Arashimuro Fishmalt, That is a very impressive case. Can this soft start circuit be used with other amp kits too? It was more difficult, but it seemed to turn out! The gallery is at: It is always impressive to see the variety of different designs that people come up with. In part, this is due to its completely symmetrical design, which was in fact an unusual feature at that time, but unquestionably it is mainly due to the use of power MOSFETs in the output stage. Good luck with the pre-amp.
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It has been proven to be good sounding and reliable over the years, even though I must admit a little tricky sometimes. In the posts in the www. The Crescendo is still very competitive I think, and should be a contender to the Hall of Fame of diy-amplifiers, if there is one! My guess is that almost everyone who built this amplifier has or had some problem with high frequency oscillations and perhaps some hum induced from the power supply.
High frequency oscillations can be hard to get rid of. There have been some tweaks published in the Elektor I have tried, beside some that I have collected from postings on the Internet.
My amplifier had a lot of high frequency oscillations, and the RC-chain on the output went up in smoke. But the solution was easy; a small capacitor across the bias resistor solved it!
I think it should been there in the first place. It is common practice in many costructions. So, here is a listing of proven solutions to kill or reduce HF oscillations: 47nF in parallel with the bias resistor P1. This killed all mine HF osc. Using non-inductive source resistors RR30 is recommended by Elektor and have worked for others.
Put 1 nF between n-channel source resistors R27 and R28 is also recommended by Elektor. This is a solution used in various builds for this reason.
This may improve sound quality. Or not. Active DC regulation for lower DC offset. Could also improve sound quality. This is used in many constructions.
Different feedback paths for LF and HF signal could improve stability. This is used in other constructions. I still have some problems with hum, and I have rewired a lot a tried many other things. Nothing helps. To compact housing perhaps? Left and right channel does not hum equally either, and it is very irritating!
On the other hand, one of the channels have a defective mos fet, but still works Anyway, I think this amplifier deserves another decade using some of the tweaks. I will be happy to receive comments and help to update the reference columns with links to diyAudio forums.
Elektor Mini Crescendo (1984)
Download PDF UK 04/2001
Crescendo Millenium Edition