Volume knop cuts gain (modded valvecaster)

[Stellan]

Hi
I have made a modded doubble valvecaster to eksperiment with from the schematic i n this thread
http://www.diystompboxes.com/smfforum/index.php?topic=63479.0
Everything is socketed, and i have not yet wired up a tonestack.
Each half is like a valvecaster except for some different values and
the gain pot cuts volume from the input by sending it to ground
instead of the variable cathode resistor in the original schematic.
It sounds good, and i can achieve everything from mild crunch to schreaming distortion
using the two channels, BUT when i turn down the volume of a channel it cleans up,
and this is happening on both channels. It sounds to me like it also looses some trebble, but
this could be beqause of the lost gain and hamonics. Anyone knows what is going on here?

[CynicalMan]

It could be that your valvecaster is overdriving your amp and turning it down reduces the distortion from your amp.

[Stellan]

Hi,
thank you for your answer, but thats not it. The amp is clean. I am getting a fairly good amount of dirt from
each chammel of the pedal, but only when the volume is turned up. Turning down the amp doesn't reduce distortion.

[frequencycentral]

the gain pot cuts volume from the input by sending it to ground
instead of the variable cathode resistor in the original schematic.

So you've got a pot at the input?

It sounds to me like it also looses some trebble, but
this could be beqause of the lost gain and hamonics. Anyone knows what is going on here?

It sounds like your pot at the input is acting in conjunction with the input cap as a variable highpass filter - not just a volume control.

Probably a bad idea to have that pot at the input. If you don't want to use a variable cathode resistor then you should consider replacing the interstage grid leak resistor with a pot wired as a voltage divider.

[Stellan]

Yeah, I've got a pot at the input - after the input cap. I will try your suggestion and place it between the stages. However i still don't understand how the volume knop can effect how much the signal gets clipped.

EDIT: How would it be different to place the gain knop between the stages? I still have a coupling cap there.

[jacobyjd]

If you put your volume control before the gain stage, it's reducing the amount of signal that gets amplified, which reduced the amount of signal that can be clipped, which means you get less distortion.

[Stellan]

If you put your volume control before the gain stage, it's reducing the amount of signal that gets amplified, which reduced the amount of signal that can be clipped, which means you get less distortion.

Oh, i probably should make it clear that the volume pot is after the last stage. It is the placement of the gain pot we where discussing. Wheter the gain pot should be before the first stage or between the stages.

[Stellan]

Ok, i have tried everything i can think of. I have disconnected the gain pot, tried different values for volume pots, and swapped components for hours, and the result is still the same. It sounds nice, but the volume pot acts like a gain knob. It sounds good with the volume down too, but a lot cleaner, and the grit i get with the volume up is coming from the pedal - not the amp.