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PostPosted: Sat Sep 12, 2020 11:45 pm 
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Hello, I just completed a Classic Fuzz kit, but unfortunately doesn't pass any sound when engaged. The LED works when engaged, and when bypassed the guitar signal passes through just fine. I've reflown every solder already at least once. I tested with the switch in all 3 positions as well with the same result.

I found a test requested in a previous post on a Classic Fuzz kit that looked like it might help. I can get continuity when engaged on the yellow path, but not orange. Thank you very much for your help!

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Last edited by t8bloom on Sun Sep 13, 2020 12:07 am, edited 1 time in total.

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PostPosted: Sat Sep 12, 2020 11:55 pm 
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PostPosted: Sun Sep 13, 2020 11:29 am 
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Do you have continuity between the middle lug of the Level pot and lug 8 of the footswitch when the pedal is engaged?

BTW, you'll only get continuity (~zero resistance) between the orange arrows with the Level pot up all the way (full CW). Otherwise you'll be getting some resistance from the pot itself.

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PostPosted: Sun Sep 13, 2020 3:58 pm 
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Thank you for your help. Yes, I do get connectivity between the middle lug of the Level pot and lug 8 of the footswitch when the pedal is engaged. Thanks!


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PostPosted: Sun Sep 13, 2020 6:27 pm 
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OK, let's check a couple of other things:

  1. Confirm continuity between lug 8 of the F/S and the tip of the output jack.
  2. Switch to resistance mode on your meter and measure the resistance between the inside and middle lugs of the Level pot with the pot fully CCW (should be ~100 Kohms) and fully CW (should be a couple of ohms at most). Disconnect your power source when you do this.

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PostPosted: Sun Sep 13, 2020 8:42 pm 
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Lug 8 to the tip of the output measures as .4 Ohms regardless of how the pot is turned. Hopefully this helps dial it in - we must be close to the source now. Thank you!


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PostPosted: Sun Sep 13, 2020 9:19 pm 
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OK, that confirms #1. How about #2, the resistance across the inside and middle lugs of the Level pot at both extremes of its sweep?

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PostPosted: Sun Sep 13, 2020 9:29 pm 
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Oh yes! Sorry I missed that. Inside to middle pin moves from 4 Ohms to 93k Ohms. Thank you!


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PostPosted: Mon Sep 14, 2020 8:29 am 
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OK, then it looks like your output signal path is fine. I think your initial test result was because you didn't have the Level pot "dimed" so there was resistance through the pot. If you want to confirm that, just repeat the initial "orange arrow" continuity test, but make sure that the Level pot is all the way CW. And if you don't get a continuity signal, switch to your meter's resistance mode--as long as the result between those two points is a few ohms or less, the output path is fine.

I would suggest checking the voltages on the three leads of each of the two transistors next. Do you know how to measure DC voltage with your meter?

Do you own a signal tester?

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PostPosted: Mon Sep 14, 2020 1:56 pm 
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You are correct, I can get signal through the orange path if I use the Ohms meter with the Level turned CW. Thank you! I have a Sperry DM-4100a tester, it can read voltages. I'm guessing this is with the pedal plugged in I got these readings

On the lower transistor, closest to the foot switch I get these readings:
E to C: 1.28 V
B to C: .64 V
B to E: .58 V

Upper transistor, closest to the Level and Bias pots:

E to C: .03 V
B to C: .59 V
B to E: .63 V

I don't have a signal tester, but I'll order one now. Thanks!


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PostPosted: Mon Sep 14, 2020 2:09 pm 
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Please measure the DC voltage between each transistor leg and ground, not the other legs. Here's the method I recommend:

Set your multimeter to the DC voltage mode, indicated by a straight line above a dotted line; use the 20VDC range setting if it's not an auto-ranging meter. Of course, your power source needs to be connected and there needs to be a cable in the input jack. If the pedal is assembled into the metal enclosure, put the black (common) probe into one of the corner screw bosses of the enclosure--this is your ground connection. If the "guts" are out of the enclosure, use the sleeve tab of the input jack for the ground connection. Then touch the red probe to the test point that you want to measure and hold it there until the reading is stable within a couple of hundredths of a volt. Repeat the process for each leg of each transistor.

t8bloom wrote:
I don't have a signal tester, but I'll order one now.

Definitely a good tool to have on hand. And the Classic Fuzz is a very easy circuit for tracing out the signal path.

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PostPosted: Mon Sep 14, 2020 3:42 pm 
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Ok got it! Thanks for helping me with this undoubtedly remedial methodology.

Bottom Transistor, closest to foot switch voltage measured to ground:
E. 0.0 V. (zero volts)
B. .58 V
C. 1.28 V

Top transistor, closest to level pot measured to ground:
E. .65 V
B. 1.28 V
C. .69 V


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PostPosted: Mon Sep 14, 2020 3:58 pm 
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OK, the bottom transistor (Q1) looks perfect--voltages are spot on. The top transistor (Q2)....not so much. The collector voltage is very low, suggesting that you may have the Bias pot turned all the way down. What voltage do you see on the Q2 collector with the Bias pot up all the way (full CW)?

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PostPosted: Mon Sep 14, 2020 4:55 pm 
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Got it. Top transistor voltages with the bias turned all the way up:

E. .68
B. 1.30
C. 5.57


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PostPosted: Mon Sep 14, 2020 6:10 pm 
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That looks reasonable. No difference in the output (or lack thereof) across the sweep of the Bias pot? If not, I think the next step should be using the signal tester to trace out the signal path.

