Hiraga "Le Monstre"

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#1,201
OK here's an update. I have it playing. I got the first channel working but the second was giving me trouble. I had used KSA992/KSC1845 for the four small transistors. 2SK246GR/2SJ103GR and MJL21193/MJL21194. On the second channel I decided to experiment since I needed to pull the devices to figure it out. So on that channel I installed 2SK2240/2SA970 in the front and BD139/140 in the drivers and the 2SK246GR/2SJ103GR for the JFETs. MJL21193/21194 in the output. I also received some 500R trimmers so I installed one in the second channel. I've got some 399R resistors in the bias slots but I'm only getting about 500mA bias.

The sound is decent. A little lacking in bass. I have it hooked up to my A/B setup and comparing it to a VSSA. They are pretty close in the treble but the VSSA is just fuller in the lower end. I think the second channel sounds slightly better than the first one so I will likely change the transistors to match the second. What bias are most of you running at?

Here's a pic of the rat's nest as it's playing. 😀
 

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#1,202
OK I got a chance to work on it some more today after doing a lot of reading on various forums. Seemed as though most folks were shooting for about 1A bias so I reinstalled 200R trimmers and then installed 1K trimmers in the 1K resistor slots and adjusted them to 1V across each 1R resistor. I have installed 2SK2240/2SA970 in the cascodes, 2SK246GR/2SJ103GR JFETs, KSA992,KSC1845 in the VAS and MJL21192/94 for the outputs is both channels. I ended up with 560R for the bias resistors in one channel and 620 in the other. Both are now within a few mA of 1A. I hooked it back up and still the bass is a little lacking. Then I remembered seeing the guys said this amp needs a lot of filter in PSU and I had been using a cap bank with just 6 X 4700uf caps for both channels. So I dug out the filters I had used in my Aleph X. Those consist of 4 X 22,000uf caps per in a CRC setup using 2 X 0.22R, 25W resistors in parallel between each cap. I hooked up one set per channel for 88,000uf per channel. There's that bass. 😀 This is a whole different animal with the big capacitor banks. I'm going to give it a little more time to burn in and then I give it a little more critical listening.

Blessings, Terry
 
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#1,204
Well I've had a chance to listen to it for a while now. I hooked it up to my A/B setup and first was comparing to a Jason Kuetemann VSSA. The VSSA was just eating it for lunch. Mids and High were sort of comparable but the VSSA had a much bigger soundstage. So this inspired me to dig out my JLH 1969 and hook that up for comparison. Talk about two very different amp. The JLH has a much better low end but not nearly as hi-fi sounding as the Monstre. The output is just about the same into 8 ohms. This is something I noticed right away when testing the Hiraga. It almost loses power when you go to 4 ohm. Most of my amps, including the JLH have a pretty big gain in output if I add a pair of speakers. Not the Hiraga. First time I've seen this. So I'm not sure if it is my component choices, but so far this amp has not lived up to the hype. It's a nice little amp and might work driving the high end of a bi-amped system but for full range it is just to timid in the lower end for me. It was a fun build. Glad I did it.

Blessings, Terry
 
#1,209
still4given said:
Yeah I read that. That's life I guess. I read through that other website again and realized the OP actually used the 2sk170 which does have a reversed pinout. I also see that he installed two 2K pots in parallel with 1k pots to set the bias. I did get a chance to try some different resistors to get closer to the 600mA bias. I'll probably install some pots tomorrow so I can find the resistor value needed to get the right current. If the amp sounds good enough I may look for the original parts.

Blessings, Terry
Click to expand...

I think that reducing the 470 ohms pot (i.e. bridging it) to say 100 ohms or 50 ohms should improve things: the pot gives local feedback through source degeneration if I may say so.

Reducing the pot will increase the current.
It should be a question of balancing till you find the right value . You might test it also open loop )

I might add that my original set I bought from the original shop in Paris had a different Idss for both parts, so the 0 Vdc position is 90 ohms one side 10 ohms the other. But it is a secret ingredient to its nice sound with the second harmonic.​
 
#1,213
#1,215
Of all the money e’er I had,
I spent it in good company.
And all the harm I’ve ever done,
Alas! it was to none but me.
And all I’ve done for want of wit
To mem’ry now I can’t recall
So fill to me the parting glass
Good night and joy be with you all

Oh, all the comrades e’er I had,
They’re sorry for my going away,
And all the sweethearts e’er I had,
They’d wish me one more day to stay,
But since it falls unto my lot,
That I should rise and you should not,
I gently rise and softly call,
Good night and joy be with you all.
 
#1,216
Decided to do a strip down and rebuild to get rid of the last residual hum. Potted my big toroidal which should help a lot.
Unfortunately whilst scoping out the circuit something shorted out and took down about half the transistors - fortunately not the big Sankens (which would have been game over) but it took down the 2SK170's and 2SK74's. Bummer as I got these from a friend and can find no reliable source. Any pointers.

Shoog
 
#1,218
still4given said:
Well I've had a chance to listen to it for a while now. I hooked it up to my A/B setup and first was comparing to a Jason Kuetemann VSSA. The VSSA was just eating it for lunch. Mids and High were sort of comparable but the VSSA had a much bigger soundstage. So this inspired me to dig out my JLH 1969 and hook that up for comparison. Talk about two very different amp. The JLH has a much better low end but not nearly as hi-fi sounding as the Monstre. The output is just about the same into 8 ohms. This is something I noticed right away when testing the Hiraga. It almost loses power when you go to 4 ohm. Most of my amps, including the JLH have a pretty big gain in output if I add a pair of speakers. Not the Hiraga. First time I've seen this. So I'm not sure if it is my component choices, but so far this amp has not lived up to the hype. It's a nice little amp and might work driving the high end of a bi-amped system but for full range it is just to timid in the lower end for me. It was a fun build. Glad I did it.

Blessings, Terry
Click to expand...

Terry you like the mosfet sound, you should test the mosfet version. I built a couple BJT type but was not my taste.
Lack the dynamic, bass etc
These mosfet look interesting, also I have the layout for.
Greetings Gabor
 
#1,220
Hi
Terry it uses vertical mosfet.

I do have something similar with lateral mosfet, it was moded from the Hiraga. The guy who built it (actually he built several of them to his friend, himself etc.)
So I designed the layout and I built it but I was unable to get read of the offset. Probably I made some mistake with the layout😕
So I gave up the Hitachi latfet version. That one here you can find.
Megalith - Cooltune DIY Audio

The vertical is nice and to me better than the BJT at least less sensitive to the PS. Has more tubby sound.
Of course it need a good PS like every Class A amp 🙂 It just not as picky like the BJT version.
Here is the schematic and the layout
 

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