Crescendo ampilifier elektor1982

[PMik]

lol! sry! for that must have had some dirty toughts while posting

[trilbies]

Howdy all, I have just registered to this Forum as an ex-crescendo builder and user. I built this amp as a project in 1984-5 and it worked great, nice to see that the ME integrated most of the protections I had built into it as a result of experience and trials. The very first power up worked well, then it went down hill. It oscillated on one side and a plate over two of the Mosfet got rid of it, i can't remember which ones though, anyhow, I have only the transformer (toroidal) and the two heat sinks left as a souvenir, thinking of rebuild it one day. This day is coming back now.


after reading about it and it's oscillation problems, I think I might go for another kit. Still using what I got, so my homework starts here.

As an electronician by trade, I made a complete dossier of the kit, I will try to put it on line when I get the time and willingness to do it. Unfortunately I haven't got any photos (AFAIK) of the thing. I am still working ona another project at the moment which is not Audio related (web cam system)

So that's all for the long winded post and I hope that I will be able to contribute/get advice from this Forum.

All the best for 2012!

G.

[Kay Pirinha]

Hi,

I've also built this amp the same time as a stereo version, and I've integrated all supplements from Elektor. I never had any problems with oscillation, but there's some hum I couldn't get rid of. The amp still works fine, meanwhile my younger son has got it.

Best regards!

[wengtech]

Hi im newbie here...
need to ask the expert, is this audio circuit worth to be build?
http://www.tasel.net/images/200W-MOS...58-diagram.jpg
are there any suggestion from you guys...
some said this is a pure class A and better than crescendo, what do you think.?

[Bensen]

"some said this is a pure class A and better than crescendo, what do you think.? "

Looking at R18 /820Ohm, it looks like it's high biased yes.

The schematic:
Cascade complementairy input with beta enhanced VAS. For Drivers I would select other parts. I would run the VAS at minimum 20mA, the BF469/470 would not handle the dissipation.
It's a Non Feedback amp, I personaly have no experience in non feedback amps.

It doesn't look like an expensive design, build it, and let us know your opinion. The BF469/470 will be very hard to get these days, you can use 2SA1209/2SC2911 as replacement for example.

[franzm]

Strange schematic, B-E juctions reversely biased at 25V, transistor polarity (gender) doesn't match with supply voltage polarity....

[wengtech]

Originally Posted by Bensen

"some said this is a pure class A and better than crescendo, what do you think.? "

Looking at R18 /820Ohm, it looks like it's high biased yes.

The schematic:
Cascade complementairy input with beta enhanced VAS. For Drivers I would select other parts. I would run the VAS at minimum 20mA, the BF469/470 would not handle the dissipation.
It's a Non Feedback amp, I personaly have no experience in non feedback amps.

It doesn't look like an expensive design, build it, and let us know your opinion. The BF469/470 will be very hard to get these days, you can use 2SA1209/2SC2911 as replacement for example.

Originally Posted by franzm

Strange schematic, B-E juctions reversely biased at 25V, transistor polarity (gender) doesn't match with supply voltage polarity....

thanks for responses...

btw this is the pcb layout:
http://www.tasel.net/images/200W-MOS...nent-layer.jpg

and i think there are lots of improvement at the layout (diff from the schematic)

i also never build a NFB power amp, but when i saw the pcb layout
i am interesting to build one.

so now, by looking at pcb layout, are there any possible error from this design?
or are there any improvement i should make...?

from the schematic it use electrolite capacitor for the input, as i know this should be better to use a non polar rather than polar cap... is it?

[Art M]

You really need to supply a correct schematic which corresponds to the layout of the board. Trying to evaluate what you have presented is a waste of time.

[wengtech]

Originally Posted by Art M

You really need to supply a correct schematic which corresponds to the layout of the board. Trying to evaluate what you have presented is a waste of time.

the layout and schematic basically match, there are only a few addition of 1 set mosfet (2sets at schematic, but 3sets at pcb) and also increasing the power supply capacitors (2 100uF/63v at the schematic, but 12pcs 470uF/63v at the pcb)

thats all no else.

[Juergen Knoop]

there are lots of junk circuits on the net. Build something you know that has been build succesfully by others.