500 series PWM compressor design

I'm very interested in this form of dynamic control. Chopping the audio 250,000 a second sounds like it would be a good way to manipulate an audio signal. Now that the timing circuits are available they're now a modern reality where previously they where too expensive and cumbersome.

Dan Kennedy has done it and with spectacular results. Dave hill has too - so has prr!

anyone interested in exploring a design for the 500/51x format?

The issue as you guys probably know used to be with the timing circuit. This looks like it might be quite useful in this application - http://www.onsemi.com/pub_link/Collateral/SG3525A-D.PDF

Check the PYE compressor. Abechap did a clone here on this forum!

Yes I know - it's tube and it's based on an ancient design - the issue with the timing circuit is no longer an issue and it's cheap and available. I think abes probably using the same in the pye.
I want to explore a 500 design. Dan Kennedy has manged to fit filters, feed forward and feedback topology and then a blend function to blend between the 2. Magnificent processor. So most certainly doable.
I found another post about pwm from 2004 and they didn't end up getting anywhere but they used the same timing circuit that I referenced which is a bit coincidental!

The Studer 961/962 stereo bus compressor comes to mind as a prime example of this technology. Schematics available at ftp.studer.ch

Jakob E.

I would be interested, 500 or 51X.  If it had the same level of controls as Igor's F76 that would be stellar.  Always tend to use the SCF at about 250 Hz for some reason...  Link-able would be good as well.  And I do like the bypass switch.  Abe's "PIE" compressor looked really tempting, but I can't cram any more rack units into my area.  I do have a 51X rack from Jeff so modules I can very easily use, making this very tempting to me (a sort of "TAKE MY MONEY NOW!" project.)
Patrick

I have been toying with the same idea for some time too.
I really like the PWM limiters in the good-old BSS FDS-320/340 crossovers. They could be very efficient 'Brick-wall' limiters for AD converters too.
The SG3525A looks like a very efficient PWM generator.
Here are the schematics from the BSS FDS-320 with a CD4053B 'chopper' and a 25kHz low-pass filter.

Here is the BSS FDS-320 side-chain and PWM schematic

this seems a good solution :

http://www.diystompboxes.com/smfforum/index.php?topic=103833.0

I made an experimental Gain Cell controlled by an SG3525 some years ago.  It worked quite well.

How far did you get with it rob? I'm in the middle of moving so I'm currently perched on the only piece of furniture left - coffee and ipad and me.
I'd love to check out the studer schematics. The thing is modernising these designs.

You might try messing around with the F76 design to see if you can turn it into a PWM comp. It seems to be a good candidate for an easy-isy alteration...the schemo is nicely laid out. Some changes to the fet stage and the detector. ..