FirstWatt J2

[EUVL]

IRFP150 would be a better choice than IRFP240, but I personally would still use 2SK3497.
2SK3497 has lower Coss and Crss, lower Vgs at bias, lower Vsat, and less early effect.
It allows you to run closer to rail.

And I always prefer Toshiba FETs to IRF. Much more consistent.
https://www.diyaudio.com/forums/pass-labs/172770-balanced-f5-question-10.html#post2353470 (post #489)
All FET JLH Class A

You need to take extra care to handle the high positive tempco of the 2SK3497 (or any other UHC-MOSFET) in your bias circuit.
But here the auto-biasing with the opto-coupler does that for you, conveniently.

To illustrate the working principle of the basic J2 topology, here is an inverted one(N-JFET input).
https://www.diyaudio.com/forums/hea...borberly-eb602-200-revisited.html#post5492307

Also auto-bias, and you can use 2SJ618 as output device for power amp.
The difference to the J2 is the current mirror, resulting in much more open loop gain, and hence NFB.


Patrick

 

[EUVL]

And as mentioned before, you can find 2SK3497 / 2SJ618 in many Accuphase "vintage" amps.

A-47, A-65, E-470, E-530, M-6000, ...
https://www.hifine.nl/A-47/content/images/large/a-47_power_amp_1.jpg
Accuphase A-47
Accuphase E-530
Accuphase M-6200


Patrick

 

[aspringv]

Cheers EVUL - I actually have ...50 of each of the K3497 and the j618 that I bought with a view to building a x amp at some stage and having enough parts to do a few other things.

Thanks kindly for the links too. I'll get reading. 🙂

 

[EUVL]

Out of topic, just once.

If you have both devices, you can take a look :
2SJ618/2SK3497上下対称半導体無帰還アンプ
2SK3497/2SJ618PowerAmplifier
mlgWX^Av

And you can find many of the Accuphase Service Manuals with schematics on the net.


Patrick

 

[aspringv]

Thanks kindly again! I'll look a bit more. 😉

 

[EUVL]

Just a draft, for now.
Measures 90mm x 70mm.


Patrick

.

 

[Zen Mod]

And as mentioned before, you can find 2SK3497 / 2SJ618 in many Accuphase "vintage" amps.

A-47, A-65, E-470, E-530, M-6000, ...
https://www.hifine.nl/A-47/content/images/large/a-47_power_amp_1.jpg
Accuphase A-47
Accuphase E-530
Accuphase M-6200


Patrick

at least half of them sounding as .......... fifi

anyway , if one is having Kosher part in drawer - why not

contrary , Peasant part , cheap , available at nearest Tobacco store .....

part being source follower, driven with crazy low impedance node - I'm not so sure that anyone can hear difference

though , as I'm always saying - if one's choice is bringing no more than better sleep , I'm content with that

 

[EUVL]

> Peasant part , cheap , available at nearest Tobacco store .....

Fits perfectly the description for the Semisouths. 🙂
How many of those you used in the build for your Danish customer ?
IMG_2441 | Zen Mod Blog


Patrick

 

[Zen Mod]

exactly one pair of Semisouths per monoblock 🙂


same as here : Pictures of your diy Pass amplifier

though ..... we are discussing role and fidelity of specifically driven source follower , working in upper half of OS

all in all - matter of personal taste

 

[Dennis Hui]

Give the scarcity of the Semisouth parts, it is certainly nice that good performing
alternatives for the current source are available.

Cheers,
Dennis

 

[Itsmee]

Ok, it's deviating from the topology, but is there any reason not to try UJ3N065080K3S for the CCS? - the opto bias wouldn't be required.

 

[vdi_nenna]

Normally-on, that mean it needs a ~negative supply to control the bias?

 

[Itsmee]

Or just a source resistor - auto bias 😀

 

[EUVL]

This is how you do it without an optocoupler when using enhancement mode FET with Vgs > 1V :
https://www.diyaudio.com/forums/att...-eb602-200-revisited-eb602_201-mcs-public-pdf
See schematics in P.3.

And of course you can turn this into a power amp with 2SJ618.


Cheers,
Patrick

 

[vdi_nenna]

Or just a source resistor - auto bias 😀

Oh, right. Since its a dual supply.

 

[Itsmee]

Could be as simple as

 

[Zen Mod]

same as in Aleph , upper CCS is not plain CCS - it's modulated

 

[EUVL]

Suggest you read the PDF linked above IF you want to understand how the MU follower works.


Patrick

 

[Itsmee]

The Aleph ccs modulation could be included.

 

[EUVL]

The Aleph CCS also needs to use enhancement mode FETs.


Patrick