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Old 18th November 2001, 09:55 PM   #1
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Just a quickie,

I've just dug up 2 pairs of these Hitachi MOSFETs. I would like to build an amplifier from them in a couple months maybe. My question is: Is it worth it? I know they are elderly by current standards, are there any good circuits to use them in Hi-Fi Land? It just seems a shame to waste them...

Many thanks.

Brownlow
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Old 18th November 2001, 11:22 PM   #2
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Try the MAPLIN 100W Class B amp. The original uses the 2SK135 /2SJ50 pair......
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Old 19th November 2001, 04:17 AM   #3
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Here's an amp that uses your MOSFETS:
http://www.omninet.co.jp/workshop/analog/FETAMP.HTM
There's another on page 2 of this PDF:
http://www.diyaudio.de/archive/bdamps.pdf

[Edited by Kilowatt on 11-18-2001 at 11:27 PM]
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Old 19th November 2001, 06:44 AM   #4
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These MOSFET's are classics, that are very hard to find.
I'm just in the process of designing a integrated amplifier with 10 complementary pairs for each channel.
They have a Rds of 0,7 ohm so you need a couple of them to drive a loudspeaker unless you use NFB and I would like to keep NFB below 6dB if possible.
They are termally stable without any resistors at the source and that's why I love them.
I looked at N. Bayer's design and it seems OK.
Not the best in the world, but OK for nice sound.

Janne
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Old 19th November 2001, 07:06 PM   #5
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Hedlund,

What is the N Bayer design? Is this a moderately powered amplifier?

Kilowatt, the design that is in PDF format, what is its wattage? Any ideas? What does it sound like?
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Old 19th November 2001, 08:36 PM   #6
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The N bayer design is the amp in PDF format that Kilowatt refered too, and that you are asking him questions about.

Janne
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Old 19th November 2001, 10:40 PM   #7
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Sorry, don't know much about the N Bayer design. I don't think it's very powerful
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Old 20th November 2001, 05:23 AM   #8
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Brownlow,

since you only have two complementary pairs the ouput impedance is to high to be used with loudspeakers,
but you can use them for a headphone amp if you want.
If you run 20 mA through the driverstage you don't even need to include them in the NFB circuit if you have one.

Janne
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Old 20th November 2001, 08:12 AM   #9
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I guess it looks like those MOSFETs should continue to stay buried after all. Besides, I was thinking of it as a future project.

Thanks to all of you for your thoughts on this matter.
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Old 20th November 2001, 12:43 PM   #10
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Brownlow,

There is no need to give up that quickly. Dig into some Elektor designs of yesteryears. Some of the designs that come to mind are the AXL, Mini Crescendo and Crescendo designs. The last one is supposed to have a reputation as an oscillator but with my own PCB design I have had very little trouble getting this amplifier going. Then there is the 1KW Elektor design, but then you need four pairs of Mosfets.

Alternately, have a look at Russel Brenden's article entitled 'Class B in a new Class' in Electronics World of the year 2000 (I forget which month exactly). Use the same circuit design and substitute the Mosfets suggested by the author with the ones you have. I can assure you that it has a brilliant sound. It is a Class B design with a modified feedback loop that makes the amplifier sound like single-ended Class A. I have used the 2SK1058/2SJ162 pair with this design with much success.

Another great design using exactly the same Mosfet pair that you have, is an Electronics World design by John Linsley Hood. It appeared sometime during 1995, 1996. According to J.L.Hood, that design sounds very open and least offensive. Electronics World has a back issue service and they can help you with photostat copies of the original articles.

So persevere and all the best,
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Sam
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