L’audiophile Le Classe A 30W — diode bridge replacement and possible sonic changes

[Jonathan1983]

Hello everyone,

I am the owner of a L'audiophile Le classe A 30w power amplifier, built by Jean Hiraga.
I would like to ask for some help identifying an original component and understanding a change I noticed after a recent repair.

The amplifier developed a fault, and the technician found that the main diode bridge rectifiers in the power supply had failed. He replaced them with newer, higher-current bridges. 
According to the technician, the original diode bridges were working quite hard and becoming very hot. He therefore chose stronger replacements, mainly to give the amplifier more safety margin and improved reliability.

The nominal amplifier supply rails remain approximately:

+25v / 0v / -25v

the diode bridges were the only components replaced during the repair.
The technician sent me a photo of the new bridges that were installed, which I will attach to this post.

Since the repair, I have noticed a clear change in the way the amplifier presents music.
I would not describe it simply as a different sound signature or a warmer/brighter character. the changes I notice are related to:

• scale
  
• depth
  
• soundstage width
  
• tonal balance
  

I am therefore trying to understand whether the replacement of the rectifier bridges could plausibly explain what I am hearing.

The technician is also going back to the workshop to look for the original bridges that were removed, so hopefully they can still be found.

if someone here have schematic, service manual, parts list restoration or any info from someone who has worked on this amplifier, I would be very interested.

what I am trying to understand is whether the behavior of the rectifier itself under the real operating conditions of this particular Class A power supply can differ enough to effect the amplifier downstream.

If anyone has experience with this particular amplifier, or with restoration of older Class A amplifiers and their power supplies, I would be very grateful for any information.

Thank you,
Jonatha.

[Jonathan1983]

I attached some photos

[Jonathan1983]

Ok,
My technician found the exact model of the original diodes bridges

the original: pb86
the new ones: kbpc3510

the problem is can't find any sources how has the pb86 in stock.

if someone can help in that regard I will be very grateful.

[Wagtbtoobz]

Hi,
Just avoid those sh... ch.... fakes... try to find a genuine International Rectifier or , better, Semikron , and push to 4 stacked // of them...

[calculette]

hello,
This is a Class A amplifier so the courant is high at the output of the rectifier and then it needs big capacitors to eliminate alternative voltage and make continus.
When those capacitors ares old (many years) a shock when the rectifier fail can destroy them.
You can look with your Metrix on alternative voltage if the continus voltage 25 volts do not contain to much alternative few mV would be correct but not more 0,5 volts.
With good capacitors the importance of the rectifier is not significative.
sorry for my english
Denis

[calculette]

With 4 batterys 12 volts you can have a perfect direct current at 24 volts but it gives only 4 hours nusic befor recharging    

[AndréJ]

Hello

On all this series of Hiraga amplifiers, 8W, 20W, 30W, a fully regulated power supply with integrated or discrete topology gives very good results, without the problems of big capacitors or batteries...
They are really superb with regulated power supplies...

Best
Andre

[nicolasd]

Français s'il vous plait, ce n'est pas un forum anglophone !

[raoul]

Français s'il vous plait, ce n'est pas un forum anglophone !

non, ici on accepte toutes les locuteurs, du moment où ils arrivent à se comprendre.

[nicolasd]

Français s'il vous plait, ce n'est pas un forum anglophone !

non, ici on accepte toutes les locuteurs, du moment où ils arrivent à se comprendre.

Bah c'est bien dommage ...