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 Forum index » DIY Hardware and Software
Help with basic limiter/VCA at end of diy synth signal path
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PHOBoS



Joined: Jan 14, 2010
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PostPosted: Thu Jan 07, 2021 4:22 pm    Post subject: Reply with quote  Mark this post and the followings unread

would it be possible to ground the switch ? I have run into similar things occasionally, sometimes also with pots.
It's a bit odd since there is no direct electrical connection.

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floating-water



Joined: Oct 06, 2020
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PostPosted: Fri Jan 08, 2021 10:56 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for getting back, It did make a difference grounding the switch but I still need to be touching one end of the crocodile clip for it to be quiet. any queries? Its less with a battery but its still there
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Psynth



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PostPosted: Fri Jan 08, 2021 4:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

It may be that it is you that needs to be grounded, not the switch. Your body can either be carrying a static charge, or act as an antenna for any e-m interference that is around - when you touch the switch that introduces noise into the circuit. By grounding yourself first, you eliminate the problem. Trying touching the switch using something insulated from your body (plastic handled screwdriver for example) and see if that makes a difference.
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floating-water



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PostPosted: Fri Jan 08, 2021 6:06 pm    Post subject: Reply with quote  Mark this post and the followings unread

The noise is always there when im not touching anything, its when i touch something, for example, the input jack, the noise stops.

For more information of whats going on inside: theres an echoplex pre amp, an lm386 amplifier circuit, a speaker, an input jack and output/headphone jack with a switch for deciding what output to use, powered by the wall. Could it just be the echoplex being noisy? It wasn't on the breadboard
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dk



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PostPosted: Mon Jan 11, 2021 2:25 am    Post subject: Reply with quote  Mark this post and the followings unread

It's most likely as Psynth said. You yourself are a giant noise source. The amp is probably picking up said noise, and when you touch the switch, you ground yourself, eliminating the noise.

One thing that would help is if you were using a metal box around the circuit... this forms a Faraday cage which shields the circuitry from RF, noise, etc. The box should be connected to ground as close to the power connector as possible. If that's out of the question, then you can ground yourself instead.

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PHOBoS



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PostPosted: Mon Jan 11, 2021 7:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

Is it a regulated supply ?
I've had circuits for which the type of wallwart I used made the difference between hum or silence.
Not sure if that matters in this case since it goes away when you touch a ground connection.

if possible you could test with batteries to see if that makes a difference.

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floating-water



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PostPosted: Tue Jan 12, 2021 1:55 am    Post subject: Reply with quote  Mark this post and the followings unread

Its a ZOOM, supposedly regulated supply, although I need to get something like a 1stop for testing guitar related gear. Would a variable power workbench supply make any difference for testing? I assume they have a lot of regulation in them? Its on the list to buy

Excuse my idiocy but im confused by 'grounding myself' ... so its not a problem with the circuit its just me? I understand we have some conductive properties but surely the circuit shouldn't be behaving regardless a slong as im going everything correctly. Definitely will be working aluminium instead of wood from now on
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dk



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PostPosted: Tue Jan 12, 2021 1:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

"It's not you, it's me!"

Well, perhaps a combination of the two. Humans are themselves a source of electrical energy, and a noisy one at that. Then you have your circuit, which seems to be susceptible to noise, and isn't in an enclosure to protect it from noise.

This is a pretty common problem in the guitar world, and one of the reasons it's recommended to shield your control and pickup cavities in guitars, especially ones used with high-gain amplifiers and/or ones that have single coil pickups. You're essentially trying to keep a grounded plane between anything that creates noise and your pickups/passive components.

The easiest way to solve this in your case is to either put your circuits in a metal enclosure, or you could probably shield your enclosure to get more or less the same effect. Shielding is usually done with wide copper tape, which is then connected to ground (as close to your power source as possible). You could also use a non-conductive cap on your switch to prevent any noise that might be left over from changing volume/color when you touch the switch, but you may find that shielding reduces it to the point where that doesn't matter anymore.

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floating-water



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PostPosted: Wed Feb 03, 2021 8:50 am    Post subject: Reply with quote  Mark this post and the followings unread

This thread become quite the plethora of topics i apologise but your tip on the copper tape worked, I know now I just have to shield any non metal enclosures.

I'm now back to the very original topic of clipping/VCA'ing the synth. After some iterations and development its now way more controlled and isn't peaking which is great but if I wanted to add a little something on the end to add some light distortion and colour any recommendations? I tried putting an output stage of a big muff on the end but it seemed to be just unity gain i thought it would add some vol. Preferably a very basic circuit
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