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MCP41100 DigiPot Volume Control Noisy Buzz, Fuzz, and Distortion
MCP41100 DigiPot Volume Control Noisy Buzz, Fuzz, and Distortion
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Old 21st January 2019, 06:06 AM   #1
phildunphy1989 is offline phildunphy1989
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Join Date: Jul 2016
Default MCP41100 DigiPot Volume Control Noisy Buzz, Fuzz, and Distortion

Hi, I just started incorporating digipots into my guitar pedal circuits. I've successfully built one type of circuit whose digipot controls volume and gain, but on my second guitar pedal circuit, I'm running into the following issue:

When the digipot (MCP41100) is set to a lower volume (physical pot is on a Arduino Nano's analog input and dictates the digipot), I get all kinds of nasty buzzy, almost gated or "spitting" fuzz type of distortion. Only when I crank the volume mostly up does it go away, but then I'm left with a huge, overpowering volume.

I've attached the schematic of the circuit and circled where the digipot is in the circuit. Nothing too complicated, just shunting the audio signal to ground. There's already a coupling cap to block DC before the pot input.

Here's what I've already tired:

-another 1uf or 10uf coupling cap after the digipot's wiper
-2.5v bias offset?: 2x 47k resistors forming a voltage divider on the digipot's input, as such (hope I did this right):
--5v ---47k---DigiPotIN---47k---Gnd

I'm not sure why the MCP41100 works on one guitar pedal circuit and not the other, as the digipot/arduino circuits are identical to each other.

Any and all comments are appreciated, thank you!
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File Type: gif LovepedalEternitySchematic.gif (10.0 KB, 28 views)
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Old 22nd January 2019, 04:28 AM   #2
PRR is offline PRR  United States
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Join Date: Jun 2003
Location: Maine USA
> I'm not sure why

On the MCP41100, and digipots generally, the analog pins must stay *between* the supply rails or they distort horribly.

In your LovePedal, Drive and Tone have +4.5V at all ends. But Vol has ZERO VDC on all legs. Any signal swing below zero will distort.
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