Classe Audio CA-400 & Obtuse Bias Procedure (scat included)

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Jump to Latest
EchoWars

EchoWars

Member
Joined 2003
I have this amp and I'm checking it out for a friend. Works fine, but we both want to know that bias and offset are good. Offset is no problem, but I've never seen such a bizarre bias adjust procedure. 24 hours warmup? Calculation formula? Reference to parts that don't exist (R8 and RV1)?

Anyone want to look at this and see if they can make heads or tails of it? GlenB has some experience with these amps, I think. Hopefully he will chime in...

https://www.yousendit.com/download/OHo3UWV0WkI4aU94dnc9PQ

(link good for 7 days or 100 downloads...best I can do)
 
Last edited:
S

Sebastiaan

Member
Joined 2004
soundevolution.nl
carlmart said:
A very interesting circuit. Seems quite well protected.

The PS is assembled with 9 sets of 4700uF caps. If the power is 400w/ch into 8 ohms, then that would need some increase.
Click to expand...

Well, most multi-watt PA amplifiers have no more then 2x 10000uF

Agree a very interesting circuit. The fact that there are no base stopper resistors at the bases of the power transistors. Also the fact that there is no output inductor/resistor in series, just a parallel Zobel to ground. I did read some horror stories however about burning CA400's wonder if this had something to do with it...

Ps: The soft-start circuit, and on/off latch switch is easy to copy for us DIY-ers and will work very well.

With kind regards,
Bas
 
G

Glen B

Member
Joined 2005
All the Classé legacy models (DR-00, CA-000 and CA-001 series) share the same lack of base stopper resistors and output indictor/resistor. I haven't heard any stories of Classé amps burning up en-masse. I've been running a CA-300 into a fairly difficult speaker for the greater part of 14 years, and it has been very stable. The CA-300 circuit is identical to the CA-400, just with one less output transistor pair, and smaller power supply.
 
Last edited:
M

Mercury3

Member
Joined 2011
Hey I realize this is an old thread but I just obtained one of these amps used and I have a question.

Mine runs much cooler than what I'm use to is this normal for the Classe CA-400? My Nakamichi PA-7's run much hotter and those are correctly bias'ed.

I'd like to check the bias on my Classe if someone could provide me with the procedure too I'd be much appreciated.

Thanks, Mark
 
B

BarSall

Member
Joined 2013
I have a CA-400 and would like to replace the 2 switches on the back panel along with the signal input relays. My amp has some intermittence on the input which clears for a few days if I toggle the 2 back switches. Any idea how the steps needed to get at the signal input board in order to change these components.

Thanks Barry
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Top Bottom