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Old 2nd June 2004, 02:25 PM   #11
DRC is offline DRC  United Kingdom
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Quote:
Never built either but I bet the P3A is a lot easier to get working ...
originally posted by me ...
refering to :-
P3A
Leach

OK, I don't know where to find "original leach EF2" (ref'd by djk) but, comparing these two, I still think the P3A is simpler ...

dave
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Old 3rd June 2004, 02:34 AM   #12
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Default May i ask you some?

You said P3A is simpler than leach.

But you put some points.... i use this way.....because army..... receiving cw instructions....... this way.... for me this is normal.....but i know you do not do that normally, those points are something to be concluded by ourself.

But can conclude a lot of things.

Simple.... is better
Simple.... is worst

And a lot of ideas can come, can you please tell us if this points had some meaning, or not had a meaning.

If had a meaning, please tell me if i am rigth, we have to conclude, that's what you want?

Since the beggining, electronics teacher told us that each amplifier stage create their own problems, their distortions.

The best amplifier is a wire with gain, not discovered yet.

This way, i can conclude, simple is better....but, if you read all forum, twice times as i read, you will see that people is putting a lot of stages, and feedbacks, and stabilizer, and mirrors, and long tails (why not normal tails, short tails, looooooog tails seems something falic.... the man with looooog arrow.....looooog car....loooog tail, theres a psychological problem related the first that use this name....this one may have short......

And i cannot understand where first teachers fail, never heard them saying, make a lot of stages, to compensate errors one of the other... this way the second corrects the third, and the fourth will correct errors from the third... and mirror to balance, because is unbalanced, supply is unbalanced, or is balanced, have to unbalance before balance...and this goes to enormous circuits... and when i assemble them.... strange sound, have a juice artificial, a damn international tang brand and a orange juice and compare them!.... if one stage is correcting the next, what will happens with the last one....oh!, it will return to input.

Have 10 old friends, all them audioholic, audiomaniac, audiocrazy, audio amateurs, the name you want..... was a damn shame when i read entire story of Mr. leach, their technical ideas in seventies, and the circuit itself....but when people start to hear... all them perceive lack of bass and say... baaaaad!....i perceive some time passed, why?... because i done the whole thing, had to think is good, if not, who i am?

Those friends like americans as i like, and they spect better sound related our referenced units (one Marantz, one Macintosh and one Death of Zen)... they never joke with that, is our club, and their we do not joke when sound judgements are done.

I will be happy if you can say clearly what you intended to say...if you intended to say something, because i also use dots........

regards,

Carlos
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Old 3rd June 2004, 06:15 AM   #13
mandat is offline mandat  Poland
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Kostas Metaxas tries to manufacture some amps according to philosopy "amplifier is a wire with gain". He has got very fast amps. He is one of these Aussies (with Greek roots) who produce very good eqpmnt.
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Old 3rd June 2004, 09:14 AM   #14
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Default I visited Metaxas five year ago.

Could not have some schematics, but i was very interested related to their work.

I will receive AKSA, i think i will be very happy to here ist sound.

Also i will know top secrets!

My friends, 10 friends, audioholics are making pressure to see schematics...i am saying no!...because Hugh do not want it.

- But hugh will never know you show us!

- But my concience will know very well.

The are studdyng hard (damn boys those friends!) the hugh pictures of AKSA 55 and the stereo unit.... the think the board is alike a sandwich, two small bords one over other, and some SMD or small capacitor plates mounted there in secret... they asking me to inspect boards and make Ray X..... i will not let them see different than normal screwed position, assembled...not to inspect solder sides of measure continuity.... have to respect agreement made.

My friends are nervous with me. and they think they discover something... take a look.

Not to get away, to much of thread subject, but i think this can be interesting thing to analise... my friends are enginneers and all kind of professions, 80 percent them have universitary degree..not stupid people and audio maniacs!

Carlos
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Old 3rd June 2004, 10:51 AM   #15
pooge is offline pooge  United States
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Regarding the "lack of bass" in the Leach amp: the electrolytic capacitor C6 in the feedback network is intended to be two series capacitors or one non-polar electrolytic. If you use a single non-polar, you must jumper the space for the second capacitor. Otherwise, no bass.
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Old 3rd June 2004, 11:07 AM   #16
DRC is offline DRC  United Kingdom
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Post I did bet that the P3A is easier to get working

Carlos,
I am sure both of these designs, built to the designers’ specification and on the designers PCBs, work real well. My practical comment (OK, maybe slightly off-topic) was purely based on the complexity of the actual circuits (as published) and the likelihood of bad components / dry solder joints etc that can prevent a circuit from working correctly. I did not mean to imply that the P3A was simpler to design, or worked any better or worse than the Leach, just because it had fewer components.

