Author Topic: What could cause power noise in a pedal even if supply is isolated (GigRig)  (Read 327 times)

Philtre

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I built a Giant Hogweed clone:

http://tagboardeffects.blogspot.com/2015/10/giant-hogweed.html
http://www.davidrolo.com/wp-content/uploads/2017/07/GiantHogweedSchematic_zps445f5a36.png

I use a modular GigRig power system with Isolators and when I have the Hogweed powered on my board with an Isolator, and the Octave button on the pedal is on, I get high pitched whistling noises.

However, if I use a completely separate power supply there is no noise from the pedal.

The GigRig system is supposed to supply isolated 9v through an isolator and yet this is happening.

Any ideas?

Philtre

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OK, I think I have the answer.

The current from a GigRig Isolator is about 130mA. I tried it with a power supply from a GigRig TimeLord and directly from a GigRig Distributor (bot options supply a lot more current) and there is no power noise when the octave switch is on.

So, my question now is - how much current do you think this pedal pulls when the octave switch is engaged?


Philtre

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Dammit, I might be wrong about that. Still getting noise even with a separate power supply and plenty of juice. Reckon it doesn't like being in a pedal chain either.

drog_trog

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maybe a couple of 100n caps going from 9V to ground may quieten it

Philtre

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maybe a couple of 100n caps going from 9V to ground may quieten it

Good call. I added one 100nF poly cap right across 9v+ and ground at the power socket and that reduced the noise a lot. There's still some noise, but it's tamed it.

lars

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Ah! The Giant Hogweed has a Rat in there. The Rat circuit is notorious for being a howler. I really like the sound of it, but in my setup I could never get a Rat to work without tons of high-pitch squeeling, even at lower volumes. I would research anything on how people were able to tame a Rat, and apply those things to your setup.
“There is always an easy solution to every human problem—neat, plausible, and wrong.”

drog_trog

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maybe a couple of 100n caps going from 9V to ground may quieten it

Good call. I added one 100nF poly cap right across 9v+ and ground at the power socket and that reduced the noise a lot. There's still some noise, but it's tamed it.

Good, i see that there is a voltage divider going on to give you Vb1 so maybe add a cap from Vb1 to ground

Rockhorst

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Use 100n or higher (you can get 10u these days) MLCC caps from any power or Vb point to ground. The cap needs to be as physically close to the IC as possible. For instance directly on the IC pins underneath the board.

Philtre

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Well, the noise only happens if the Octave switch is on and the Octave Up pot turned high, so something's happening on this part of the circuit. Noise is worse if other pedals are before it on the chain.

drolo

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Hi Phil,
Not sure how those isolator blocks from irig work, but I would assume it uses a DC/DC converter and its switching frequency might not play well with this pedal.

Try a 1n cap across the collector and base of T1.Or from base to ground, see which works best, you might need to try a few values. I actually found that shaving some of the hi end off helped with the octave being more prominent.



Philtre

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Hi Phil,
Not sure how those isolator blocks from irig work, but I would assume it uses a DC/DC converter and its switching frequency might not play well with this pedal.

Try a 1n cap across the collector and base of T1.Or from base to ground, see which works best, you might need to try a few values. I actually found that shaving some of the hi end off helped with the octave being more prominent.

Hi David, Thanks for taking time to offer help, much appreciated. :-) I'll try your suggestion.

Philtre

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BTW - I should say thanks to David Rolo for coming up with the Hogweed and making the schematic available. I thought it might make this thread a bit more interesting if I showed you what my clone looked like. :-)


drolo

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That looks great, funny I seem to recognize that image from somewhere ... :)
hope it works better with the added cap
« Last Edit: August 14, 2018, 03:50:45 AM by drolo »