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imaginarytime 15th October 2012 02:48 AM

100K pot implications in the 3875 kit.
Pots are expensive and all else equal hard to have delivered to addresses in the US.

Mouser has the Alps RK27 at 100K but not the 50 or 25K.

Peter Daniel often suggests 50K pots for the 3875 kit. For example, he's said,
"100k will work correctly, although it may not be the best choice here."

Can anyone expand upon the tradeoffs of 100K and what the implications of not making the 'best choice' will be?

I'm going to build the 3875 kit and I would like to take as many variables out of the equation as possible.


ashok 15th October 2012 09:29 AM

There are two issues here. One is the noise of the pot , higher resistance higher noise content. Second is the chip amp probably has a 22K input impedance ( Rin). So the pot will be loaded down by that making the 'actual' taper different from what the pot has. This results in the volume going up more slowly with rotation than if the load impedance was higher.

The noise in this case is very low for the signals levels you have and the altered taper doesn't matter too much. So the conclusion is that you can use it without worrying ! The input impedance of the whole amp will vary from 100K at zero volume to 18 K at full rotation . So no problem there also.

Peter Daniel 16th October 2012 04:08 PM

I used 100k pot with LM3875 chip and didn't really find any problems.

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