Beast with a Thousand JFETs - Page 10

jan.didden · 4th September 2009, 09:59 AM

Quote:

Originally Posted by Nelson Pass

I bet you would.

Does anyone have problems opening Nelson's graph from this post? On my PC it keeps saying "loading..." indefinitely.

jd

zhoufang · 4th September 2009, 10:44 AM

Does it read 0.0024% THD at 1W without any NFB?

Spooky Electric · 4th September 2009, 10:54 AM

Converted it to jpg.

Atilla · 4th September 2009, 11:34 AM

Quote:

Originally Posted by zhoufang

Does it read 0.0024% THD at 1W without any NFB?

Yes, I believe it does

soekris · 4th September 2009, 11:53 AM

What about using smt jfets, in sot23 ? Linear are supposed to launch their LSJ74 soon, you could mount them on a thin PCB that you glue directly on a big heatsink.... Any thermal problem solved.

I know that Nelson don't like stuff he can't see, but it much easier to have a machine mount 1000's of smt parts....

zhoufang · 4th September 2009, 12:25 PM

Quote:

Originally Posted by Atilla

Yes, I believe it does

If we assume that the 588 jfets is for one channel in push-pull setup and unbalanced mode, driving into 8ohm load, then at 1W RMS each jfet will be driving a +/- 0.85mA (1.7mA pp) of load.

And it will be at 8Vpp.

Comparing with THD measurement of B1 buffer, this thousand JFET amp's performance seems to be too good.

The only explaination that I can think of is that the symmetrical output stage help to significantly cancel of the distortion.
Or else there could be some intellegent design in it, which I can't wait to see more details.

soekris · 4th September 2009, 12:42 PM

Distortion sounds not too far off, Borbeley's paper claims 0.0078% THD at 3V into 1Kohm with a single pair. 1W into 8 ohm is 2.8V, and 500 pairs into 8 ohm is like single pair into 4Kohm....

Søren

oliverniekamp · 4th September 2009, 01:16 PM

There might be an X hidden in between 1000 Jfets?

Diomedian · 4th September 2009, 01:19 PM

I'm not sure if the AP machine measures THD+N or not, but I'd imagine that most noise would be averaged out over so many pairs.

jan.didden · 4th September 2009, 01:25 PM

Quote:

Originally Posted by Floyd42Flake

Converted it to jpg.

Works. Muchos gracias!

jd

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4th September 2009, 10:44 AM	#92
zhoufang diyAudio Member Join Date: Nov 2008	Does it read 0.0024% THD at 1W without any NFB?

4th September 2009, 11:53 AM	#95
soekris diyAudio Member Join Date: Jun 2009	What about using smt jfets, in sot23 ? Linear are supposed to launch their LSJ74 soon, you could mount them on a thin PCB that you glue directly on a big heatsink.... Any thermal problem solved. I know that Nelson don't like stuff he can't see, but it much easier to have a machine mount 1000's of smt parts....

4th September 2009, 12:42 PM	#97
soekris diyAudio Member Join Date: Jun 2009	Distortion sounds not too far off, Borbeley's paper claims 0.0078% THD at 3V into 1Kohm with a single pair. 1W into 8 ohm is 2.8V, and 500 pairs into 8 ohm is like single pair into 4Kohm.... Søren

4th September 2009, 01:16 PM	#98
oliverniekamp diyAudio Member Join Date: Sep 2001 Location: Düsseldorf Germany	There might be an X hidden in between 1000 Jfets?

4th September 2009, 01:19 PM	#99
Diomedian diyAudio Member Join Date: Nov 2004 Location: Halifax, N.S.	I'm not sure if the AP machine measures THD+N or not, but I'd imagine that most noise would be averaged out over so many pairs.