By now everybody knows I love building oscillators (even amplifiers which oscillate.)
I was reviewing the Bob Cordell Audio Magazine THD Analyzer from Audio Magazine in July 1981 and comparing it to Cyril Bateman's sub-ppm oscillator in 2002 -- seems to me that Robert's article should be refreshed -- perhaps the AGC circuitry could be simplified with a voltage controlled amplifier like the SSM2018 -- perhaps the rectifier could be simplified with two rail-rail opamps. Run the final amplifier in Class A (isnt' that what they do in the SG505?) I wonder how many of the Cordell analyzers were built.
Hofer's paper "A comparison of Low Frequency RC Oscillator Topologies" is worth downloading from the AES website.
I was reviewing the Bob Cordell Audio Magazine THD Analyzer from Audio Magazine in July 1981 and comparing it to Cyril Bateman's sub-ppm oscillator in 2002 -- seems to me that Robert's article should be refreshed -- perhaps the AGC circuitry could be simplified with a voltage controlled amplifier like the SSM2018 -- perhaps the rectifier could be simplified with two rail-rail opamps. Run the final amplifier in Class A (isnt' that what they do in the SG505?) I wonder how many of the Cordell analyzers were built.
Hofer's paper "A comparison of Low Frequency RC Oscillator Topologies" is worth downloading from the AES website.
Well, I built one, and it smokes any commercial unit except for Audio Precision. The floor of mine is 0.0002% midband, with very little rise over the audio range. The HPs won't touch it. IMO, the oscillator section is awfully good as is, and I don't know if an update would improve it much. I have considered trying the new National opamps instead of the 5534s, but like most of the things I consider, it'll never rise high enough on the priority list to get done.
This is the output section of the SG505. With the LME49710 you wouldn't need to do a balancing act.
An externally hosted image should be here but it was not working when we last tested it.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.