NOStalgia - the all-FET JLH/PLH Class A amplifier - Page 2

revintage · 23rd January 2012, 01:54 PM

Heja Knut,

Quote:

Since the input transistor is a JFET, I don't need an input capacitor either.

How do you expect to get 0V at the output with the FET gate tied to ground? As long as there is a current-flow through the feedback resistor R14 and a source/gate-voltage in the FET this will be impossible. But I might have missed some hidden twist

?

Other FET variations is to be found in the gigantic JLH-thread. JLH is a nice topology anyway!

knutn · 23rd January 2012, 06:30 PM

Thank you for your interest. Hopefully I will be finishing the assembly in about two weeks. So I am looking forward to the first listening test after that....As always: enough time is a problem.

JRKO · 23rd January 2012, 06:34 PM

Quote:

Originally Posted by knutn

Thank you for your interest......As always: enough time is a problem.

JLH/PLH has been floating in my mind for some time......

Unusually I have too much time on my hands......and not enough brains

knutn · 23rd January 2012, 06:36 PM

Quote:

Originally Posted by revintage

Heja Knut,

How do you expect to get 0V at the output with the FET gate tied to ground? As long as there is a current-flow through the feedback resistor R14 and a source/gate-voltage in the FET this will be impossible. But I might have missed some hidden twist

?

Other FET variations is to be found in the gigantic JLH-thread. JLH is a nice topology anyway!

The voltage at the source of the JFET is about minus 1.8 V when the output is at 0 V. This is enough to have a suitable current in excess of 1 mA in the P channel JFET. it works just fine.

And I agree with you about the topology.

revintage · 23rd January 2012, 07:14 PM

I smell something burning

.........

knutn · 23rd January 2012, 07:43 PM

Data sheet for the JFET: http://www.fairchildsemi.com/ds/MM/MMBFJ177.pdf

Dzius · 4th February 2012, 07:43 AM

That's very interesting amp indeed. Some DIY-ers are concern about resistors and capacitors. More advance care about transistors. But there is more in what comes out of speakers - sound characeristic i.e. harmonic distortion content. With PLH one can change from Push-Pull signal amplifing method to Single Ended, or choose and many stages between the two. (Like 2/3 AC current ratio suggested by Nelson). From this point of view it's very interesting to see in what extent sound change accordingly. That's why I think every DIY should built PLH but probably only some understand what it's about. I would like to build a one. Knut your cirquit is particulary interesting since there are no capacitors at the output, so one thing less to bother. Looking forward your final results. Thank you for PCB drawings. Pawel

23rd January 2012, 07:14 PM	#15
revintage diyAudio Member Join Date: May 2007 Location: Eskilstuna, Sweden	I smell something burning......... __________________ Brgds Lars

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23rd January 2012, 06:30 PM	#12
knutn diyAudio Member Join Date: Mar 2006 Location: Oslo	Thank you for your interest. Hopefully I will be finishing the assembly in about two weeks. So I am looking forward to the first listening test after that....As always: enough time is a problem.

23rd January 2012, 07:43 PM	#16
knutn diyAudio Member Join Date: Mar 2006 Location: Oslo	Data sheet for the JFET: http://www.fairchildsemi.com/ds/MM/MMBFJ177.pdf

4th February 2012, 07:43 AM	#17
Dzius diyAudio Member Join Date: Sep 2010 Location: Warsaw	That's very interesting amp indeed. Some DIY-ers are concern about resistors and capacitors. More advance care about transistors. But there is more in what comes out of speakers - sound characeristic i.e. harmonic distortion content. With PLH one can change from Push-Pull signal amplifing method to Single Ended, or choose and many stages between the two. (Like 2/3 AC current ratio suggested by Nelson). From this point of view it's very interesting to see in what extent sound change accordingly. That's why I think every DIY should built PLH but probably only some understand what it's about. I would like to build a one. Knut your cirquit is particulary interesting since there are no capacitors at the output, so one thing less to bother. Looking forward your final results. Thank you for PCB drawings. Pawel

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