Foxx/Wolfshirt Problems

[Brad Hill]

Hi folks!

Troubleshooting my build...I've got very little output and it's clean (not distorted at all).  I've noticed that D3 and D4 are "shorted" (i.e. same voltage measured in same direction) but I'm not sure if that's an issue in this circuit.  I have also measured the following voltages so I'm hoping someone can point me in the direction of the most likely culprit(s).

Voltages:

Supply at board = 9.14

Q1:
C = 5.38 (General Guitar Gadgets (GGG) calls for 2.20)
B = 0.00 (GGG calls for 0.73)
E = 0.00 (GGG calls for 0.16)

Q2
C = 4.77 (GGG calls for 7.50)
B = 5.38 (GGG calls for 2.20)
E = 4.74 (GGG calls for 1.60)

Q3
C = 6.94 (GGG calls for 7.28)
B = 0.83 (GGG calls for 0.78)
E = 0.21 (GGG calls for 0.22)

Q4
C = 7.53 (GGG calls for 7.63)
B = 0.82 (GGG calls for 0.84)
E = 0.24 (GGG calls for 0.26)

Any help would be much appreciated!

[mauman]

If it's a Madbean Wolfshirt2020: Q3 and Q4 voltages look pretty good.   Q1 and Q2 voltages don't look right.  Check the orientation of Q1 and Q2 to ensure they're inserted correctly, there are multiple holes.  Q1 & Q2 should be inserted the same as Q3. (Q4 is rotated.)

Also verify the values of the resistors around Q1 and Q2 (R2 thru R7 and R9). 

A picture would also be helpful!  Mike

[Brad Hill]

OK.  I'll see what I can do for a photo.  In the meantime, I'll investigate those resistors (I did check that the colour codes match what they are supposed to be but didn't measure or test to see if they might be bridged somewhere they're not supposed to go).  I'm also set to go in with the audio probe to see where the signal might get messed up.

Could the caps around Q1 and Q2 be suspect as well (given the voltages I've measured)?  How about those "shorted" D3 and D4 diodes (keeping in mind that I measured them IN THE CIRCUIT)?

[jimilee]

It's highly unlikely the caps are the issue unless you melted them. Check all your parts and orientations. Reflow all of your solder joints. This usually fixes about 90% of problems. It will be a little easier to look over instead of guessing once you have those pics up.


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[mauman]

+1 to jimilee's suggestions. 

Re: the diodes D3 and D4, they're tied nose to tail in the circuit, so if you measure them in-circuit they should look the same in either direction.  They're clipping the signal by the same amount during both positive and negative excursions. 

[Brad Hill]

Well, I measured resistors, I checked and re-checked orientations and potential solder bridges, I poked and I probed and I almost packed it in for the night.

By pure dumb luck, I decided to touch R6 with my iron where it looked like I had an extra blob of solder on the leg and something moved around like a piece of debris...turned out it was part of the resistor's leg - it was broken off right at the mass of the resistor!  I replaced it with a new 100k, re-tested the voltages and everything looks MUCH better (my Q3 collector is now closer to 6.8 rather than GGG's 7.28 but everything else is nice and close).

I didn't get to REALLY fire it up since it's about midnight and I live in a townhouse but I'm looking forward to test driving it tomorrow!

Thanks for the feedback...it helped me zero in on those R2-R9 resistors!

[mauman]

Congrats!  Let us know how it works out.

[Brad Hill]

IT'S ALIVE!!!

One of the resistor's pads was a little suspect so I soldered in a jumper to the next component...just to make sure...but, aside from that everything is sounding great.  I'm going to put it up against my rehoused Danelectro French Toast later today but, on its own, it's a pretty excellent fuzz.

[jimilee]

Nice! Broken resistors are sure hard to spot. I once had one that wouldn't show up until the pedal warmed up a little bit. Drove me mad.


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