Hi George,
we know you meant to say that the worst Rs of the pot is it's value divided by 4, so bat's we are not.
The more important issue when short, low capacitance cables are used, is whether an RF filter is fitted inside the power amp input.
For the 20k pot, I would suggest that the RF filter capacitor should be less than 150pF (0.8uS) and for a 5k pot we can tolerate just 680pF. Some would fit caps of only one third of these values (0.25uS) and say they can hear the difference from using anything higher.
AKSA,
please come in and talk to us.
we know you meant to say that the worst Rs of the pot is it's value divided by 4, so bat's we are not.
The more important issue when short, low capacitance cables are used, is whether an RF filter is fitted inside the power amp input.
For the 20k pot, I would suggest that the RF filter capacitor should be less than 150pF (0.8uS) and for a 5k pot we can tolerate just 680pF. Some would fit caps of only one third of these values (0.25uS) and say they can hear the difference from using anything higher.
AKSA,
please come in and talk to us.
Looking at the bandwidth of his Aksa 55 he has limited it to -1db @ 35khz I would say this was determined by his input filter, good practice is to have all filters even on the feedback after this faster and faster.
Yes if his cap to ground on the input rf filter is 1000pf to ground then with the output of the passive pot at 2500r that creates a lowpass of -3db @ 63khz this is still ok, but any more than 1000pf at it will start cutting into the top end 20khz. But I have yet to see an amplifier with a input rf cap over 1000pf!
Cheers George
Yes if his cap to ground on the input rf filter is 1000pf to ground then with the output of the passive pot at 2500r that creates a lowpass of -3db @ 63khz this is still ok, but any more than 1000pf at it will start cutting into the top end 20khz. But I have yet to see an amplifier with a input rf cap over 1000pf!
Cheers George
Hi,
1000pF and a 20k pot is a killer (~=5uS).
F-3db=31.5kHz. This is clearly audible top cut.
Even changing to 5k pot only brings the top cut down to 1.3uS. This is still audible.
Many recommend the RF filter be in the range 0.5uS to 1.5uS but some argue that these too affect the top end and suggest we go even lower to about 0.2uS to 0.3uS. I use 0.68uS and it works for me.
1000pF and a 20k pot is a killer (~=5uS).
F-3db=31.5kHz. This is clearly audible top cut.
Even changing to 5k pot only brings the top cut down to 1.3uS. This is still audible.
Many recommend the RF filter be in the range 0.5uS to 1.5uS but some argue that these too affect the top end and suggest we go even lower to about 0.2uS to 0.3uS. I use 0.68uS and it works for me.
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