Another JLH, my 2SJLH PMOSFET DC Class-A amp

[mtlin12]

Hi, I recently tried to modify JLH 2003, Pass' PLH and Wayne Stegall's One-Bend Amp design,
and now I have completed a DC-coupled 2SJLH-200 that is easy to set up.

I'm 60 now, still not too old but time is running out just like my France made Oscilloscope,
the CRT just faded out, also my XP PC & Creative's Xi-Fi sound card, so I have no testing data.

I have no theory, can not use SPICE, I simply like to DIY with my two testing PCBs designed 15 years ago.

Here is my circuit, using simple blue LED as the Vref about 3V, it is very easy to adjust to
about 2mA for the first stage.

But first thing to do is adjusting SVR2 to set R5 about 3.4V than the output stage will about 2A!

Then adjust SVR1 to set zero DC level, I found it is very easy and stable within <+/- 30mV.

First picture output resistor R3 & R6 I use 10 ohm just for testing, setting 1.5V then R3 & R6
changed to 0.47 ohm 5W same as PLH.

Second picture is my old differential SPLIT AMP, the structure is very similar, all use cascode JFET
as input stage, 2SJ77 & 2SK214 as 2nd stage, 2SJ200 & 2SK1529 or double-sziklai transistors.

 

[huggygood]

very interesting !!

 

[U130421]

more open loop gain

My be this can inspire you further.CCS on input.
Of what CCS 6ma is made of?

 

[mtlin12]

DN3545 + LM334Z and a diode
http://www.euleitaudio.com/images/EU-01_MKII/EuLeit_EU-01_MKII_Preamp_V2.2_WO_SCH.jpg

 

[N101N]

mtlin12,
there is not much JLH spirit around here, it behaves just like a generic symmetrical amplifier.

kokoriantz,
that CCS does not inspire me, anyway, it is a bad thing.

 

[mtlin12]

mtlin12,
there is not much JLH spirit around here, it behaves just like a generic symmetrical amplifier.

1. If you reverse the N-ch JFET to PNP transistor, and 2nd stage P-ch MOSFET to NPN with a CCS, output stage P-ch 2SJ200 to MJ15003, then u will see it as a JLH 2003.

2. You can also compare this to Pass' PHL, only mine is 3 stage design.

 

[N101N]

mtlin12,
OK. I was having the 1969 single-ended topology in mind. The 2003 topology is uninteresting to me.
Anyway, I like the JFET input and the MOSFET output. The 2SK214 / 2SJ77 are really great, but not for voltage amplification. Q2 should be a bipolar transistor as well.

 

[U130421]

How it sound like? Can you listen the following music and describe, please?
YouTube from 9:40 to 13:20
YouTube sing sing sing & Peggy lee .
If it is not so good , compare it with high end amps the same music by a vendor Mark Levinson Krell etc. ,than get a comparative idea. To design is intelligence but to tune is art.

 

[mtlin12]

mtlin12, OK. I was having the 1969 single-ended topology in mind. The 2003 topology is uninteresting to me. Anyway, I like the JFET input and the MOSFET output. The 2SK214 / 2SJ77 are really great, but not for voltage amplification. Q2 should be a bipolar transistor as well.

JLH 1969 is a great design, I still have a lot to learn, but it seems not so fashion as JLH 2003 does.

I also don't like bootstrap or OTL design, all modern audio design books from Japan that I read taught me " use CCS & DC-coupled from input to output".

Usually the 2nd stage I use Pch-JFET like 2N5461, but then the circuit will become too complicated as my old design EU-01.

So I try to simplify my new pre-amp design, then I remember that I have a lot of 2SJ77, why not use PMOS as S.E. 2nd stage.

And it becomes this 4 FET High Votage supply, no NFB, DC-coupled my new pre & headphone amp FET-60, its gain is high and fixed ( audio range) can directly drive my 0dB High Power Buffer, only to protect my HPB & AKG 501, I still have to add 2 caps (1 EC and 1 PP) at the output.

It sounds pretty good, but I know the distortion will be a little bit high if I use low current for 2SJ77. High current then I need a larger heat sink.

 

[EUVL]

Another version with P-JFET input and N-MOSFET output :
All FET JLH Class A


Cheers,
Patrick

 

[mtlin12]

Just wonder how do u trim DC level?

 

[EUVL]

Trim TR2 (2nd stage CCS).
See last schematics in post #19.


Patrick

 

[mtlin12]

But still got to use Ci 1000u BP , for me it just not a pure DC-coupled design.

 

[EUVL]

No need in final build, especially when using 2SK1530, etc.


Patrick

 

[EUVL]

When built today, we probably have to use NJFET front end and PMOS outout, like you did.
2SJ74 is hard to come by.


Patrick

 

[mtlin12]

No need in final build, especially when using 2SK1530, etc.


Patrick

Good for you.

When built today, we probably have to use NJFET front end and PMOS outout, like you did.
2SJ74 is hard to come by.


Patrick

I know that, I only got 100 sets of 2SJ77, so it is just for DIY fun.

 

[N101N]

mtlin12,
JFETs and the 2SK214 / 2SJ77 have high channel resistance that does not benefit voltage amplification. A larger current reduces the resistance.

EUVL,
At last that unnecessary ugly bootstrap capacitor is gone...

 

[mtlin12]

The 2nd stage sinks only a few mA, so I think 2SJ77 is no problem.

I do not have many 2SK214, but it can be easily changed to IRF610.

 

[N101N]

mtlin12,
I am not urging you to redesign or make changes to a working amp. (Maybe it is better to leave things as they are.)

It should be a (certain type of) bipolar transistor, just like Q2, adding two resistors, keeping the small drain-source voltage across the JFET.

 

[mtlin12]

Many thanks!