Benchmark Mic Preamp from 1984 - Active Preamp History

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JR.
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Re: Benchmark Mic Preamp from 1984 - Active Preamp History

Post by JR. » Wed Mar 20, 2013 4:05 pm

gotcha.. sorry I was too lazy to look... I remember those guys with their own third front during the VCA wars with their VCAt (voltage controlled attenuator). :lol:

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mediatechnology
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Re: Benchmark Mic Preamp from 1984 - Active Preamp History

Post by mediatechnology » Wed Mar 20, 2013 7:31 pm

I had never heard of the VCA Associates mic preamp. I think that's what made it unique to me.

I didn't get any web hits on it either so I guess we have the pdf scoop on that bit of history.
I wonder if anyone has a hybrid in the flesh.
I think I have a TransAmp for the museum.
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JR.
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Re: Benchmark Mic Preamp from 1984 - Active Preamp History

Post by JR. » Thu Mar 21, 2013 10:26 am

I vaguely recall hearing about it, but I was already rolling my own pre using quieter devices by then.

I was more interested in their VCAT but didn't care for adding a fixed gain stage to a cut only device to make a compressor/limiter. The noise floor of those early VCAs was much worse than modern technology.

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mediatechnology
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Re: Benchmark Mic Preamp from 1984 - Active Preamp History

Post by mediatechnology » Mon Jul 01, 2019 4:56 pm

A new entry into the active mic preamp museum is the 1972-era Neuman PV26b:

Image
Neumann PV26B Schematic

Large format: https://proaudiodesignforum.com/images/ ... ematic.jpg

Fully-balanced.
"Current" feedback.
Split AC and DC feedback loops.
Common mode rejection realized in the output transformer.
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Re: Benchmark Mic Preamp from 1984 - Active Preamp History

Post by Gold » Mon Jul 01, 2019 5:43 pm

FWIW this was never considered a microphone preamp by Neumann. The PV76 was the microphone preamp. I have that schematic too. This was used post output fader on an SP172 for “relative disk level”. I’m sure it was used in their multichannel mixing consoles somewhere too. The tricked out line amp is the PV46.

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mediatechnology
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Re: Benchmark Mic Preamp from 1984 - Active Preamp History

Post by mediatechnology » Mon Jul 01, 2019 7:07 pm

The topology of the PV26 is almost identical to a modern active mic preamp.
The 1968 "Demrow" circuit wasn't a mic preamp either but it is the first example I've found - and forms the basis of - the 1984 "Cohen" topology.
The PV26 is a 1972-era Demrow topology adapted to audio.
It bridges the gap from 1968 to circuits shown later in the late 70s.

Does the PV76 have a similar topology?
I would think it would have an input transformer.

One thing cool about the PV26 is that the differential output driving the transformer doesn't require a coupling cap.
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