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28 July 2015
After a short illness, Graeme passed away today.
A good mate who will be sadly missed.

Ian Du Rieu



Back in 1984 Graeme J. Cohen designed a very nice low noise microphone amplifier.
It was originally published as AES Preprint 2106 "Double Balanced Microphone Amplifier" and sold as the Philips OM1556 hybrid.

This circuit has been the subject of much discussion and debate, some of it incorrect.
We have managed to coerce Graeme out of hibernation and get him to put pen to paper and make a few notes about this amplifier. (Yes, it really was "pen to paper" as he doesn't own a computer.)

Double Balanced Microphone Amplifier Notes (5.5 meg file)

In the book "Microphone Engineering Handbook" (Michael Gayford, 1994  ISBN 0750611995), Peter J.Baxandall has done an extensive 6 page analysis of Graeme's mic amp circuit.
MEH Chapter 8.4 (2 meg file)

As Chapter 8 has a number of related topics it is included below.
MEH Chapter 8  (23 meg file)  Includes 8.4 above.

Graeme's recent investigations include distortion measurement using 2 tones in a 3-4 ratio.
3-4 Ratio Distortion Measurement  (800K file)

A list of papers penned by Graeme.

Graeme's presentation "Stereo or binaural headphones for sound location" to the Australian Acoustical Society in Melbourne, November 2014 can be found here.
 

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