Stax CA-X -> CA-X Pro. Is it a crazy idea - or not?

Hello all,

I am about to become the happy (?) owner of a Stax CA-X (and DA-80). The pair are functioning, and actually don't sound that bad, but I have plans...

At the very least, I'm going to replace the more perishable parts (electrolytics) and possibly the power devices on the DA-80, as suggested by EchoWars in a thread somewhere. So far, so good. And theoretically easy.

However, still thanks to EchoWars, I now have the schematics and parts lists not just for the CA-X, but for the CA-X Pro: different flat amp, with DC-servo circuitry. So I started thinking... what if I created a couple of "pro" flat amp modules?

The parts may be an issue to find: active devices are

UP07 / UN07 (low power JFET - g*d knows what to replace them with)
2SK117 (findable, though the two Idss grades may be an issue)
2SK150 (dual N-channel JFET - another unobtainium part?)

So, forum, two questions for you all:

1) Do you vote yay or nay? Do you think it's a completely crazy idea to recreate what is a nearly 40-year-old design? All the (very few) reviews and comments I have found seem to indicate that the PRO was significantly better-sounding than the already pretty good CA-X.

2) Do you have any ideas WHAT to use for the blessed parts above?

Thanks in advance for any comments and responses!
 

cagiva

Member
2011-05-21 11:53 pm
Hi, I have a Stax CA-X pro preamp. I have never heard the CA-X,but all i can say is the pro is an amazing sounding preamp. I believe the main differences are in the pre itself,not the power supply. I am not tech savvy but i can take the cover off and send you some photos, if that helps. I live in Australia. cheers Kreso.
 

elektroj

Member
2011-11-18 1:49 am
The parts may be an issue to find: active devices are

UP07 / UN07 (low power JFET - g*d knows what to replace them with)
2SK117 (findable, though the two Idss grades may be an issue)
2SK150 (dual N-channel JFET - another unobtainium part?)

So, forum, two questions for you all:

1) Do you vote yay or nay? Do you think it's a completely crazy idea to recreate what is a nearly 40-year-old design? All the (very few) reviews and comments I have found seem to indicate that the PRO was significantly better-sounding than the already pretty good CA-X.

2) Do you have any ideas WHAT to use for the blessed parts above?

Why not. It sounds like a fun project. :)

UP07/UN07 - check Blowtorch thread. (2SJ103/2SK246 "GR" ?)
2SK117 - I see no problem finding them.
2SK150 - Are they in the "pro" version? I don't see them in my "regular" CA-X schematic. What grade? Y, GR or BL? They could be found here and there, btw.
 
Hello all,

I am about to become the happy (?) owner of a Stax CA-X (and DA-80). The pair are functioning, and actually don't sound that bad, but I have plans...

At the very least, I'm going to replace the more perishable parts (electrolytics) and possibly the power devices on the DA-80, as suggested by EchoWars in a thread somewhere. So far, so good. And theoretically easy.

UP07 / UN07 (low power JFET - g*d knows what to replace them with)
2SK117 (findable, though the two Idss grades may be an issue)
2SK150 (dual N-channel JFET - another unobtainium part?)

So, forum, two questions for you all:

1) Do you vote yay or nay? Do you think it's a completely crazy idea to recreate what is a nearly 40-year-old design? All the (very few) reviews and comments I have found seem to indicate that the PRO was significantly better-sounding than the already pretty good CA-X.

2) Do you have any ideas WHAT to use for the blessed parts above?

Thanks in advance for any comments and responses!

the CA-X/DA-80 combo is flat-out wonderful. as far as the preamp goes, there is no need to do more than rework the power supply of the preamp (that being said, it's no small matter -- i'm not 100% sure if anyone besides me has ever attempted it, actually!). i seriously doubt it would be worth the trouble to make your own Pro boards (granted, i have not seen the reviews you speak of), but i'd also be lying if i didn't at least think about doing that at one point ;)

the amp is relatively easy to replace capacitors on, and it responds well to these new parts. you could also replace several polypropylenes on the main amp boards with polystyrene film/foil (a la Multicap RTX) if you'd like -- no idea how much this helped the sound, but it's one fine amp now that i'm done. leave the power devices if they are still working! my buddy is trying to figure out a busted DA-80, and the new power devices might be a cause of the oscillation it seems to have, although there must be something else wrong with it too.

i have cannibalized some UP/UN devices from a completely different preamp. if you have need of these, let me know and i can point you in the right direction.

DSC00672.JPG
 
Hello to all STAX fans. I own a STAX CA-X PRO. Unfortunately, it has a defect. When switching on and off in the left channel, the DC voltage jumps up to 4 volts. High-frequency excitation in the right channel. As a result, if you turn on STAX and the terminal amplifier at the same time, the fuses on the terminal amplifier burn out. If you turn it on and off sequentially, everything works fine. The service said that these are transistors UP07 and UN07. I'm not allowed to make repairs. I want to hear your advice. Maybe someone knows this defect. Thanks everyone.