tc1044 squeal

[BoleBezKontrole]

Firstly, hello everyone and thank you for sharing your vast knowledge here. I was thinking about posting sometimes and I was both overwhelmed and inspired by the community so I was just lurking in the end... I have couple years of experience in electronics and programming but nothing too crazy. I'm excited to learn from everyone around here.

So, I was trying to build EQD Plumes (2 times) and Keeley Oxblood from tagboardfx, they both use 1044 voltage inverter and I can't seem to make them quiet. There's always squealing with gain maxed (I like testing/having the whole range).

Already tried:
- checking for shorts and misplaced components
- adding more filtering on positive and negative lines (larger electros and 100nf mlcc)
- using 7660s and 1054 (with pins unlinked)
- using battery power and tl071 buffers
only thing that seemed to help was putting another pedal in front (I've tried with SHO, TC Spark and Digitech Drop). That seems to eliminate the high pitched squeal and leave only the "usual high gain motorboating/sizzle".

If anyone has any ideas about reducing the high pitch squealing without putting another pedal in front or some explanations why this seems to help the situation, I'm all ears. Thanks for all your shared knowledge and for this amazing community.

[WormBoy]

Given that powering by battery doesn't help, and neither changing ICs (and IC types) for the charge pump ... my guess would be that the issue is with the layout on the stripboard, or with your wiring. If others did not report such issues with that layout, wiring would be my prime suspect. Either the grounding is not optimal/effective, or the power, or there is a proximity effect from the input wire being too close to other wires or components (or some components being too close) ... How are you testing the circuit at the moment?

Sometimes putting a (buffered) pedal before the affected circuit helps. Not sure why that should be so; I can only imagine that it's an impedance thing  .

[BoleBezKontrole]

I've been testing without a box (just a simple alligator clip testing rig), so I don't expect it to be completely noiseless, but I didn't expect that high pitched noise either lol

Thanks for your reply, I will try to rearrange the wiring to see if it helps. As i said, it goes quiet with an SHO in front, but stays noisy with ic buffers in front... maybe a mosfet buffer would help? I'm really just guessing.
But, what did help is a capacitance multiplier before the inverting stage on the board, now the squealing noise appears only when every pot is almost maxed out. I might try and adjust the corner frequency later today to see if i can completely eliminate the noise.

EDIT: I forgot to say, I've tried 2 different layouts for Plumes, both turned out to be noisy

[WormBoy]

I've been testing without a box (just a simple alligator clip testing rig), so I don't expect it to be completely noiseless, but I didn't expect that high pitched noise either lol

This could be the cause of the problem ... a non-perfect connection to the power ground may imply that any 'pollution' of the ground can creep into the audio parts of the circuit. Therefore, the problem may disappear when you box the circuit properly. However, that is risky, of course. What I sometimes do is to make a mock-up on a piece of hardboard: drill all the holes for pots/switches in the correct relative positions, and add jacks and power connector to the same piece of board. That allows me to wire everything neatly, without having to drill/finish an enclosure.

As i said, it goes quiet with an SHO in front, but stays noisy with ic buffers in front... maybe a mosfet buffer would help? I'm really just guessing.

That's weird ... I would have predicted that an IC buffer would work better than a mosfet booster ... Well, another case where my my intuition fails  .

But, what did help is a capacitance multiplier before the inverting stage on the board, now the squealing noise appears only when every pot is almost maxed out. I might try and adjust the corner frequency later today to see if i can completely eliminate the noise.

You mean low-pass filtering of the signal in the circuit? Would be a pity to sacrifice highs if its not really needed. Unless you don't like highs anyway, of course.

[BoleBezKontrole]

Hi again,
yesterday I tried soldering the jacks and grounding pot casings, that seems to have little to no effect.
I've also fiddled around with filter of the capacitance multiplier, that really didn't matter either, it was already clearing 99% of the supply ripple.

What I've found helpful is having low pass filter in front, but the pedal's response felt weird... So I've kept just the 1nF cap from input to ground as used in MXR Dist+ (supposedly to block RF noise, but I'm no expert). That worked great, no extra high end seems to be lost and I think this is the solution I was searching for. Maybe changing the cap value has some effect on the response, but this seems like a bullseye.

So I hope this thread could help someone that gets stuck with this kind of problem (there's a lot of similar cases on forums). Thanks WormBoy for all your help!

[bradg]

I have also built 2 different Plumes layouts (tagboardeffects and effectslayouts) that both squeal - and tried the usual fixes as well. Placing a 1n cap from input to ground reduced the squeal, but now I just get a lower frequency squeal when volume and gain are in the higher ranges. The issue is much more pronounced with the bridge (humbucker) pickup. The circuit sounds so good that I really want to get ths figured out and box these things. Still working on it...

[Willybomb]

When I've had a squeal issue, I've usually been able to deal with it by sticking a Klon buffer in front of it.  A Boss pedal will kill the squeal pretty much every time but I haven't been able to get their output buffer working, just the input buffer, but using just the input buffer doesn't work - there's some sort of black magic going on in the DS-1 buffers I haven't been able to replicate on vero.

I made a Boneyard once that squealed (on the original v1 etch), and the only thing that fixed it was to put a 160k resistor to ground from the footswitch effect input lug.

[bradg]

Thanks, Willybomb. I recently built a Cornish buffer, so I'm going to try that. The Plumes already has a 1M pulldown resistor on the board.

[bradg]

On my test rig, a Cornish or JHS buffer circuit placed before the Plumes makes the squeal worse. But a buffer pedal (with same JHS circuit inside, powered by the same source) placed in front of the test rig fixes the squeal. What does that mean? Maybe boxing this thing would take care of it.

[BoleBezKontrole]

From what I've experimented with; having just a random buffer in front doesnt fix the squealing, but having a pedal (or buffer) that inverts the signal helps negate the oscillations. So this is what I think happens:
- Plumes has 4 stages and the output signal has the same phase as the input signal. So, the signal from the output somehow gets picked up at the input and amplified again ie. constructive interference happens. By sticking the inverting buffer in front input and output signals become 180° out of phase which means that destructive interference happens which should mean that oscillations are cancelling themselves.
Just to clarify, I'm not an expert and this may be waaay off. This is just me trying to explain stuff to myself using sparse knowledge of physics and electronics. I've used this with other pedals that have the in and out signals "in phase" and it helped negate the squealing.
Sorry for the long read and good luck!

[Scruffie]

Problems with the plumes - Very high input impedance (I suspect this might be a big cause of issues), no RF filtering, extremely high gain (vero seems like it's asking for trouble here), no r/c power filtering and given the active EQ on top of all that gain, I think I'd have split it in to two duals.

I don't think a buffer is the solution, I think tidying up the circuit is.

[bradg]

Phase-inverted buffer FTW! No more squeal. Thanks, everyone!