hi-cut problems

[megawhat]

yo!

I just tried testing out a hi-cut control in my amp. a fixed bias LTP amp.
I only had a 0.0022uf cap and a 500K audio pot to hand.

It only seems to be having an effect for me when I get close to maxing out the dial. I have the wiper wired to one line feeding a power tube grid stop, and one outer lug wired in series with the cap to the other line. one lug is disconnected.

would a i get a better more smooth and usable sweep using a 4n7 cap and 250K log pot?

[iknowjohnny]

I used a much smaller pot. I can't recall the size, but i know it was much smaller than 500k. I think 50k if i recall. But it probably depends on the cap too. Also try a bigger cap. i got a really nice smooth tone with a .022. The only problem i found with it is that once the thing has enough effect to make a worthwhile difference, you lose a lot of volume. basically it's a frequency selective volume control, so all you're doing is turning the volume down on the treble frequecies.

[Bob-I]

would a i get a better more smooth and usable sweep using a 4n7 cap and 250K log pot?

Yes, the cap is too small, pot too big. I have .0047uF and 250KA and it's very effective without cutting volume.

[megawhat]

cheers!

[PCollen]

I used a much smaller pot. I can't recall the size, but i know it was much smaller than 500k. I think 50k if i recall. But it probably depends on the cap too. Also try a bigger cap. i got a really nice smooth tone with a .022. The only problem i found with it is that once the thing has enough effect to make a worthwhile difference, you lose a lot of volume. basically it's a frequency selective volume control, so all you're doing is turning the volume down on the treble frequecies.

F(-3dB)= .159 / (R*C)

The RC of 250K/.0047uF and 50K/.022uF give nearly the same F(-3db):
135 Hz and 144Hz, respectively. But the later values, as previously stated are all wrong and you're getting phase cancellation of nearly all your frequencies.