First Pedal Problem: No Sound from Fuzz Dog's Axis Fuzz

[JMac26]

Hi there,

I am attempting my first pedal build, the Fuzzdog's Axis Fuzz. I am at the stage of testing the effect before soldering the OptoPuss bypass, but am not getting any sound other than buzzing.

I am following this instruction document: http://pedalparts.co.uk/docs/Axis-V3.pdf

Here's the OptoPuss document: http://pedalparts.co.uk/docs/OptoPuss.pdf

I have a 9v battery with the positive terminal connected to V on the board. The battery's ground is connected to the input/output jack grounds and the ground on the board. The tip of each jack is connected to the respective in and out on the board. Is there anything I am missing here?

I am going to use the OptoPuss Bypass switch which is on a daughter board, so I have left off the 2k2 resistor (R12) and also the document suggests leaving out R8 and C7 for a better sound, which I have done for now. I don't know if this makes any difference to the circuit working? As far as I can tell the R12 is just to protect the LED.

I've attached some pictures of where i'm at so far, if anyone has any suggestions for what the problem could be I would be very grateful!

[idy]

Leaving R8 and C7 off is OK and the R12 is just for the LED. Sure you have the transistors in the right places? 3904 and 3906 are complementary, opposite polarities (NPN and PNP.)

Then I suggest attaching a capacitor to your alligator clip and use it as a signal probe. Does sound reach the pcb? Base of Q1? Base of Q2? volume control?...

[JMac26]

Thanks for the reply. I've double checked the transistors and they are in the right place and the correct orientation. Yes i'm going to try checking ground continuity and then will look into setting up a signal probe.

[JMac26]

Leaving R8 and C7 off is OK and the R12 is just for the LED. Sure you have the transistors in the right places? 3904 and 3906 are complementary, opposite polarities (NPN and PNP.)

Then I suggest attaching a capacitor to your alligator clip and use it as a signal probe. Does sound reach the pcb? Base of Q1? Base of Q2? volume control?...

I tried what you suggested with the signal probe. I have signal at the base of Q1 but not the base of Q2. Does this mean Q2 is damaged? 

[Marcos - Munky]

Since Q2 base is connected to Q1 emitter, the signal is interrupted around Q1. This doesn't really mean Q1 is damaged. Try to reflow Q1 solder joints.

Also, welcome to the forum!

[JMac26]

Since Q2 base is connected to Q1 emitter, the signal is interrupted around Q1. This doesn't really mean Q1 is damaged. Try to reflow Q1 solder joints.

Also, welcome to the forum!

Thanks!

I've checked continuity between Q1 collector and R9 so the signal is getting to R9. However, when I check continuity between R9 and Q2 base, there is nothing. (I've tried swapping the probes and different legs of the transistor just in case, with no luck). This doesn't really make any sense to me, as it should just be an open circuit between R9 and Q2, right?. Would this suggest a fault with R9, I have already tried re-flowing the solder on this and on both transistors.

Also, there is continuity between Q2 and R7, which makes me think it's something to do with R9

[duck_arse]

also welcome, JMac26.

signal at the base of Q1 indicates no more than signal passing C1. what indicates more is the voltages. please measure the voltages on the transistor pins, and the supply voltage, always our first steps, and post them here.

[JMac26]

also welcome, JMac26.

signal at the base of Q1 indicates no more than signal passing C1. what indicates more is the voltages. please measure the voltages on the transistor pins, and the supply voltage, always our first steps, and post them here.

Thanks!

I am new to this so apologies if this seems incorrect. I have my multimeter set to continuity checker. The readings I believe are in mV:

Q1
- 875mV (Positive probe on emitter)
- 867mV (Positive probe on collector)

Q2
- 843 (Negative probe on emitter)
- 764 (Negative probe on collector)

Also, the battery i'm using measures as 8.5V.

[idy]

Use voltage setting. Black probe to ground, red probe touch the three legs of each transistor.

[JMac26]

Use voltage setting. Black probe to ground, red probe touch the three legs of each transistor.

Apologies, thanks for the tip. Here's what I measured:

Q1
- Emitter - 4.51V
- Base 3.94V
- Collector - 4.45V

Q2
- Emitter 0V
- Base 0V
- collector - 6.72V

[idy]

Careful with those dashes (I guess?) that look like minus signs. You will not see voltages below zero in this circuit.

Q2 voltages are bad.

You can be sure that Q1C and Q2B are not connected! If they were they would be the same voltage. Can you visually see where there should be a trace between these two on the PCB?

