IC Big Muff on vero - high pitch whine when engaged

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WuKong
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Post by WuKong »

Hi all, been a few years out of the DIY game and my first foray back into it has gone a mess - any advice appreciated! Had to make a new account as I lost my last!

It's an Opamp Big Muff on vero from gila_crisis, bypassed is fine and clean but when engaged it's just a loud high pitched whine that reacts to all of the pots, no guitar signal it's just the squeal.

Same through DC or battery, in or out the box. I've checked the wiring and double checked for any bridges with a meter and also knifed just in case.

I might have a bad batch of opamps, but I've tried 3 of each and all the same - they are ua741cn and jrc4558d

I couldn't find any similar situations through search or even any readings to compare with, hence I'm bothering you all for help :scratch:

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WuKong
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Post by WuKong »

Yes I know, please forgive my sin for the all-yellow wiring :slap:
SmartSelect_20210612-155134_Gallery.jpg
SmartSelect_20210612-154836_Gallery.jpg
SmartSelect_20210612-154920_Gallery.jpg
Thank you kindly

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stolen
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Post by stolen »

Hi!

The whine is caused by a feedback loop. This might be parasitic (i.e., caused by capacitors/transformers that don't really exist as components but emerge from the proximity of conductors) or layout/build specific. Since your layout is verified and your wiring layout seems noncritical, we don't think it's a parasitic effect. Bad OPAs causing this is unlikely in our opinion.

We'd go about debugging something like this: As trivial as it sounds, check if there is no short between input and output (with the effect turned on). A single wire strand is often hard to see and would explain the behavior perfectly.

Frankly we're more of a perfboard girl and don't have a lot of experience with stripboard, but from looking at it we're not quite sure if all of your cuts properly isolate - it would be worthwhile to test the conductivity across each cut to make sure this is not an issue. We're not sure if you already tested for that from your description, apologies if we misunderstood.

If your build passes both of these tests, you could check for parasitic feedback: Simply move the wires in the box and see if the whine changes. Try this at a couple of different potentiometer positions to make sure. If this is the case, braiding the wires to the "sustain" potentiometer and moving it away from C10 could help.

Not sure if any of these solve it, but it's a start!

All the best,
stolen.

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Post by julessouren »

On the bottom side picture, top left corner (same as top side picture bottom left corner?) you have the top row (ground) bridged to the one below it. This grounds C5, R9 and R10.

Edit: did miss a cut on the 2nd row, 2nd column on the bottom? If so, then scratch the above and/or verify the track cut.

Toilet time is up, hope this might've been useful!

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Post by WuKong »

Thanks so much for the helpful replies!
So far I've checked every trace with a dmm and also inspected with a magnifying glass and scraped between traces- still the same issue..

So now today I've just rebuilt it from scratch and checked every joint with a dmm after soldering every part and then double checked visually and again with the dmm and guess what? Exactly the same noise :slap:

I've been tapping parts for loose connections or any audio changes when moving wires etc and nothing..

Are the capacitors I've used ok? Everything else checks out and I'm lost :(
SmartSelect_20210617-194539_Gallery.jpg
SmartSelect_20210617-194549_Gallery.jpg
The bottom ground is on purpose this time too as I jumpered to the wrong line and figured it didn't matter down there?

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Post by stolen »

Hi!

We just noticed, you seem to be using tantal caps in a few places (C1, C9, C13) - are these polarized correctly? For all of them the positive side should be facing downwards (referring to the stripboard render above).

All the best,
stolen

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Post by WuKong »

Are they always polarized? I've seen bigger ones that are and have markings to show polarity, but these small ones had no markings or shorter sided leg to show so - I just put them in with the value markings facing left :roll: :slap:
stolen wrote: 17 Jun 2021, 12:26 Hi!

We just noticed, you seem to be using tantal caps in a few places (C1, C9, C13) - are these polarized correctly? For all of them the positive side should be facing downwards (referring to the stripboard render above).

All the best,
stolen

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Post by stolen »

Hi! Tantals are always polarized. They usually have a strip that indicates the positive side. If they don't - good luck. Generally you might want to avoid those cap types if possible.

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Post by WuKong »

These just have value markings on like a ceramic.. doh.
I'll order some replacements and see how it magically fixes it, thanks!

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Post by WuKong »

Ok well I've changed the tants for boxes... same issue and no change :beatdeadhorse:

Couple things I've noticed though:
- the sound bleeds through into the bypassed signal (I always had the effect volume low before because of the ugly noise so I never noticed before)

-while poking and moving wires I noticed the sound sometimes disappears when my thumb is mashed over the traces in the bottom right corner while my other hand touches the grounded case, it's around the sus 1 and 3 board connections but I cant get consistent results to isolate which trace?

Again I've more than triple checked for bridges on both builds.. I was thinking maybe it's a bad switch bridging internally but it's the same with both builds so? Stumped :slap:

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Post by Manicstrat2112 »

If you have more than one of each op-amp, try changing those. If you have any from a different supplier even better. Either way try switching them out and see if anything changes. Sometimes it can be as simple as that. Also you can try twisting your ground and input wire together like so Image
that fixed the whining on my Friedman BE overdrive... or you can try shielded cable on the input and output.
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Post by WuKong »

Thanks I'll give the twist a shot! I've tried ua741,lm741,jrc4558,tl072 and 5532 from 3 different suppliers now so dont think it's the ICs
Gonna try changing the other caps from ceramic to another type see what that does.. losing hope! Is there a better (more used and supported?) layout for this circuit than the one I used?!

