Graeme Cohen - Microphone Amplifier History and Design

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mediatechnology
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Graeme Cohen - Microphone Amplifier History and Design

Post by mediatechnology » Tue Aug 05, 2008 8:46 am

Ian Du Rieu has obtained permission from the author to post Graeme Cohen's August 16, 2006 presentation to the Adelaide Section of the Audio Engineering Society titled "Microphone Amplifier History and Design."

The entire document is here: http://leonaudio.biz/AES/Aug-15-2006/ae ... ug_15f.pdf (20 MB)

Other AES presentations may be found here: http://leonaudio.biz/AES/

They also did a mic comparison: http://leonaudio.biz/AES/May-16-2006/photos/

Here are a few of the schematics from the Cohen paper:

Image
Langevin AM16. Image courtesy of Graeme Cohen and Ian DuRieu.
http://www.ka-electronics.com/images/jp ... n_AM16.jpg



Image
Neve BA284. Image courtesy of Graeme Cohen and Ian DuRieu.
http://www.ka-electronics.com/images/jpg/Neve_BA284.jpg



Image
Morgan Jones 1995 Fully Balanced Tube Preamp. Image courtesy of Graeme Cohen and Ian DuRieu.
http://www.ka-electronics.com/images/jp ... e_1995.jpg



Image
Cohen Philips OM1556 Preamp. Image courtesy of Graeme Cohen and Ian DuRieu.
http://www.ka-electronics.com/images/jp ... ematic.jpg

The entire schematic collection in the paper is huge and the above are just a few examples. Here's the complete list of schematics in the pdf http://leonaudio.biz/AES/Aug-15-2006/ae ... ug_15f.pdf (20 MB)

Western Electric 8-C
German Broadcasting 1940s
RCA 1940s
Langevin 1949
Siemens & Halske 1952
Telefunken V72a 1962
Radiotron Designers Handbook Examples
Altec M11 1960
Cohen Tube 1997
Morgan Jones 1995 Fully Balanced
AKG C24 Schematic
Treharne 1958
Langevin AM16 1964
BA284
Bailey, Wireless World
Jensen JT-990-C
Jensen Twin Servo 990
Jensen JT-13K6-C NE5534
Cohen 1984 Double-Balanced
Cohen OM1556
SSM2015 and AN-115
THAT1510/1512


Thanks Graeme and Ian for sharing this with us!
For more information see: http://leonaudio.biz
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Re: Graeme Cohen - Microphone Amplifer History and Design

Post by emrr » Wed Aug 06, 2008 11:56 am

Nice compilation. Here are some corrections:

The WE 8-C is a 1920's amplifier.

'Early RCA 1940's is somewhat incorrect; that's the BA-1A from 1945. There are 4 previous generations of AC powered RCA, and at least 2 DC powered before that so I'd call it mid-period RCA.

'Langevin 1949' should be 1947.

Langevin AM-16 is 1961. John Hall is credited with this design, and he subsequently left Langevin and went to Altec where his name can be found on the similar PP 9470A/9475A amps of 1964.
Best,

Doug Williams
Electromagnetic Radiation Recorders

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Re: Graeme Cohen - Microphone Amplifer History and Design

Post by Ian DuRieu » Thu Aug 07, 2008 1:03 am

emrr wrote:Nice compilation. Here are some corrections:
Thanks for the corrections.
The PDF file at http://leonaudio.biz/AES/Aug-15-2006/ae ... ug_15f.pdf has been updated.

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mediatechnology
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Re: Graeme Cohen - Microphone Amplifer History and Design

Post by mediatechnology » Thu Aug 07, 2008 6:24 am

Thanks Ian and Doug.

Finding the dates on a lot of that stuff is tough. When I did the Ballou research for Handbook for Sound Engineers 4th edition I had to scour old databooks and datasheet copies. SImple questions like "when did the dbx 2150 VCA get introduced" was tough even for the people at THAT to answer who were there at the time. We finally had to get the answer to that one indirectly from the patent date on one of the "inventions" embodied in it. At that time dbx didn't put dates on their datasheets and we couldn't find anything more accurate than about +/- 2 years.

