Low Hum DC Jack - Valve Caster Build

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Muzzatron5000
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Post by Muzzatron5000 »

HI all,
Ive been lurking around forums trying to work this one out.

So i've made a couple of Valve-Casters now and really digging the sound!! Especially with a strat. :-)

Works fine with a battery, but when I plug in my DC power I get a very low hum. I have a decent Alctron DCT-200 power supply with 12v & 9v options.

After reading some posts I added a 640uf Capacitor across the pos-neg input and it did reduce the hum. But not much. I added another cap and it reduced again. But still annoying. (could probably add several caps to get rid of it)

I used an oscilloscope app just to see what frequency it was pushing. See attached.

Driving me nuts really. Cause the VC sounds so good!!!

I dunno. It's seems like some sort of earth issue, but is not a little hum more like a sub bass hum.. So i dunno?

Any thoughts would be appreciated !!! :-)
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plush
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Post by plush »

Check your DC power for ripple. Don't forget to turn DC coupling on your scope.
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Manfred
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Post by Manfred »

Possibly there is an internal ground loop try the following rewiring.
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Muzzatron5000
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Post by Muzzatron5000 »

Manfred wrote: ↑10 Jul 2021, 06:33 Possibly there is an internal ground loop try the following rewiring.
Yes OK - I will give that ago. I am still new to pedals, so learning as I go.

I was wondering about the shield to shield ground, whether that was needed.
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Muzzatron5000
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Post by Muzzatron5000 »

OK So, I rewired as you suggested and didn't reduce the hum. So was feeling frustrated. The rewire did tidy things up I must say, so that was all good.

Then I realised on the bottom of my power supply there were 8 of these little dip switch buttons. There were all switched to the on position.
So I turned them all off and the hum freakin stopped!!!!! :-)
Attached is the corresponding info.

I am really happy! I thought I was just making bad pedals. All good now.
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DIP Switch NORMAL.jpg
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Manfred
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Post by Manfred »

I am sorry, I assumed that the power supply was working properly.
The ground wiring now without internal ground loops even if that had no effect here now
I am happy with you that your device now works.
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Post by Muzzatron5000 »

Manfred - thanks. It got me on the path to solving the problem. :-)
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