[ginettaman]

Hi,
have just received my Pimeta PCB and new alps pot with switch.
I just want to check resister value, schematic says 1m, but I think it should be 10 x pot value (10k) so that is 100k, can anyone who has built with the new pot confirm what they used.

Thanks.

 

[bg4533]

I have not used the new pot, but you are right in thinking 10x the value of the pot. 100k is a good choice.

 

[Syzygies]

This is an interesting question. As Tangent explains in various places, one wants a value large enough to minimize the variation in impedance your source sees as you adjust the volume pot. 10x is a rule of thumb. Go too low, and the sound could change at different volume levels. Go too high, e.g. 1M, and you could introduce unwanted resistor noise.

People praise various stepped attenuators that do present a varying impedance to the source, so this issue could be overstated. It undoubtedly depends on your source.

On the other hand, Input Capacitors for Headphone Amps is required reading. Using a 499K resistor for R2 may be of little benefit over 50K as far as input impedance goes, using a 10K pot, but it is enormously helpful in lowering the RC filter's "corner frequency" if one chooses to use input caps.

For people using input caps, I'd propose using 499K resistors for R2, for any pot 50K or less. Discussion?