Hiraga The Monster...

[gaborbela]

Hi
I'm in the proces to build the Monter Hiraga amp. I ordered the pcb from Kristijan .I have the enclosure ,transformer I have all the original partsd acsept the signal mosfets.
I have 2SK170BL & 2SJ74BL . On the original shematics it was used the Y tipe of mosfets , unfortunatly I cand find them nowere.
I know a lot of guys built these amp sucsesfuly that why I want to ask for some help.
Do I need to change some parts if I use the BL tipe of mosfets ?
Do I need to do some modification on the circuit ,
Or if somebody knows were I can buy the Y tipe of mosfets I would gladly buy them ,even I spent a lot of money on these project.
Please help me so I can put these amp together with out burn done some transistors or anything else.
Thanks for any help
Regards

[rmgvs]

No problem that you use types with other suffixes. At maison de l'audiophile in Paris they have supplied many kits with other types. If you don't change anything you will get another standing current in the amp than the adviced 500-700 mA. No problem as long as you have enough cooling. You have to change the 1k resistors, just try first with a variable pot of 1k and then change it to fixed values (I guess you will end up around 470 or 560 or 680 ohms).

[gaborbela]

HI
Thanks for the answer ,I will try to use 1k trimpot how you advise.
Do you know if I have to replace the 100ohm trim pot .Some people say yes but nobady sure about it.
I try to build as close to the original as posible ,only because I found the BL tipe of mosfets HAVING these problem.
Thanks one more time
Regards

[rmgvs]

No, just put the trimpot in as prescribed. You need this to adjust the amp to a dc-offset of around 0 mV. This has nothing to do with using other suffixes of the little fets. Maybe some people do the trimming of the 100 Ohm pot first and put in exactly the right values of 2 fixed resistors instead. See absolutely no reason why you should do this. If you like the sound of the amp using the other 2 pots of 1 k, you could leave these in place also, no big problem (I once built one doing exactly this and the amp has been on continuously for almost 15 years at a friend of mine and plays his tunes without ever having any problems).

[amplifierguru]

Hi gaborbela,

The 'Y' grading of 2SK170 etc.. has the lowest Idss of 1-3 mA , the other grades are all higher. This simply means that they need a higher resistance in their source cct to establish proper operating conditions by restricting Idss from higher levels.

Once you establish optimum operating point, there is nothing wrong with replacing the pot with resistors which are less partial to change of contact resistance.


Cheers,
Greg

[gaborbela]

HI
Thanks for the help . please let me know if I anderstud well. You say the 2SK170Y &2SJ74Y has the lowest IDSS . So i will have to use lower resistor for these tipe .
It simple mean the 1K resistors will have to be replaced with a lower value .(ex 680ohms or beter i use trim pot 1K and adjust until the ID curent reach around 700mA for the amp).
What happen if I go higher until 1A ?
I'm planing to use Capacitance Multiplier Power Supply from ESP.
Before I built the Class A Hiraga and I tried all kind of power supply but only these was good for me.
I have 10-0-10V 300VA toroid for the Monter H. It will give +-14V if I use regular power supply,wich is to high.
I would like to know what is your opinion on these and if I understud well the 1K resistor replaceing.One more question ,I see the people use 47uF capacitors on the pc board ,my pcb was design by Kristijan from Croatia and he did't use it.
My experience with the Class A only use 100nF capacitors and no electrolitics.
Thanks
Regards

[amplifierguru]

Hi gaborbela,

Yes you will use lower value source resistors for the Y grade and higher values for the BL or V grades.

Sorry, can't comment on the cct without schematic as I don't have it in my head or documented.

Cheers,
Greg

[rmgvs]

If I remember right it is just the other way around: the Y has relative high resistance and low current and BL and GR types have higher current and so lower resistance. Anyway: with a pot you will discover it soon enough.

Total idle current: 1 amp is okay as long as you have enough cooling but with around 14 Volts it generally is no problem with dissipation. It all depends on the speakers you use: using a simple 8 ohm load given the voltage of 12-14 V no more idle current then 700-800 mA is needed for 8 Watts of class A. Some people have tried currents as high as 3 amps and claim the sound quality is getting up (but this is all not described in the original articles).

About voltage: Hiraga has chosen 12-14 Volts so that the amp can be used with batteries. If you use a normal power supply without batteries I see no reason why you shouldn't use a higher voltage up till 18 Volts or so (and eventually a higher current) to get more power (up to 15 Watts shouldn't be a problem with the original transistors, later they used substitute transistors that also were used with the Hiraga 20 Watt amp).

About the cap's on the pcb: there were several version of the 20 Watt ampiflier and some used small electolytics too. I always did use them but never tried without. If the pcb has no spare room for these, just fit some small ones underside the pcb.

[gaborbela]

HI
Thanks ,it realy help me .I read somewhere at the DIY page do not go higher with the power supply than +/-13,5 ,so when I ordered the transformer for these amp I choose 10V ac. I was afraid to go with a higher voltage. 8W with out distorsion it sould be enough .I have a Philips tube amp with a single EL95 each side it gives 4W per chanel and not bad at all. I have a 2x15V AC transformer what I used for the Class A but that is to high. I have enough heat sink I dont need ti worried about it.
What tipe of capacitor do I use on the pcb. I can order Black Gate or so . Do I have to matche the mosfets . When I orderd the pcb Kristijan said there is no need for it.
For the power supply I use Philips BC or Mepco or Mallory I will see wich one feet better ,wich one provide better sound. I use 100nF Rifa bypass capacitors on them . On the pcb for 47uF I'm not sure ,right now I only has Philips (axial tipe) avaleble.I planing to use Pure Silver wire 14Ga with heatsrink.I dont realy like to use teflon for tubing ,teflon with silver always give sound what I realy dot want.
Thanks for the help.
Regards

[rmgvs]

I never matched the fets myself. Sometimes I bought matched sets in Paris, but several times I just used the one I could get my hands on. I guess some type of matching is inherent already in the coding Y, BL, GR etc. Did never encounter differences in perceived sound quality however (but have not measured things to underpin this).

In my opinion 'good' but normal caps from Philips do the job perfectly. You can try whatever you like, more expensive parts will generally not be worse. I did experiment quite a lot with the resistors and there I found worthwile differences in sound quality. Cheap Philipses metalfilm can better be avoided here, choose metalfilms types from Holco, Dale, Beyschlag etc. Of course the recommended types from Paris are very good too.

I'm curious about your experience in using different power supplies with your Hiraga. Can you hear differences using the capacitance multiplier versus the standard big caps passive power supply? Or was it just for getting away with hum and noise?