[sdiy] Blackmer VCA cell

[Ben Bradley]

I just posted this in a thread on Analog Heaven, and it reminds me to
ask here. There's been a dbx "Blackmer cell" high-quality VCA circuit
since the 1970s, but as far as I know its only use has been in
recording studio equipment. Has this device ever been used in a music
synthesizer or (guitar-type) effects pedal? I presume my explanation
below (much high cost than CA3080) is why not, but does anyone know
more?

Post to AH:

There's a "pro-audio quality" (much lower distortion and noise than
OTA-based circuits) VCA based on a Blackmer cell (apparently Patent #
US3714462) - it's a different circuit from the long-tail-pair based
OTA circuit, and I presume the reason it's not seen in music
synthesizers is because of dbx (now THAT Corp) holding the patent, and
only making and selling chips rather than licensing the patent to
anyone else, and the much greater cost of the chips. As far as I know
the chips have always been several dollars each, many times the CA3080
when it was in production. I would have thought the Blackmer patent
would have run out by now, I don't know of any other manufacturer
using the Blackmer cell design.

The article in the first link says "The voltage-controlled amplifiers
found in most recording consoles and analog effects products are based
on the "Blackmer gain cell" developed by David Blackmer of dbx, Inc."
- I've been familiar with their use in recording consoles, and the
"analog effects" here surely refers to studio compressors, companders
and noise gates. I've not heard of Blackmer cell VCAs ever being used
in effects such as guitar pedals - I've only heard of CA3080 and
similar chips (which when in production cost less than a dollar) used
in such effects and music synthesizers. I'm a bit surprised no synth
maker used these, as they're worth the extra price in some
applications, such as setting the "final output" volume control for
each patch. If I recall correctly, the Chroma Polaris used a CA3080
there.

http://www.thatcorp.com/History_of_VCAs.shtml
https://www.edn.com/gain-control/
https://patents.google.com/patent/US3714462