green pre voltages and possable problems

I was powering up a green pre built from th older PCB some things I noted.

C12 has no forming voltage, C11 does. What I did I reversed C12 and lifted the end of R21 that goes to C11 I soldered that lifted end of R21 to pin one of the second IC. They both have about 2Vdc to help kepp them in good shape.

I measured the voltage across both C4 and C5 Both have reverse voltage.

I am working on something for C14

Before I go and reverse them I would like to ask What some of the voltages across C4,C5,C11 and C12 are in built and working units on the older PCB. What I mean if you place the + meter lead to the cap + and - meter lead to the cap- what do you read does the cap have a forming voltage and is it the "right" way?

Damn Gus,
I pulled my green out of the rack to do this and realized I left my DMM at work. I know I've got another one around here. If no one's given it to you by tonight, I'll get it.

Good luck. Joel

I just hooked up another green pcb build C4 and C5 have -.7V installed as the schematic and top view of the board I am using show. C11 and C12 have 0V. Both are just boards with parts. I am waiting on two resistors for the gain control so I soldered a 47okm in for the gain control. I hand matched all the resistors for both channels on each board and match between boards They are as close as my DMM can read. I used four matched 2n4001s for Q1 and Q2.

Something might be wrong on one or both boards I built I used old rc5532s date code looks like 1984.

Maybe a page with Voltages at some points would help taken from a known good board.

C4,C5,C14,C11 and C12 forming V + or -

Q1 C and E . Q5 C and E ref to ground.

pin numbers 1,and 7 of both opamps ref to ground

Looking at the circuit drawn by P.C. xxxxxxx_2.ckt 20/09/2002 This is the one with a TL072 and a LM833. Has there been a change?

I would think C4 and C5 should be reversed.

Hi Gus

Thanks for the work on this cct. Here are the voltages :

Supply : +14.8, 0 , -15.2 (No Rotary Gain switch connected, no signal)

IC 1 no NE5532 IC1 with NE5532
1. 0v 1. ?3.34
2. 14.8 2. 12.08
3. 12.2 3. 12.08
4. ?15.2 4. ?15.1
5. 12.2 5. 12.08
6. 14.8 6. 12.08
7. 0.07 7. ?3-34
8. 14.8 8. 14.7

IC 2 no NE5532 IC2 with NE5532
1. 0.07 1. ?0.11
2. 0.07 2. ?1.4
3. 0.00 3. ?1.4
4. ?15.2 4. ?15.1
5. 0.00 5. ?0.01
6. 0.01 6. ?0.01
7. 0.01 7. 0.00
8. 14.8 8. 14.7

IC 3 no NE5532 IC 3 with NE5532
1. 0.11 1. 0.004
2. 0.11 2. 0.001
3. 0.00 3. 0.00
4. ?15.2 4. -15
5. 0.00 5. 0.00
6. 0.05 6. 0.00
7. 0.05 7. 0.001
8. 14.8 8. 14.8

I've faithfully duplicated the polarisation of the caps in the original cct.

Regards
Peter

Peter

Thanks. I had a solder short on the one board that had the strange voltages. I am working on a mod for the gain setting cap and the two output caps. I don't know when the greens will be done.

Gus

Update.

I measured the nodes C4 and F1 and C5 and F2 they measure - in repect to ground about 1/2 volt I then made C14 two caps +s connected together - s to the pads on the PCB for C14. I connected a 100K from the center of the caps to ground. This makes sure the caps have about .5V of forming Voltage Problem is the effective cap value is 1/2 of the cap value with two in series.

one end of R21 was lifted(c11,R13,R14 node) and connected to pin 1 of IC2.

C11 and C12 changed to 2 220uf at 50V again +s togeher -s to pcb pads 100k from the center to +15V again to keep forming voltages.


The 100K should min any PS noise to the output and not load/disturb the rest of the circuit.

This is nothing new I first read about hooking up caps like this in some Jung Marsh articles from the late 70's early 80's IIRC.

I think Keith wrote(at the old place) some SSL stuff did this with caps.

note I have not finished the pre yet

Anyone see any problems with this?