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-   -   Beast with 1000 JFETs redux ? (https://www.diyaudio.com/forums/pass-labs/364186-beast-1000-jfets-redux.html)

woofertester 9th December 2020 02:02 AM

Beast with 1000 JFETs redux ?
 
Yesterday I listened to a Youtube of 2019 BAF where Linear Audio was presenting and Nelson commented that he wanted to redux The Beast and would appreciate lower cost JFETs that did not require lowest noise figure.

Has there been any discussion about possible configurations of The Beast using parts that can be acquired from Digikey or Mouser?

I have been thinking of possible parts to use and running parts through the curve tracer. More parts on order to also run through the curve tracer.

A possible proof of concept would be a 200mA bias version for a headphone amp.

The JFETs will like have to be SOT23 package. I have an initial favorite for both N and P. I will post measurements when I have all the measurements finished.

My thinking is to cascode the JFETs using the hockey pucks from the F4 Beast. This will allow using higher Idss JFETs and operating the JFETs at ~3V Vds and also operating the JFETs un-degenerated. Most of the heat winds up in the pucks.

The voltage rails can be normal First Watt rails if desired.

Just getting started with possibilities.

codyt 9th December 2020 12:22 PM

Really like the idea of a beast headphone amp!

woofertester 9th December 2020 01:26 PM

Quote:

Originally Posted by codyt (https://www.diyaudio.com/forums/pass-labs/364186-beast-1000-jfets-redux-post6442559.html#post6442559)
Really like the idea of a beast headphone amp!


The size would be manageable compared to any other headphone amp.

Early estimate is 13 JFETs to obtain ~200mA bias. Stereo push-pull followers would be 52 JFETs total. If JFETs are $0.22 each, Total JFET cost is $11.44.

codyt 9th December 2020 02:03 PM

Nice, that’s more reasonable than I thought. And I like the SMD choice for this. Look forward to watching your progress!

Antoinel 9th December 2020 02:28 PM

Idea
 
Quote:

Originally Posted by codyt (https://www.diyaudio.com/forums/pass-labs/364186-beast-1000-jfets-redux-post6442559.html#post6442559)
Really like the idea of a beast headphone amp!

Hello codyt. Please see post #33 in the thread Different headphone amps. woofertester's suggestion to use multiples is interesting.

Best
Anton

codyt 9th December 2020 02:59 PM

Very nice, and perfect timing actually. I’ve got parts ready to breadboard a B1 rev2, and I see in your schematic that it would take very little to give yours a try with nearly the same parts. I’ll give it a listen, thanks!

Nelson Pass 9th December 2020 05:01 PM

Actually there is such a piece, now in the hands of another DIYer.

Also, Mr. Fullrange and I are in the process of a 1,000 fet version construction -
a little more work to go.

:snail:

woofertester 9th December 2020 05:31 PM

Quote:

Originally Posted by Antoinel (https://www.diyaudio.com/forums/pass-labs/364186-beast-1000-jfets-redux-post6442667.html#post6442667)
Hello codyt. Please see post #33 in the thread Different headphone amps. woofertester's suggestion to use multiples is interesting.

Best
Anton

Hello Anton

Yes what I am doing is similar. One difference is that the inexpensive JFETs I am looking at have much higher Idss than 2SK170BL. At 15V Vds, the power dissipation would be too close to maximum. So, the JFETs need to be cascoded.

I like your idea of trying just one pair. Easy to do on a breadboard. Thanks

cheers

woofertester 9th December 2020 10:37 PM

Quote:

Originally Posted by Antoinel (https://www.diyaudio.com/forums/pass-labs/364186-beast-1000-jfets-redux-post6442667.html#post6442667)
Hello codyt. Please see post #33 in the thread Different headphone amps. woofertester's suggestion to use multiples is interesting.

Best
Anton

Quote:

Originally Posted by Nelson Pass (https://www.diyaudio.com/forums/pass-labs/364186-beast-1000-jfets-redux-post6442785.html#post6442785)
Actually there is such a piece, now in the hands of another DIYer.

Also, Mr. Fullrange and I are in the process of a 1,000 fet version construction -
a little more work to go.

:snail:

Nice to hear. I look forward to seeing some schematics and pics of the official versions. In the meantime, play, play, play.

Zen Mod 9th December 2020 10:39 PM

I have pics, if not schematics........ but I'm not allowed .......

practically, I didn't even wrote this

:clown:


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