JFET opamp

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slow_riot
Super Deluxe Wiggler
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JFET opamp

Post by slow_riot » Mon Apr 01, 2019 10:19 am

For a personal project I designed a new amplifier topology based mostly around one which Fred Forssell published which he uses for his mastering converters:

https://www.forsselltech.com/media/atta ... _Opamp.PDF

I needed an amplifier to drive a pair of ESL loudspeakers which are literally enormous capacitors around 1 square meter, and can drive some amplifiers which rely on negative feedback absolutely crazy. I had hoped to design something which didn't rely on negative feedback at all, but this is hard and not really necessary. What I did end up with was something that is quite tolerant of capacitive loading.

It has a complementary input structure based around 2 pairs of NPNs and PNPs, which has worse DC performance but better AC. The FJET outputs are faster than BJTs and have less crossover distortion. It measures worse than IC opamps but will be more pleasing to the ear.

It seems probable that this design will feature in the upcoming modules. The low production volume means I can hand match (something essential to the oscillator modules), and I think the slight price increase can be justified.

Does anyone have any comments or suggestions either way? I try to keep the prices down but it's also nice to explore what's possible, I always say the philosophy of the company is design focussed.

christie
Common Wiggler
Posts: 166
Joined: Wed Aug 24, 2016 1:43 pm
Location: California

Post by christie » Sat Jun 01, 2019 6:20 pm

I have some experience in this.

How many watts do you need? Solid state only?

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