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Old 28th July 2008, 06:52 PM   #1
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Default Bypassing a volume pot

If an amp specifies the use of a 100k volume pot, what is the proper way to bypass it so as to be free of volume control?

I ask because I have a Alpha pot in my headphone amp that is driving me nuts. The vol control on the audio source is fine by itself.
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Old 28th July 2008, 07:17 PM   #2
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Replace the pot with 100k resistor. Connect it where went the wiper out and then connect it to ground. Usualy 100k will be connected from grid, before any grid stopper, to ground.
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Old 28th July 2008, 07:47 PM   #3
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Do you have a schematic? The answer may be that you don't need to add any resistor or that a bigger value resistor might be a better choice.
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Old 28th July 2008, 07:55 PM   #4
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I've got a couple things in mind, but for the sake of argument let's analyze this one:

Click the image to open in full size.
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Old 28th July 2008, 08:05 PM   #5
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For that example there's no need to replace it with anything.
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Old 29th July 2008, 08:36 PM   #6
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Hi Labrat,

If you are unsure, the safest way would be to parallel R1 (1M) with a 100k resistor and feed the signal directly to the connection where originally the wiper went (junction of 100k, 1M and 100R resistors).
This way your amp still has ~100k input impedance.

If I understand the basics right, leaving the input open (without the 100k resistor) would increase your input impedance (mostly determined by R1=1M). In most cases that might not be a problem but I am always scared of picking up RF if the input impedance is too high.

My 1 1/2 cents worth...

Martin
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Old 29th July 2008, 08:46 PM   #7
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All good advice. Thanks!
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