Any VCA comp DIY-able projects that fit in stomp boxes?

[midwayfair]

I'm on a bit of a comp kick lately. I've built a few Orange Squeezers (my faves), a Dyna/Ross (with another board on the bench waiting for something interesting to happen), some optical comps (breadboarded the Really Cheap Comp and some others, boxed up the Afterlife/Flatline, might build Sabro's Diamond or Rothwell clone layouts to keep unboxed boards around for comparison), and MerlinB's Engineer's Thumb, which I really like.

Looking at the types of compressors, it looks like VCAs are one family I haven't touched at all. Is there a project anyone can recommend? I know these are typically more complicated, but I'm limited to perfboard or buying an etch if necessary.

[Fender3D]

MXR Dynacomp made history (and an hellova background noise  )

[Mark Hammer]

And what do you treat as the difference between a "VCA" compressor and an "OTA-based" compressor?  How does a Dynacomp/Ross not count?  That's not a reprimand.  It's just that the distinction you wish to make is not immediately clear.

[midwayfair]

You're right, I should have been more specific.

Going off the info here, folks:

"Technically most comp circuits could be described as VCA's in a sense, but in practical usage it means an IC chip that contains transistors that follow your incoming signal level (voltage) to determine how much gain to apply. VCA's are typically associated with fast, clean compression with precise controls over attack and release. Symetrix, dbx, Boss CS-3, Maxon CP9Pro+, and Alesis 3630 are examples of VCA comps. Most cheaper rack comps are VCA controlled. The THAT Corporation, originally a division of dbx, produces most of the VCA chips you'll encounter." http://www.ovnilab.com/articles/comptypes.shtml

[frequencycentral]

So I think you have touched a VCA compressor if you've built a Dyna, the CA3080 is used as a VCA in many synths.

[wavley]

The RMS detection that gives the sound to a lot of classic vca comps, sometimes some good distortion comes from the VCA portion, sometimes bad.

You might look at the schematics of things like the DBX 160VU or a Valley People Dynamite for RMS detectors that lend a pleasing sound to the VCA.

[Fender3D]

oh
Voltage Controlled Amplifier might be confusing....

[Mark Hammer]

When you look at a large number of "VCA" circuts for either DIY or commercial analog synths, a great many of them are naked 3080 or 13600/13700 circuits, with a buncha stuff tacked on for minimizing control voltage bleedhrough or making control linear, log, or whatever.

As such, the difference between an "OTA-based" compressor and a "VCA-based" compressor is really more one of the degree of complexity of the gain control, and whatever elements are included in the chip or circuit to eliminate the undesirable elements.  I mean, I suppose the Dynacomp is a "current-controlled" rather than voltage-controlled amp, if we want to be picky, but then so is synth "VCA module" that uses a 3080 and converts an external control voltage into a control current.