My Ross Compressor does not sustain now - any help appreciated

[glweid]

After trying a few mods to my TonePad Ross Compressor ( to help with my One Spot 9v noise) it seems now my compressor does not sustain any longer. It's acting only like a basic booster. The Sustain and Level pot's increase only the volume (and noise) but I do not notice any sustain increase when the note/chord volume drops.

It used to work fine before I hacked around on it and I don't see any recognizable connection problems ... weird. I change out the Op Amp since it was easy to do and that did not change anything.

I guess I need to take voltage readings per http://fuzzcentral.tripod.com/compressor.html and post to the forum

If you have any tips let me know

Thanks !

[Mark Hammer]

The compressor uses a 3080 transconductance amp.  This chip sets the amount of gain applied on the basis of current fed to pin 5, which is termed the Iabc pin.  It "works" by reducing gain when a big signal comes in and restoring gain as the signal dies out.  It does this by essentially "subtracting" the envelope current from a preset current controlling the gain level.  So, without any input signal, there is THIS much gain, and with an input signal there is THIS much less.

The Compression control on the pedal is essentially a series resistance that limits the amount of current going into the Iabc pin (pin 5) on the 3080.  If you stick a bigger resistance there, then it can't be affected as much by variation in the envelope amplitude coming off the transistor just before the compression control.  It's a bit like declaring personal bankruptcy - if you have no money then they can't take as much away from you when the bills roll in.

If variations in the Compression control are not doing anything other than changing the volume level, and its essentially full tilt all the time, except for when you turn the volume down, then it would seem that the envelope/rectified output is simply not being subtracted. 

I'm guessing that one of the mods you tried to do was to add variable or preset recovery times by monkeying around with that 150k resistor and 10uf cap, right?  It may be that one or both of those components (or their replacements) were not installed properly or something nearby is shorted, preventing that last transistor from having a rectified signal to combine with the default control current.

[glweid]

Mark

I put your mod  (with the switch) to change the 150K resitor values for the recovery time. It worked originally and does seem to still affect the tone when switched.

I put the 10uf cap back (on the +9v feed) that I was changing for the One Spot noise. I checked the botton of the board for shorts and don't see any but I'll double check that I got the polarity right on the 10uf when I put it back in and get a magnifying glass to look at the board more closely and let you know what I find.

Thanks for all of the good info and help

[Mark Hammer]

If the cap has a bad solder joint (or instance, some tarnish around the leads so that when you soldered it there was a nice little hill of solder around it but not a true conductive joint), my guess is you'd possibly be experiencing what you're experiencing now.  BTW are you sure you put the cap back in with the proper orientation?

[glweid]

Cleaned up a few solder joints and it's working again !

Thanks again Mark for the suggestions !

[Mark Hammer]

Were they where I thought they'd be or was I way off? (Congrats, by the way)

[MartyB]

My Dynacomp build requires a good battery.  if the voltage gets to around 8 (unconnected) the effect doesn't work.  Notes just kinda crumble away.

[glweid]

Mark,

Yes I think it was the solder joint by the 10 uf that fixed it. Found my resistor T-Pee for the recovery rate was leaning was too close to another resistor so I straightened that out also.

I also removed the Cd cap (220 pf) on the input and that brightened it up a bit more so it sounds extremely clean.

I now hear the sustain kick in on the decay but I'm still wondering how much sustain I should expect.

Should it be super long ?? Since I don't have another to compare it too I want to make sure everything is 100%.

Thanks to the board again !

[Mark Hammer]

Yes I think it was the solder joint by the 10 uf that fixed it. Found my resistor T-Pee for the recovery rate was leaning was too close to another resistor so I straightened that out also.

I also removed the Cd cap (220 pf) on the input and that brightened it up a bit more so it sounds extremely clean.

I now hear the sustain kick in on the decay but I'm still wondering how much sustain I should expect.

Should it be super long ?? Since I don't have another to compare it too I want to make sure everything is 100%

Thanks for the feedback.  I'm sure this will be useful troubleshooting information for others in the future.

How long should the sustain be?  I think people expect a little too much of compressors because they often have compressors "explained" to them by promotional literature.

Keep in mind that the comprssor does not increase sustain at all.  Rather, it creates the illusion of sustain by evening out the volume changes in a note, both by taming the big volume change at the start of the note, and increasing the volume a bit as the note starts to die out.

Of course, what drives that smoothing out of the volume are the properties of the note itself, so if the note itself dies out fairly quickly, the circuit will not keep the note alive longer than it normally lives.  The sustain you think you hear is really the quietest parts of the note decay being boosted.  Once the note is gone, it's gone, and no boosting can help that. 

What often gets attributed to compressors is more likely to be the amplifier turned up and helping to shake the body of the guitar.  If you have ever tred to get a wine glass "ringing" by rubbing the moistened edge of the glass with the tip of your finger, you will know that it takes a bit of rubbing to bring the glass to the point of oscillating.  That's one more example of the old bodies-at-rest-vs-bodies-in-motion thing.  The glass has to "get rolling" first and that takes a bit of time and energy.  Similarly, if the guitar body is being vibrated by high amplitude sound waves, it takes a bit of time before the body itself starts to resonate and shake the string a little linger.  The joint action of the compressor keeping the volume loud for just a little longer, and the amp being loud enough to do something to the guitar body with that continued volume, is helpful in allowing the finger vibrato of the player to result in a note that sustains longer.

If you wanted to get real dangerous, I suppose you could increase that 150k resistance to 180k or even 270k.  This would slow down the recovery time even more and cause the volume increase/restoration to be essentially "pushed back" until much later in the lifespan of the note.  The problem this creates, though, is that it is tailored for playing styles where there is generally much more time between successive notes.  If you have short gaps between notes (i.e., pick fast at any point), this slowed recovery rate ends up blurring distinctions between notes.  In other words, it stops being just a compressor and starts to get in the way of more expressive playing.  That's probably why you won't see any commercial pedals that extended that recovery time beyond what the Dynacomp and Ross have used: a 10uf cap in conjunction with resistances between 10 and 150k.

[glweid]

Mark,

Again thanks for the clarification and explanation on the compressor characteristics, very helpful. Based on what you have said it sounds like my compressor is functioning as it should be, I definately hear the string volume levels even out, especially when stumming hard or picking loudly on one string compared to another. And you described the "sustain" perception well. The compressor is really not causing the note to sustain longer than it normal, it is adjusting the volume level (up/down) based on the incoming levels causing it to smooth out, especially in chords.

I adjusted the trim pot to sound the best with the sustain set to max, so I can get the entire range of the sustain control working

Cheers
Gary Weideman

[tocs100]

Hi Mark. This is my first post, and you really seem to be the ROSS expert, so here goes:

I want to have someone modify a Ross comp to use as a vocal de-esser. Here's what I know and don't know:

Know:
1) Sustain knob is the threshold level, from 15 to 40dB, perfect
2) Attack occurs at 4 ms, okay, but 1 ms would be better
3) Recovery time is 1.2 sec., WAY too long, need 1 ms attack

Don't Know:
Ratio. 10:1 or higher would be perfect.

I read in another thread that you didn't know the ratio. Could you A/B your Ross with a rack comp possibly? (As well as supply the cap values for the attack and recovery mods above?) I'd really appreciate it.

[tocs100]

 ???Bump.

[tocs100]

Bumperoni with sugar on top?