choke and cap question

[Raj1]

Hi,

I found this info on the audio consulting website regarding mains chokes,




"Make them resonate with a parallel oil capacitor and get more 100/120Hz rejection and better sonic results"


Does this mean putting a single cap accross the input and output tags of the choke?

What size minimum shold the cap be?

Thanks
Raja

 

[dhaen]

Yes you can. It's just a parallel tuned circuit. (Who can remember the formula offhand?) Ouch it's been a lot of years since I used it.....
A quick search found this article:
http://lists.contesting.com/_amps/1998-02/msg00030.html
I don't know whether there are any merits for audio, but one drawback is that it will pass all non 100Hz signals, eg interference.

Edit: f=1/2pi rootLC
It's what was in my mind, but who wants to make a fool of one's self...

Edit: Link fixed, thanks Tom

 

[Tom Bavis]

Good article! (link should end with ".html")

As mentioned, you really need another filter section, since it only filters the fundamental ripple frequency, and there are lots of harmonics of line frequency.

Here's an early example - 1930's Philco http://www.philcoradio.com/tech/images/70a.jpg

6 uF electrolytics don't give a lot of filtering...