Parentheses Fuzz: Distortion switch kills the signal.

[clipped_diode]

Click here to see the "completed" build outside of an enclosure.

I've only done three kits before sourcing parts for this PCB, so I'm still relatively new to DIY pedals. I expected some trouble from the finished pedal because throughout the build several pads popped off and the copper plate is slightly exposed in a few spots. (Ultimately, I don't think the pads caused a problem because in each instance at least one side still had a pad.)

I am using an audio signal probe to diagnose. This post is probably a little premature because I'm still trying to understand the schematic, but here's what I know right now.

1. True bypass works.
2. The effect seems to work. I get a heavy distortion (almost 8-bit velcro ) and an octave sound. I'm not sure how much this pedal is meant to clean up but even with distortion all the way off it is still heavily distorted. EDIT: Playing with a guitar it is clear that this is way more "gated" sounding than it should be. I have to strum HARD for a short spike of sound that quickly falls off. (Like velcro settings on Fuzz Factory or similar.)
3. Turning the octave knob down lowers the total output volume.
4. If I switch the octave switch, the output dies.
5. If I switch the boost switch, the output dies.

I don't have LEDs installed so it's not clear if the sound dies when I engage or disengage the switches. I assume the octave OFF kills the sound because I can hear an octave otherwise. It's not clear to me if the boost is ON or OFF however.

EDIT: Updated title to reflect current issue. It's the distortion switch that kills the signal. Octave switch does nothing. I got the boost side working after replacing a part.

 

[clipped_diode]

Thanks all. I am not sure what a testing rig would be, but I am getting consistent power readings now. Unfortunately the sound is still coming out of pin 6 like velcro and I'm not getting sound out of pins 2 which I believe should be producing sound. Here are my notes on power and sound.

IC1
PIN	POWER	SOUND
PIN 1	8.46 V	Gated fuzz, about as loud as bypass signal
PIN 2	4.10 V	None
PIN 3	4.18 V	Clean
PIN 4	0.00 V	None
PIN 5	0.50 mV	Very quiet, distorted
PIN 6	8.64 V	Gated fuzz, extremely loud
PIN 7	9.21 V	None
PIN 8	9.02 V	Gated fuzz, extremely loud

Q5
LEG	POWER	SOUND
LEG 1	9.20 V	None
LEG 2	1.20 V	Gated fuzz, loud
LEG 3	0.80 V (but multimeter flashes numbers erratically)	Gated fuzz, loud

For reference, below is the part of the schematic relevant to the IC and here is a link to the full schematic.






Also note that I directly wired pin 2 to C11 and then C11 to pin 6 because of a broken pad on C11 (see photos below). Let me know if you think I misread the schematic here.

 

[Nostradoomus]

I would desolder your PF5102 and put a socket in there, this circuit is pretty picky as the output buffer can overload pretty easily...I had to try a few before it sounded good...actually ended up with a 2n5458 in there like Proco does. Your opamp voltages aren’t bad...dunno why Pin 5 has any voltage, it’s not connected to anything.

 

[clipped_diode]

I would desolder your PF5102 and put a socket in there, this circuit is pretty picky as the output buffer can overload pretty easily...I had to try a few before it sounded good...actually ended up with a 2n5458 in there like Proco does. Your opamp voltages aren’t bad...dunno why Pin 5 has any voltage, it’s not connected to anything.

Thanks. I can try swapping out the PF5102 and using a socket in the coming days. But I think the issue is further upstream in the schematic, right? Because the sound is leaving the IC with a heavily gated sound. Is that how it sounds coming out of your IC?

Regarding pin 5 voltage, the reading is actually mV, so it's actually an incredibly low reading. I edited my post to update it.

 

[Nostradoomus]

Couple things to check just for fun...R22 and R21 are the correct value? 560r and 47r?

30pf cap between Pin 1-8 correct value?

Each end of the 1M resistor at R6 measuring around half of the supply voltage?

Distortion pot the correct value?

 

[clipped_diode]

Couple things to check just for fun...R22 and R21 are the correct value? 560r and 47r?

Yes — these are the correct values, and each end measures around 4.10 V.

30pf cap between Pin 1-8 correct value?

Yes it is a 30pf cap I ordered from Pedal Parts Plus. Small Bear had none in stock. It was the only PCB component I ordered from Pedal Parts Plus. Unfortunately I didn't test it before installing it and I can't get a reading on it mounted to the PCB.

I am may just directly wire this connection just to eliminate another potential point of failure.

Each end of the 1M resistor at R6 measuring around half of the supply voltage?

The top measures 4.18 V and the bottom is 4.60 V.

Distortion pot the correct value?

Yes — Alpha A 100K.

 

[Nostradoomus]

Hmmm, the 30pf cap could be your issue. It’s pretty integral to the gain bandwidth of the chip. You can check it by desoldering one leg.

The LM308 is not a stable chip by any means, the Rats sound came partly by the designer putting a 47r resistor in place when he meant to put 470r, overloading the op amp. You could try upping the value of 47r to 100r to try and tame it a bit.

 

[clipped_diode]

Hmmm, the 30pf cap could be your issue. It’s pretty integral to the gain bandwidth of the chip. You can check it by desoldering one leg.

The LM308 is not a stable chip by any means, the Rats sound came partly by the designer putting a 47r resistor in place when he meant to put 470r, overloading the op amp. You could try upping the value of 47r to 100r to try and tame it a bit.

