Intermittent pitch instabiliy when touching VCO faceplate/pots

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wrecksmoondee
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Intermittent pitch instabiliy when touching VCO faceplate/pots

Post by wrecksmoondee » Mon Feb 22, 2021 3:21 pm

Reaching out in hopes of a diagnosis. I have experienced more than one VCO undergo pitch warbles and jumps when touching/lightly pressing the faceplate and/or potentiometers (I know that potentiometers aren't buttons). Any idea why this might happen?

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maudibe
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Re: Intermittent pitch instabiliy when touching VCO faceplate/pots

Post by maudibe » Tue Feb 23, 2021 5:52 am

Bad mains earth? Power up to the limit? Your just a sexy beast and your modular can't resist having a flutter? :hihi:

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wrecksmoondee
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Re: Intermittent pitch instabiliy when touching VCO faceplate/pots

Post by wrecksmoondee » Tue Feb 23, 2021 8:10 am

maudibe wrote:
Tue Feb 23, 2021 5:52 am
Bad mains earth? Power up to the limit? Your just a sexy beast and your modular can't resist having a flutter? :hihi:
I reckon the latter, haha :despair:

Power isn't up to the limit. I don't really know anything about the earthing in this house. I'm patching between cases, but it happened even within one case. It certainly is bizarre. Almost like it's receiving wonky CV from my hand.

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Re: Intermittent pitch instabiliy when touching VCO faceplate/pots

Post by Elahrairah » Tue Feb 23, 2021 3:06 pm

Often the faceplate is "grounded" as in it's connected to the 0V reference. cheap/most VCO use the power rails as references, and touching it willpull the voltage. It's very unusual for the 0V to be impacted this way, it implies the system and your body are at different potentials. The case is not well grounded, and you could use a strap, keep the instrument more at the same voltage as your shoes.
I guess it's a two-prong power cable and not a three. Don't exactly know the solution short of replacing that.

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wrecksmoondee
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Re: Intermittent pitch instabiliy when touching VCO faceplate/pots

Post by wrecksmoondee » Tue Feb 23, 2021 5:07 pm

Elahrairah wrote:
Tue Feb 23, 2021 3:06 pm
Often the faceplate is "grounded" as in it's connected to the 0V reference. cheap/most VCO use the power rails as references, and touching it willpull the voltage. It's very unusual for the 0V to be impacted this way, it implies the system and your body are at different potentials. The case is not well grounded, and you could use a strap, keep the instrument more at the same voltage as your shoes.
I guess it's a two-prong power cable and not a three. Don't exactly know the solution short of replacing that.
I can confirm a three-prong power cable. Puzzling, eh?

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Re: Intermittent pitch instabiliy when touching VCO faceplate/pots

Post by XODES » Tue Feb 23, 2021 5:34 pm

When you push the shaft of a potentiometer, what will generally happen is that the wiper, that has a spring effect on a conductive surface, would simply get a slightly different surface contact with it, possibly resulting in a change of resistance, and a shorter life. Don't do that.

Depending on construction, there could be similar explanations when pressing the front panel. Some designs using stacked PCB have pins on the back way to close from the components on top of the PCB underneath, which might also result in such effects... or worse.

Some manufacturers, for some reason do not solder the "mechanical" tabs from their potentiometers. Some do, yet they leave these floating, while it would be better to have these grounded. I can't remember right now what was the VCO I had with this kind of issue, yet grounding the potentiometer body had a positive impact on this undesirable effect.
Image   Image   Image   Image

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Re: Intermittent pitch instabiliy when touching VCO faceplate/pots

Post by ima_jrk » Tue Feb 23, 2021 10:40 pm

Count yourself lucky! Make Noise is charging customers $600 for the same effect in the Strega!

I am also inclined to think grounding issue but I would assume it would happen with more than one. Which modules do it and which don’t?

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Re: Intermittent pitch instabiliy when touching VCO faceplate/pots

Post by wrecksmoondee » Tue Feb 23, 2021 10:48 pm

ima_jrk wrote:
Tue Feb 23, 2021 10:40 pm
Count yourself lucky! Make Noise is charging customers $600 for the same effect in the Strega!

I am also inclined to think grounding issue but I would assume it would happen with more than one. Which modules do it and which don’t?
LOL!

I've observed it with an A-110-4 and A-111-2; Synthtech E300 doesn't seem to exhibit it.

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