Break Action Dual Overdrive, one channel noise

[tony311]

Hello, I have successfully built a few pedals, but I am a newbie and not sure what to look for when a problem arises. I believe this noise I am hearing is a simple issue but I cannot for the life of me work it out. The Pedal is a Dual channel overdrive similar to the JHS Double Barrel.

The noise is a high pitched whistle, I have attached a sample as well as the circuit.  I have tried new ic's but this made no difference. Altering any of the pots or switches doesn't make any difference to the noise either. The channel does work, but at low volume, this whistle is evident.  The noise is not there in bypass. The other channel works perfectly with no noise.
I would really be grateful if someone could guide me as to where to look.
Sample. https://youtu.be/87XW0cLBqSM

[ElectricDruid]

You could try cleaning up the connections where the foot switches connect to the main PCB. It's oscillating, so somehow the output is getting back to the input. Make sure there's no muck between those connections.

[Rob Strand]

If you are using a power supply to power the unit, see if the problem is still there when powering from batteries.   If it's a switch-mode power supply try placing 220 ohm 1/2w (or two 470 ohm 1/4 in parallel) across the 9V and 0V, like a dummy load.

From the video the problem is only occurring on the left side.   If that's the channel with the Q2 in the signal path then that might be further evidence of a power supply issue.

I'm not convinced of oscillations as the pots don't have an effect.

There's a small chance the noise is from outside the unit and the fact the metal parts of the pots and switches are not ground might let the noise in.   However the fact the pots do nothing makes me think that's not the case.  When you mount the PCB in a metal enclosure it will obviously shield the PCB and make a ground connection to the pots and switches.

[antonis]

Could we see your own build's schematic..??
("based" and/or "similar" don't say much about items values..)

[ElectricDruid]

I'm not convinced of oscillations as the pots don't have an effect.

No, that's a good point. If it were oscillating, turning both volume knobs down to zero should kill it. If the noise is still there, Rob's probably right and it's power supply switching noise getting in somehow. The test for that is "Does it still do it with a battery?" like he said.

[tony311]

Thank you to all for your help. I am very surprised, but the noise is gone with a 9V battery. I have never had this power supply cause me this issue. It has actually stopped noise on other projects so I have always trusted it. It is a really good low noise supply so perhaps, something has gone wrong with it. I will investigate the power supply next.

For now, this project can be boxed up. Thank you again. I usually do try a battery, but as I said, this supply has been very low noise and reliable so far.

[ElectricDruid]

You could try putting a 47R resistor in series with D10/1N5817. That will make that 100uF capacitor into a much more effective filter for power supply noise.

[tony311]

You could try putting a 47R resistor in series with D10/1N5817. That will make that 100uF capacitor into a much more effective filter for power supply noise.

Thank you. I will give that a try.

[tony311]

You could try putting a 47R resistor in series with D10/1N5817. That will make that 100uF capacitor into a much more effective filter for power supply noise.

Excuse my naivety, but do I put the resistor in series as in the diagram attached??
On another note, is there a filter of sorts, that I can buy or build to put on the DC output of my bench supply? Thank you.

[antonis]

P.S.
D10 / R order doesn't matter, as long as both are placed between power supply and C23.. 

[ElectricDruid]

+1 what Antonis said.

[tony311]

P.S.
D10 / R order doesn't matter, as long as both are placed between power supply and C23.. 
Thank you.