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Old 14th January 2010, 09:55 AM   #171
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Dear Mr. Pass .

I am translating PLH article into Korean to post it my personal BLOG .
Ask permission to author before posting .
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Old 14th January 2010, 07:48 PM   #172
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Of course.

Thank you for translating it.

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Old 14th January 2010, 10:20 PM   #173
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Default Thank you

I am translating some interesting (and important) Class A audio articles.


Quote:
Originally Posted by Nelson Pass View Post
Of course.

Thank you for translating it.

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Old 11th April 2012, 10:38 AM   #174
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PLH_with_Regulated_Supply.pdf

PLH_RSU_PCB.pdf
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Old 11th April 2012, 05:00 PM   #175
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Nice! Are you going to make a run of circuit boards?
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Old 11th April 2012, 06:53 PM   #176
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I've got transformer with secondary 2x35V AC, which was left from dismantled Zen V9. Additionaly I've got radiators, so came to conclusion that the PLH is a good candidate to do something out of that.
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Old 18th April 2012, 10:16 AM   #177
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PLH_PCB_v7BW_Black.pdf
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Old 1st November 2012, 01:28 PM   #178
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Quote:
Originally Posted by gbullimore View Post
right, cases finished parts ready to order, just a couple of questions!

P2 needs to be 3w (10 turn or 1 turn)
i understand R4 being 3w also,
but P1 and R6 just 1/4 w ?
i asssume P1 (& P3) as a 10 turn to acuratly set the bias.

lastly whats the general opinion on running a 40v supply with 63v 10000uf cap 0.5ohm then 40v 10000x2 caps. this is in the external psu case with 48000uf in the amp case itself.
is it really bad to run a 40v cap at almost 40v? the ambient temp will be 25c or so.
can p2 be adjsuted whilst the amp is running?

ah and why does nowhere in the uk sell mica washers for T0-247? i can only find t0-220 in mica, or silicon in T0-247.
I just found this post, and i'm a bit ashamed to say i got the first monoblock up and running today, 5 years after starting !!!
hopefully it will be closer to 5 days until the other monoblock is up and running!
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Old 4th November 2012, 08:26 AM   #179
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Go on gbullimore ! There at least one person waiting for your final results.
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Old 7th February 2013, 02:25 PM   #180
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Default PLH "Disappointment"

I recently completed a pair of PLHs following on from a long held desire to build a JLH class A which I first remember from Wireless World in the 70s. (At least I think I remember it, I certainly had Wireless World delivered when I was in my early teens around 68 to 72).

Now I've got the time and money and a lot more patience, I decided to revisit my callow enthusiasms and try and actually understand the the workings of the old radios and amplifiers that were scattered around my teenage bedroom.

Having slain the radio beast (different forum) I then moved on to the Class A question. I built a couple of pairs of JLHs a year or so ago with current components and was not disappointed, particularly the second pair which I put a bit of style into and bumped up the voltage, quiescent current and heat dissipation. Not only did it look better, it sounded/sounds amazing.

Then I discovered the PLH and, realising that I knew nothing about FETs, decided to give it a go, and to make it LOUD. I made it as published except for the replacement IRFP240s and an increased voltage of 65V.

Mr Pass doesn't explicitly state that it's a bit of bugger to set up, but does go into detail about how to do it. So after several sets of FETs had either simply gone pop, or eventually fried, I read his instructions properly and realised that not only is the output pair quiescent current dependent on both P1 and the balance of P3, it is also dependent on temperature and very sensitive to supply voltage. Having worked this out, I redesigned my power supply to include a zener in the capacitance multiplier bit and bought some big heat sinks. It still never really stabilises and would require some sort of temperature control in a commercial product.

So, why am I disappointed? Well, I didn't expect it to sound better than the JLH, just LOUDER, which it is, but the bass is ill-defined. There's a lot more of it at the lower end, which is fine, but it seems to swallow up all adjacent frequencies so, for instance, the ridiculously over-recorded double bass on the more recent Jacques Loussier records which sounds so fantastic on my JLH just sounds wooly on the PLH. Similarly Eminem (excellent recordings, who'd have thought).

The same holds true using different input sources (Cambridge DAC, Cambridge Azur CD) and loudspeakers (Mission 781, Quad 12L).

So what have I tried: power supply, 1KW transformer, 22000uF 100v cap, almost immeasurable ripple with no input, less than 40mV at high volume: audio output capacitor, reducing this from 10000uF to 1000uF improves things. Input capacitor, reducing this to 1uF also helps.

Comparing the PLH with some of my previous commercially bought amplifiers brings me back down to earth though; the PLH is very good, just not as subjectively good as my JLH.

I had decided to recycle the parts, but, having listened to the PLHs all day (keeping an eye on the current), they really are too good for that.
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