Pro Audio Design Forum

Is this part of some larger circuit ?

Not that I'm aware of.
Isn't Q1 simply serving as a high-impedance buffer for Q3?
I liked the circuit because it was really old.

DC Feedback Stabilizes Bias On FET/Bipolar Pair," Howard Russell, Texas Instruments, EDN, November 15, 1970. This is another article that I've been saving for 40+ years that has limited availability on the web. https://proaudiodesignforum.com/images/jpg/DC_Feedback_Stabilizes_Bias_on_FET_Bipol...

Well, now that its gone I can't remember: Did it take two switches to alter the time constant? The Differential Deboo Integrator only requires one switch to vary the C: http://www.proaudiodesignforum.com/forum/php/viewtopic.php?f=6&t=559&p=6321 Just found a copy that I saved offline. Hope th...

1979 patent for 3Bx showing the non-linear capacitor: http://www.waynekirkwood.com/images/pdf ... 177356.pdf

"Check For Op Amp DC Offset Shift," John Dunn, Electronic Design, March 4, 1993. I've used this trick before to check servos that don't have a passive pole at the input (thanks JR) as well as using it as a general op amp evaluator. When slow DC-precise op amps or fast ones with asymmetric...

There doesn't seem to be an entire catalog for Sperry Gas Discharge Displays published on the web so I scanned mine. https://proaudiodesignforum.com/images/jpg/Sperry_1973_Cover.jpg Sperry Information Displays 1973 Catalog Cover Sperry Information Displays 1973 Catalog : https://proaudiodesignforum...

From Electronic Design's November 1956 issue (republished in 1996) we learn that Burr Brown's first op amp wasn't meant to be an op amp. Burr-Brown co-founder Tom Brown looks back at the significance of this amplifier, one of the most important devices in the company's history: "This was a cas...

"DC Servos and Digitally-Controlled Microphone Preamplifiers," Gary Hebert, THAT Corporation, AES 137th Convention, Paper 9198. Microphone preamplifiers for professional audio applications require a very wide range of gain and low noise in order to provide a high-quality interface with th...

"AC Voltmeter Has Unique Features," M.J. Salvati, Electronic Design, November 21, 1994. Though it's built with standard components, this AC voltmeter contains many features not typically found in commercial meters; the most unusual is a selection of rectification modes. The meter response...

Over the years I've collected a lot of Function and Signal Generators from HP, Krohn-Hite, Wavetek and Heathkit. Before that, being too poor as a kid to buy them, I played with the Intersil 8038 and Exar 2006 function generator ICs. I wound up collecting a lot of schematics of Signal and Function G...