SSlmixed.com Forum

Tech discussion => 4K,6K,8K Series => Topic started by: marcmozart on February 13, 2013, 05:23:57 PM

Title: 4K E/G Modifications (Increase of Coupling Cap before the Channel VCA)
Post by: marcmozart on February 13, 2013, 05:23:57 PM

I found this a while ago on Gearslutz:

http://www.gearslutz.com/board/1216798-post6.html

Run that AP with a frequency/phase plot. See that phase lead shift in the low end? Not too pretty, is it? That's a result of simple 2pi /rc/sq of selecting too small of a coupling cap. A 10 uf in front of the VCA is one sore spot with me. I would increase that a decade and call it a day. Remember, each coupling cap stage is a 1 pole high pass filter. A few stages, no problems, run hundreds and you will find a 10 or 12 pole filter with rather poor phase response and some non linear phase shift from the fact that all the roll-offs are not tuned to each other but are set somewhat randomly.

Fix them and then run that phase plot and see 1~2 degrees at 20 hz. Don't forget the polyprop film bypasses across them. A nicely fixed up 4k will shake your world if that low end is fixed.

Warning! You will find the high pass filter in regular use afterwards. A couple of nice poly film caps there will allow it to become your friend.

Jim Williams
Audio Upgrades

Full thread with more details: http://www.gearslutz.com/board/high-end/117824-ssl-4000-e-g-modifications.html

Title: Re: 4K E/G Modifications (Increase of Coupling Cap before the Channel VCA)
Post by: Matt Sartori on February 14, 2013, 08:39:41 AM

Double post:

http://forum.sslmixed.com/index.php?topic=261.0

 ;)

Mattia.