Crescendo ampilifier elektor1982

[lineup]

Here is a better ORIGINAL Crescendo 1982 schematic scan.
I found the link by searching this forum.
http://img347.imageshack.us/my.php?image=cres1c9wn.jpg

I hope it uses same refering label numbers for resistors as danne uses.

 

[danne_linkinpar]

I test my Crescendo today again and i have change the resistors and tody the R15,R16 and R9 gone upp in smoke why, sombody now???

 

[Jay]

hi danne,

may be you put 12V zener in place of 3v9 zener? They look similar. The 12V one is slightly fatter, and has higher series number.

 

[danne_linkinpar]

I hav eproblem whit oscillations in my crescendo somone that can help me+?

 

[Bensen]

Make sure that your gate resistors are as close as possible to the gates of the MOSFET's! Put a ceramic cap of a few 100n between the + and - rail as close as can be to the FET's.

 

[AndrewT]

Hi Bensen,
do you mean drain to power ground? or +drain to -drain?

 

[Bensen]

Hi Andrew,

No I ment: just placing one ceramic cap between the power rails. And this as close as possible to the MOSFET's.

 

[AndrewT]

Hi,
just as done with opamp bypass!
Never seen this on a power amp.

 

[refosk]

I had built the original crescendo from 1982, it works fine with low volumes but when I volume it up I get strange distorsions heard like brp,brp,brp when bass is playing. And this bass distorsions are very loud. Can someone sugest me what to look for?

 

[joensd]

Maybe P1 is dirty/corroded and so bias current might not be set properly.
Check bias current and if you set it up turn the pot slightly forth and back (that sometimes is enough to "clean" the contacts;
if it´s too bad and current alters, change it)

Otherwise check all voltages and report back the ones that are not at least similar to the original schematic.

 

[danne_linkinpar]

Have you a photo of your amp?

 

[refosk]

I can set bias current without problem and the voltages are near that one in the schematics. Is it possible to be some kind of power supply isue? I have two 300W toroids one above other. It is difficult to find a error for me because I don't have an osciloscope.

And danne_linkinpar, sorry I don't have any pictures.

 

[danne_linkinpar]

I have bulit that and it been finish about one week now and my works fine even with high level!

Photo

http://www.minhembio.com/forum/index.php?act=Attach&type=post&id=20074

 

[Bensen]

I had built the original crescendo from 1982, it works fine with low volumes but when I volume it up I get strange distorsions heard like brp,brp,brp when bass is playing. And this bass distorsions are very loud. Can someone sugest me what to look for?

I had just the same experience as you. Only with high power bass music.
You should try something, touch the housing of the MOSFET's with your hand, when you hear these distortions. When I did that, the distortion dissappeared. --> this was oscillation caused by the wirewound source resistors.

Greetz
Ben

 

[AndrewT]

Hi Bensen,
when you touch the FET case and the oscillation stops, what electical mechanism is stopping the oscillation.

Can this be used as an alternative form of stability improvement?

I have seen reference to adding a cap from FET heatsink to ?either ground? or ? Vrail? to cure an oscilation. Would this be the same problem?

 

[danne_linkinpar]

How big current do you use to the mosfets?

 

[Bensen]

Hi Bensen,
when you touch the FET case and the oscillation stops, what electical mechanism is stopping the oscillation.

Can this be used as an alternative form of stability improvement?

I have seen reference to adding a cap from FET heatsink to ?either ground? or ? Vrail? to cure an oscilation. Would this be the same problem?

electical mechanism. I have no idea?

That could be also a cure to stop oscillation, but I never tried it. And I don't have problems anymore.

How big current do you use to the mosfets?

I think it is 100mA/mosfet

 

[danne_linkinpar]

Have you try to increase the current to 250mA/ mosfet,Bensen?
Bensen did your amp works fine?

 

[PMik]

Bonking this tread on top ...

We are some taking new interst in this amp

 

[GK]

Bonking this tread on top ...

We are some taking new interst in this amp

I think you mean "bumping". Bonking is what you're traditionally supposed to do to your wife for the first time on your wedding day.