John Curl's Blowtorch preamplifier

[scott wurcer]

Please, just kidding the JC-80 is way too complicated for a hobby circuit. I'm still working on my preamp in a pipe.

I had to borrow a digital QuanTech from the fab development guys because the old ones require a bunny suit and clean room to get at. First BF862 out of the bag measured 2.3nV at 10Hz and .6 at 100kHz @5mA.

[john curl]

How about the rest? Any problems?

[scott wurcer]

The problem with these is that they need to be soldered to an adaptor (SOT-23 only). I have to find a socket. I was testing about 8 different FET's for my microphone project. You were right on the 2SK222 1.3nV flat right across the band only 1.7 at 10Hz at only 1mA 9.1mS too. These Sanyo FET's were only a tiny bit worse than the Toshiba ones at half the Ciss. I wonder if they make P-channel.

[Steve Eddy]

Originally posted by scott wurcer
Please, just kidding the JC-80 is way too complicated for a hobby circuit. I'm still working on my preamp in a pipe.

Thanks for reminding me, Scott!

I finally got the chassis made up for you for the monoblocks. How do you like the Preamp in a Pipe^tm logos I had engraved in the covers? Nice touch, eh? Simple, yet elegant.



se

[Sigurd Ruschkow]

Scott - that is interesting information!

Did you try any BF861A/B/C JFETs?

If space is scarce, and lower noise is wanted, one can put several SOT-23:s on top of each other to save precious PCB space

I did not find any P-ch for the 2SK222.
P-ch devices are sooo rare.


Sigurd

Originally posted by scott wurcer
The problem with these is that they need to be soldered to an adaptor (SOT-23 only). I have to find a socket. I was testing about 8 different FET's for my microphone project. You were right on the 2SK222 1.3nV flat right across the band only 1.7 at 10Hz at only 1mA 9.1mS too. These Sanyo FET's were only a tiny bit worse than the Toshiba ones at half the Ciss. I wonder if they make P-channel.

[Bob Cordell]

Originally posted by Edmond Stuart


Care to explain why you think that an AC simulation may provide more reliable results than a transient simulation? Or is it just a wild guess?

Also, how would you interpret the results? The phase shift of a signal with 1 and 10V amplitude respectively (for example), will certainly be different from a AC analysis with comparable (1...10V?) DC offsets.

Cheers.

Hi Edmond. Yes, it's just a guess of mine that doing an AC analysis with different DC offsets would reveal PIM. I have not tried it yet. The idea is that the phase data in the AC analysis can be read with very good precision. I believe that 1/1000 of a degree of the 7 kHz sinusoid used for PIM testing corresponds to about 0.39 ns, which should be pretty good PIM resolution. That is on the order of the resolution of my PIM analyzer, IIRC.

Of course, PIM is measured with a 60 Hz large signal, so measuring it with SPICE using a varying DC offset means that we are assuming that DC behavior is similar to 60 Hz behavior.

Cheers,
Bob

[john curl]

Guess? We don't need no stinkin' guesses around here! Put up or get out of the way!

[scott wurcer]

Originally posted by Steve Eddy


Thanks for reminding me, Scott!

I finally got the chassis made up for you for the monoblocks. How do you like the Preamp in a Pipe^tm logos I had engraved in the covers? Nice touch, eh? Simple, yet elegant.


se

Steve that looks like 40yr old technology ala "High Times".

[john curl]

Scott, I thought that using a Quantek was a 40 year old, has been, effort!

[MikeBettinger]

Originally posted by scott wurcer
Steve that looks like 40yr old technology ala "High Times”.: jinn:

Not 40 year old technology! Those are the newest high-tech devices designed using the latest computer thermal and flow simulation software, fully profiled for thermal expansion characteristics, seals between chambers guaranteed to 2 militorr, cryogenically treated, surface finish will withstand chemically reactive environments, and all for a bargain price of only $3300.00 ; which, of course, includes performance verification and calibration for the first 9 months. After which you can purchase the factory extended support option.

Best regards...