contour on marshalls

[Chef]

When i turn the "contour" control on a marshall amp/pedal, what is it altering (electronically).  From listening to it i dont think its just changing the EQ (although it almost sounds like a "scooped mids" effect), it seems to produce a completley different sounding distortion altogether.

Sorry if this is obvious to some people.

[Steben]

I looked at the schematics and it is in fact a control between notch filter (scooped) and a high-roll-off (treble cut) filter.
Something that was widely discussed in here but I can't remember when.

[Chef]

ah,

Great, thanks,

Adam

[Chef]

can you tell me where you got the schematics, i'd like to have a look.

Cheers

[Steben]

www.drtube.com/marshall.htm

Look at valvestate 8040 or 8080. It's the "tone control after the tone control" of the distortion channel (with diodes of course...).