SRS Labs SR555, Operation Manual

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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