Debugging My Parentheses Fuzz

[debrad]

Hi Everyone!

Having searched the forum and read several threads on troubleshooting the Parentheses Fuzz, I still can't seem to solve the problem I'm having so I'm hoping you might be able to help me out...

A friend of mine recently asked me to debug a pair of Parentheses builds he was working on. The first thing I noticed was that a) neither board had any function in the distortion, octave, or boost circuits..and b) neither board had any measurable voltages beyond D100. Fortunately, one board roared to life after swapping the polarity of the DC jack so I was hoping the same would be true for the second. Swapping the DC jack polarity DID fix the octave and boost circuits on this one but the distortion is still not working right.

Engaging the distortion switch completely silences the output and when I run audio into the pedal I can only trace it to the board's input pad. By the time the signal reaches the first component (R1), it's just a frequency tone. I can alter it with the distortion controls, boost it with the boost switch, and switch octaves with the octave switch but I can never hear the actual audio that I'm sending into the circuit.

Does this sound like a problem between the input pad and the first component or is it more likely that an issue downstream is impacting the signal at R1 (I get the same tone at R2, R3, R4, and Q1)?

I look forward to your suggestions!

Thanks,

- brad -

 

[Robert]

You should have the same signal on R1 as you do on the Input pad. When the distortion switch is on those are electrically the same points.

If you have a DMM measure the resistance between the input pad and R1.

Post a pic of the build if you can.

 

[debrad]

Thanks PedalPCB...I'm kicking myself for not checking the continuity before posting (that's one of the first debugging steps, no?).

Anyway, a couple of interesting things about the resistance: if I follow the trace from the input pad to the connection at R1, there is infinite resistance; however, if I measure to the opposite side of R1 (i.e. the R1 pad at the "top" of the), the resistance is very low (~0.4 ohms).

Also, if I measure the resistance between the input pad and the "bottom" pad for R2, the resistance is again very low and yet the resistance between the bottom pad of R2 and the bottom pad of R1 is infinite.

Finally, if I crank the amplitude and use a set of alligator clips to jumper the input pad to the bottom connection of R1 then I can hear my audio.

Looks like the R1 connection is probably my culprit; however, does it make sense for me to be seeing such a low resistance between the input pad and the "top" side of R1 (i.e. input to ground)?

 

[Robert]

Post a pic of the PCB and wiring, there are a few different revisions of the Parentheses PCB so it's hard to say without seeing which one you're working with.

 

[debrad]

Amazing how much more detail you can see in these photos...even compared to my magnifying headgear! Lots of resin dust may appear like solder "hairs" (I've looked close and there aren't any bridges) and what appears like a solder bridge on the distortion switch in one photo is shown to NOT be a bridge in the other (yes, I have double checked!).

 

[debrad]

I couldn't get any continuity between the input pad and the first component pad (R2 I believe) no matter what I did so I quickly soldered in a jumper and the distortion circuit roared to life! I think one the input pad must have lifted (R1 and R2 were showing continuity so my assumption is that they must have still been OK)

Feeling pretty sheepish about making my first forum post before doing such an obvious debugging step but VERY grateful for the quick response from The Admin (thanks so much!).

I'm very impressed with the board, the sound quality of the resulting circuit(s), and the awesome service so I can hardly wait to order a board of my own and put it together!

- brad -

 

[Robert]

Feeling pretty sheepish about making my first forum post before doing such an obvious debugging step but VERY grateful for the quick response from The Admin (thanks so much!).

Hey, you fixed it. That's all that matters.

In my experience the simplest issues are sometimes the hardest ones to find... and you were right on top of the problem.

 

[debrad]

Thanks!