Fuzzy Foxx Trouble

debrad

debrad

Active member
Hi folks!

Troubleshooting my build...I've got very little output and it's clean (not distorted at all). I've noticed that D2 and D3 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!
 
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I'll try to get some photos. As Nostradoomus says, Q1 and Q2 look pretty messed up but it appears Q3 and Q4 aren't too bad.

I installed sockets for the transistors so I just stuck some 2N5088s in to see if everything worked...no dice! I also swapped the four of them around to see if that might highlight a faulty one but the measurements remained the same.

I'm also set to go in with the audio probe to see where the signal might get messed up but was hoping the forum members might be able to help me focus on a smaller area of the circuit. I'll start with the resistors around Q1 and Q2 but their colour codes seem to match what's supposed to be there (I didn't measure or test to see if they might be faulty or bridged...).

Is there any chance the caps around Q1 and Q2 could be causing any problems given the voltages I've measured? How about those "shorted" D3 and D4 diodes (keeping in mind that I measured them IN THE CIRCUIT)?
 
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D3 and D4 are clipping diodes, the anodes are opposite each other, if you used germanium diodes the forward voltage on them is low so they may look like a short, as long as you have them installed correctly according to the board they should be good.
 
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Thanks Chas.

Just before giving up on this one for the night, I tried to use my iron to remove what I thought was a blob of solder from the leg of one resistor and it turned out that resistor had a broken lead! I swapped in a resistor and now all my voltages align pretty nicely with the General Guitar Gadgets values (Q3 collector is still a little low but everything else looks SO much better!).

Thanks to everyone who chimed in with suggestions...your help is MUCH appreciated!
 
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I just checked mine, the voltages are close to what GGG says they should be. I was going to suggest looking at resistors on the feedback path from Q2 emitter to Q1 base. So what resistor was it, I'm curious.
 
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