[sdiy] Blackmer VCA cell

[David G Dixon]

Doesn't the linearized 2164 VCA (the famous Irwin circuit) work more or less
like a Blackmer cell?

 

-----Original Message-----
From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Ben
Bradley via Synth-diy
Sent: Friday, October 22, 2021 8:10 PM
To: *SYNTH DIY
Subject: [sdiy] Blackmer VCA cell

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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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