Ross Compressor Mods (Mark Hammer?)

[thermionix]

I'm so glad this thread bubbled up to the surface yesterday.  Led me to more reading and schematic comparison, and eventually to plugging the soldering iron in at 3AM. 

What I have is a BYOC 2-knob compressor, which is essentially a Ross clone, except for some reason they used a 100K level pot, instead of 50K.  I built it "paint by numbers" a couple years ago because I know jack about compressor circuits.  I included the "vintage parts" option with the NOS 2SC1849s and metal can 3080A, also used switchcraft jacks and a heavy duty 3PDT.  Seemed pretty cool, maybe a little dull sounding.

After studying up, I decided to clip off the 220pF cap and parallel a 100k resistor with the level pot to give it more of a classic Dynacomp voicing.  Very pleased with the results.  Gave me some "snap" back, not so dull any more.

Then I went to try the Mark Hammer attack/release switch mod.  Only mini toggle I had was a DPDT on-off-on, so I set it up to parallel in either a 47k or 15k, to approximate the values Mark was suggesting.  Middle position leaves the 150k stock, obviously.  Man, what a cool mod!  If anyone is considering it on their Ross/Dyna, I definitely recommend it.  The pedal is so much more versatile now.

Thanks Mark (and others)!

[Mark Hammer]

You're welcome.  Not really my idea.  I just ended up looking at a lot of compressor schematics, and realized what they all had in common that the Dynacomp/Ross didn't have.

I've told this story many times before, but it bears repeating.  A local buddy, named Tim Larwill, makes the favourably-reviewed Retro-Sonic line of pedals.  Back before they became as common as they did, Tim made a nice 2-knob Ross clone.  I drew his attention to the gain-recovery mod, and we conspired to add it to his unit.  I worked out a set of values that would provide an even proportional change in recovery time to provide a fast-medium-slow setting, using a 3-position toggle (what EHX uses now for their Soul Preacher and Nano Soul Preacher), and Tim incorporated it. 

Some time later, I noticed Tim had changed it to a pot, and asked him what was up with that.  He replied that customers had asked for a pot because they felt kind of hemmed in by a "mere" 3-position switch.  Of course we both knew that 98% of such customers were likely to set the pot to either the fully CW or CCW position, simply because smaller differences were hard to notice for most folks.  But Tim always tries to give the customer what they want, so a pot it was.

Personally, I think a 2 or 3-way switch is sufficient for the vast majority of players.

[thermionix]

A pot wouldn't be bad, but I don't have room for one in my pedal.  I don't know what the circuit would do at 0k, so maybe 10k resistor in series with a pot?  Audio taper?

[Mark Hammer]

A pot wouldn't be bad, but I don't have room for one in my pedal.  I don't know what the circuit would do at 0k, so maybe 10k resistor in series with a pot?  Audio taper?

Fixed resistor and pot is what everybody else does.  Tried and true.
But I'm telling ya, if you can hear the difference between setting such a control to 8:00 and 1:00, you'll be a scientific curiosity.  This is not a control that yields immediately audible changes, like an EQ or gain control.  The audibility of the change depends on how quickly you play.  And since players constantly vary how many strums/picks they shovel into each second, it takes extreme changes in gain-recovery time to be able to hear the impact on all notes.  Fast (10k) and slow (150k) may well cover all bases for most people.

[thermionix]

I hear ya, just curious.  After some time, I might find myself heavily favoring one position on my new switch, and just hard-wire that value in.  I have a bit of an aversion to mini toggles as it is.  Too fragile.  Right now I'm digging the faster speeds more than the stock value.

[Mark Hammer]

Makes one less inclined to need a "Blend" control, eh?

[thermionix]

Hadn't considered that, but I suppose it would.

[nonost]

Hi!

Any release mods? Or does the attack mod actually change also the release time?

Thanks

[Mark Hammer]

The gain-recovery time IS effectively "release", though bear in mind that the release in question is gain reduction.  With a longer gain-recovery time, it takes longer for the squish to back off and the signal to come back up again.  Faster gain-recovery can sound like "attack", because any quickly-picked notes after the first one/s occur at pretty much full amplitude.

[nonost]

Ey Mark, thank you! It looks like lots of stompbox compressors don't have an involved circuit so you can have both "real" attack and release. That's what I'm learning from reading around. I don't see it as a big problem, at least for guitar. In studio it's another story but for many scenarios theya are very good enough

Cheers