DIY Audio Projects Forum

Jean Hiraga "Le Monster"
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Author:  mwhouston [ 15 Feb 2018, 20:47 ]
Post subject:  Jean Hiraga "Le Monster"

I thought I may have started a thread with this amp but can't find it. I populated the Hiraga brds. 20years ago but then they just sat around. Amps now finished. Meant produce 8W of pure class A and is a DC amp. Only four stages. A couple of FETs split the signal then each side amps one half.

Only 80,000uf of storage where many farads are suggested. On my 19ltr 2-ways and sounds great. Stacks of low forceful bass and fully-sick-3D soundstage. Needs a few days burn in but already very enjoyable.

Author:  Gio [ 15 Feb 2018, 21:00 ]
Post subject:  Re: Jean Hiraga "Le Monster"

Good work Mark. I'm glad I'm not the only one who has populated boards sitting around unused.

Schematic and pcb from original Le Monstre article are here: ... e-Monstre/

Author:  laurie54 [ 16 Feb 2018, 02:30 ]
Post subject:  Re: Jean Hiraga "Le Monster"

I have built and use two of these amps. One for my tweeters and the other is for background spkrs. I loved them from the first i heard them. And i was lucky enough to get 20 each of the original 2SK170 and 2SJ74 at a cost of $20.Can. Shortly after they disappeared and then showed up in places for amounts like $46. for one set of 2 x 2SK170's. Then the knock offs. Gees hard to keep track but they are slowly being found / manufactured again. TG! The 2SK170 is very popular.

Author:  mwhouston [ 16 Feb 2018, 05:21 ]
Post subject:  Re: Jean Hiraga "Le Monster"

I have a number of 2SK170s.

Author:  laurie54 [ 16 Feb 2018, 13:38 ]
Post subject:  Re: Jean Hiraga "Le Monster"

The 2SK170 are popular in many projects. On another note Mark, if i find it, i have a phono preamp that used, I think 12 BJT trans for the front end (per chnl). It is dead quiet. I also built the JFET RIAA phono pre that you built with batteries for supply. Both pre's are dead quiet but i didn't have the time to A/B the two types as far as sounding but both work as well as the other. I moved and they are now in boxes,,,,,somewhere here.

Author:  mwhouston [ 16 Feb 2018, 17:29 ]
Post subject:  Re: Jean Hiraga "Le Monster"

All my Le Pacific and Boozehound MC stages use this FET.

Author:  mwhouston [ 25 Feb 2018, 17:50 ]
Post subject:  Re: Jean Hiraga "Le Monster"

All finished. Had awful problems with the PS and then getting DC offset down but all good now. I have been enjoying this amp for over a week and find it very natural as did a friend on his gear. Relaxed sound with good solid bass and balanced mids to treble. There is some nice warmth in the mids which I think helps with the relax feel this amp exudes. Most happy but even happier to sell it on to fund next projects.
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P2253674 (800x600).jpg

Author:  sfltrack [ 06 Apr 2018, 13:55 ]
Post subject:  Re: Jean Hiraga "Le Monster"

How do you set the bias? I'm just about ready to hook up my boards and where do I measure the voltage?

Author:  mwhouston [ 08 Apr 2018, 02:59 ]
Post subject:  Re: Jean Hiraga "Le Monster"

Make the bias pot a 25 turn. Bias is hard to get even close but can be done. Even with a 25T its hard.

Author:  ILoveHiFi [ 24 Apr 2018, 17:17 ]
Post subject:  Re: Jean Hiraga "Le Monster"

To change the bias current increasing the reistance of both 1k resistor will do the trick. higher reisstance means more voltage drop accross the 1r 5w resistor and V=IR means theres more current.
Making the 5w resistor 0.5ohm will doubble the bias current approx. Bias current will variy more due to temp changes though.
This reduces the voltage drop during load accross the resistor and can increase the max output power slightly

Making the 1k resistor to 560ohm will take you back to nearly orignal bias current however the open loop gain is nearly halfed to distortion is nearly doubbled in theory. Slew rate is higher though, the amp becomes faster due to less feedback and lower output impedance so internal capacitances of output stage can be charged faster

Changing the 100ohm pot to 50ohm would also approximately doublle the bias current, theres arround 0.05 to0.5v (VGS of fet gate is 0v) at the source of the input fets typically.
The output is like ground so theres about 0.05to 0.5v accross source of input fet to output which sets bias of mosfets.
100r pot should also be multi turn so fine tirmming can be done

Open loop gain of amplifier can be increased by groudning the base of 2sc1775 and 2sa872 to ground via a 12v 22-220uf cap. this allows the input to be fully cascoded and increase gain. Scope testing is required to check for oscillaitons with and without 8r load with this mod. More gain means more feedback, more feedback means higher chances of high frequency oscillation(parasitic osc)

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