CIRCUIT DESCRIPTION Cont.
Q7 & Q11 make up a voltage amplification stage. Again, to operate properly, the same amount of current must flow
through these transistors. Thus the voltage drop across R21 & R22 must be the same.
Adjustable bias is provided by Q8 & it's associated components. 1.2volts is provided to the Base of Driver Transistors
Q14 & Q15, and -1.2 volts is provided to the base of the Driver Transistors. This provides + or - 0.6 volts to the bases
of the output transistors (Q18-Q25) in parallel, biasing them on.
Transistors Q12, Q13, and associated components comprise the Current Limiting or Short Proof protection circuit.
There are usually two conditions which demand excessive output current from the amplifier. A shorted speaker cable,
or a load impedance which is below the minimum rating of the amplifier. If these conditions occur, the voltage drop
across the Emitter Resistors (.33Ω 5 Watt) will dramatically increase. On the positive side of the amplifier, C11
charges through R25 & R27. On the negative side C12 charges through R31 & R32. This will cause Q12 & Q13 to turn
on. This limits the amount of signal which is available to the Base of the Driver Transistors (Q14 - Q17).
DIFFERENCES IN VERSIONS:
In all versions (SR6520/8520, SR6520P/8520P, & SR6520PD/8520PD) the power
amp remained unchanged; normal schematic revisions were not related to version changes. The "P" version added
Phantom power, which caused the preamp PCB assy to change by adding traces to carry phantom power to the XLR
microphone connectors, and added a +15V regulator circuit to the preamp PCB assy in order to provide the phantom
power. The "PD" version added digital effects (PCB assy 041875) and a ribbon cable to connect the PCB's together
(P2 to P3), along with some obvious cosmetic changes
WARRANTY PHILOSOPHY ON DIGITAL REVERB MODULE:
Replacement, rather than repair of the 041092
module is the recommended warranty procedure for failures of the module.
PARTS LIST
NOTE: SHADED ITEMS ARE FOR REFERENCE ONLY
NOTICE:
Reference designators 100-199 refer to and are listed only for channel 1. Channel 2 designators are 200-299
etc. Part quantities are listed only for the SR-6520PD (6 channel version).
PREAMP
PRINTED CIRCUIT BOARD ASSEMBLY
QTY PART # DESCRIPTION REFERENCE DESIGNATION
1 037832 PCB. ASSY PREAMP SR6520P (STUFFED)
1 037875 PCB. ASSY PREAMP SR8520P (STUFFED)
1 049148 PCB ASSY PREAMP SR6520PD (STUFFED)
1 049271 PCB ASSY PREAMP SR8520PD (STUFFED)
1 028577 CABLE ASSY REVERB 30" (SR6520/8520/P)
1 038534 CABLE, JUMPER 3CKT RIBBON
P2 TO P3 (SR6520/8520/P TAPE IN)
1 048914 CABLE, RIBBON 8CKT RIBBON @ P1 (SR6520/8520PD)
1 028485 CAP AE RDL 16V 470uF 20% C11
1 028492 CAP AE RDL 16V 1000uF 20% C10
21 028465 CAP AE RDL 25V 22uF 20% C14,16,25,103,104,111
1 028474 CAP AE RDL 25V 100uF 20% C7
1 033605 CAP AE RDL 50V .15uF 20% C29
1 037943 CAP AE RDL 50V .33uF 10% C37
1 033606 CAP AE RDL 50V .47uF 20% C27
17 028459 CAP AE RDL 50V 2.2uF 20% C3,12,18-20,105,106
13 028460 CAP AE RDL 50V 4.7uF 20% C5,114,115
20 020909 CAP CD 1KV 47pF 10% C4,6,13,15,21-24,112,113
12 069724 CAP CD 1KV 100pF 10% C101,102
12 025984 CAP CD 1KV 180pF 10% C107,108
1 007029 CAP CD 1KV 220pF 10% C34
6 025986 CAP CD 1KV 390pF 10% C110
1 025777 CAP CD 1KV 470pF 10% C42
1 020842 CAP CD 1KV 500pF 10% C9
1 033588 CAP PF RDL 100V .01uF 10% C36
2 033578 CAP PF RDL 100V .001uF 10% C32,40
1 036234 CAP PF RDL 100V .015uF 10% C41
1 033590 CAP PF RDL 100V .022uF 10% C26
1 033591 CAP PF RDL 100V .033uF 10% C31
16 033596 CAP PF RDL 100V .068uF 10% C1,2,8,39,116,117
1 033579 CAP PF RDL 100V .0015uF 10% C30
1 033580 CAP PF RDL 100V .0022uF 10% C35
2 033581 CAP PF RDL 100V .0033uF 10% C17,38
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