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Update for Elektor Crescendo Power Amplifier 1982

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#161
Jet02 said:
🙂In the past , i studied and built many sort of V-Mos amplifier, so I know very well the original Crescendo and i have enjoyed a long time the mini-crescendo too. About high frequency, it is easy to find where to damp it it without altering the audio signal path.
🙁Sorry for my bad English , i am French and i live near Paris.
Later i shall try to post a picture to show a good way you to cure HF issue.
😕How is it possible to send a picture in this forum?
Click to expand...

Jet02 said:
I found how to post with documents...!...
How is it possible to send a picture in this forum? Just use "go avanced" instead quick reply option...
I shall use it later to show a good an d easy way to cure HF.....
Best regards!
Click to expand...
Attach you pics and other docs
How to attach images to your posts.
 
#165
danne_linkinpar said:
I have problem whith oscillations in my Crecendo 250W mosfet, it oscillations is about 4 Mhz??
Click to expand...

Sorry for the late answer, but the problem are the resistors between the source connectors and the speaker connector. If the joint between the source connectors and the PCB is not good enough, you have additional resistors here, which will cause instability. Secondly, consider a low pass filter on the input. 680 pF and 3.3 kOhm are working fine.

Best wishes, Holger
 
#166
Crescendo Realization with FMMECh PCB for TO3

I want to share my recent rebuilding of my crescendo, with the TO3 FMmech boards. For the moment, all is mounted in a temporary wood board, but i'm in the way to choose a decent aluminium enclosure to finish this project. Absolutely no oscillations at any load, dead silent and well performing wiht my stereo set!!
 

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#178
hello scafas,

here is my modification done 2 years ago, according Rays page. Left side is the orignal , which was built 1985.
On the right side you see the modified board with Dale CMF 55 resistors and mica ,Panasonic FC, WIMA MKP and Frolyt bipolar capacitors. Also MJE350 and 340 as driver transistors and most important the source resistors as Metal Band resistor MPC 74, no wirewound resistors.

BR
Günni
 

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#179
schillg11 said:
hello scafas,

here is my modification done 2 years ago, according Rays page. Left side is the orignal , which was built 1985.
On the right side you see the modified board with Dale CMF 55 resistors and mica ,Panasonic FC, WIMA MKP and Frolyt bipolar capacitors. Also MJE350 and 340 as driver transistors and most important the source resistors as Metal Band resistor MPC 74, no wirewound resistors.

BR
Günni
Click to expand...
other mod on Rays page:
- Use poor induction resistors for R27 to R30
- increases C16 from the Zobel network to 100nF and uses a MKP
- isolate T8 and T10 from the heat sink and connect them to zero
- Mount 22k load resistors for T8 and T10
- T8 and T10 may be needed. they are replaced by MJE340 and MJE350
- place a 100 nF capacitor on P1
- reduce the polystyrene from C2 to 100 pF
 
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