[sdiy] Blackmer VCA cell

[Roman Sowa]

2164 is Gilbert cell
not far from Blackmer anyway
2181 has Blackmer

Roman

W dniu 2021-10-23 o 06:41, David G Dixon via Synth-diy pisze:
> 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
>
> [CAUTION: Non-UBC Email]
>
> 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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