Hiraga Le Monstre

[Arkless Electronics]

Just done one of these for a customer and must say it joins the ranks of the super amps in my personal list...
VERY good sound indeed and maybe the all time winner so far on transparency and instrumental timbre.
In spite of only 8WPC and rather high output impedance (valve amp type damping factor) the bass is also superb. I had my doubts about it, higher THD than I would like (about 0.5%), poor damping factor etc... but it more than lives up to its reputation. Magnifique Monsieur Hiraga

It came to me as "some sort of diy build" but every mistake that could be made with the PSU and grounding, had been made.... it gave 1W for 1% THD and max power of 2W for about 10% THD and all with slight mains hum as it arrived. The customer was not the builder and I won't embarrass the actual builder... no names no pack drill

New dual mono PSU's, pair of 120VA transformers (for 8w each output power), dual pi filters and 198,000uF smoothing capacitance per channel, grounding and wiring layout all redone, slight changes to resistors on amp PCB's to compensate for the devices that had been used not being particularly well matched (if I hadn't done this THD would have been more like 5%!) and job's a gud 'n

 

[Stunsworth]

Just a quick note to say I enjoy there build/repair threads.

 

[sq225917]

Any pics of this rare beast jez?

 

[Arkless Electronics]

Any pics of this rare beast jez?

 

[Snufkin]

It has some serious heat sinkage; is that necessary or just the case it came in?

 

[Snufkin]

I suppose that leads to another question: Can you over cool components?

 

[Arkless Electronics]

It has some serious heat sinkage; is that necessary or just the case it came in?

It's just the case it came in. As is the mains switch, speaker sockets etc. Yes with those heatsinks and only 8W class A it barely gets warm!

 

[sq225917]

Sink those trannies directly and itd be happy in half that case with degree c/w to spare.

 

[martin clark]

A 'Monstre' is one of those builds on my 'to-do' list - it's only been there about 15yrs...
Deceptively-simple schematic that has some critical dependencies, it seems to me.

 

[Arkless Electronics]

A 'Monstre' is one of those builds on my 'to-do' list - it's only been there about 15yrs...
Deceptively-simple schematic that has some critical dependencies, it seems to me.

Very true Martin

 

[S-Man]

Just resurrectd my JLH 10W class A.
I wonder how the Hiraga would compare in terms of SQ?

 

[Arkless Electronics]

Just resurrectd my JLH 10W class A.
I wonder how the Hiraga would compare in terms of SQ?

From my memory of the last JLH I heard the Hiraga is in a different league. So may things can come into play though that i'ts impossible to say that all would be like this. When high open loop gain and big NFB are eschewed then choice and matching of devices becomes critical!

 

[S-Man]

Interesting! I might have to lash one up.
The JLH is "close, but no cigar" for me.

 

[Arkless Electronics]

Interesting! I might have to lash one up.
The JLH is "close, but no cigar" for me.

Yeah about the same here... WAY better than any Naim or Quad or other "normal everyday class A/B high feedback amplifier" but not in the very top rank. I wouldn't be surprised if minor tweaking could get it right up there though.

Be aware the the Hiraga is much more difficult to get right than its simple circuitry may imply...

 

[keith1962]

Jez,
This amp is sounding very nice now it is back in the system. Got it playing from 1800 Hz up powering BMS TPL150s in my active system and it is indeed as good as you say.
KR
Keith.

 

[Arkless Electronics]

Jez,
This amp is sounding very nice now it is back in the system. Got it playing from 1800 Hz up powering BMS TPL150s in my active system and it is indeed as good as you say.
KR
Keith.

Thanks Keith and I'm really pleased it's delivering the goods in your active system. I'm missing it in mine already!

 

[df_genius]

Nice work there, have you got any experience of the "Super" Class A Hiraga? I've got some of the Jims Audio boards with the on-board front-end regulation somewhere. What transistors did you use in that build - the original schematic looks to specify "Y" grade 2SK170/J74 which aren't exactly easy to source

 

[Arkless Electronics]

Nice work there, have you got any experience of the "Super" Class A Hiraga? I've got some of the Jims Audio boards with the on-board front-end regulation somewhere. What transistors did you use in that build - the original schematic looks to specify "Y" grade 2SK170/J74 which aren't exactly easy to source

Is that the "20W class A Hiraga" I assume? No I've not tried that. The boards came to me already stuffed and although all the "correct" devices were used they were not particularly matched... if at all.. the output devices for example are not the same make! Hence I had to do a little jiggery pokery with some resistor values to get it to correctly balance and to give reasonably low distortion figures.

 

[JemHayward]

Please someone remind me I really don't need another power amp, but...

How much would it cost to build one of these (approx) and could someone with a multimeter be able to get it working properly? I have a big heatsink that I have had 'in stock' for about 40 years and I feel I should put it to use...

 

[Arkless Electronics]

Please someone remind me I really don't need another power amp, but...

How much would it cost to build one of these (approx) and could someone with a multimeter be able to get it working properly? I have a big heatsink that I have had 'in stock' for about 40 years and I feel I should put it to use...

Cost largely down to casework and PSU choices... Although originally a DIY project in a hi fi mag this is not an easy amplifier for the DIYer. It looks very simple, and it is, but because it has such low NFB and non existent PSRR virtually everything about it is pretty critical. I couldn't have got this one working correctly without a low distortion oscillator, THD analyser and oscilloscope. It would be easier for the beginner to build several Hackernaps than one of these.

Semiconductors for it are hard to find and if I was building one for myself I would use alternative and slightly better devices for everything other than the input FET's which have no real equivalents other than the fairly recent replacements from Linear Systems which are not cheap. If all devices were matched well enough then you could probably get away with less test gear BUT matching them properly is not in itself easy... you will need to build matching jigs if you haven't got proper equipment such as a Tektronix 576 curve tracer. You can't just use the Hfe range on a multimeter as output devices need matching at around 0.7A and others at say 20mA but most meters will be a fixed 1mA.
If going for the ideal matching this also gets expensive as you need to buy lots of devices in order to pick only the best matching ones...

The lack of PSRR means that the PSU must be free from ripple... a PSU that was silent on say a Hackernap would probably cause very audible hum through the speakers if used for this. Those are 33,000uF caps in the photo above and they form two pi filters with the small resistors....

However... within its 8WPC rating it may well be a new leader in "the best amp I've ever heard at any price" league table!

I'm tempted to design (OK already have...) my answer to Le Monstre, with more power, say 20-30WPC, different topology but same low feedback etc and I probably will build one for myself.