Switchable PS filter caps?

[eddie25]

I have an amp with a power supply similar to a typical 'wreck with parallel 47uF caps for the first node. With some guitars the amp is a little stiff and with some it is perfect. I had an idea to switch the ground of one of the caps so I could switch from 94 to 47 on the plates. I would probably place it within the cab so it's not hot switchable, but I need to know if this is a bad idea. Thanks!

[C Moore]

I will let the more knowledgeable answer the hows and why.
Just mentioning that Vox does/did this with their CC Models. No sure if they have carried that over with the C Model or not.....I believe the switching is shown on page 2
best

[matt h]

(deleted)

[C Moore]

Yeah...it looks like a DPST that adds caps// to the Plates and Screens of the EL84.
I own one of these amps, and I have never even payed any attention to it until now.
I did a ton of work to my CCH, but just never consider that "Smoothing Switch".
Anyway....I am No Tech, will be interesting to see what the smart guys think about all of this stuff.
Seems like a great idea.
What amp is this for.?

[Stevem]

Just a regular SPST switch is all that is needed to put in parallel the added 47 uf fiter, but you will need to first place the amp in standby to avoid a loud pop that the switch closure would otherwise make.
It would be a good move in after thought to use a DPDT switch and use both side of it as DC voltage will tend to pit the contacts after a while and this move will give you twice the switch life!

[Roe]

I've tried this. You really need a power resistor across the switch. Vox uses 10k, I tried 100k

[tonewood]

I have an amp with a power supply similar to a typical 'wreck with parallel 47uF caps for the first node. With some guitars the amp is a little stiff and with some it is perfect. I had an idea to switch the ground of one of the caps so I could switch from 94 to 47 on the plates. I would probably place it within the cab so it's not hot switchable, but I need to know if this is a bad idea. Thanks!

I may have missed something but I think two 47uF caps in parallel is 23.5uF.

[pops]

I have an amp with a power supply similar to a typical 'wreck with parallel 47uF caps for the first node. With some guitars the amp is a little stiff and with some it is perfect. I had an idea to switch the ground of one of the caps so I could switch from 94 to 47 on the plates. I would probably place it within the cab so it's not hot switchable, but I need to know if this is a bad idea. Thanks!

I may have missed something but I think two 47uF caps in parallel is 23.5uF.

Two 47uF caps in parallel is 94uF OP is correct. If they were in series it would be 23.5.

[Structo]

Nope

Caps in parallel add the value where as in series, they halve the value if both caps are the same.

Opposite of the resistance formulas.

[eddie25]

Cool, thanks for the input and the schematic guys. I'm gonna try it. It's gonna be on top of the amp, close to the caps. It won't be switchable unless you remove a panel from the cab, but I'll still probably add the resistor cause you never know.

[guitarmike2107]

94 to 47 is stiff both ways, I would have thought you would be better trying to get 16 or 22 for the lower filtered option up to 69uf (22 +47)for stiffness