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

[jacco vermeulen]

Sorry about the delay.
I have 40 years of audio history articles, i could open up a museum if i knew how to archive.

[jacco vermeulen]

Here is the AXL.
This one i built, using the 135/50.
Intended for 60% class A at 30V or in AB at 45V.

I added two Mosfets, with 1.8A bias at 30V it did 25 watts class A both in 8 and in 4 Ohm like the ML2.

Before building it in a chassis i had it on a wooden panel with dual powersupplies.
Switching from one channel in class A to the second in AB with a relay enabled me to compare.
First time i noticed Mosfets sound cold and hard in AB, warm and soft in class A, by the end of the 80s opamp/mosfet designs made this even more apparent.

[jmateus]

This schematic is the crescendo, right ?, published by Elektor in 1982...
For the time it was a good amplifier, I had a chance to build it, it's still
in my stach but already retired...
However it gave me many hours of pleasure....

[jmateus]

Of course I'm refering to the previous one, not the AXL....
How was the quality of the AXL, I've never had a chance to build it,
actually I was considering that when this discussion started...
How was the quality compared to the Crescendo?
Do you think It's worth to bother with it?

[sivan_and]

Hi Arne Karlson !!

WOW GREAT !!!! Scan..

Thanx a lot..

Sivanand

[jacco vermeulen]

Originally posted by jmateus
How was the quality compared to the Crescendo?

Sorry for answering this late.

I never liked the Crescendo, when it had just come out i thought about building it for my first diy preamp, but was advised not by my DIY buddy, a professional electronic with absolute hearing and 25 years more age and experience.

The AXL was quite good then i think, later i tried the 1985 RadioBulletin's 20 watt class A, it outperformed the AXL.
The 20-watter was designed by Menno van der Veen, now the transformer guru at Plitron and Amplimo.
The 20 watt class A is easy to find on the web.

I still think they are both worth the build because they were cheap and easy to build, Hitachi Mosfets were the easiest to buy power devices in the '80s.
My friend gave me 2 Toroidal transformers for no charge, in the 1980s i was a poor polytech student.
At the time i had to use autocad R10 to R13 to design PCB's, Xeroxing the layout on transparents or PCB-foil was easier.

The Crescendo i would not recommend, many state that it was notorious to oscillate, in '82 it was one of the few high-power DIY designs.
Its successor seems to be a lot better, after trying the 1st edition i never bothered.

I do not dare recommending it with the JLH on this forum.
But if, like me, you still have some Hitachi 48/49/50/133/134/135
Mosfets, it is fun to try them.
The best investment i made was buying a used Variac.

[sivan_and]

Jaac wrote: The best investment i made was buying a used Variac.

Modify it and use it as a torroid...I did ...
PS: 2nd hand variac's are cheap ,Remove the brush assembly..Wrap it with a good insulating material, then Wind the secondary over it..

[jmateus]

Hello Jacco

Indeed I have a similar opinion about the Crescendo and this is why
this amplifier never saw the mains voltage for a few years, until a
week ago! This is funny because when I plugged it in I was sensing
already a feeling of disappointment, phsycologically I was sensing
something wrong...And there it was, the sound that I forgot for a
few years was disappointing to me again...

Among several amplifiers that I built for so many years, I keep with
a certain sense of gratitude the big JLH, class A , that came into life
two years ago, and if I don't favour it over the tube amplifiers that
my "factory" produced, it is however my best solid state amp, inclu-
ding in this number another pair of JFET monoblocks that I built
according to a design of Mr. Slone which I considered a very good one...

Anyway, now comes the big slam! Have you heard about the class
D amplifiers? Or more specifically about the class T amps? I am
reading all there is about this technology and I am impressed....
I have a friend who already heard a class D amplifier and is saying
wonders about it...Woul I say the same? I don' t know...I'm waiting
and I'm hopping that I won't be disappointed.....

[ynotthea]

jacco.... please post mar 85 - AXL with 2SK134/2SJ49, schematic and pcb (if possible). I have built my AXL in 1997, and now it has problem with the 100mfd electrolit capacitor. It just blew...and I am afraid there's something wrong with other circuit parts. Unfortunately, I lost my magazine. Please help me out....my mail is ynotthea@yahoo.com
thanks in advance

tony
indonesia

[mosfetsound]

I builld 2007 in chinese Factory 20 pcs. Elektor Crescendo Amp for PA with IRFP9240 /IRFP240 Mosfets.

The Sound from Crescendo is more warm and natural

The mosfet amp is working very stable, but the sound from Class D is more powerful in bass and clear in High Frequency.