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Old 23rd August 2005, 07:37 PM   #11
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Default Re: best small signal FET?

Quote:
Originally posted by hesener
The topology I am thinking of is a input differential pair, followed by source followers to get a low output impedance (using monoblocks close to the speakers, the cables can get long-ish). Signal swing should be ~3V out, the gain of the whole thing does not need to be very high... sorry it's hard to be more precise but - as several people pointed out - the circuit and the devices correlate a lot.
If you like the simple idea of a differential input stage driving an output follower, have you considered using a step-up transformer for the differential input stage instead of an active stage?

It'll give you 100+dB common-mode noise rejection even from unbalanced sources, it can take either balanced or unbalanced input, it gives you ground isolation, extremely low noise and distortion, and Power Supply Rejection Ratio? What power supply?

se
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Old 23rd August 2005, 08:00 PM   #12
jcarr is offline jcarr  United States
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Martin Rupp:

For whatever reason, I couldn't get babelfish to translate the pdf. Babelfish returned a message about a "bad template" of something like it.

??

Greg:

>The 2SK389 is the most suitable dual matched high transconductance Nch JFET<

Absolutely not, as the design of the 4-2SE is just as much about the physical structure of the circuitry as it is about the schematics. During the design process I was revising the physical structure against the schematics and the schematics against the physical structure, over and over until I achieved an optimization level for both that I was nominally satisfied with.

Rather than the 2SK389, I'd look for the most electrically suitable dual-JFET that you can find in a compact, round metal-can package. Now this doesn't mean that the 2SK389 is a bad part, because it isn't. But it isn't suited for what I had in mind for the 4-2SE.

hth, jonathan carr
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Old 24th August 2005, 12:37 AM   #13
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Hey Kwak -

a folded cascode is a cascode all the same . The load is LOW and the capacitance is not a big issue!
Crap about dark sound - dark sound doesn't win awards! What have you ever done....

Oh.. Johnathon has something superior ... but it's a secret? Oh revelation ... is that in your mind of minds... never mind.

Oh.. the B***s*** that flows in Audio.
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Old 24th August 2005, 01:14 AM   #14
jcarr is offline jcarr  United States
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Greg, you've played coy in the past, as this thread that you started amply demonstrates.

My new 150W R2R design!

If you think that my keeping some details to myself is B***s*** , then surely you also qualify.

regards, jonathan carr
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Old 24th August 2005, 01:16 AM   #15
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Just make sure you do some nice (discrete) low noise regulators to partner it.

Cheers,
Greg
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Old 24th August 2005, 01:28 AM   #16
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Hi Jonathan,

The guy was just asking for a device to use! directions. Not a design expose.

I put a couple of tried and proven types up - and get shouted down. No alternatives given. Or am I being a little precious?


Cheers,
Greg
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Old 24th August 2005, 01:58 AM   #17
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amplifierguru is one of the best experts here and his advice 99%
of the time is highly scientific, what more do you guys want?

cheers
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Old 24th August 2005, 02:23 AM   #18
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>The 2SK389 is the most suitable dual matched high transconductance Nch JFET<

Absolutely not, as the design of the 4-2SE is just as much about the physical structure of the circuitry as it is about the schematics. During the design process I was revising the physical structure against the schematics and the schematics against the physical structure, over and over until I achieved an optimization level for both that I was nominally satisfied with.

Rather than the 2SK389, I'd look for the most electrically suitable dual-JFET that you can find in a compact, round metal-can package. Now this doesn't mean that the 2SK389 is a bad part, because it isn't. But it isn't suited for what I had in mind for the 4-2SE.

hth, jonathan carr [/B][/QUOTE]


My SE (Steve Eddy) buffer uses the 2N5566 as an input JFET. But this is a cascoded single ended, current sourced, dc coupled, discrete circuit. Not differential.
I like the idea of a folded cascode, but the AD829 is not an option. Too low current.
Thanks for giving us a target to shoot for. Hope a reasonalbe diy option comes along.

George

George
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Old 24th August 2005, 03:01 AM   #19
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Quote:
Originally posted by jcarr
For whatever reason, I couldn't get babelfish to translate the pdf. Babelfish returned a message about a "bad template" of something like it.
Hi Jonathan,

Babelfish won't translate the entire PDF. Instead, open the PDF in one window. Then use the "Text" tool in Acrobat to select text. Copy and paste into the window with babel.altavista.com running in your web browser. (I think the word limit is 150 words at a time.) Then copy those results (one chunk at a time) into a word processor or text editor.

Here's a sample to show the method works:

Stereoplay is admits for it, after inexpensive High end to search. Like that the test of a 25000-Euro-Vorstufe was violently disputed in the conference of topic. Read here exclusively, why the Lyra Connoisseur 4-2 L SE found the way in the long run nevertheless in the booklet.

I guess it only sort of works, because then you need to translate the translation!

Cheers,
Charlie Hansen
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Old 24th August 2005, 03:35 AM   #20
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Hi Panelhead,

You could of course use the 2N5566 or NPD5566 (national DIP) - with a lower transconductance . A Pchannel complement would be the AH5020CJ (National DIP) analog switch as used by Mr. Borbely some decades ago.

Cheers,
Greg
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