"Composite Op Amp For High Performance," Siliconix AN81-3, July 1983

[JR.]

IIRC Brad Wood (RIP) was working on a crazy low noise JFET MC preamp as one of his later projects.

He may have left some evidence around the internets, I don't see much on his old facebook page where I think he may have shared it once.

JR

[mediatechnology]

Brad gets the credit for introducing me to the ZTX851.
At the time he hadn't used it but had read the new edition of Horowitz and Hill and pointed me in that direction.

[billshurv]

Found it. This is the list from Gerhard posted on DIYAudio. The CPH5902 is the one that looks most interesting even if you have to ignore the built in bipolar. Of course linear might finally pull their fingers out and sort out production of the LSK489...

[mediatechnology]

The CPH5902 is one they got from Sanyo's product line. Interesting. Thanks for the list.

https://www.onsemi.com/PowerSolutions/p ... id=CPH5902

This is the parametric table of ON JFETS. ON has nice tables.

https://www.onsemi.com/PowerSolutions/p ... 6/products

[mediatechnology]

Looks like Amber took Siliconix advice and used this in the 3501 front-end:


Amber 3501 Front End Using the Siliconix Composite Op Amp Topology.

Note that the 5543's inputs are grounded and the compensation terminals are used for the FET front-end.

Amber 3501 front-end pdf: https://proaudiodesignforum.com/images/ ... _Input.pdf

[JR.]

Nice for decades ago...

I was always apprehensive about the 553x compensation scheme while it was fine when used sensibly. I didn't like any open loop wiggles in or near the audio passband.

FET front end with 600 ohm drive capability now off the shelf.

JR

{edit] another hybrid approach I considered way back when was using a decent front end mixed with a LM359? an old Norton amp similar to the popular lm3900 but much better /edit]

[mediatechnology]

FET front end with 600 ohm drive capability now off the shelf.

None currently available are probably good enough for a distortion analyser front-end without some external bootstrapping to reduce CM distortion.

[JR.]

FET front end with 600 ohm drive capability now off the shelf.

None currently available are probably good enough for a distortion analyser front-end without some external bootstrapping to reduce CM distortion.

I'll take your word for that. My experience with designing relatively modest performance test gear (TS-1) was much harder than it appears, albeit using that eras technology.

JR

[mediatechnology]

Found a bipolar input version of an NE5534 Composite Op Amp.


"Designing Low Noise Amplifiers," Adams, Electronics and Wireless World, June 1989. NE5534 Composite Op Amp.

[JR.]

Ironic perhaps that the front end should be a Nat Semi LM394... Who would write that ap note?

JR

[update]
LM 394 datasheet shows several applications with supermatched pair as front end... oddly (or not) they all used Nat semit op amps for back ends.
https://www.digchip.com/datasheets/part ... 94-pdf.php [/update]