Hiraga "Le Monstre"

-Your transistor blew up due to the 2PC 1K resistors (high bias).
You do not need to afraid it blow up again as long as you take care the mentioned things (set up etc)
I built mine about 12 years ago but I still remember I used 2PC 1K trimmers set up to 560R.
My rail voltage was 12.5V under load. I biased my amp up to 1.5A measured after at total warm up.
I did use the original power Toshiba/Hitachi transistors, JFets based on the original schematic.
I ordered those from the US. After I built the 20W Hiraga I sold the Le Monstre.
My advice do not invest too much money into until you will have a decent listening test:).
What will happens if you aren't satisfied with her sound?:eek:
The reason I mentioned Dan to you because he did a lot of experiment on this amp.
 
DSC_0921.jpg


Trim pots arrived, just connected the multimeter up to it.



I joined pins 3&2 together, then by turning the screw anti clock wise (with the markings on the component facing me) the resistance drops. Conversely if I join pins 1&2 together i get a much lower value but you have to turn the screw clockwise to lower the resistance. So it can work both ways? Im just joining pins 3&2 together.
 
Re: Trimmers:
Yes it woks both ways, just measure the resistance between Pin 1 and your connected 2/3 pin.
Take a notice how the resistance changes when turning CW and CCW respectively, for adjustments in the circuit.

With desoldered power transistors, measure the voltage over R2 and R3 if you didn't take them already out, and calculate the current over them. I would expect somewhere around 5mA.
From that value, you can work out the approx. resistance needed for your trimmers and the desired bias current. How much should the bias be?

I would start with low resistance settings anyway.....
 
Member
Joined 2005
Paid Member
-Your transistor blew up due to the 2PC 1K resistors (high bias).
You do not need to afraid it blow up again as long as you take care the mentioned things (set up etc)
I built mine about 12 years ago but I still remember I used 2PC 1K trimmers set up to 560R.
My rail voltage was 12.5V under load. I biased my amp up to 1.5A measured after at total warm up.
I did use the original power Toshiba/Hitachi transistors, JFets based on the original schematic.
I ordered those from the US. After I built the 20W Hiraga I sold the Le Monstre.
My advice do not invest too much money into until you will have a decent listening test:).
What will happens if you aren't satisfied with her sound?:eek:
The reason I mentioned Dan to you because he did a lot of experiment on this amp.
What power supply rails are your using Vishalk.?

Gaborbela has made some good points,
It is really worth getting it working properly and listening before finishing this one off.

It really can be sounding amp.once it is all set up..

-Dan
 
DSC_0926.JPG

DSC_0929.JPG

DSC_0930.JPG

DSC_0931.JPG

Hi Dan, rail voltages at 17.8v and 15.2V with load.

Today was a good day guys! I replaced the transistors and resistors. After that i powered it up with the light bulb tester and had not issues.

After that set the bias to 0.6v left it for an hour readjusted till it stayed at 0.6v.

tested the dc offset and set it to below zero (0.3mv i measured on my scope).

After that i decided to put a signal into it using my function generator and measured the waveform and output power on the scope.

Got a nice 8.2wrms before clipping at 10khz. Thought this all looks ok lets hook up a speaker and play some tunes.

Had the biggest smile and sense of achievement, it bloody worked and sounded luuusssshhh.

Very happy, left it playing and it seems to be fine, temperature is around 45degrees.

Next is to try a different bias setting, the other amp board i will use the MJL and test how they sound.
 
Thanks to all those who helped, ordererd some more transistors, sanken and some more mjls.



Want to play around with temperatures and bias levels. Although 0.6A sounds very nice. I tried 1A last night but didn't like how it sounded, I also felt it had lost drive in the music. Or maybe I was just tired working late at night.



Want to try a higher bias like 1.5A see what happens. But I think once I stop playing around I'll probably stick to 0.6A.


What are your Ideal bias levels?
 
1.5A bias

DSC_0942.jpg


So got it rigged and connected to my setup, I've set it to 1.5A, left it on for 2 hours playing music and the bias stayed and 1.5A, but man did those temps rise. Those one 1R resistors were boiling, heatsink temp stays at around 61degrees.


But I tell you what, it sounds brilliant, the bass was better and more defined and the music felt more alive.
Just leaving it playing music to see how it handles it.

But so far very impressed, but also like the fact I can adjust and try to see what fits my listening needs.
 
how hot is too hot?

So i pinned down those arcol 10w 1R to the heatsinks and guess what, yup not boiling hot anymore. Thought they would be ok free air but clearly meant to be mounted on additional heatsink.

In terms of heatsink temperature, running this little monster at 1.5A for four hours the heatsink temp seems to be hovering around 64 degrees at a room temp of 23 degrees. So what is my safe limit?

The mini fan works really well, those heatsinks were designed to have a fan blowing through them and it really works, i'm not even running the fan on full power so its a quiet. Even so it drops the temperature by 5-10 degrees depending on where i set it. I don't really want to use them but handy if its needed.

Really enjoying the sound it's producing, going to finish the other channel tomorrow with different transistors and see what sounds better.
 
Member
Joined 2005
Paid Member
So i pinned down those arcol 10w 1R to the heatsinks and guess what, yup not boiling hot anymore. Thought they would be ok free air but clearly meant to be mounted on additional heatsink.

In terms of heatsink temperature, running this little monster at 1.5A for four hours the heatsink temp seems to be hovering around 64 degrees at a room temp of 23 degrees. So what is my safe limit?

The mini fan works really well, those heatsinks were designed to have a fan blowing through them and it really works, i'm not even running the fan on full power so its a quiet. Even so it drops the temperature by 5-10 degrees depending on where i set it. I don't really want to use them but handy if its needed.

Really enjoying the sound it's producing, going to finish the other channel tomorrow with different transistors and see what sounds better.

Hi Vishalk,

Well done first of all. Is great that you have it working.
I would say it is up to you how much bias you want and how much heat you can handle on your setup, design value was 0.5/0.6A from memory but some more may be worth it to give you more power while still being in class A.

-Dan.
 
Thanks Dan

I have one more technical question, i was setting up the other channel today and accidentally shorted a wire, this caused the fuse the blow and one of the transistors to go. I thought no big deal i should've been more careful.

Decided to put those MJL in, after soldering them setting the bias to 0.6v i decided to measure the dc offset, it was at 6v so thought id turn the potentiometer it turned until it hit 3V but then the potentiometer hit its limit and just clicked.

My question is aside from a faulty tranny what else can cause high dc offset? Is it because i have used other transistors or has one of the smaller transistors gone?

It still plays music, i used an old speaker laying around, only thing is when it's connected it draws the speaker cone in (probably because of the dc offset).