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Old 18th August 2002, 02:47 PM   #1
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Default Weird Design: need help!

Hello,

I found this design at a convention in Japan. I won't bother explaining how I got them.

It is a design for a low power amplifier for headphones. It uses a pair of mosfets and a pair of something called VFET. I don't know what it means, but the original designer suggested that I should use something else. I have been putting off for nearly 2 years now.

After messing around with Pspice, I came up with something workable with 4 mosfets per channel. I have been asking people at Headwize, but they seem to be more interested in something else. I am not sure it really works. I am not quite sure I am using right parts either, I just grabbed IRF510 and IRF9510 because I used them before.

<img src="http://www.people.cornell.edu/pages/ti20/HPAInvPPReal2.JPG" img>

Thanks,

Tomo
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Old 18th August 2002, 03:42 PM   #2
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since you've got the xsistors why don't you tack it together and see. it appears to me that the output is between gnd and gnd so you wouldn't get much out.
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Old 18th August 2002, 03:58 PM   #3
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Hello,

This amplifier uses 4 independent dual power supplies. 2 to set the gate voltages and 2 "floating" to supply current to the mosfets. (for stereo)

+-15V PSU is completely independent of +-20V PSU. In fact, 20V PSU is floating. Gnd is connected to +-15V PSU. Common of 20V PSU, can swing, I guess. As you can see, it gives me some good output with some gain. (Input was 1V AC)

Tomo
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Old 18th August 2002, 04:08 PM   #4
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Hmmmmm.......groovy .....Have you built it or just simulated it ?
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Old 18th August 2002, 04:26 PM   #5
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Hey,

It works with some very rare mosfet called VFETs (2SK82 and 2SJ19). I do not know what it is. As for current post with all mosfets, the design is essentially extension of original design (w/ Vfets). The picture shows my results of bias point calculation and freq analysis. The latter isn't reliable but former should be somewhat correct.

But no, I have never build this thing. I am very curious about what you guys would say. Besides, I am not even sure why it give me gain

I guess I almost am posting to entertain me ... But I do hope you are getting entertained as well.

Tomo
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Old 18th August 2002, 05:33 PM   #6
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Vfets are lateral mosfets. As opposed to Dfets(IR etc.) They are far superior (IMHO) for audio....Lower threshold, more linear, temperature stable....
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Old 18th August 2002, 05:53 PM   #7
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Duuuuuh......V for verticle .......Anyways I prefer lateral
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Old 18th August 2002, 06:55 PM   #8
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This circuit is interesting for three of reasons:

First, it is single stage, and it looks a bit like one of the
upcoming Zen Variations projects.

Second, it makes use of the "inverted power supply"
we remember from Strickland's TNT amps.

Third, it has an extremely clever use of cascoding.
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Old 18th August 2002, 07:00 PM   #9
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gotta link that explains the "inverted PS" in 1/2way simple terms? throws me for a loop....
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Old 19th August 2002, 04:15 AM   #10
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Default But but ...

Hello,

I wonder it actually works. Because, as I have mentioned, I am not using the original parts which are MOSFETS (2SK134 and 2SJ49) and VFET (2SK82 and 2SJ19).

Also, I really wonder how the gain is controlled. It has to do with the R14 resistor. But nothing conclusive came up.

Please note that this is not my creation. This is made by a unique individual who reside in Yokosuka City, Kanagawa Prefecture, proximity of Tokyo. (I can't read his Kanji name ... a man forgets, ok!?) He built this for a headphone amp convention in Tokyo by a group called Aedio. Unfortunately, the track end at Aedio because I am not good enough to earn their trusts and I am not very good with Japanese.

I won't be building this amp any time soon due to economical and situation problems. However, I would like to know more about the new variation when it comes out.

Thanks,

Tomo
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