ampage Tube Amps / Music Electronics	For current discussions, please visit Music Electronics Forum.

ampage archive

Vintage threads from the first ten years

previous: Bruce In other electronic industries, it'... -- 9/27/1999 4:40 PM

Re: Solen caps in guitar power supply.

9/27/1999 7:08 PM
KG	Re: Solen caps in guitar power supply. Couple of notes on the parallel cap-- If you've got an O scope, and can check the signal on the supply rail (be sure to use a blocking cap) then you can see if you really need a parallel cap. If there's no signal-dependant AC on the rail, your cap is fine and needs no help. If the bypass cap helps eliminate some ACV, then put it in. There is an issue with these bypass caps in that there can be a resonant circuit set up due to the low values of inductance in the caps themselves. Every cap has a resonant frequency, and you just MIGHT push one down into the audio band if you aren't really careful. The bypass cap works to lower the impedance of the power supply at VHF, where the inductance of those big old 'lytics causes a rise in ESR and effectively a drop in capacitance. This can cause oscillations, which is the reason for the bypass in the first place. If your ESR is not high at HF, then the bypass cap won't do anything but lighten your wallet. It MAY even set up a resonant circuit, as I've described above. In a nutshell, it's not ALWAYS a good idea to bypass your lytics with films. Somtimes it can actually do harm, although it's admittedly not likely. Just some other issues that may have been overlooked... Ken

9/27/1999 7:08 PM

Re: Solen caps in guitar power supply.

Couple of notes on the parallel cap--

If you've got an O scope, and can check the signal on the supply rail (be sure to use a blocking cap) then you can see if you really need a parallel cap.

If there's no signal-dependant AC on the rail, your cap is fine and needs no help.

If the bypass cap helps eliminate some ACV, then put it in.

There is an issue with these bypass caps in that there can be a resonant circuit set up due to the low values of inductance in the caps themselves. Every cap has a resonant frequency, and you just MIGHT push one down into the audio band if you aren't really careful.

The bypass cap works to lower the impedance of the power supply at VHF, where the inductance of those big old 'lytics causes a rise in ESR and effectively a drop in capacitance. This can cause oscillations, which is the reason for the bypass in the first place. If your ESR is not high at HF, then the bypass cap won't do anything but lighten your wallet. It MAY even set up a resonant circuit, as I've described above.

In a nutshell, it's not ALWAYS a good idea to bypass your lytics with films. Somtimes it can actually do harm, although it's admittedly not likely.

Just some other issues that may have been overlooked...

Ken

Replies:

Bruce q{There is an issue with these bypa... -- 9/28/1999 6:14 AM
Fred Just been reading the posts on usin... -- 9/29/1999 3:16 AM