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Old 8th May 2009, 05:10 AM   #1
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Default Kaneta method's all FET power amplifier

Hello
I'm interested on these amplifier , any idea about the two diode I marked with 2 arrow.
There is no value there , probably not sender diode because I see for Sender they use different symbol .
If you have any idea please let me know !
Thanks

Kaneta method's all FET power amplifier

"I recommend this amplifier as a best choice, considering quality,accessibility and stability.
This one is a masterpiece of Kaneda method's amplifiers."
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Old 8th May 2009, 05:13 AM   #2
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Hello
I see the image not so cear I tought better to post the website .
http://www.geocities.jp/mutsu562000/...m/e/hp004e.htm
Thanks
Regards
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Old 8th May 2009, 06:20 AM   #3
satoru is offline satoru  United States
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Hi,

Those are 1S1588 by Toshiba (discontinued). Spec reads 300mW, 35V, 360mA max, 3 pF, 2 ns, Vf = 1.0V at 100 mA, etc. You can use 1N4148 as substitute. Drop me a PM if you want 1S1588. I have excess of this diode which I purchased more than 20 years ago in Japan...

Good luck!
Satoru
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Old 8th May 2009, 10:06 AM   #4
h_a is offline h_a  Europe
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You sure you don't want to use a pot additionally in these positions? You are at mercy of the VGS of the output laterals concerning output fet bias.

Have fun, Hannes
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Old 8th May 2009, 12:53 PM   #5
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Hi,
Quote:
Those are 1S1588 by Toshiba (discontinued).
Or you just could use a better sounding continued resistor.
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Old 11th May 2009, 12:21 AM   #6
satoru is offline satoru  United States
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Hi,

There are a couple of reasons Kaneta didn't use resistors there. The first reason is rather a historical one. He used to use pile of D battery cells as power source for a while (before he switched to R core transformer based power supply circuit). He was in need of reducing the idling current for the output pair, thus the output pair idle current was set in the region where it has positive temperature coefficient. He used diodes to set the idle current and glued the diode to output FET for stabilization of the idle current. He didn't care much about the variation of the idle current itself.
The second reason is related to the 5.6Kohm resistor to the ground. If you use a variable resistor in the place of diodes, I'm not sure from where you may want to connect that 5.6Kohm to ground... The discussion whether you want that 5.6Kohm resistor there or not is a separate issue. So, if I'd want to replace diodes with variable resistor, I'd remove the 5.6 Kohm and give the output pair large enough idle current (with large enough heat sink, of course!).

Good luck and enjoy!

Satoru
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Old 11th May 2009, 01:55 AM   #7
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satoru,
how come you know all that? However, the explanation is not convincing. A single fixed resistor is preferable.
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Old 11th May 2009, 03:08 AM   #8
satoru is offline satoru  United States
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Hi,

The release of this amplifier circuit overlaps with a period I tracked most of Kaneta's articles. Kaneta does weird stuff on a belief that "it sounds better". I'm not defending his designs at all. I agree that a simple resistor would be a better solution (granted that you remove the 5.6Kohm resistor, which doesn't make much sense to be there either). I'm just describing what I think the reason behind of the two diodes sitting there.

The owner of a small parts shop in Kyoto told me once: "Kaneta's amplifiers sounds very good. But I don't like him since he says so nasty things about amplifiers designed by others". He was a very nice old men who listened patiently to many questions from a beginner (me ).

Oh, the current going through the diodes depends on the Idss of two 2SJ72 which is rather difficult to know before hand. Of course, you can measure it and calculate the value of the bias resistor. But it won't be too good for a design to be published in a DIY journal where you cannot assume much about the skill level of the readers... Yes, I agree with you that a fixed resistor would be the best!! Actually, if I'm going to make this amp now, I'd do exactly as you suggested.

Thanks!
Satoru
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Old 11th May 2009, 04:15 AM   #9
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Hello Satoru
You mentioned to use 1N4148 instead what is in the Kaneda schematic .
You also wrote you have some of the orig Diode . If I can use the 1N4148 with any sound degradation that would be also OK to me !
How much would be 4 pc?
These is an interesting am .
I did tried the Kaneta preamp , but I used cheap parts and not bad at all .
Now I purchased Dale resistors and re build it using better quality components .

Lumba Orig
Yes I did found trim pot which sounded much better than the Dale or RPM resistors in the M Hiraga amplifier .
Hard to believe ? For me to !
But I tested many time and after I left the trim pot inside the PC board rather one of the resistors mentioned above .
Satoru if you build these amp before me , probably yes because I'm busy with another project , these week I will meet the spine surgeon probably I need lo back surgery .
Please let me know the result if you done with the amp at first .
Thank

Regards
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Old 11th May 2009, 04:31 AM   #10
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HI
I see J72 is hard to find part either ,
Can I replaced with J74 or J103?
These two Jets I have readily available at home .
Regards
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