Thank you for answer
JLH gave me many questions yet unanswered.
PLH more clearly but still.
(Contribution of upper/lower half)
Then can we think R* replaced by constant voltage source to bias q3 ?
And input from front q1's drain is again mixed via potentiometer to make adjustable upper/ lower gain contribution?
Are these same or equivalent with original intention of PLH designer?
JLH gave me many questions yet unanswered.
PLH more clearly but still.
(Contribution of upper/lower half)
Then can we think R* replaced by constant voltage source to bias q3 ?
And input from front q1's drain is again mixed via potentiometer to make adjustable upper/ lower gain contribution?
Are these same or equivalent with original intention of PLH designer?
really thanks.
I tried to capture base idea about JLH / PLH.
currently PLH .
So Really haapy to hear designer's idea.
R* can be conceptual but not easy for me .
It can work/implement in various ways.
I will try to design circuit as written. (and many question may arise)
(PLH is similar but differs from ZV4 /Aleph evolution lineage.)
Thank you Mr. Pass.
I tried to capture base idea about JLH / PLH.
currently PLH .
So Really haapy to hear designer's idea.
R* can be conceptual but not easy for me .
It can work/implement in various ways.
I will try to design circuit as written. (and many question may arise)
(PLH is similar but differs from ZV4 /Aleph evolution lineage.)
Thank you Mr. Pass.
Hi
I understand that R* in Fig. 7 is there for the control of ac current flowing through Q3. For example, if ac current is increased through Q2, the ac current through Q3 is decreased, or vice versa. Then, Q2 and Q3 play a "push-pull".
Meanwhile, I redraw P2 and C2 in Fig. 8 as shown, to include R*. In this example, if we make value of R* zero (by turning the wiper towards ccw), we would see a constant current through Q3 independent from amount of ac current flowing through Q2 because the voltage between the gate of Q3 and the output will be always remained the same due to the bootstraping C2. If so, Q2 plays "single-ended". But, if we make value of R* greater than zero (by turning the wiper towards cw), we would see ac current change through Q3 as explained above. Then, Q2 and Q3 play the "push-pull". The greater value of R*, the higher percentage through Q3.
Cheers,
>
<
I understand that R* in Fig. 7 is there for the control of ac current flowing through Q3. For example, if ac current is increased through Q2, the ac current through Q3 is decreased, or vice versa. Then, Q2 and Q3 play a "push-pull".
Meanwhile, I redraw P2 and C2 in Fig. 8 as shown, to include R*. In this example, if we make value of R* zero (by turning the wiper towards ccw), we would see a constant current through Q3 independent from amount of ac current flowing through Q2 because the voltage between the gate of Q3 and the output will be always remained the same due to the bootstraping C2. If so, Q2 plays "single-ended". But, if we make value of R* greater than zero (by turning the wiper towards cw), we would see ac current change through Q3 as explained above. Then, Q2 and Q3 play the "push-pull". The greater value of R*, the higher percentage through Q3.
Cheers,
>
<Attachments
C2 works bootstrap to q3 , but to q1 it is not.
(Even q1's drain and q2,q3's mid points are of same phase voltage. And we may make c2 act like aleph's FB.)
My original qeuestion was about an idea related to:
1. replacing c2 with constant votage source.
2. insert R* in serial with C2
3. mix each input via separate potentio meter
and so on.
But current schematics seems very nice because it works!
(with simplicity) Thats wonder .
Cheers.
(Even q1's drain and q2,q3's mid points are of same phase voltage. And we may make c2 act like aleph's FB.)
My original qeuestion was about an idea related to:
1. replacing c2 with constant votage source.
2. insert R* in serial with C2
3. mix each input via separate potentio meter
and so on.
But current schematics seems very nice because it works!
(with simplicity) Thats wonder .
Cheers.
Thank you
I am translating some interesting (and important) Class A audio articles.
I am translating some interesting (and important) Class A audio articles.
Of course.
Thank you for translating it.
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!
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.
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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