I can imagine how difficult it is to pin a date on something made in the 1930s.
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Re: Graeme Cohen - Microphone Amplifer History and Design

Post by JR. » Thu Aug 07, 2008 7:38 am

My dad worked for WE and RCA, among sundry other related companies (Vitaphone, Muzak,,) . He was sent over to England in '30's to record coronation of King George (?). He was a recording engineer for RCA in NYC when he died in 1950's.

I have some of his early engineering notebooks which are dated and well documented. Just not about circuit design.

JR
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

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Re: Graeme Cohen - Microphone Amplifer History and Design

Post by mediatechnology » Thu Aug 07, 2008 7:50 am

JR - Your Dad serves as an example to the rest of us to date something we document and to write it down in the first place. Do you have any of his old recordings?

Even if it isn't related to circuit design seeing some of his notes would be fascinating. We are working on a collection of stuff for the Document sub forum and it would be cool to see something like that.

I never knew Muzak was an RCA company. Your Dad must have worked during some of the Sarnoff era. There was an article a year or so ago about the restoration of the RCA Broadcast equipment documents in Radio World. Your Dad's stuff may have a place there.
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Re: Graeme Cohen - Microphone Amplifer History and Design

Post by JR. » Thu Aug 07, 2008 8:59 am

I'm kind if busy at the moment but I have some cool stuff I can scan in... engineering sketches of movie cameras mounted into old model A (T?) Fords and such.

AFAIK Muzak was not connected to RCA but a letter from the president of WE was addressed to my dad c/o MUZAK. Another data point is we actually had a MUZAK receiver in our house growing up.

One lacquer that I recall hearing but haven't been able to locate for decades is an out take, of the Leopold Stowkowski cursing out the NBC orchestra in Italian when they flubbed a classical piece. My sister had some of dad's personal papers and wouldn't give them to me last time I visited her. She died about a year later, so I have no idea where that stuff went. Dad recorded guys like Perry Como and Harry Belafonte. I visited the NYC studio once but I was pretty young so don't recall much. We had an RCA tape recorder in the 50's and I messed around with recording my mini-bike doing drive by's and such.

Dad also worked at Vitaphone, the joint venture between WE and Warner brothers to make talking pictures... He worked in machinery dept.. His notebooks contain stuff about speed accuracy, wow and flutter, type stuff... Things we take for granted today.

I'd give my left nut, to be able to sit down with him as an adult and ask about his life. He died when I was like 10 YO. Sometimes life sucks....

JR
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

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Re: Graeme Cohen - Microphone Amplifer History and Design

Post by Ian DuRieu » Thu Aug 07, 2008 9:30 am

mediatechnology wrote:when did the dbx 2150 VCA get introduced
Speaking of dbx VCAs, I have an old dBx 163 circuit where the VCA was done in discrete components.
It used 2 dual transistors. 2SA798 & 2SC1583
Any interest in seeing the circuit?

JR: I'd be interested in seeing the "cool stuff".

Cheers
Ian DuRieu

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Re: Graeme Cohen - Microphone Amplifer History and Design

Post by mediatechnology » Thu Aug 07, 2008 10:08 am

Speaking of dbx VCAs, I have an old dBx 163 circuit where the VCA was done in discrete components.
It used 2 dual transistors. 2SA798 & 2SC1583
Any interest in seeing the circuit?
I would. I have the patent drawings for that gain cell I think but I've never seen it with the 2SA798 and 2SC1583. That must have been a later discrete VCA. That would be a great post for the "Document" forum.

JR: Your Dad did a lot of cool stuff. I grew up around airplanes, avionics and ham radio.
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"States Ordered To Fraudulently Inflate COVID-19 Cases 15 Times Actual Rate"
https://banned.video/watch?id=5efab695672706002f367a0a
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Re: Graeme Cohen - Microphone Amplifer History and Design

Post by JR. » Thu Aug 07, 2008 11:11 am

I have a picture of my dad's ham rig from before he was married... No amateur radio at the house when growing up, but I did my share of SWL.

----

IIRC early DBX VCA were selected discrete (to-92) (edit- that would be to-18) metal can transistors, wedged into a common thermal heatsink to hopefully keep them at similar temp.

JR

PS: one of my early patents at PV was for a class A VCA with DC servo loop to avoid selecting parts or DC trims... Of course after DBX started selling VCAs inexpensively I just used that, because it was quieter/better than my cheapo class A VCA.
Last edited by JR. on Wed Jul 29, 2009 9:08 am, edited 1 time in total.
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

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