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RE: SCA-35 12AX7 in phonostage

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Eli Duttman

In Reply to: RE: SCA-35 12AX7 in phonostage posted by Stewen on May 16, 2012 at 12:00:39

Look at the schematic. As is the case in many units from that time frame, active (via NFB) EQ is employed and both the RIAA and NAB curves are supported. NFB can alter the equation significantly.

I find myself being a "stuck phonograph record" and repeating the same advice over and over, again. Given today's realities, replacing the complex OEM source selection switching with an inexpensive Lorlin 2-6 position/2 pole non-shorting switch from Mouser is SENSIBLE. Hard wire a pair of I/P jacks to a good phono setup and make all the other inputs line level. Reducing the number of mechanical contacts in the lines mV. level signals flow over is important.

Naturally, I'll grind my own axe and recommend a phono setup I'm associated with, but "there's lots of fish in the sea". Regardless of the phono circuitry you settle on, don't forget a DC heater supply, which might have to be outboard.

BTW, have you given thought to the fact that the 7199 has all but disappeared?

Eli D.

SCA-35 Manual (Open in New Window)

Follow Ups:

RE: SCA-35 12AX7 in phonostage - Stewen 08:04:42 05/17/12 (2)
Thanks for answer ! I´ll try that interesting preamp some day . The guy who owns the SCA-35 just want me to fresh it up with some new components
that I found is needed and perhaps let me do some changes ..... therefore
my question about the 47K anoderesistor . What do you guys think about increasing it a bit ? Or can you suggest some other change except that
EFB change that seems to be a good mod. Stewen
- You lost me a bit Stewen - 1973shovel 10:20:51 05/17/12 (1)
  I'm thinking it is a translation issue. When you said:
  
  "Or can you suggest some other change except that EFB change that seems to be a good mod."
  
  If you're thinking about the EFB, I strongly recommend it for the SCA-35, and ST-35 as well. It was inexpensive, easy to do, and it made a big improvement in the sound of the SCA-35.
  - RE: You lost me a bit Stewen - Stewen 03:30:38 05/18/12 (0)
    Yes , I certainly have decided to do that biasmod ! But still I wonder about that 47K anoderesistor . What would happen to the distorsion-level if I increased it to , let´s say 100K ? ( of course with some other change , if necessary , for example some increase of the cathoderesistance , to keep
    workingpoint not too far from the original . Perhaps I´m totally wrong here , the circuit might be optimal constructed ..... ? It´s just that the
    lowest dist. from a 12AX7 often comes from anoderes. in the 220-470 K region . Sorry about my partly bad english but I hope You´ll understand..
    Regards Stewen

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