Burning Amp BA-3

[Abx74]

Hi, my BA3 has started to sing few minutes ago.
My case is a 4U 300mm, Output bords are P-BACO, bias 0,2V and stable offset around +/- 0,2mV, dual mono 24V PSU.

I just check, my sinks are almost cold even after almost 45min. How high can I rise the bias ?

Damien

 

[Zen Mod]

50 to 55C on sinks

if PSU is up to task

 

[Abx74]

Thanks, and I think PSU will be ok (300VA and 4x47000 per channel).
Front end has its own dual mono PSU.

Damien

 

[MASantos]

Hi, my BA3 has started to sing few minutes ago.
My case is a 4U 300mm, Output bords are P-BACO, bias 0,2V and stable offset around +/- 0,2mV, dual mono 24V PSU.

I just check, my sinks are almost cold even after almost 45min. How high can I rise the bias ?

Damien

What value are your source resistors?

If 1ohm then you only have .2A running through each mosfet. At 24V that is under 5W per mosfet.

With 1ohm source resistors then you can at least go to .4V and have 9.6W dissipation on each mosfet. That should give you some heat on the heatsinks.

 

[Abx74]

Ok thank you. I use 1ohm source resistor. I will try 0,4V tomorrow and will see.

Damien

 

[bcmbob]

Hey Guys,

Been a while, but I have a question I hope is not bad form or impolite..

I have narrowed my many builds down to the liquid cooled BA-3 and the chip based Fremen Edition. I'm several versions behind on the FE and plan to do one more build. U.S. builders have no known (so far) domestic and/or economical sources for R-Core transformers. Performance improvement in that amp maxes out ~ 300 Amps. The units I have found so far have a shipping cost equal to or greater than the transformer itself.

Does anyone have info that would be helpful in an attempt organize a small GB of ~ 10 - 13 pieces? The source can be domestic or foreign as long as the total cost can be somewhat reduced.

If so, please PM me as I have no intent or desire to post here again on a non-Pass subject. This one is solely an attempt to access the enormous Pass community.

Thanks.....

 

[WalterW]

Hi Bob nice to see you back

 

[bcmbob]

Thanks Walter, had a few things to work through but i'ts to be back in the flow.

 

[qwertyl]

Anyone knows what is the purpose of R129/R130 and C102/C103 on this schematic?

 

[Zen Mod]

I know

 

[qwertyl]

I know

Would you like to share your knowledge?

 

[Zen Mod]

RC filtering/isolation of bias circuit from rails

 

[qwertyl]

RC filtering/isolation of bias circuit from rails

Thanks, that's what I thought. It was not part of the initial design and PCBs from diyAudio Store don't have place for these extra parts. So, I assume it is not strictly necessary, but rather nice to have...

 

[Abx74]

Good, BA3 is running for a few hours and it's really really a good amp.
It's quite different than a F5 but I find it better... but too much gain for me... I'd like to have a bit more than F5 so... 220 ohms for R13 on BA3FE board is a good value ?

Damien

 

[Zen Mod]

try it

 

[Abx74]

Hi, one more question,
can I use a 10ko potentiometer instead of the 50ko in place?

 

[Zen Mod]

besides both being nonsense , where exactly ?

 

[Abx74]

Of course, I mean for volume attenuation...

Damien

 

[Zen Mod]

if your source is happy driving 10K , why not

 

[Abx74]

So, another question: How could I know that?
My first source is a CD player (a Vecteur L4.2) with an AKM AK4395 dac and Sowter output transformers.
The second one is a Lenco L75S with a Pearl I phono stage.

Thanks.

Damien