2SK2586 and 2SJ555 combo Mosfet - diyAudio
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Old 24th October 2013, 10:35 AM   #1
ttan98 is offline ttan98  Australia
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Join Date: Apr 2006
Location: Melb
Default 2SK2586 and 2SJ555 combo Mosfet


I built a Class A amp that used these 2SK2586 and 2SJ555 as output power MOSFETs. These fet are made by Renasas and are quite cheap $2 each. My amp works quite well.

Those of you who have experience in using different types of output mosfets can advise me whether I should change these combo to better quality mosfets e.g. FQA12P20 and FQA19P20. Or should I continue to use these combo.
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Old 24th October 2013, 10:55 AM   #2
EUVL is offline EUVL  Europe
diyAudio Member
Join Date: Oct 2003
There are MANY Japanese DIY pages on those UHC-MOSFETs.
You can find them in google.co.jp.

One of them here has some subjective comparisons that you are looking for.

audio: 電流帰還アンプ

But as said, subjective.
And many things can change that conclusion -- circuit topology, implementation, operating point, ... etc.

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Old 25th October 2013, 12:58 AM   #3
ttan98 is offline ttan98  Australia
diyAudio Member
Join Date: Apr 2006
Location: Melb

Thanks for your response.

More info., if I implement these fets the following way:

1. Class A bias around 1.13-1.3A, 20- 25 watts /channel
2. F5 or Profet or Triphon tolopogy
3. Single ended.
4. PCB based possibly hardwired later

any suggestions of which type of Mosfet to pick from, I read somewhere that you recommend Toshiba 2SJ201/2SK1530 for F5 amps and your F5 balanced amps. Would you recommend the same fets if I later change the topology to that similar to JHL amps.
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Old 25th October 2013, 07:54 AM   #4
EUVL is offline EUVL  Europe
diyAudio Member
Join Date: Oct 2003
The 2SK2586/2SJ555 differs from the 2SK1530/2SJ201 in the following ways :

1) The former has much higher capacitances
2) The former also has much higher transconductances
3) The former has much higher tempco (meaning much more sensitive to temperature)
4) The former is not a true complementary pair, as the latter is.

So if you know these differences, you can try to adapt any topology to suit.
It is not a simple 1:1 substitution thing.
Even though it will most likely work, you are not getting the most from the devices.
So you need to tailor the circuit to suit.

Yes we do use the 2SK1530/2SJ201 for the F5X, for good reasons.
But we also recently built a very good All-FET JLH using 2SK3497 (which is also a UHC-MOSFET).

All FET JLH Class A

And it is a very nice, smooth-sounding single-ended amplifier.
One thing we did not manage is to avoid using NTC in the MOSFET biasing circuit.
If you google in Japan, you will see that ALL circuits using UHC-MOSFET has some NTC in the biasing to cope with the high tempco of such devices.

The purist will say that NTC is not linear and will affect sound.
We did not try to measure. But listening did not review audible differences.

There is no such thing like which one is better.
Each device has its own characteristics, and the preference is almost always subjective.

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