Another crescendo ME question

[kro5998]

I just picked up a crescendo ME on ebay. Didn't know it was a crescendo,just bought it for the case.

It has a Thell PSU,transformer and case.Also loudspeaker protection and on delay.

It sounds quite good, better than my Marantz PM17.

Has anyone tried to lower the rail voltagge on these amps?
Mine runs on 56Vdc and i want to lower this to 24Vdc with according higher bias.

Do i need to change resistor values to increase the current through diff pair and driver stage?

 

[anatech]

So if you like it, why changew the design ????
-Chris

 

[kro5998]

Another Crescendo ME

Hi, I just want to try how it sounds when i run it closer to class A, I was planning to use the case for a class A project but now i am curious how it will sound with more bias.

 

[amplifierguru]

Why not tweak up the existing cct for more.

 

[anatech]

Lowering the rails will change all kinds of things. Problem is you would have a different amp. Keep in mind that higher bias current does not mean better sound, depends on the design.

-Chris

 

[kro5998]

another crescendo ME

I understand that it might not sound better but you never know before you try.
I had a look at the specs of the output pair (2SJ201/2SK1530) and they can take 12A and dissipate 150W.
They only start to get lineair at 1A so increasing bias might improve the sound.

Kees.

 

[amplifierguru]

I did a commercial MOSFET pwramp using J115/K405's and it had low bias and unmeasurable distortion (on regular test equip).
Bring it on...

 

[anatech]

Hi Kees,
Watch your SOA curves for those and derate for temperature. Otherwise, go try it. You could run the drivers and outputs from an external supply to try higher bias levels. Careful not to overdrive the output stage but at least the rest of the circuits will operate as designed.

-Chris

 

[joensd]

Hi,
you could just up the bias of your existing crescendo of course.
Drawback is the very high power dissipation.
Maybe you should just try it to hear the difference and temporarily install some fans for extra dissipation.
http://www.diyaudio.com/forums/showthread.php?threadid=2033&perpage=10&highlight=&pagenumber=4
(post 35)

I tried 1A on my crescendo ME and it didn´t make a difference to me.
(which means nothing of course)

Running it from +-24V would assume quite a few changes so...

greets