Cap before tonestack

[Smokebreak]

I have 3 gain stages and a plate fed tonestack. I'm going to add in a switchable 4th stage which would then plate drive the
tonestack.
I don't really want to run plate voltage to the switch(from 4th stage), so I was going to put a cap in front of the switch, that would then be in front of the Marshallesque tone stack. A large enough one in series with the treble cap won't affect it's value that much, but what about how it would affect the slope resistor and the freq response, and do I actually have some additional control over freq shaping with that extra cap? I was gonna go with 47n.

Edit : can I just treat it like any other simple RC filter?

[DonMoose]

As a quick stab, a series cap at least 5x the sum of all the caps in the tone stack should be big enough.

[Leo_Gnardo]

I was gonna go with 47n.

Seen it done in some amps, with values 22n to 100n. Your 47nF should be fine.

[Smokebreak]

Thanks guys, I see this is also a way to be able to use smaller voltage capable caps in the TS

[BTF]

Peavey does that often- .047uF 400V or 630V bypass, then they use the low voltage caps afterwards to lower costs.

Good Luck!

[Smokebreak]

Yea that worked out nicely. Amp sounds good, but almost too much gain...I was also getting some strange action on some single notes...when I pluck, after about 1 sec, it was almost like the amp would pluck the note again. Not quite as dramatic as that, but definitely a little strange decay/sustain action.

So I'm poking around, checking voltages, and my 3rd and 4th stage node has 340V supply. All good. Plates are 45V. What?? I've been using those blue RN resistors lately for plates, and didn't realize that I had a stash of 1M as well as 100K...

[matt h]

(deleted)

[Smokebreak]

I'm assuming that was because my plate resistors were 1M. Got 100Ks in there and it went away.