Active electronics and compressors, can't they just get along?

[vanessa]

I've read that some compressors have a hard time handling active electronics when [AE are] set at higher output volumes. I've seen some commercial units (EBS Multicomp) employ a active/passive switch that supposedly takes care of the issue. I would like try to do something like that myself say in a Ross Compressor build. What would I be looking to change [values] on the Ross to make it active friendly for bass and guitar (or just bass for that matter)? 

[Mark Hammer]

In theory, you can either:
a) turn down the input signal hitting the sidechain/rectifier
b) turn down the gain in the sidechain
c) reduce the range of action that the sidechain output has

In the Dynacomp, the sidechain gain is partly provided by the CA3080 itself, which boosts and feeds its output to the rectifier circuit.  The outputs of Q3 and Q4 are summed at Q5 and fed to the current control pin on the 3080 in a manner that turns down the gain when the input is hot.

I don't know how to set the default 3080 gain in that circuit, but my hunch is that if the 500k compression-amount pot was replaced with a 1M unit, you could likely constrain the gain-reduction action a lot more, such that input transients would not have as great an effect on gain-reduction, no matter how hard you whomp the strings.  Just a guess, though.  Wait for other opinions here.

[R.G.]

You are dead on, Mark. Compressors are designed for a fixed amount of signal range in. The change to make is a switch for stock versus a padded-down input.

Compressors are designed to take in a certain range of input signals and compress them by X amount. Making the input much bigger - like with active pickups - means they just run max compressed and probably distorting all the time.

[vanessa]

Mark- When you suggest a 1M pot, I'm thinking that a switch to put a 500k (or so) resistor in series with the pot might do the trick?

If I was to go the Orange Squeezer route instead, what would be a good mod for active electronics on that one Oh Master of the OC?



(Thank you!)

[Mark Hammer]

Mark- When you suggest a 1M pot, I'm thinking that a switch to put a 500k (or so) resistor in series with the pot might do the trick?

If I was to go the Orange Squeezer route instead, what would be a good mod for active electronics on that one Oh Master of the OC?



(Thank you!)

Yes and no on the first one.  I don't know that a 1M pot is the ideal, merely that more series resistance lowers the control current driving the 3080 and 1M is the next standard value up from 500k.  The ideal route is probably to start with a 500k or 1M trimpot in series with the existing 500k pot.  Set the compression pot to min compression, and the trimpot to max resistance.  Plug your active bass or whatever in, and gradually turn down the resistance of the trimpot until you start to hear some sort of compression/limiting kicking in.  Note the resistance of the trimpot at that point, and make your suggested add-in fixed resistor the next standard value up from there.  So, if it takes 317k of series resistance on top of the existing 500k for the compression to juuuuuuuuusssst start to be audible with the active bass, then adding a 330k fixed resistor to the existing 500k pot and 27k resistor should get you from no compression to lots more compression, I suppose.  Alternatively, you can replace the 27k unit on the PCB with a"for-active" value, and then toggle in a second selected parallel resistor to drop the combined resistance down to the stock 27k range.  For instance, 30k in parallel with 330k gets you 27.5k.

For the OS, the mod might be as simple as switching between a Ge diode and an Si unit, given that the silicon diode would chop another 250mv or so off the signal amplitude.