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Old 6th December 2008, 10:15 AM   #1
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Default Stax CA-X Preamp

Anyone have any service info on this one? It was a $4000 preamp when new, and I have one here with issues. Awfully big and heavy for a preamp, and is quite seriously constructed internally.

Unit is all FET, and uses some devices that I've never heard of and can't find... UP07 and UN07 (P-chan and N-chan FET's) in a TO-126 package, besides a few more common 2SK117's and 2N5465's.

Is there perhaps a sub for these devices? Does anyone have a schematic?
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Old 7th December 2008, 01:23 AM   #2
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So...no one had ever heard of this thing? Or the FET's used?

Or have I simply become persona non grata here at DIY Audio for some reason?
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Old 7th December 2008, 08:09 AM   #3
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Weather you have become a person not to be helped, I do not know. I have, however, noticed the fact that if you help people out, you wil not be helped when in dire straits.
You can send me a private mail, I have the complete schematic.

Regards
Roar
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Old 7th December 2008, 03:20 PM   #4
lineup is offline lineup  Sweden
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I searched the internet for more than 1 hour
for eventual schematic, manual or technical information of the Stax CA-X preamplifier.
Stax CA-X is an 'All FET Preamp' from 1978. CA-X Pro came 1979.
It is expensive.

The closest in design idea maybe is the Borbely All FET Line and Phono preamplifiers.
The actual circuit of Stax CA-X would be interesting to know.
A bit different than Borbely, I am sure.
Quote:
http://www.stax.co.jp/Export/History.html
1978
Dual-Mono construction all FET pre-amplifier with Super-shunt power supply CA-X
1979
Dual-Mono construction all FET pre-amplifier with Super-shunt power supply and DC type flat amplifier CA-X Pro
Quote:
http://www.borbelyaudio.com/products.asp
Pre Amplifiers
EB-707/432 Low-cost All-FET MM/MC Phono Preamp
EB-703/325 All-FET Line/Headphone Amplifier
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Old 7th December 2008, 07:17 PM   #5
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www.earsp.site40.net

UN07/UP07 are 250mW JFETs, complementary replacements are (selected) J103/K246.
A few other brands used the UN/UP devices.

(EW needs a hug and a Xmas present)
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Old 7th December 2008, 07:40 PM   #6
jam is offline jam  United States
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jacco,

I am impressed..............you read Japanese!

Jam
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Old 7th December 2008, 08:12 PM   #7
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Jacco, I must take exception to your claim. They are MOSFETs, and not JFETs. I happen to have some of them. Furthermore, they are in a TO-126 package, whereas the 2SK246 use a TO-92 package.

Regards
Roar
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Old 7th December 2008, 08:57 PM   #8
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Quote:
Originally posted by Roar Malmin
Jacco, I must take exception to your claim. They are MOSFETs, and not JFETs. I happen to have some of them. Furthermore, they are in a TO-126 package, whereas the 2SK246 use a TO-92 package.

Regards
Roar

I do see JFETs in the simplified schematic of the CA-X file in Jacco's link.
Click on CA-X取説
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Old 7th December 2008, 09:14 PM   #9
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Guys, does this look like a JFET to you?

Regards
Roar
Attached Images
File Type: jpg un 07 copy.jpg (39.0 KB, 1120 views)
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Old 7th December 2008, 09:18 PM   #10
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Quote:
Originally posted by Roar Malmin
Guys, does this look like a JFET to you?

Regards
Roar
It looks like a MOSFET.
By the way do you live in Hokksund?

Jeg bodde der i mange r fr jeg flyttet til Bergen. Jeg er i Hokksund noen ganger hvert r, har en bror som bor der og en bror i mot.

Stinius
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