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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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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Re: Benchmark Mic Preamp from 1984 - Active Preamp History

Post by Bill Wilson » Sun Nov 24, 2019 10:41 pm

Paul Buff brought out his Transamp around 1975. In 1977 I was service mgr. for the Nashville MCI dealer. I met with Paul at Quadraphonic Studio; where we installed a Transamp in place of one summing amplifier, as a test toward improving the noise figure in the MCI 500 series console. It did provide a modest improvement.

In 1978 I left the dealership & went into business for myself. I was the first Neotek dealer in the country. The microphone preamp was an improved version of the Transamp, just not potted. Several years after dissolving my affiliation as a dealer for Neotek. I had the mike preamp pcb made, closely matched the first stage componebts & sold them as a stand alone piece. Several customers claimed they were the quietest mike pres. they had heard.
The circuit diagram can be found in Technical Documents ubder Neotek.

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Re: Benchmark Mic Preamp from 1984 - Active Preamp History

Post by mediatechnology » Mon Nov 25, 2019 8:06 am

Bill - Thanks for sharing that. Where is the NeoTek link?

Here is some of what I have on the TransAmp: viewtopic.php?f=12&t=114

I had one of those TransAmp replacements for the JH-500C at Dallas Sound Lab that we experimented with and also had some of the TransAmp and ECG-101 modules at MicMix.

The late Joe Neil had removed around 80 TransAmps when he upgraded his preamps just before he died. He was planning on selling the modules. I wonder where his stuff wound up.
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Re: Benchmark Mic Preamp from 1984 - Active Preamp History

Post by Bill Wilson » Wed Nov 27, 2019 5:08 pm

Sorry Wayne: I had forgotten I was on the wrong forum. It can be found on <Groupdiy.com> Look at the technical forum for Neotek, it is either the last or next to last post. By carefully matching the resistors around the discrete transistors on the front end; the CMRR approaches 100 db. I used 5% carbon film & matched the values. Still have about 15 of them available.

An interesting tid bit: Audio Engineering Associates recommends an input impedance of 100k balanced, in order to get the best performance from their ribbon mikes. Interesting note I an the original Audio Engineering Associates, 1958. I contacted Wes Dooley several years ago & informed him of this fact but told him I would not use the name to avoid confusion. I coined the name for my location master taping business, late 50's-68. Did records for 4
small Christian labels as well as my own; Kingsway & Wilson Custom recording.

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Re: Benchmark Mic Preamp from 1984 - Active Preamp History

Post by mediatechnology » Wed Nov 27, 2019 5:15 pm

You're welcome to post a link.
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