However, it seems to me that the designers of these amplifiers seem to have approached the same basic design (PP class AB) from two different perspectives. As I see it, in the Leach the forward path has been engineered for the minimum error with a compound feedback arrangement to keep those extra bits in check at HF. In the P3A the forward path is less accurate but the reduced group delay allows more (and simpler) global feedback to correct the errors. Only a double blind listening test should decide if the extra complexity of the Leach is worthwhile, but I seriously doubt that I would hear any difference.

PS
I made my second post in response to a post saying that the only difference in component count (between P3A and Leach, although an earlier variant) was 2 small signal transistors. This didn't really tally with my memory so I went back to check and I reposted with links to what I consider as the reference designs and restated my first post (complete with ellipses ).

dave (ellipses – too many years programming C)
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Old 3rd June 2004, 06:30 PM   #17
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Default Yes, all them good! no such a difference

But something different of wave form and distortions exists... i cannot say what is!...have no theorical conditions to discuss.... this way i feel like an human can feel.... the voices of a coral music.... the precision off a cello.... the thunder of drums and delicacy of little bells, cymbals.... the warm of flute, the magnificence of the harmonica... we can hear them in real world, and we can hear them recorded... this way, one can do better some instruments, other can do better reproduction of others... as an audio maniac, audioholic, i like to think about comparisons.... but all them is compared in high skies...high level quality both of them.... one simple, other, state of art design from seventies....incredible how they can be compared sometimes.... as a bicicle asking to surpasse an Ferrari in road.... we have some joke about that.

On Volkswagen damage was attached into a ferrari... and they go. both drivers combined that when Volkswagen sound its buzzer noise signal is to ferrari reduce speed.

And they passed in front of a Police, he took the radio and inform. A ferrari and a buggy..... 150 miles an hour.... from eat to west, road number zst mile 241 point.... and believe me or not.... the buggy is asking to pass the ferrari!!!

Carlos
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Old 4th June 2004, 01:05 AM   #18
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Try the index page and then click on"

"Build a Low TIM Amplifier - Parts 1 and 2 - Articles I wrote for the Feb. '76 and '77 issues of Audio magazine that many people have asked me to post. Several following versions are included. The Leach Amp plans linked above are for the latest version of this amplifier. This is a PDF document which might take several minutes to download. I recommend right clicking on the link and saving it to your hard disk. The amp pictured in Fig. 1 has been running over 8 hours a day, 5 days a week, in my office since the article was published. "

Delete predrivers.
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Old 4th June 2004, 04:47 AM   #19
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I have build both amps using my own PCB layouts, and with minor modifications to both amps.

My main modifications are:

Leach:
Changed the number of output transistors to 10 (5 sets)
Changed the protection to match 5 sets of transistors.
Changed the LF cut off cap in feedback to 470uF not polarized giving plenty of bass.
Decoupling rail voltage, by using 1uF on each collector of the output transistors.
Resistor between emitters on driver transistors is bypassed by 1uF.
Bigger Emitter resistors on input (330ohm) to decrease open loop gain
I used other transistors because I could not get the original and prefer flat pack types.
Input: BC546/556
Bias and protection: BC546/556
VAS: MJE340/350
Driver: MJE15032/15033
Output: MJL2381A/1302A

P3A:
Current source for input replaced by transistor/transistor type ala Leach, same current.

I think the leach amp is more work, but it’s worth it. But the P3A is a very nice amp, the only problem is that it runs into voltage limitations when comparing to the Leach amp.

For a first project I will definitely favour the P3A as this has much fewer parts, and therefore less risk of error when assembling.

\Jens
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Old 4th June 2004, 08:31 AM   #20
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Default I will assemble again some day.

Not more Leach amplifier this way. Rasmuleach or Leachssen this way.

Very good idea, and was in front of our eyes and i do not see it.

Low pass condenser may change whole audio.

thanks,

Carlos
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