Chopper stabilization and servos far predate audio in the precision instrumentation field.
TL072 B grade is 3mV and over temp 5mV - admittedly with 50 Ohms source resistance. Nevertheless, its low enough to get good consistent results. I dial the offset out anyway because the servo opamp output feeds into the amp protection circuit. Measured on the output hot or cold the offset is never more than +- 1.5mV.
As usual....
I am pretty sure audio predates controlled fire. Or did you mean the use of chopper amplifiers in instrumentation predates the use in audio circuitry?
After using an external trim on an FET input opamp, any idea how much temperature will change things?
Erno Borbely wrote up a project called DC 100 (i think) that would be good reading for folks interested in trying direct coupling
also, look for internal images of some Ayre power amp and preamp products to see some of the transistor coupling strategies that were helpful. probably have to spend a little time figuring out pieces of the schematic to really appreciate that however.
mlloyd1
also, look for internal images of some Ayre power amp and preamp products to see some of the transistor coupling strategies that were helpful. probably have to spend a little time figuring out pieces of the schematic to really appreciate that however.
mlloyd1
Erno Borbely wrote up a project called DC 100 (i think) that would be good reading for folks interested in trying direct coupling
also, look for internal images of some Ayre power amp and preamp products to see some of the transistor coupling strategies that were helpful. probably have to spend a little time figuring out pieces of the schematic to really appreciate that however.
mlloyd1
Erno's article was in Audio Amateur 2/84 part two the DC 100.
As usual....
I am pretty sure audio predates controlled fire. Or did you mean the use of chopper amplifiers in instrumentation predates the use in audio circuitry?
After using an external trim on an FET input opamp, any idea how much temperature will change things?
Low enough to be of absolutely no concern in an audio application. On a TC or SG conditioner, a different story however.
You can safely count on 10uV/C Vos drift, but often much lower than this. Watch out for bias current in JFET input opamps with high source resistances though.
Yes as usual, AC coupling and forget about it was de rigueur in audio for decades.
Yes, so what, someone else was doing it before that. I'm confused though Mr. Marsh claims to have "invented " it in the 70's do you guys disagree?
I had at one time a mechanical chopper stabilized tube amp that predates both of you. I have no irons in the fire here, the "sound" of capacitors is unique to the audio industry, and has no not mattered much to anyone else (unless they could measure the result).
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Used to be, 40 years ago. OPA189 has 5.2nV/rtHz @1KHz, at par with most of the current cheap jfet input op amps.
Maybe you should look at the datasheet? Maybe you didn’t realize it’s chopper stabilized?
Just because CMOS was too noisy in 1970 or whenever the last time you were curious doesn’t mean it still is. Look at OPA2156.
TLE208X costs about the same, is jfet input, and has double the OPA189 noise http://www.ti.com/lit/ds/symlink/tle2081a.pdf
O tempora, when I was young and restless, I could guess 75% of a linear IC internal schematic by looking at the metal mask only.
O tempora, when I was young and restless, I could guess 75% of a linear IC internal schematic by looking at the metal mask only
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