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28 July 2015
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.
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.
As Chapter 8 has a number of related topics it is included below.
Graeme's recent investigations include distortion measurement using
2 tones in a 3-4 ratio.
Graeme's presentation "Stereo or binaural headphones for sound location"
to the Australian Acoustical Society in Melbourne, November 2014 can be
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