R-Comp Not working

[schnarf]

Edit: just updated the voltages because I accidentally took the readings without a plug in the input jack.

Just finished building this one, and i get almost no output, some hiss, and very very flubby slightly distorted notes, and like I said, they're very quiet.

Vbattery = 9.38

U1 - I don't know how the pin numbering works, so I'm going from the upper right of the pcb side, counterclockwise.
8.65
8.21
8.20
0.00
8.88
3.05
9.36
8.76

Q1:
C: 7.12
B: 2.58
E: 2.21

Q2:
C: 6.83
B: 0
E: 0

Q3:
C: 9.19
B: 0
E: 0

Q4:
C: 9.19
B: 0
E: 0

Q5:
C: 9.21
B: 8.90
E: 9.21

Thanks in advance!

[pbrommer]

Let me take a shot (I'm no R.G., et al)

First, who's layout are you using? It's hard to figure out the pins without it.
Second, you've got a problem with Q3 and Q4. There should be no voltage on the B and E at all.
Third, I think the Q2 is off since the voltage on the E is a little high.
Fourth, the emitter shouldn't be higher than the base in this circuit (methinks).
With this, you probably have a short somewhere or something connected incorrectly to V+

Well, that's all I can do for now. Just giving you some ideas on where to look and think about.

Patrick

[Processaurus]

I'm not sure what pcb you're using.  Looking at an IC from the top, and so the notch or mark is facing up, you start at the top left corner (pin 1), and go counter clockwise, ending on the pin in the upper right corner (pin 8 in the case of your CA3080 IC).

[schnarf]

I'll check out the problems with the transistors. I'm going from the GGG/R.G. Keen PCB. By chance I ended up properly naming the IC pins.

[schnarf]

I just updated the values. Turns out I took the readings with no plug in the input jack so the circuit was off. Same problem though.

[R.G.]

Patrick, you may not be me, but you sure give good advice. Actually, not being me may be an advantage in that. 8-)

On the corrected voltages:
U1 - Problems here!
1-8.65: no matter
2-8.21: way too high
3-8.20: ditto; I think your biasing string of resistors is not connected to ground at the bottom; check the two 1M's
4-0.00: ground is good
5-8.88: a big problem here; pin 5 is the Iabc input and cannot be pulled higher than two diode drops. If you measured this on the pad of the PCB, you may be OK with a bad solder joint not making connection to the actual chip pin. If you measured at the chip pin, there's a good chance the chip is dead. This is the only fragile place on a 3080.
6-3.05: OK-ish. About the right bias point
7-9.36: Power supply, OK
8-8.76: no matter

Q1: OK, but collector seems a little low. Don't know how that happens, other than maybe a partial bad solder joint.

Q2: Big problems. Unless you accidentally measured or reported wrong, this one is not connected. As I remeber (and I'm doing this from memory of the schematic) the base is connected to pin 6 of the 3080. The base shows 0V, so it can't be connected because you measured a different voltage on pin 6; otherwise, you have a bad measurement.
C: 6.83
B: 0
E: 0

Q3:Ok-ish
C: 9.19
B: 0
E: 0

Q4:OK-ish
C: 9.19
B: 0
E: 0

Q5: Looks like no pull down to ground through emitter and base resistors.
C: 9.21
B: 8.90
E: 9.21

My best guess is that you may either have some measurement problems, or some soldering problems, or both. If it were mine and I read those readings, I'd inspect the soldering very carefully and maybe resolder all the joints with fresh rosin core solder.

[markm]

5-8.88: a big problem here; pin 5 is the Iabc input and cannot be pulled higher than two diode drops. If you measured this on the pad of the PCB, you may be OK with a bad solder joint not making connection to the actual chip pin. If you measured at the chip pin, there's a good chance the chip is dead. This is the only fragile place on a 3080.


I can attest to this first hand......I've fried a few in my time!

[schnarf]

I resoldered some joints and it's all working. Thanks so much for your help. How should I adjust the trimpot?

[Jay Doyle]

I resoldered some joints and it's all working. Thanks so much for your help. How should I adjust the trimpot?

No kidding here. Adjust it to where the background noise without an input signal from your guitar is highest.

Yes, it sounds counterintuitive, but it works.