Stax CA-X Preamp

[EchoWars]

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?

[EchoWars]

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?

[Roar Malmin]

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

[lineup]

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.

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

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

[jacco vermeulen]

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)

[jam]

jacco,

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

Jam

[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

[QSerraTico_Tico]

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

[Roar Malmin]

Guys, does this look like a JFET to you?

Regards
Roar

[stinius]

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 år før jeg flyttet til Bergen. Jeg er i Hokksund noen ganger hvert år, har en bror som bor der og en bror i Åmot.

Stinius