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boidos 11th February 2009 09:49 PM

Is setting an alps volume pot to the full position the same as bypassing?
Hi All,
I am looking to use some shunt stepped attenuators with my class d amps.
Is setting its alps volume pot to the full position effectively the same as bypassing it? Or should I be removing it for maximum quality sound?


Ed Holland 11th February 2009 10:10 PM

Not quite exactly the same, but it should be good enough for most practical purposes. Try it first.

The long answer:
The pot, set to maximum, will present a load equal to its maximum resistance value to the source of any signal. At the simplest analysis, this will still result in a small attenuation, dependant upon the impedance of that source. Since the alps pot is probably 10's or maybe 100's of kOhm, and the source impedance is likely 100's of Ohms, the attenuation is negligable - after all the input impedance of the next stage may well be comparable to or less than the pot's resistance.

Of course there is always some parasitic capacitance added by the pot, but this is not something I'd worry about.



Xoc1 12th February 2009 02:16 PM

If you can bipass the volume control you should.
The wiring which typically snakes around the amp introduces a certain amount of hum and noise.
The Pot becomes a pull down resistor. Typically this has a very poor temperature coefficient. 500ppm is not unusual for some carbon types!
This is exactly what you are trying to avoid by using a stepped attenuator.
Also some pots are very microphonic.

boidos 12th February 2009 07:57 PM

Removing the volume pot
Hi, thanks for the reply. Any tips on the easiest way to remove the volume pot.?

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