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I need comments about "100W power amp. elektor april 1982"

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The 1982 Elektor amplifier must be the Crescendo.
I built it with left-over components, for comparing it with later Elektor amplifier models.
Though built by many people, it was said in the 80s to be a poor audio amplifier, nearly 10 years later i built it and had to agree.
The design is not very stable, and Mosfets IMO sound kind of nasty in AB mode. I still have a number of the mosfets used in that design. They have been off production for years, the shops that still sell those devices ask steep prices for replacement Hitachi's.

I thought the circuit needed a very high voltage powersupply for the rated output, 75 volts, so i used a small high voltage regulated supply for the front end, and a lower voltage powersupply for the output Hitachi Mosfets. It saved on dissipation, and i could use the toroidal transformers and electrolytes i had.
If it sounds better than the GC, it may comment more on the GC.
 
"100W power amp. elektor april 1982"

this should be the one :)
 

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Yes!...this one, ...John Mateus constructed this one and told me

That distorted the high frequencies.

I suggest him to:

- Reduce C7 and C8 to 10 picofarads
- Reduce C6 to 27 pf
- Remove 470pf from the input, unless you have one radio
amateur near you....less than 1000 feet,
- Include some capacitor (100N) in parallell with D1
- Remove the "distorters"; T5,T6,D2,D3,,R19,R17,R15 and R13
- Include a 1 uf non polarized capacitor from bias coletor to
emitter (t2)
- Increase C7 (input cap) to 2u2, use poliester, non polarized

Glue a cartoon (isolation) over a copper plate, the same amplifier size... and put it under the amplifier board, and connect this plate to ground...the amplifier likes to oscilate, that's the reason they put the "hinderburg", enormous "Aphocalipthic" capacitors from base to colector in the darlington units...they have big gain and like to oscilate....10 pf is enougth to block oscilation without destructing the wave shape.

I do not know if Mateus made those changes, he is a big friend o me...but the one is older than "mathusalém"....and may be forgot made the amplifier, and if that thing is an amplifier or an ashtray....ahahahaha...he will say terrible things to me.

Say terrible things...but talk with me..... if you forgot me friend, will be worst!!!

regards,

Carlos
 
I've build that one back then for 'pa' use. With some friends we supplied music at small parties etc. I built it with 500VA transformer and some huge caps (2*20kuF iirc), well at least huge for me in those days ;) It's not suited well for PA use, shorten the output and you blow the darlingtons. I did include a dc protection circuit that saved the speakers when it happend.

As for hifi use, i guess there are better designs (as for pa).
But it served me well back then. It was the only amp that could drive the bass units. Some commercial stuff we had could not (even when they were rated more watts). And i used a small 'cool-tunnel' with a big pabst in front, it could go full throttle all evening.

We needed someone at the fusebox to switch it on. The stotzes kept going off:D

The only modification i made to the schematic were two diodes 1n4148 from base of T1 to T2 (both in a different direction) to keep the input voltage within some limits.

Still have it up on the attic, sometimes i use it to make some noise:) :)
 
Elektor 1982

There was some confusion regarding this (or the other) amplifier.,

It turns out there are TWO diferent amplifiers published in 1982 by
Elektor, one is this with darlington outputs originally BDX66 and 67,
the later published latter in December 1982 and baptized as the
Crescendo with MOSFETS outputs...

In January 1983 Elektor published Accessories for the Crescendo
a circuit for power up delay, protection and so on... In November 1983 there was an article with Modifications called Crescendo revisited with a very small modification to prevent oscillation.
In May, 1984 Elektor published another version of the Crescendo
this one smaller, with less power, which I built too....I guess I
was a big fan of the Crescendo at the time....But I'm cured now!

I built both, the Crescendo first and still working after all these years,
however it wasn't the amplifier of my choice, the quality wasn't
that good but still occupies a big cabinet stached under a small
desk. What is it doing there? Nothing, taking space.....

However, a few years latter I built the one with darllington outputs
which doesn't have a name, probably because doesn't have parents
(é filho da p....), but in fact it is a much better sounding amplifier even
though it ended up again in a box full of junk.... A couple of months
ago, due to the fact that I had a different design (only aestheticallly
which made me not to recognize the amp), I built the SAME amplifier
and spoke to Carlos about it asking him to do an evaluation to the guy...
About that Carlos and I had a little quarrel because (again) I did not
recognize the amplifier on the simulator as the simulator didn't have
any darlingtons in its data base....

Well, to made story short I built the amplifier AGAIN and for that
I did another layout which was completely different from the first
one (how could I recognize the beast from the other animal?).
I did not change any value of components except the small input
cap for radio freq., and the amplifier is perfectly stable and easy
to adjust, supplies the power for which it was designed (around
50Watts) and finnaly is very pleasant to listen to. Nothing of that
Hi End nature, but very pleasant...

And this the history of the atribulated and already famous Elektor
amplifier...Do you guys want to know something? Even though
it doesn't have a reputation of certain amplifiers that everybody
is talking about as being this or that, not to speak about the ASKS
more elaborate ..or less definitions, this amplifier is definitelly a
WINNER. End of story......
 
AXL amplifier

I forgot to add that in March 1985 Elektor published another amplifier,
again with MOSFETS outputs (same ones obsolete now, $18.00 a pop)
called AXL amplifier, designed to work class A, B or AB, depending on
the power supply and bias...
At the time the 2SK134 and 2SJ 49 were $4.50 each.....

This is a very interesting design, different topology than the previsous
ones (crescendo and derivates), with the possibility of being constructed inexpensively mainly for electrostatic headphones, for
an active speaker system or a small hi-fi installation.

The input stage featured a dual symetric differential amplifier formed
by 4 cascode pairs... I haven't seen this kind of technique since that
publication, this is why is interesting to me....

This one I never built, but....I'm thinking, may be I'll build it now!
 
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