Dynacomp/Ross to Slow gear/auto swell mod

[au_loki]

Anyone done a mod to their trigger circuit to make it autoswell like a Slow gear pedal? The challenge is on. Later au_loki.

[Mark Hammer]

Unlikely to work, at first glance.  Remember that the modus operandi of the compressor is to always aim for max gain unless dictated otherwise.  "Swell" effects presume that gain always starts at zero, unless dictated otherwise.

[Processaurus]

Also remember the dynacomp gets its envelope signal to do the compressing (actually closer to limiting) from the output of the gain control element, and struggles to keep everything coming out of the 3080 at the same volume, until it runs out of gain as the note trails off.  This is a "feed back" design, as opposed to a "feed forward" design where the envelope signal doing the control of the gain element is tapped from the input, which would be a better candidate for a swell type effect.  With one of those designs it seems like it wouldn't be a difficult to make a swell effect by making the compressor over react to loud signals and turn down the gain too far on the attack of a note, but that effect would be at the mercy of the picking volume going in, as opposed to something like the slow gear, which triggers a synthesized envelope.

I made a dynacomp and slow gear in the same box, to try to get the slow gear to trigger more consistently, and it worked just OK.  There was a cool discovery that the slow gear sound mixed out of phase with the dynacomp sound feeding it made a neat short decay, banjo like enveloped guitar sound.

[au_loki]

Thanks Gents for your great responses.
I have a spare D/R Comp PCB and would be interested in anyone's idea for a small "Slow Gear" mod board that can be cut in to the CA3080 pin 5 section - I am sure that it has been done before.

Later au_loki

[R.G.]

The trick to doing this is to make a good trigger circuit. The rest is right out of the Dyna.

You need to process the guitar signal to make a nice full-on/full off signal when the note is present or not. Usually this involved full wave rectification and filtering, or something like the sample/hold envelope circuit, followed by a comparator. Pretty standard stuff in the synth industry, and done in some effects.

Then you put a parallel resistor/diode from the output of the comparator to a cap to ground. The resistor sets the charge rate of the cap, the diode lets it discharge quickly. The R and C determine the ramp-up timing. Then you buffer the cap output like the emitter follower transistor on the Dyna, and add a resistor to pin 5 from the transistor emitter. The size of this resistor determines the gain at full "on" in conjunction with the output load resistor from pin 6 to the bias voltage.

You need to make SURE that the resistor from the emitter to pin 5 of the 3080 does not allow more than 1mA to flow into pin 5 under any circumstances, or it will kill the 3080.

[petemoore]

   I typed/deleted 4 long pages...
  The Dyna can duck a little more before ducky-stuck in muck limitation is exceeded. A good design as is and a bit more recovery time can be had but there's not a big window as far as value/response changes to where it doesn't get stuck.
  the 280 is nice simple design, other photocell designs are also easier to follow as far as.
  Vary the LED current by:
  Attenuate the input by fullband or LP [the high notes sometimes fail to produce the strength/response of low notes triggering the Env detector.
  Vary the LED Current limiting resistor.
  Watch the LED and see it can be 'pinned to bright' so it only 'lets up' during quiet input times by increasing it's average input current.
  I was able to get lower min. R using 2 LDR's...also fixed R or pot can be thrown in with.
  Watching the Simple Compressor [IIRC that was the name] evolve into not quite so simple and more or less 'deluxe' compressors...gave rise to the thought that design choice may allow the needed perfection or flexibility while abating to some degree the build and use complexity.
 

[au_loki]

Ducky stuck - sounds painful, even for a CA3080! I mucked (no pun intended) around with a 'slow attack' setting on a multieffect box and ok but I reckon it is a bit more controllable with a volume pedal - now I'm off to find me some sticky ducks. Later au_loki.