Axis fuzz clone help

[bluebunny]

Comparing with many other schematics for the Axis fuzz, this one posted by brudy92 is correct except for the unfortunate symbol used for the 2N2906.  It is indeed a PNP, despite the outward-pointing arrow.  Here's an example:

[Fancy Lime]

Hi brudy92,

The wiring diagram you poster looks correct. On the gray PCB template we can also see that Q2 is oriented correctly. However, the traces to Q1 are on the backside. Can you post a picture of the backside of the PCB? If you don't have the template for that, a photo is probably fine. The photo of the front looks like one can see the traces through the black coating. You might need to hold it to the light in a certain angle for the traces to show nicely.

But I think I found the problem: Do I see that correctly in your photo that the resistor in R1 position is red-red-black-SILVER-brown? That would make it 2.2Ω but it should be 2.2MΩ and have the code red-red-black-YELLOW-brown. If there really is a 2.2Ω resistor to ground instead of a 2.2MΩ, that would explain why there is no sound. That so-called anti-plop resistor forms a voltage divider with the impedance of your guitar. It needs to be much larger than the guitar impedance to not suck tone and volume and 2.2Ω is in fact much much smaller than any guitar impedance. The rest of the resistors seem correct, although I cannot see the multiplier of R9.

Please also double check all capacitor values and orientations and the transistor part numbers. I could not see those on the picture. Also: can you tell us what the value of "level" pot actually is? The schematic you posted says "2KB", which I assume is supposed to mean 2kΩ linear. That is going to get you very low output volumes. If it indeed is a 2k, you might want to replace it with a 50k or 100k and I for one would go with audio taper (aka "logarithmic", "log" or "A"), not linear (aka "B").

Future tip for easier debugging: Try to orient all resistors the same way, so that the codes can all be read from top to bottom or left to right. Makes it easier to spot such errors on a quick glance.

Since there are a number of errors in the schematic and maybe even in the parts that were supplied with the kit (if it was a kit, not just the PCB), I think the manufacturer and their future customers would greatly appreciate if you let them know about the errors, once we have collected and fixed all of them.

Hope that solves it and good luck,
Andy

[brudy92]

Nope, 2N3906 PNP is the correct BJT to use as Q1 in an Axis Fuzz, it's just the symbol in the schematic that is wrong.
Andy

This is what I thought.  They've got V+ going to the emitter of Q1.  I thought it would need to be PNP to work in this setup, but TBH it's a little over my head.

But with multiple obvious errors on the schematic, who knows how much else is wrong.

You're schematic is good except all of your signal out is going to ground. 2k pot to out is wrong.

Sent from my SM-S327VL using Tapatalk

What should I do to correct this?

[bluebunny]

Use a 47K (or 50K) pot like the one in the schematic above.

[Fancy Lime]

And if the Resistor that is supposed to be 2.2MΩ really is 2.2Ω as it looks, replace that too. That one dumps all your input to ground at the moment. Change that and the Level pot, and let us know if it works.

Andy

[brudy92]

And if the Resistor that is supposed to be 2.2MΩ really is 2.2Ω as it looks, replace that too. That one dumps all your input to ground at the moment. Change that and the Level pot, and let us know if it works.

Andy

Hi Andy, thanks so much for your help. I put the 2.2m in and it worked. Unfortunatly when taking out the 2k pot for the 50k I melted the board and can't get the points to solder...so back to not working lol I think I'm just going to buy a new pcb and try again with some of the tips I learned here. Thanks all who commented

Bryan

[Fancy Lime]

Hi Bryan,

my pleasure. Sorry to hear about the misfortune with the pot soldering. Better luck next time! But be assured, you're not the first one to have this sort of problem. I discarded many builds that worked fine until I changed some tiny little detail and screwed the whole thing up in the process. I still have an Ampeg SVT simulator lying around that sounded fantastic until I decided to change one, just one capacitor and its been dead ever since and its a complete mystery to me what is wrong with it despite days of probing. These things just happen, I guess.

Cheers,
Andy