Switchable filter capacitors

[Steveo]

Any reason it would not be a good idea to have a switchable filter capacitor? My amp has a normal 2204 filter cap arrangement. So my question concerns the 50/50uf multicap for its main b+. I was pondering the idea of adding another 50/50 cap in parallel with it but on a high voltage switch for a kind of tight mode. Would the high voltage be kind of dangerous for this application?

[pompeiisneaks]

It's not necessarily dangerous, but to get a switch rated for that high of voltage can be expensive, and hard to find. Especially in a small form factor for inline switching of B+ rails. Most of what I'm finding that's a switch like I'd imagine on mouser.com has a limit of 250VDC. Basically due to higher voltage switching allowing for arcing and the like it becomes harder to get them to work.

I searched for a while and couldn't find one that wasn't some kind of industrial emergency stop type button, huge and not feasible for an amp. I'll bet there are some, but not easy to find.

[xtian]

Every damn standby switch is doing the duty you're describing. And yes, they sometimes get pitted and intermittent from pitting.

[pompeiisneaks]

Every damn standby switch is doing the duty you're describing. And yes, they sometimes get pitted and intermittent from pitting.

Oh weird, I was looking at several switches that were of that type and they rated them all at AC only and no mention of DC. but you're right, I never though of that DOH.

but you are definitely denoting the point I was making is that regularly switching DC is a lot harder on switch contacts than AC. The arc that happens on disconnect can either cause carbon buildup or pitting and over time can end up making the switch fail to work a lot sooner than a lower voltage DC switch would.

I don't know what I was remembering about this discussion but I'd swear I'd seen explained in many places that dc switches of high voltage are not the best... I must have confused it with some other kind of switching... ugh.

Sorry!

~Phil

[Roe]

you need a 10-100k power resistor across the switch unless you want to blow fuses. 100uf on the mains is sufficient though. 200uf is overkill on this amp

[Guy77]

Another idea is placing your cathode bypass caps on a switch, this can also create the tightening effect your after ( by using smaller values) and would not require switching high voltages.You could also place higher value preamp cathode bias resistors on a switch to get a tighter sound.

Cheers

Guy

[Colossal]

Vox did this on the AC30CC2. The switch is labeled Vintage/Modern. 22uF are bypassed with 10k when switched out (Vintage mode). Vintage mode is 22uF - Choke - 22uF, Modern is 44uF - Choke - 44uF.

Cap Switching.png

[martin manning]

Nice find, Dave!

[Steveo]

Cool thanks a lot. I may try something like this vox.

[Roe]

vox ac30s/50s/100s benefit from higher filtering. But about 33uf on the screens is perfect on an ac30