Sizing a volume control???

[faux_vedette]

How do i choose what value of pot to use between my CD player and my Power amp??? I did a search...


My amp has a 100K input impedance and i dont know what the output is??

What happens if i go to high or low? is 50K ok???

[AndrewT]

Hi,
put in a pot about 10 times the output impedance of your CD player.

If that is unknown then use 10K.

This gives a maximum source impedance to your power amp of 2k5 which will form a low pass filter on your signal. 2k5 and 1000pF is-1db @ 30kHz and -3db @ 63kHz. This may show as a slight softening of the extreme treble. But shortening the coax pushes the roll off higher up the freq range. If you use a 50K pot then you need to reduce the 1000pF to 200pF for the same roll off frequencies.

A short length of coax from pot to power amp is essential for passive preamps like this due to the high source impedance that the pot gives. 2m is usually OK.

[faux_vedette]

Originally posted by AndrewT
Hi,
put in a pot about 10 times the output impedance of your CD player.

If that is unknown then use 10K.

This gives a maximum source impedance to your power amp of 2k5 which will form a low pass filter on your signal. 2k5 and 1000pF is-1db @ 30kHz and -3db @ 63kHz. This may show as a slight softening of the extreme treble. But shortening the coax pushes the roll off higher up the freq range. If you use a 50K pot then you need to reduce the 1000pF to 200pF for the same roll off frequencies.

A short length of coax from pot to power amp is essential for passive preamps like this due to the high source impedance that the pot gives. 2m is usually OK.

Thanks for the into. But i am a little confused. Ok i understand using a pot 10x the CD output Impedance, got that. But if a 50K pot would have less HF roll off. why wouldnt i just make that my first choice?

I understand it would make my source impedance higher. but what would i be trading off by doing so?

[AudioFreak]

No. For a given input capacitance, the 10k pot will have less roll off.

[faux_vedette]

Originally posted by AudioFreak
No. For a given input capacitance, the 10k pot will have less roll off.

Got it, i missread the first statement and thought it said 2000pf not 200pf!