Hiraga "Le Monstre"

Got both channels working perfectly. Biased at 0.98A. Put trimmers in one channel to allow both channels to be matched perfectly. Offset less than 15mV and sounding damn fine on my test speakers.
Heatsinks are staying at room temperature after a short run time

Will post some photo's later when I get a chance.

Final build out and test in the main system hopefully by Sunday.

Shoog

Will you to use buffer's batteries in power supply?
What about noises level on 50 Hz and 100 Hz?
 
Will you to use buffer's batteries in power supply?
What about noises level on 50 Hz and 100 Hz?

I am getting no noise/hum at the speakers at the moment - but that may change when it goes in the main system. The power supply is a simple capacitor and cap multiplier one and there will be no batteries going in - ever.

Transistor line up is:

2SJ74/2SK170
BC550/BC560
BC327/BC337 (with TO92 heatsinks)
2SC2921/2SAQ1215



Shoog
 
Some photo's.

Shoog
 

Attachments

  • Power supply.jpg
    Power supply.jpg
    482.6 KB · Views: 981
  • Le_monstre.jpg
    Le_monstre.jpg
    486.2 KB · Views: 942
nice amp you got there !. I have some small problem with mine..when one channel source connected no hum, when second added - i have small 100 hz hum spikes on scope ( not so audible, therefore i don't take any measures to eliminate hum)...DIY PCB from internet similar to Hiragas original PCB. I think there is problem with local decoupling...
 
Last edited:
nice amp you got there !. I have some small problem with mine..when one channel source connected no hum, when second added - i have small 100 hz hum spikes on scope ( not so audible, therefore i don't take any measures to eliminate hum)...DIY PCB from internet similar to Hiragas original PCB. I think there is problem with local decoupling...

It maybe that there is a slight impedance difference on the earths of your two channels. I took extra special care to use heavy gauge ground wire with all returns taken to a single star ground through equal length wires. Star ground earthing has never let me down on any build I have used it on.

Shoog
 
I am getting no noise/hum at the speakers at the moment - but that may change when it goes in the main system. The power supply is a simple capacitor and cap multiplier one and there will be no batteries going in - ever.

Transistor line up is:

2SJ74/2SK170
BC550/BC560
BC327/BC337 (with TO92 heatsinks)
2SC2921/2SAQ1215



Shoog
Better to look noises in RMAA or Spectra+. Levels of 50 Hz and 100 Hz must be not bigger than -100 db (-110...-140 db in ideal).
 
So i finally got the beast commissioned. There were a few issues with the DC protection circuit but they got ironed out enough to risk it on the main system.
Good and bad news, it works and it sounds great. very clear and detailed without sounding fatiguing.
The bad news is it hums, well less a hum and more of a buzz. I scoped it out and really couldn't find what was going on. About 10mV of noise - but really it was everywhere and I am not at all certain that beefing up the power supply would have any impact at all. Its quite a bit more sensitive than my existing valve amps (which are already very sensitive). Ideally I would like to knock back the sensitivity a bit as at the moment it wont be compatible with either of my pre-amps.
So good and bad and a little way to go before I can put this one to bed.

Shoog
 
After a bit of wire tidying I have got both channels quiet. On a hunch I swapped over the input cable and the residual hum moved channels - which shows that the problem is located in the preamp. Don't yet know if I will be able to close the case and maintain hum free operation.
Going to knock back the sensitivity with a resistor divider at the input. 200mV sensitivity is 10x what is required with modern components so this is ridiculous as it stands.

Shoog
 
So I have finally got the hum/buzz down to about 1mV which is just about acceptable for general use in my system.
I rebuilt the power supply to have a single star ground which shaved a few mV of hum off.
I redressed the earth return wires to take them further away from the power transformer.
I changed the earthing at the RCA socket such that the socket earth went to the star ground and the internal signal wires shield terminated at the circuit board earth - helped a little.
I placed snubbers on the secondary of the transformer and the diodes which cleaned up the supply lines a lot - but not much impact on the buzz.
All of these changes cleaned up the hash on the output a lot, with each modification producing a flatter sharper scope trace - but there was still a significant first quadrant spike of about 3mV which would not go away. It turned out that this was power transformer ringing produced by charging spikes. I decided to place 0.5R resistors on each of the secondary legs which killed about 2mV of hum. So I have about 1mV of spike left, and I feel that this can only be cured by taking the transformer out of the case, which I am unwilling to do. I may try placing a ceramic snubber on the first cap to see if it bleeds off any more spike - but I doubt it will.

Sounding fine and clean and extended, with a nice rounded presentation. Its now become a keeper.

Shoog