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PostPosted: Mon Sep 14, 2020 6:18 pm 
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Ok sounds good, I'll wait for that to arrive and we'll see what we can find. I'll confirm the if the signal doesn't change over the bias as well. Thank you again for your assistance here!


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PostPosted: Thu Sep 17, 2020 9:35 pm 
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Signal tester arrived and has yielded some interesting results! When engaged and tapped at the 5 pin the pedal successfully works as a fuzz pedal. I then disconnected the signal tester and plugged in the guitar and amp normally. If i jumper pins 5 and 8, the pedal works as normal. Please let me know what you think. Thanks!


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PostPosted: Fri Sep 18, 2020 10:17 am 
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t8bloom wrote:
Signal tester arrived and has yielded some interesting results! When engaged and tapped at the 5 pin the pedal successfully works as a fuzz pedal. I then disconnected the signal tester and plugged in the guitar and amp normally. If i jumper pins 5 and 8, the pedal works as normal. Please let me know what you think. Thanks!


Are you saying that you can hear fuzz when you touch the signal tester to pin 5 of the footswitch? And the volume knob works? And the fuzz knob works? And the bias knob works? And the fat, full, thin switch works? It all works with the signal tester at pin 5? And if you jumper pin 5 and 8, and connect the out jack to your amp, the pedal works as it should?

Does bypass work too?

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PostPosted: Fri Sep 18, 2020 10:58 am 
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Edited my original answers after a re-test. The volume works, but not the bias I believe - I had them backwards previously.

Are you saying that you can hear fuzz when you touch the signal tester to pin 5 of the footswitch? Yes

And the volume knob works? Yes

And the fuzz knob works? Yes

And the bias knob works? NO

And the fat, full, thin switch works? Yes, all work and have different sounds

It all works with the signal tester at pin 5? I reran all of these tests with the pedal plugged in as normal with pins 5 and 8 jumped, but fundamentally it does make a fuzz sound at pin 5 with the signal tester

And if you jumper pin 5 and 8, and connect the out jack to your amp, the pedal works as it should? Yes, minus the bias, it doesn't seem to do anything except crackle a little when I turn it.

Does bypass work too? Yes, works perfectly in bypass

Thank you for your help! I know we're mighty close now.


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PostPosted: Mon Sep 21, 2020 10:21 am 
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t8bloom wrote:
Edited my original answers after a re-test. The volume works, but not the bias I believe - I had them backwards previously.

Are you saying that you can hear fuzz when you touch the signal tester to pin 5 of the footswitch? Yes

And the volume knob works? Yes

And the fuzz knob works? Yes

And the bias knob works? NO

And the fat, full, thin switch works? Yes, all work and have different sounds

It all works with the signal tester at pin 5? I reran all of these tests with the pedal plugged in as normal with pins 5 and 8 jumped, but fundamentally it does make a fuzz sound at pin 5 with the signal tester

And if you jumper pin 5 and 8, and connect the out jack to your amp, the pedal works as it should? Yes, minus the bias, it doesn't seem to do anything except crackle a little when I turn it.

Does bypass work too? Yes, works perfectly in bypass

Thank you for your help! I know we're mighty close now.


I'm at a loss as to how this is even physically possible. Pin 5 is the circuit input. Pin 8 is the circuit output. I suppose if you had 5 and 8 jumpered, you could create a feedback loop. But without the jumper between 5 and 8, it just simply isn't possible for you to hear fuzz at pin 5 with the signal tester.

Remove the jumper between 5 and 8.

Do you still hear fuzz at pin 5 with the signal tester?

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PostPosted: Mon Sep 21, 2020 10:37 am 
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Thank you, this has me confused as well - I've been thinking about it all weekend. Given the scratching I can hear when the bias pot is turned my best guess is that the bias pot is potentially damaged and maybe sending it all to ground, and we are somehow picking up a loop. I'll retest at pin 5 again today and report the results. I was also considering removing the bias pot entirely and/or jumping it's input/output to see if that helped as well.


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PostPosted: Mon Sep 21, 2020 2:03 pm 
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I'm fairly certain now that I must be getting fuzz somehow through ground. When I have the signal tester on switch lug 5 I get fuzz tone. However neither the volume or bias pots do anything in this state. I can also get fuzz tone from lugs 4 and 9, on the right side of the lowest resistor, any of the 3 way switch poles and even the input positive. I suspect the bias pot given the behavior in a previous test so I'll remove that one next and see if that will work if I bypass with a jump.


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PostPosted: Mon Sep 21, 2020 4:34 pm 
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Well I'm willing to call this board a basket case. I can't see or detect anything obviously wrong, but it just doesn't work as expected. I removed the bias pot and tested it but it was fine. I'm at a loss for what is going wrong, but I still really want this to work. Is there a way to order just the board and small parts again? I think at this point it would be easier to just rebuild the board. What is the proper protocol for this kind of thing? Thank you!


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PostPosted: Tue Sep 22, 2020 3:46 pm 
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I am experiencing the same issue and I have run all the same multimeter tests, though I’m waiting on a signal tester to perform those tests. I’m extemely interested in any other insight and what you decide to do with your build from this point.
Thanks!


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PostPosted: Tue Sep 22, 2020 3:53 pm 
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1985RS wrote:
I am experiencing the same issue and I have run all the same multimeter tests, though I’m waiting on a signal tester to perform those tests. I’m extremely interested in any other insight and what you decide to do with your build from this point.
Thanks!

Please start a separate thread for your issue, describe your problem as specifically as possible, and provide a set of photos. These need to be LARGE, well-lit, well-focused shots of BOTH sides of the PCB and all of your switch and jack wiring.

Even those problems that display similar symptoms may have very different causes, so we like to restrict each thread to a single customer problem.

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