[sdiy] Blackmer VCA cell

[Dakota Melin]

Serge systems used a circuit referred to as the “clone”. It was closely
related to the blackmer gain cell. Modern Random Source Serge
implementations use the THAT2180 / 2162 heavily.

On Fri, Oct 22, 2021 at 11:15 PM Ben Bradley via Synth-diy <
synth-diy at synth-diy.org> wrote:

> 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
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