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Old 6th February 2010, 10:54 AM   #11
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Quote:
Originally Posted by AndrewT View Post
I think you underestimate the peak current requirements of fast transients.
Hey Andrew

Actually you might be right there ......I havenet done any transient yet
I been testing for max output -- but because of the performance of the MJs I assumed I had 60Amps peak (12.6 continuous) per rail available - which is huge.

...can we take this to another thread later today or tomorrow? I'll post my project up (all of it)

...I'm just a bit concerned for poor P-Robertson,here, coming back to his thread thinking "WTF" .....LOL
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Last edited by PhaseLockLoopy; 6th February 2010 at 11:04 AM.
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Old 6th February 2010, 12:35 PM   #12
polsol is offline polsol  South Africa
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Originally Posted by PhaseLockLoopy View Post
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.
Actually I was just following up on the OP question of +7 years ago. This was one of JLH's last designs. I think that a kit was offered at the time but never heard what the sound quality was like.
I am thinking of building it to see but would like to check out the design on LTSpice as a first step - hence my query on the FETs and their .models.
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Old 6th February 2010, 12:46 PM   #13
polsol is offline polsol  South Africa
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Originally Posted by Mooly View Post
Check out Exicon/Profusion

JLH's amps all had one thing in common... they really made music.
Thanks for the reply. Yes the 10W LJH Class A always seems to get good reviews - in any one of it's many guises.

Had heard that the Exicon MOSFets were not always well received but at least they're TO3. No small signal on the Profusion site though.
Do Exicon have they're own web site? Have been trying to find it.

RS indicate many types of MOSFet as available but they don't appear on the manufacturer's site. Tends to be confussing.

Would be nice to get a reference to a manufacturer's site for small and large signal MOSFets that are considered good for audio and have Spice models....
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Old 6th February 2010, 01:05 PM   #14
polsol is offline polsol  South Africa
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Quote:
Originally Posted by PhaseLockLoopy View Post
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
I don't think it's so much of a JLH appreciatation society but rather quite a number of people appreciated JLH's contribution to amp design from 1969 onwards.

AFAIK, the original JLH class A is still considered very good even after all these years.
Ultimately, I want to have a 'reference amp' to compare other designs to, possibly my own one day. I think mosfets should give superior sonic results because of their linearity but then this is a hot topic so we'll stay away from it. Just my thoughts - hence the query on his mosfet amp design.
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Old 6th February 2010, 03:56 PM   #15
Mooly is offline Mooly  United Kingdom
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JLH's designs were my inspiration for this one of mine which uses lateral FET's,
My MOSFET amplifier designed for music.
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Old 6th February 2010, 09:47 PM   #16
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Originally Posted by PhaseLockLoopy View Post
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.
Then you'll LOVE this, JLH=TTL. Everything you asked for above in spades!

My beef with JLH is overbias in the center, not enough bias at extremes...
Entirely because base current is the only thing gets regulated or steered.
Turn a blind eye to quiescent output currents, and hope for the best.

On the other hand, that same blind eye makes paralleling them easy.
I can't think of any other advantage...

JLH is fixable, but thats not what I'm attempting to show here.
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Old 6th February 2010, 10:01 PM   #17
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Originally Posted by kenpeter View Post
Then you'll LOVE this, JLH=TTL. Everything you asked for above in spades!

My beef with JLH is overbias in the center, not enough bias at extremes...
Entirely because base current is the only thing gets regulated or steered.
Turn a blind eye to quiescent emitter currents, and hope for the best.

On the other hand, that same blind eye makes paralleling them easy.
I can't think of any other advantage...

JLH is fixable, but thats not what I'm showing you here.
eeeeeeek

ROFL
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Old 8th February 2010, 06:21 PM   #18
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Sorry to be bashing JLH. Its not all that bad, and as I said, fixable...

Merely replacing the bipolar output devices with MOSFETs and some
appropriate resistors from gate to source corrects a lot. Square law
vs Square law helps restore the quiescent current profile such that
the little Iq current is in the middle, and big current at the extremes.
And temperature co-efficients now bend in a much safer direction.

The biggest new prob introduced by MOSFETs is matching threshold
voltages. And to include a compliment of similar, but opposite threshold
up front, assuming you want the DC to cancel.

Nelson Pass' PLH is probably the circuit you are looking for.

Last edited by kenpeter; 8th February 2010 at 06:40 PM.
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Old 8th February 2010, 06:31 PM   #19
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If you wanna fix JLH, but stay all bipolar, thats do-able too. You gotta do
something bout making the output currents behave by a rule. Rather than
merely spray and pray a drive current to one base or the other...

four transistor emitter follower (diamond buffer) as power output stage?

See schematic of post #87 in the above thread...

Its a good circuit. Just don't expect my "explanation" of it to make
any sense. Cause I was simultaneously talking bout something else.
My mind was scattered all over that day.

Last edited by kenpeter; 8th February 2010 at 06:37 PM.
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Old 8th February 2010, 08:09 PM   #20
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Hi KenPeter

If you wish to give my designing a bashing go here Trying to build...an...OMG

I love Dallas by the way -- spent some time at Texas Motor Speedway with Team Texas
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