My (homemade but working) Axis reads:
Q1
E 4.45
B 3.72
C 3.33

Q2
E 2.7
B 3.33
C 6.07

[JMac26]

Careful with those dashes (I guess?) that look like minus signs. You will not see voltages below zero in this circuit.

Q2 voltages are bad.

You can be sure that Q1C and Q2B are not connected! If they were they would be the same voltage. Can you visually see where there should be a trace between these two on the PCB?

My (homemade but working) Axis reads:
Q1
E 4.45
B 3.72
C 3.33

Q2
E 2.7
B 3.33
C 6.07

Thanks, that makes sense. Yes those were dashes not minus aha. I've tried looking at the pcb under a light but its difficult to see the trace between them on the pcb. The only connection I can see going to the Q2 base is coming from the one of the R8 pins (which is currently empty, as suggested on the instruction document). But the signal would still pass through this without this component, right?

[antonis]

Q1
- Collector - 4.45V

Take measurements on respective points to see what's happening..

[idy]

So there is a trace from the unpopulated R8 to Q2B, does that trace also go to Q1C? It needs to!

Here you would test for continuity. From Q1C to Q2B. Apparently not connected!

[JMac26]

So there is a trace from the unpopulated R8 to Q2B, does that trace also go to Q1C? It needs to!

Here you would test for continuity. From Q1C to Q2B. Apparently not connected!

So the only connection I can see that goes to the base of Q2 is coming from one side of the unpopulated R8. The other side of the unpopulated R8 goes to Q1 collector. This is the connection I am looking for. But it should still work without the resistor in place right? What could cause the signal to not pass between those two points?

[antonis]

So the only connection I can see that goes to the base of Q2 is coming from one side of the unpopulated R8. The other side of the unpopulated R8 goes to Q1 collector.

No..!! 

According to schematic, BOTH Q1Collector & Q2Base should be connected to the SAME R8 pad..

[JMac26]

So the only connection I can see that goes to the base of Q2 is coming from one side of the unpopulated R8. The other side of the unpopulated R8 goes to Q1 collector.

No..!! 

According to schematic, BOTH Q1Collector & Q2Base should be connected to the SAME R8 pad..

Yes sorry you're right, it's because the lines are on opposite sides of the board so i'm getting confused. But yeah I can see where connections between those two points are supposed to be, both going via the same R8 pad. What I don't understand is why no voltage / signal is passing through. If there's the correct voltage on Q1 collector, then it should go straight to Q2 base, right?

[iainpunk]

If there's the correct voltage on Q1 collector, then it should go straight to Q2 base, right?

it might be that the double sided board relies on the lead form R8 to make the connection? solder a tiny piece of component leg in the hole, and solder both sides, than check for function, i would bet on this if i were allowed to bet.
if that's not the case its probably a bad solder point, or if that's not the case as well, it might be a bad track, which you can fix by putting some wire from solder point to solder point across the bit that's bad.

cheers

[Marcos - Munky]

Yeah, some of the double sided boards (the more well made and sometimes more expensive) have tinned through holes, that means there are a metal layer inside the hole that connects whatever is connected to each side of the hole. The simpler double sided boards doesn't have this connection, so you have to use the lead of the part that goes thru this hole to connect each side.

The latter isn't a "bad" board, since they're cheaper and easier to be done and the connection by the part's lead is simple enough. But, since there is a note on the build instructions saying you can leave out this exact resistor, there should be a note saying to put a piece of lead connecting each layer of the board - and there isn't a note saying that. Actually, from one of the pics on the build doc, the holes seems to have tinned thru holes. See page 3, the round hole bellow "A" and the square one bellow this round one. I'd bet on a bad/broken track, easily fixable using a piece of wire.

Just to be sure, put your meter on continuity mode. Both probes on that R8 pad, one on each side. Just be careful for them to not acually enter the hole and touch each other. Is there continuity?

And also test the continuity for this:

So the only connection I can see that goes to the base of Q2 is coming from one side of the unpopulated R8.

[JMac26]

If there's the correct voltage on Q1 collector, then it should go straight to Q2 base, right?

it might be that the double sided board relies on the lead form R8 to make the connection? solder a tiny piece of component leg in the hole, and solder both sides, than check for function, i would bet on this if i were allowed to bet.
if that's not the case its probably a bad solder point, or if that's not the case as well, it might be a bad track, which you can fix by putting some wire from solder point to solder point across the bit that's bad.

cheers

I think you're probably right. Unfortunately, trying to solder a component leg into the R8 slot, i've melted the connection on the pcb and now the solder won't go into the hole