Thanks. I clipped one leg of the 30pf cap and still wasn't getting a reading. So I cut the other leg out and tested it off the PCB. No reading. Tested some polarized caps I have lying around and the multimeter is working fine. I'll order a new 30pf cap and hopefully that solves the issue.

Took forever to arrive the first time so I'll shop around.

 

[Nostradoomus]

Some meters have trouble reading caps at such small values, but I’m not sure which one you are using. I have one of those eBay transistor tester things that reads small caps pretty well.

Well now that you have the cap out have you got an LM741 by any chance? If you do swap the 308 out and see what it does. If not try putting the cap back in and upping the 47r.

 

[clipped_diode]

Some meters have trouble reading caps at such small values, but I’m not sure which one you are using. I have one of those eBay transistor tester things that reads small caps pretty well.

Well now that you have the cap out have you got an LM741 by any chance? If you do swap the 308 out and see what it does. If not try putting the cap back in and upping the 47r.

I have this AstroAI. Unfortunately I don't have an LM741 on hand.

 

[Nostradoomus]

Hm well I think most DMMs are not super capable of doing 30pf but if you have a larger cap like 470pf measure it then measure both of them together and see if it adds up.

Did you leave enough leg to re-solder it back? I would try the 47r to 100r swap before you spend more money

 

[DGWVI]

Any standard single opamp will work in the circuit, if you have any lying around.
Do the controls for the Rat have any bearing on the sound?
And, just to be thorough, the octave is disengaged? It's a very gated circuit

 

[Nostradoomus]

If you have the compensation cap out yeah you can try some others. TL070 Or TL061 seem to be favourable but chuck anything in and see how it goes.

 

[DGWVI]

If you have the compensation cap out yeah you can try some others. TL070 Or TL061 seem to be favourable but chuck anything in and see how it goes.

I've not any issues using other singles with or without the comp cap. Even the 308 runs fine without it (one half of my dual distortion+ uses the 308, and I've built an opamp Big Muff using on in the clipping stage)

 

[Nostradoomus]

Weird. My Rat goes directly to ass territory if I mess with it haha

 

[DGWVI]

I've had some rats go haywire (huge sag, and gating) with the Fairchild metal can versions, but the DIP versions don't seem to care

 

[Nostradoomus]

Mine are DIP versions too, who knows. This circuit was designed around exploiting the flaws in the LM308 so it’s not exactly stable hahah

 

[clipped_diode]

Following up here. I replaced the 30p capacitor. It did not change the sound at all. I am getting an intensely gated fuzz from pin 6 of the IC, and basically the same sound out of the output. The fuzz is so extreme that the octave makes no real audible difference, but just to be clear — yes, I am testing it with the octave off. This is not a gated-but-usable sound. It sounds like you're tuning an AM station between stations and getting flashes of silence (when it's under threshold) and flashes of blow-your-ears-out white noise that vaguely sounds like the main vocal melody of the song I'm in fact playing through the pedal.

The issue is happening at the IC before the audio signal leaves pin 6. The audio signal enters at pin 3 mostly clean (or octaved if that switch is on). But it leaves pin 6 a total mess. I have a hunch that the issue is with the power. I don't understand how the power is coming in as "VCC" on the schematic, but on the actual PCB the power traces multiple components sometimes before hitting my target component. That means there is an opportunity for error. But I'm not seeing that clearly depicted on the schematic. How do I check every point of power before it hits the IC? And how do I check all of these lines that branch off and run through resistors/caps and then to ground?

The only ICs I have are ones that are in working pedals I've built. I have a BYOC Rat clone that has the LM308N I have been using. I have a BYOC Klon clone with two TL072s and a 7660SCPA. I have an Aion Lovepedal clone with an NE5532P. A replacement LM308N will be here in a few days.

Things I will try now:

1. Directly wire the IC to the 30p cap.

2. Replace R22 with a 100R resistor. I'm skeptical this will solve the issue because the gate is really intense (absolute silence) and the fuzz, when it's past the threshold, is totally blown out. But it's easy enough to try.

 

[Chuck D. Bones]

IC1-6 is not supposed to be at 8.64V. Pins 2, 3 & 6 should all be near 4.5V and more-or-less equal. Something is wrong in IC1's feedback circuit. With power off, SW1 in the middle position and IC1 out of the socket, measure resistance from pin 2 to ground. The reading should start low and climb as C13 & C14 are charged up by the meter. Should get to 100K or higher, depending on the meter and the leakage in C13 & C14. Also, make sure C13 & C14 are oriented correctly.

 

[clipped_diode]

IC1-6 is not supposed to be at 8.64V. Pins 2, 3 & 6 should all be near 4.5V and more-or-less equal. Something is wrong in IC1's feedback circuit. With power off, SW1 in the middle position and IC1 out of the socket, measure resistance from pin 2 to ground. The reading should start low and climb as C13 & C14 are charged up by the meter. Should get to 100K or higher, depending on the meter and the leakage in C13 & C14. Also, make sure C13 & C14 are oriented correctly.

Thanks. Measuring resistance with the red probe at pin 2 and the black probe at pin 4 I don't get any resistance reading. I also tried the black probe on the enclosure and got the same result. Does this indicate a problem with C13 or C14? They are both oriented correctly.

 

[Chuck D. Bones]

That's good. The resistance is off the scale, as it should be. See if any of the other pins on IC1 read resistance to ground.

Then measure the resistance between pis 2 & 6 with the distortion pot at zero, noon & max. Those measurements should be 0 Ohms, 15K and 100K, more-or-less.

One more resistance measurement: pin 1 to pin 8. Should be off the scale.