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Post by phatt »

WuKong wrote: 20 Jun 2021, 15:36 Thanks I'll give the twist a shot! I've tried ua741,lm741,jrc4558,tl072 and 5532 from 3 different suppliers now so dont think it's the ICs
Gonna try changing the other caps from ceramic to another type see what that does.. losing hope! Is there a better (more used and supported?) layout for this circuit than the one I used?!
Number one rule in this game; Don't rely on Layouts!!! :secret:

Yes they help but you won't learn much.
Get the Schematic (if possible or learn to draw out the circuit before you commit to a build)
You then use the schematic to verify your Layout and connections as you build. (far better chance of success)

BTW a ua741 is a single opamp while the others are DUAL opamps they are NOT interchangeable as they use different pins. Just google the data sheets,, they will show which pins are active.

OK likely this is new to you so it will take a while to learn how to build pedals.
I know most of us want to take the short cut and just build from a layout but unless you know for absolute certainty the layout is valid it may not work.
I Bread board EVerything I wish to build before I commit as I've found that to be the Faster way because you can find all the potential hick-ups before you solder stuff.

Judging from your observation that your finger stops/alters the issue suggests that you have a ground problem, i.e. you may have an open ground somewhere.
Maybe check the Case Ground is connected to the Circuit ground?
This is where a schematic comes in very handy as it's so much easier to check which points are ground (and also the virtual Ground or bias voltage).

Note; it's always wise to post the schematic as well as the layout,, more likely to get help other wise we have to chase around the net trying to find it.
Oh and try not to use the same colour wires as it's so much harder to follow.
HTH, Phil.

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Post by deltafred »

Lots of good advice from Phil.

I will just add that if I have to Google for a schematic that is where I STOP.
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Post by WuKong »

Thanks for the advice - I've built dozens of pedals as well as low watt tube amps in the past but maybe 7 years ago so I've forgotten a lot.. I just got back into it with this circuit and old lazy me saw it was verified and jumped to it :slap: yellow wire is because it's what I had around and I always take wiring very slow and carefully following correct connections (even more so with same colours) - I was just keen to use an old Muff enclosure and add an IC version to my collection.

I've seen online a few people have had this same issue for this circuit (77/8 IC Muff) with various layouts but no definitive answers or reason why..

IC2 calls for a single opamp and IC1 is Dual, which is why I listed such ones I've tried in their respective positions.

I've been cross referencing a 77 version schematic and already made the 2 adjustments recommended (adding a 10uf and pushing r10 to ground (both connections come from the sustain pot which is where I feel the issue lies)
EH_BigMuffPi_OP-77.png
If I jumper(with my finger) Sustain lug 3 to the Input signal then the effect is perfect, but the bypassed signal then gets the oscillation. Just something else I noticed poking around?

I've seen somebody online had changed the 560k (R8) down to 51k which fixed the issue for them, why would this be? Is it worth trying?

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Post by phatt »

More likely the bias is not stiff enough,, hard to say.

Thanks for posting a schematic,, that helps a lot.
At a glance; This looks like it has a few design flaws and IF it was me.
I would BBoard it first.

R5 is likely way too much gain hence you noted someone lowered R5 and resolved the problem.
But it's still suspect. :?

the way it's wired on schematic it will be noise prone at high levels,,I would make IC1A a buffer,, that alone will help.

The bias voltages looks really wacked @#$%^&^*(?
Unless I've missed something better minds can see???

R2 & R3 don't need to be that large and C2 needs to be much larger (try 10uF)
Same goes for R11 & R12 and C8.

AFAIK,, the positive input on an inverting stage just needs a stiff bias, no need for hiZ there.
So 10k/10k and 8k2/10k with 10uF caps will do the same but deliver stiffer bias and less chance of instability.

*BTW if you use a TL071 at Ic2 then you can just use 1 bias voltage.
That removes 2 resistors and a cap from the board.*

Now i've not built this circuit but P1 (sustain) looks odd.
I would try making R8 a pot which will allow much more control over how hard IC2 is driven.

As mentioned,, I would certainly not build this without first testing it out on a BBoard as it's a fair bet it could be improved.

This may help you;
https://aionfx.com/app/files/docs/corvu ... tation.pdf

Scroll down for what looks to be a more accurate schematic. (but still not great)

Cheers, Phil.

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Post by deltafred »

Are you powering it with a battery or a power supply?

If power supply is it switched mode (lightweight) or linear (older and heavy because it has a 50/60Hz transformer in it)?

Some circuits work fine on (some) switched mode, others don't.
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Post by The G »

Maybe the noise is not in the circuit, but in the environment. Try shutting down everything you don't need or testing it in an electromagnetically clean place. Try to reduce the variables as much as you can - battery powered, put it away from anything or shielded, see what happens when the input us grounded, these kind of things.

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Post by WuKong »

Fixed! It was the 560k - saw a few others online with the same issue and solution too, makes me wonder why all the layouts and schematics of this circuit are like this?!

Dropped the 560k down to 470k and working perfect and dead quiet now

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Post by HunkFunkPedals »

Digging up an old post.

I built this but one side of the tone bypass switch turns the whole pedal off. I'm troubleshooting but if anyone has any ideas I'm all ears.

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