555 Operation Manual - page 9
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6. Circuit Description
The transimpedence amplifier consists of opamps U1, U2 and gain resistor R7 (R3 for SR555). Input
current coming through J1 and R1 will pass through R7 and sink to the output node of U2. A
corresponding voltage will be present at TP1. The bias voltage signal from J2 is low‐pass filtered and fed
to the non‐inverting node of U1. R8 through R10, C3, and C25 form the low pass filter, and are buffered
by a follower U3. SW1 is used to enable or disable the bias voltage. TP2 is either grounded or equal to
the follower U3 output voltage. U4 and RN1 form a fully differential amplifier / low pass filter whose
differential output is proportional to the current signal from J1 (bias voltage is subtracted).
U5 and U6 regulate the DC power inputs from connector J5 to provide internal ±15V power supplies.
U11 provide the +5V and used by U10 and overload LED.
7. Parts Lists
a. SR555
Part
Number
Reference
Value
5‐00570
C3,C25
.1U
5‐00299
C4,C5,C8,C9,C10,
C11,C17,C18,C24
.1U
5‐00260
C6,C7
470U
5‐00383
C12
470P
5‐00377
C13,C14
150P
5‐00848
C19,C20,
C21,C22,C23
1.0U
3‐00230
D1,D5
1N5240A
3‐00945
D2
BAT54S
3‐00010
D3
GREEN
3‐00011
D4
RED
3‐00003
D6, D7
1N4001
1‐01344
J5
DB‐9 Female
1‐01320
J6,J7
5 PIN
6‐00174
L1,L2
6611 TYPE 43
4‐00191
R1,R12,R13
49.9
4‐01760
RN1
668‐A‐2001‐A
4‐00925
R2,R6,R23
10
4‐02539
R3
10.0M
4‐01021
R4
100
4‐01213
R5
10.0K
4‐01551
R8
1.0M
4‐01309
R9,R10,R24
100K
4‐00800
R11
1
4‐01184
R15,R17,R18,
R19, R20,R30
4.99K
4‐01181
R16,R21
4.64K
4‐01347
R22
249K
4‐01088
R25,R26,R27,R28
499
2‐00022
SW1
DPDT
3‐00998
U3
OPA227
3‐02155
U4
THS4131
3‐00711
U5
78L15
3‐01301
U6
79L15
3‐00728
U7,U8,U9
LM393
3‐00662
U10
74HC14
3‐00116
U11
LM78L05