'Ducking' or 'Swelling' a Dyna/Ross or OS ?

[petemoore]

  I have an OS and a Ross comp.
  I suppose what I'd like is a Swell pedal, or something that overcompresses.
  Say...attenuates signal quite noticably when loud low notes [higher input voltage to Env detector] are sourced.
  The mods I did find googling were the opening up freq range, cap upgrade and low battery mods...low battery mod might be cool...I still can't hear clips...I'm not real sure what that does to the circuit function or the sound.
  The Ross does some light 'ducking', I should try boosting the input and re-adjusting the comp knob.
  ..anyway, I'm looking for ideas/comments on whether it's do-able...on occasion, some ramp-ripple might actually be cool!
  I know there is a slough of Dyna mods I'd like to read, but I can't seem to find the ones I want now...any help appreciated !
 

[Mark Hammer]

What we hear as constant level from a compressor is the gain being suddenly reduced, and gradually increased in a manner that perfectly complements the actual level of the note.  In theory, if the gain is pulled down a bit farther than enough to offset the initial peak, and then returned more slowly than it takes to achieve constant volume, one ought to get a swelling or "overcompression" effect.  In principle, it also helps if you feed it a signal that has greater dynamic range in the first place.  The classic version of this is a top-notch Tele with a great bridge pickup, set to "extra-twang".  That huge transient peaks could set a great many compressors into seizures, and produce a kind of "sucking" sound that was like trying tho stuff the signal out of a suasage casing.  The best example that comes to mind was the tone that Jim Messina (of Loggins and Messina) used to often get, but alot of other country players get it too.

Seems to me that some tweaking of the component values of the 150k resistance (higher) and 10uf cap (lower) in the rectifier part of a Dynacomp, and *maybe* dropping the 27k resistor after the Compression pot down to 24k might get what you're after.  Be careful with that 27k part, though.  3080s will fry if you feed more than 1ma to their Iabc input, so you don't want to drop that resistance much more.

[markm]

Pete,
If you want one that'll do that build a DOD 280a clone. It'll swell quite well! 

[petemoore]

  Very much so, and thank you Mark !
  After I put the 15k back and added the 330k instead to the base of Q5, also swapping the Base cap to ground 10uf for a 3.3uf..Q5 must be the transistor that drives the envelope...reduced shunting of signal getting into Q5 did the trick nicely, indeed, and has a tendancy to dive unless the comp knob is turned [my comp knob is turned around I think] most/all the way...must be reduced compression because it gets a little louder that direction.
  Also it doesn't seem to want to sound like it used to...go figure, but I'm thinking about making the 150k a 150k + 500k VR pot...I think I can work with that and leave the 3u3 cap where it is...I Like that it can be set so more bass can be attenuated..Very Nice, copious amount of Bass Note squash now, quite the tool !!!