The JE-990 (990) OP amp by the late Deane Jensen is an impressive piece of engineering. I was highly impressed when I first read the AES article:
http://www.technicalaudio.com/pdf/J...ted/Jensen_JE-990_opamp_JAES_reprint_1980.pdf
and the application note for the LM-394:
http://www.ti.com/lit/ds/snls385a/snls385a.pdf
http://pe2bz.philpem.me.uk/Parts-Ac.../AN-222-SuperMatchedBipolarTransistorSets.pdf
I still like the JE-990 to this day.
Jensen is known for their audio transformers and some background about the company and founder is given here:
http://www.iso-max.com/history/
The 990 was first described in 1980 as a public domain design in the AES Journal:
"JE-990 Discrete Operational Amplifier"
JAES Volume 28 Number 1/2 pp. 26-34; January/February 1980
It was designed for use with Jensen transformers, and has found it's way into many Pro-Audio applications. It is a fairly standard OP amp topology, diff pair input loaded by a current mirror, standard VAS with a Beta multiplier, Baker clamp, pole-zero Cdom compensation, and additional HF compensation on the emitter resistor. The LM-394 Supermatch Pair transistor is used in the diff amp which provides low DC offset, low noise and distortion. It is essentially a low power amp that will easily drive 75 ohm loads.
The LM-394, current mirror load, Beta multiplier, Baker clamp, and pole-zero compensation were all innovative for the time.
John Hardy is probably the best known supplier of the JE-990, and also produces several pro-audio mic preamps based on Jensen transformers and the JE-990. He has some nice documentation with the JE-990 schematic here:
http://www.johnhardyco.com/pdf/990.pdf
http://www.johnhardyco.com/pdf/M1M2M1p.pdf
Edit: Why is it that only the first post can be edited? I'd like to fix the broken links here.
http://www.technicalaudio.com/pdf/J...ted/Jensen_JE-990_opamp_JAES_reprint_1980.pdf
and the application note for the LM-394:
http://www.ti.com/lit/ds/snls385a/snls385a.pdf
http://pe2bz.philpem.me.uk/Parts-Ac.../AN-222-SuperMatchedBipolarTransistorSets.pdf
I still like the JE-990 to this day.
Jensen is known for their audio transformers and some background about the company and founder is given here:
http://www.iso-max.com/history/
The 990 was first described in 1980 as a public domain design in the AES Journal:
"JE-990 Discrete Operational Amplifier"
JAES Volume 28 Number 1/2 pp. 26-34; January/February 1980
It was designed for use with Jensen transformers, and has found it's way into many Pro-Audio applications. It is a fairly standard OP amp topology, diff pair input loaded by a current mirror, standard VAS with a Beta multiplier, Baker clamp, pole-zero Cdom compensation, and additional HF compensation on the emitter resistor. The LM-394 Supermatch Pair transistor is used in the diff amp which provides low DC offset, low noise and distortion. It is essentially a low power amp that will easily drive 75 ohm loads.
The LM-394, current mirror load, Beta multiplier, Baker clamp, and pole-zero compensation were all innovative for the time.
John Hardy is probably the best known supplier of the JE-990, and also produces several pro-audio mic preamps based on Jensen transformers and the JE-990. He has some nice documentation with the JE-990 schematic here:
http://www.johnhardyco.com/pdf/990.pdf
http://www.johnhardyco.com/pdf/M1M2M1p.pdf
Edit: Why is it that only the first post can be edited? I'd like to fix the broken links here.
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