An excellent power amp from france from the 70's

Don't dismiss it just because it is old and uses strange schemat layout.... The quality of the concepts is at least as good as many contemporary designs.

Strengths:

Single ended much of the way quasi comp output stage
Regulated front end
Class A input stage with PP EF output and nested feedback
Multiple nested feedback
Full protection with clip indicator]
Elegant phase inverter
Asymmetrical bootstrap
Elaborate, well designed compensation

Weaknesses:

High component count (20 transistors for 70W!!)
Electrolytic couplers and bypasses throughout
6 presets!!
Unipolar supply


The most outstanding quality of this design is the nested feedback and the use of a full on, non-differential input voltage amp and buffer to drive T6, the 'formal' VAS.

France as a country appears to foster 'revolutionary' thinking; just as I like French cars, I like this design, and I can't see why it should attract criticism. That said, of course, I have not heard it, but I'd bet it sounds damn good....

Thanks Gaetan, good circuit!

Cheers,

Hugh
 
Hello Hugh and all the guy's

Yes, it was a damn good amp, as good as Naim, Radford, and other high end amp of the 70's and 80's , I remember the opinion of a very known golden ear guy here in Quebec, he placed Audiotec with the best amp of that time.

I have myself a Radford HD250 from the 70's and even before doing recap it was a damn good amp, now it's even better.

Btw, I know that not much guys would build that Audiotec but it always good to see other amps design.

Bye

Gaetan
 
More than 20 years ago I went through a sort of "conversion" about the merits of French engineering when we bought a secondhand 7 seater Peugeot 'wagon almost by accident as it was the only thing that we could fit all five kids into without having to buy a van. Now it did have some eccentric features but it WORKED WELL and worked reliably for many moons.
But working on it and servicing it brought to mind something that I was told about Europe and the "After life". It was the difference between Heaven and Hell.

It goes like this: In Heaven the English are the police, the Germans the engineers, the French are the cooks, the Swiss the organizers and the Italians are the lovers.
Whereas in Hell the English are the cooks, the Germans are the police, the French are the enginners, the Italians are the oragizers and the Swiss do the loving.
 
Jonathon,

I LOVE that gag, have always admired it. In Oz we are so far removed from Europe, yet we have European sensibilities, that we can be mightily amused by the strengths and weaknesses of our continental cousins.

I have been an audio designer for about fifteen years, and when I saw the Audiotec design I recognised many of the milestones I have passed in my never ending quest for the holy grail.

Hugh
 
Hello

I've been, for many years, very empress by the technology of a french car, the Citroen.

Here in Quebec, especially in Montreal, we are in heaven and hell... since we are french and english living close together since 400 years and in the 19th century there was coming the irish.

And I'm myself french from my dad and irish from my mom.

Btw, now outside, here in mountain, the temperature are at -31 degree.. brrrrr... and there is a very big snow storm coming tomorow :xeye:

Bye

Gaetan
 
To partipate in the debate, I always heard that we do have good engineers in France, what we miss is maketers. The local audio market is full of well marketed and good looking English products (with their own particular sound) but I'm not sure you can find many French makes across the Channel...
 
Thank you Gaetan.... very good to see an old nice design

I have no doubts sounds good..... that output condenser, if big enougth, do not bother sonics the way people thinks.

A lot of them never tested those things... goes repeating things... this happens a lot.

The output condenser blocks DC, and also introduces inductance.... you see that now a days we install inductances in series into the output.... so.... things have not changed so much as many folks think.

The input voltage stabilizer is great!... double voltage for first and second stage...very nice arrangement...also output... seems toten pole or something alike..... i have to watch it once again.

Here is hot today dear Gaetan.... 31 degrees celsius.... the weather is bothering a lot... also town watter stock is finishing and we are controling those things..not cleaning automobiles or taking care of garden.

Yes Donk, for sure they perform a little bit worst than the most modern ones, but sounds good and can outperform some modern units also.....ou daddies, grandfathers and old folks (alike me) were not deaf dear Donk.... they had some critic ears and they were always trying better sound alike we did.... old technology gave not to them all the tools we have now a days, but for sure they made the best possible with the tools they had.... Also old folks had, in the past, alive sound to compare with the recordings and amplifier reproductions or their time...so... they had reference too.

My Christmas gift to you dear Donk, is to ask Santa Claus (or Klaus) to open your way to find some old unit to listen and evaluate once more.... i know you have already made that hundred of times.... one time more... a lucky moment facing a tube amplifier, some old design from Mac Intosh for example....old units will not measure very well...but produce a blind A to B testing and maybe you will have more inputs to your evaluations.

regards,

Carlos
 
Hello

You are lucky Nordic and Carlos, I don't like cold, this morning I have done hitch-hiking to go to the village... brrrr coooollllldddd :eek:

About old audio gear, few weeks ago I was at a friend who have a Linar amp and Spendor S100 speakers, he just buy an old
Mc Intosh MCD7005 cd player who have a TDA1541 Dac. We compared it with his $1000. dvd player, we was using Naim, Vtl, Verve, cd music, and the Mc Intosh cd player was so much cleaner and musical than that dvd player.

Donk try to listen an old Radford or Marantz tube amp.

Bye

Gaetan
 
gaetan8888 said:
Hello
I've been, for many years, very empress by the technology of a french car, the Citroen.

<off-topic>
Ah yes, the magic carpet ride provided by the hydropneumatic suspension.

Have had the BX, XM, and Xantia myself, and now the C5.
Every new generation has a 'stiffer' suspension, but still a dream to drive :car: :cloud9:

Contrary to popular belief I have never had major problems with these French cars, apart from the XM.
But then again: you definitely should not drive a car without oil... ouch! :bawling:
</off-topic>

Remco
 
AKSA said:
Don't dismiss it just because it is old and uses strange schemat layout.... The quality of the concepts is at least as good as many contemporary designs.

Yes, I agree with you, Hugh, this schematic is very nice, a lot complex and with very interesting solutions.

I don't know how it sound, maybe better than an actual amplifier.
Otherwise, I think that nowadays a DIYer tends to approach and search a more "modern" design.


Thank again to Gaetan, for let us know some secrets of this amp.
 
Hello

Yes, there is lot of psu voltage, because the input /Vas; the driver ; and the output ,do have their hown psu.

I've found that schematic two day ago on but there is a mistake in the psu voltages, so, according to another book about JBL amp, the outputs should have a rail of 41.5 volt, the drivers should have a rail of 46.5 volts, and the the input /Vas should have a rail of 52 volt.

Bye

Gaetan
 
Excelent that JBL..beautifull simple and clever design

Of course will sounds great...have lovely rail resistances.... beautifull bootstrapp, nice power supplies...interaction between them is minimum this way..... interesting complementary..... the compensation.

This one will sound very nice...... it is already inserted into my list..i will construct and listen to it.

Almost every amplifier sounds nice.... if you believe distortion is the annoying factor to sonics....perceive that a good amplifier can have 0.1 of distortion.... and excelent one will have 0.08 of distortion (numbers used as example folks..do not search for those number real life... used as reference only..to explain the idea only).... what this means when you connect those folks into a 3 percent distortion speakers.

The difference you will perceive, comparing the excelent with the very good will be minimum.... the speaker distortion will harm everything...so.... we exercise a lot constructing low distortion units... this is all effort..but really, this is only perfectionism.... the problem, the real problem, do not leave inside amplifiers...the problem creator leave inside the speakers.

There are other reasons, not only distortion that affect the result..because of that we are always searching, researching, trying to find the main causes and how to compensate them.

nice..thanks.

Carlos