Flock Harmonizing Fuzz - getting feedback squeal

mcluff

mcluff

Member
Maddening problem with my Flock Harmonizing Fuzz. Thanks to this thread, I've tried re-flowing the rotary switch pins (and pretty much everything else), swapped out ICs and such. Still, no joy!

The problems:
  1. Persistent feedback squeal where the pitch changes based on the "track" knob.
  2. Nothing changes with the rotary switch
Squeal detail: doesn't go away if you stop sending audio through it.

Here's my quickie video of the problem:

IMG-6599.jpg IMG-6600.jpg
 
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My flock did the exact same thing. I ended up swapping out 46 and 24 and reflowing. I think ultimately I had a bad 46 (I may have overheated it in reflows) combined with flow issues on the rotary child board. If you have header pins from Tayda they are hard to get the solder to stick to them in some cases and it’s next to impossible to see what’s going on under that board sandwich.
It sounds like you did all the same trouble shooting. Have you checked all the joints with a magnifier maybe something is not connecting. You could also trace the sound and see where the oscillation starts up. Good luck I know how frustrating this one can be. But it’s worth all the effort once you remedy it.
 
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mcluff said:
Maddening problem with my Flock Harmonizing Fuzz. Thanks to this thread, I've tried re-flowing the rotary switch pins (and pretty much everything else), swapped out ICs and such. Still, no joy!

The problems:
  1. Persistent feedback squeal where the pitch changes based on the "track" knob.
  2. Nothing changes with the rotary switch
Squeal detail: doesn't go away if you stop sending audio through it.

Here's my quickie video of the problem:

View attachment 40737View attachment 40738
Click to expand...
Resurrecting a zombie thread, I'm having the same feedback issue with my flock. Did you ever get this one sorted?
 
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Is it me or is C1 backwards on that schematic?
Also, I have a really loud whine on pin 1 of my TL72, and an intermittent burst of noise every few seconds. Can someone post working voltages for the ICs please?
 
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Paul_510 said:
Is it me or is C1 backwards on that schematic?
...
Click to expand...
No, not backwards.

Have a look at the input cap. here:

ElectroSmash - Big Muff Pi Analysis

Circuit, List of Materials / Parts List, Input Booster Stage, Shunt Feedback Common Emitter Stage, Input Booster Voltage Gain Calculation, Input Impedance Calculation, Input Booster Frequency Response, Clipping Stage, Sustain Circuit, Clipping Amplifier V
www.electrosmash.com www.electrosmash.com

and at the following — notice that all the polarised caps have their + side facing towards the nearest transistor
(C1 C4 C5 C13 C14 C3 C17 C2):

Ibanez_OD850_FirstEd_Schematic.jpg





Sorry I can't help with your other question.



EDIT: Here's a Wampler schematic where it points away 🤷‍♂️...
www.wamplerpedals.com

How to design a basic overdrive pedal circuit - Wampler Pedals

www.wamplerpedals.com www.wamplerpedals.com

tone-control1.png
 
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Thanks for the schematic @Sturgad that's really helpful. Just tracing it through

I'm getting signal from TL072 to pin 14 (SIGIN) of CD4046BE, but VCOOUT on pin 4 is that constant squeal sound

I removed the CD4017BE and CD4024BE from the sockets and listened again, the same squeal is present on VCOOUT so it's definitely the source of the noise

I've used a TL072CP as a substitute for the TL072IP - I think this could be the problem

It should be a fair substitution but here the first half of the op amp is being driven directly into the second half to square the signal off for the PLL. Perhaps there's an extra bit of noise or something that's faffing it up

OP shows TL072CP and the three successful build reports I've found al have TL072IP (here, here and here)

I tried an NE5332 and that changed the issue but did not fix it
 
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ftumch said:
I've used a TL072CP as a substitute for the TL072IP - I think this could be the problem

It should be a fair substitution but here the first half of the op amp is being driven directly into the second half to square the signal off for the PLL. Perhaps there's an extra bit of noise or something that's faffing it up

OP shows TL072CP and the three successful build reports I've found al have TL072IP (here, here and here)

I tried an NE5332 and that changed the issue but did not fix it
Click to expand...
FWFW . . . There is no measurable/detectable difference between a TL072CP and a TL072IP. They are swappable with zero issues. I used the TL072IP in mine and many other builds without problems.
And the VCOOUT of the 4046 is a clock signal and should be part of the audio chain at all. If that's the noise being heard, you may want to dbl-check the authenticity of the 4024 & 4017 chips - they should not be leaking the clock signal into the audio.

If you please, what are the exact part IDs on the CMOS chips you're using?
 
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