dale116dot7
Well-known member
I just got my variable-mu compressor going. Pictures later this week. It's roughly based on a single channel of a 670, but very roughly. The biggest challenge was matching the tubes. Some parts values needed to be tweaked to use parts I had around. I just swapped the 6BA6 tubes around 'till I got it to work without any control voltage feed-through (compression thumps). In hindsight, I should have got more 6BA6's and had an easier time matching them. I got 10 and used 8. Should have got 20 of them.
Tube complement:
6BQ5, 6U8, 0B3 - voltage regulator
6BA6 x8 - main part of compressor
12AX7, 12BH7, 6GW8 x2 - control amp
Transformers:
Hammond 850N x2 (signal amp in and out)
Hammond 850G (control amp in) - should change this to 850N or something like that.
Amveco 62025 (control amp out) - not ideal, it's on my list of things to change out too.
All but the 0B3, 6BA6's and tube sockets were salvaged parts or stuff I had lying around. Project cost was about $200CDN (not including stuff obtained years ago and sitting in my garage).
It sounds pretty good. Different than any other compressor I've used. It really gives vocals a 'presence' in the mix - a solid like a brick outhouse sort of sound.
Oh yea, the purpose of the powerful control amp is to charge up the CV capacitor with an attack of .2 msec. I always wondered why there was such a powerful amp in a Fairchild when Altec and other variable-mu compressors didn't do that.
-Dale
Tube complement:
6BQ5, 6U8, 0B3 - voltage regulator
6BA6 x8 - main part of compressor
12AX7, 12BH7, 6GW8 x2 - control amp
Transformers:
Hammond 850N x2 (signal amp in and out)
Hammond 850G (control amp in) - should change this to 850N or something like that.
Amveco 62025 (control amp out) - not ideal, it's on my list of things to change out too.
All but the 0B3, 6BA6's and tube sockets were salvaged parts or stuff I had lying around. Project cost was about $200CDN (not including stuff obtained years ago and sitting in my garage).
It sounds pretty good. Different than any other compressor I've used. It really gives vocals a 'presence' in the mix - a solid like a brick outhouse sort of sound.
Oh yea, the purpose of the powerful control amp is to charge up the CV capacitor with an attack of .2 msec. I always wondered why there was such a powerful amp in a Fairchild when Altec and other variable-mu compressors didn't do that.
-Dale