Volume pot value

[tyla]

Hello. I wanna build a passive volume control and looking for the correct pot value. Source is Rane SM26 splitter/mixer with output impedance 125Ω. Destination is this diy/clone amp I bought on eBay. Music Box A1 Hdam HiFi Power Amplifier Perfect Classic 2SC5200 2SA1943 Amp DIY | eBay

After googling "Marantz HDAM input impedance ohm" it looks like it might be input impedance 47KΩ on the amp? Is this a common value?

So whats the proper pot value to have between 125Ω source and 47KΩ destination??? Yes I know I have volume control on both the Rane SM26 and the PowerAmp but these are hidden inside a rack and I wanna have a easily accessible vol control.

Thanks for your help

 

[Mooly]

125 ohm source impedance is pretty low and so a 10k or 22k pot would be ideal. You also want a log pot for volume (ideally).

 

[AndrewT]

The advantage of using a lower impedance vol pot is that it can drive the next stage more easily.

The maximum output impedance of a vol pot is:
{Vol pot resistance + Source impedance } / 4

This should be less than 20% of the next stage's input impedance and preferably 5% to 10% for good voltage transfer.

Your 125ohm source impedance is already down @ 1.25% of the input impedance of the 10k vol pot. You could even use a 5k vol pot, but these are not so common.
The maximum output impedance of the 10k vol pot is {125r+10000r}/4 = 2531r
The next stage can be anything above 12656r and preferably >25k
47k, or 50k, or 100k input impedance for the stage after the 10k vol pot would be ideal.

 

[tyla]

Thanks! Will try 10k!