Coron 10 breadboard build - sound pulse?

[Hemmel]

Hello all!

I've built this
https://www.diystompboxes.com/pedals/dist10.gif
on a breadboard and I get this weird pulse that sounds like someone strumming a high E-string at around 3 strums per second.

Using the audio probe, I find I can hear it - albeit at different volumes - just about everywhere on the circuit.
The breadboard is fed by a 9V battery.

Any ideas? Pictures coming soon, if requested.

Thanks
Hemmel

[GibsonGM]

Sounds like oscillation due to high level of gain.  What happens if you turn down the 500k pot to 'zero'?
In/out leads too close together often cause this, esp. if they're 'too long'.   

You can try routing them away from each other, and also adding some capacitance across the 741's power pins (7 & 4) at the chip...oh, 100n maybe..experiment with the value.

Breadboards can add to weird capacitances and make this worse, too.  Sure, a couple of pix would be helpful...

[Hemmel]

Sounds like oscillation due to high level of gain.  What happens if you turn down the 500k pot to 'zero'?
In/out leads too close together often cause this, esp. if they're 'too long'.   

Yes, when I play around with the 500K pot, the volume of the pulse gets lower/higher.
My in/out leads are exactly the same as other builds I've done on this breadboard, where no oscillation occurred.
They are not that close together.

You can try routing them away from each other, and also adding some capacitance across the 741's power pins (7 & 4) at the chip...oh, 100n maybe..experiment with the value.

I will try that.

Breadboards can add to weird capacitances and make this worse, too.  Sure, a couple of pix would be helpful...

Pics coming tonight.
I don't know if I can post this here because it can be considered self-promotion, but I was streaming this build on a popular streaming site.
@admins : can I post a link to my streaming channel?

[GibsonGM]

Don't know about your link being OK

...maybe not the cause, but you might also check that the electro caps are oriented correctly...

[duck_arse]

what's a streaming channel? where is it, interwebs-wise?

[Hemmel]

(...) check that the electro caps are oriented correctly...

One thing I had to do because of availability, is use 200V rated caps instead of 16v rated. Don't know if it could help with the oscillation...

[Hemmel]

what's a streaming channel? where is it, interwebs-wise?

Replied through PM

[GibsonGM]

higher voltage rating is fine...

[Hemmel]

Well, I found out what was causing the oscillation.
At first I thought it was a bad cap, which measured at 1µF instead of 10. So I replaced it.
Still the oscillation was there.

Then I decided to breadboard another circuit, right next to it. I went for the Blue Clipper since it's an easy and quick build.
The oscillation still occurred on this new circuit.

Then using the audio probe I identified that it was the 9V source that was giving out the oscillation.
Turns out I had a mini voltage meter plugged into the circuit, on 9V and ground.
As soon as I removed this meter, the oscillation stopped.

[ElectricDruid]

Then using the audio probe I identified that it was the 9V source that was giving out the oscillation.
Turns out I had a mini voltage meter plugged into the circuit, on 9V and ground.
As soon as I removed this meter, the oscillation stopped.

Oooh, now that *is* interesting! Good find! 

I have a home-made power supply on my bench that has one of those mini voltage meters on it. Thus far it's been pretty quiet, but that's definitely worth knowing to look out for.

[Hemmel]

I am going to test if putting the + lead on the 9V rail but with a filtering cap in between, maybe that'll cut the oscillation out.
But I'm wondering if the cap won't interfere with the voltage reading...

I'll test it and get back to you

What cap would you suggest?

[GibsonGM]

Mess around, see what works. Start with 10u maybe, from + to - .   Then 47u, 100u...

Another trick is putting a low-value R in series with your 9V followed by a cap to gnd (say, 22R with 100u cap).  This allows enough current to power most stomp circuits, but creates a filter that can help with clicks/ticks and things. Be aware that in doing a series R like that, you want to bear in mind its power rating and what the following circuit calls for, which will be the real limiter of current draw. (theoretically you could as the power supply for enough current that the series R could heat up/burn - not in most typical stomp box applications, tho!)

[antonis]

I have a home-made power supply on my bench that has one of those mini voltage meters on it. Thus far it's been pretty quiet, but that's definitely worth knowing to look out for.

If it has some kind of current limiting configuration, with sensing resistor set before load, it should be quiet enough..

[antonis]

Turns out I had a mini voltage meter plugged into the circuit, on 9V and ground.

Some of those digital meters require special wiring..

[Hemmel]

Some of those digital meters require special wiring..

I'll try with a simple cap and/or resistor first 

[GibsonGM]

Antonis is right (of course, he is a philosopher).  Do check the wiring for the meter.  It COULD make some noise, so the cap alone may work, or R > C to ground may also be needed. 

If the power supply is built for audio, it should be filtered already...seems you don't get noise without the little meter?

[Hemmel]

It's a very small meter. It's very hard to see what the components used on it are.
That's why I figured I'd try out with a cap and/or a resistor first.

[GibsonGM]

Did you remove it (is that how you know it caused the noise?)

[Hemmel]

Did you remove it (is that how you know it caused the noise?)

Yes, after removing the voltage meter the noise went away immediately.

[ElectricDruid]

It's a very small meter. It's very hard to see what the components used on it are.

Let me guess: A cheap microcontroller and a LED display. That'll be about it. The microcontroller reads the voltage using an ADC input at maybe 10or 12 bit accuracy if you're lucky, then outputs the reading by turning on the relevant LEDs. The rest is firmware.

The noise is digital hash caused by the microcontroller switching lots of LEDs on and off rapidly, I expect.