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Old 6th July 2002, 08:27 PM   #1
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Default mosfet class a/ab amp

hi all audio fanatics! this is my first post in this forum. i was wondering if anyone has built the class a/ab mosfet amp by j l hood which appeared in electronics world mar/may 1989 ? it looks like a stunning design!!
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Old 6th July 2002, 09:14 PM   #2
Geoff is offline Geoff  United Kingdom
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I haven't built this particular JLH design, but I would be most interested in seeing the schematic if you could post it here or email it to me. You will see from my website, which also has my email address, that I have been following JLH's articles for many years, but this is one that I have missed.

Geoff
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Old 6th February 2010, 04:36 AM   #3
polsol is offline polsol  South Africa
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Default Anyone tried the JLH Class A/AB?

Just wondering if anyone has tried this in the last 7 years or so?
The amp uses VP080, VN1210, 2SK133 and 2SJ48 mosfets. These are difficult, but seemingly not impossible to get hold of.
However:
1) Finding them on the actual manufacturer's website is nigh impossible - hence limited information.
2) There seem to be no spice models for them.
3) Perhaps there are newer, better alternatives to these mosfets now available - and also with the spice models or data suitable for LTSpice?

It would be nice if the manufacturers stated they were suitable for audio use too.

Comments/suggestions gratefully accepted!

Cheers!
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Old 6th February 2010, 07:32 AM   #4
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Default Jlh

Whole load of JLH here The Class-A Amplifier Site -- even one where they tried to make something that resembles a Krell KSA -- only with a chassis made of wood.

Personal opinion, I know - but after designing amplification for over 2 decades you get to know what works and what is a bit ..........er..........well...... of a minger.

Linsley Hood stuff is very basic - noisy - with crummy damping factors, insignificant slew rates - offering pretty below average performance ,(even for back then) - we tended to use them as training tools -- mainly because they are cheap and the parts list is short.

Dont get me wrong - great for enty level, have a go type of thing but
If you are seeking quality - I'd scour the world for better.
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Old 6th February 2010, 08:13 AM   #5
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by polsol View Post
Just wondering if anyone has tried this in the last 7 years or so?
The amp uses VP080, VN1210, 2SK133 and 2SJ48 mosfets. These are difficult, but seemingly not impossible to get hold of.
However:
1) Finding them on the actual manufacturer's website is nigh impossible - hence limited information.
2) There seem to be no spice models for them.
3) Perhaps there are newer, better alternatives to these mosfets now available - and also with the spice models or data suitable for LTSpice?

It would be nice if the manufacturers stated they were suitable for audio use too.

Comments/suggestions gratefully accepted!

Cheers!
I can recall this amp... never built it though. It used FET's for the drivers and VAS I seem to remember. The outputs are lateral FETs and there are several new devices that would work well.
Check out Exicon/Profusion

Lateral Mosfet

JLH's amps all had one thing in common... they really made music.

I surprised PhaseLockedLoopy finds them poor performers. Perhaps he could recommend one of his own designs instead, or some other equally good performer.
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Old 6th February 2010, 09:53 AM   #6
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Oooooh lets not go into my projects just yet -- I'm going to be starting a thread on that later as it just so happens I am developing Pure Class A bipolar.

But...As I say -- its down to personal preference -I find them all a bit simplistic - but one could expand out a bit and examine other designers such as Carver - or Hafler

...here's the DH250 FET

...as an example of what I mean...one of the biggest improvments that can be made to any amplifier is how power is provided and delivered - in the JLH link in my previous post - they try and use common, cheap plastic package regulators ....hmmmm ... not my preference I have to say.

....here's mine for comparison
Attached Images
File Type: jpg hafler.jpg (171.0 KB, 451 views)
File Type: jpg psu.jpg (125.6 KB, 431 views)
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Last edited by PhaseLockLoopy; 6th February 2010 at 10:01 AM.
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Old 6th February 2010, 10:07 AM   #7
AndrewT is offline AndrewT  Scotland
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Hi,
Quote:
Linsley Hood stuff is very basic - noisy - with crummy damping factors, insignificant slew rates - offering pretty below average performance
is it the amplifier you don't like
or
Quote:
hey try and use common, cheap plastic package regulators
is it the regulator that you don't like?
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Last edited by AndrewT; 6th February 2010 at 10:11 AM.
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Old 6th February 2010, 10:20 AM   #8
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PhaseLockLoopy, your regular does not include Emitter resistors for the Pass Transistors. I think it is important to share the current load.

About 47-100uF caps from Base of Q1, Q4 to Ground would improve performance and C11,12 could be of higher value. C11, 12 will run out on sustained music peaks.

A supply, whether regulated or unregulated, which allows for relatively uncompressed transients is desirable, provided the amp's output stage is designed to handle the peak currents.
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Old 6th February 2010, 10:44 AM   #9
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Hi guys

If I've walked into a JLH appreciation society - I apologise if my personal tastes dont fit - I just thought some alternatives exist that could be improvements

Hi Andrew -- both really -- as I said for me personally - its all down to the cheapskateyness they seemed to extol.

Hi Samuel - absolutely - if I were delivering to much larger amplifiers - But under drive conditions down to 2 Ohm inductive loads, with the rest of the amplifier on the end that, peak issues havnt proved to be the case. I may improve that further when I do the bigger 300W version. There is enough stable current in there to sink a battleship. I may post the whole design this weekend - I'm still testing the bench prototype. You'll find it is consistent at that max power.
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Old 6th February 2010, 11:45 AM   #10
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by PhaseLockLoopy View Post
But under drive conditions down to 2 Ohm inductive loads, with the rest of the amplifier on the end that, peak issues havnt proved to be the case. I may improve that further when I do the bigger 300W version. There is enough stable current in there to sink a battleship.
I think you underestimate the peak current requirements of fast transients.
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