Klaus Boening balanced phono amp

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Sort of DIY. It is a design by Barry Porter that was published in ETI. With a bit of luck I can find the date.

Uses 2 LM394 for each input as a front to an NE5532A. Rest is NE5534A balanced to unbalanced convertor. Then RIAA with another NE5534A and a servo loop to get the DC out. Servo loop I added myself, also extra stabilisation to the frontend so the rest can run on +/-20V.

Soundwise it is clear, but the main difference was a lot less hum and noise compared to the previous one. But you may have to re-wire your arm. If you connect the cartridge to a balanced input it may not be connected a ground somewhere. Also the connection to the preamp needs to become balanced.
 
Ok, I'll be doing it!

Yes, that is true! My desk is full of parts, lots of them!

Nearly finished the charging pcb for now.
But now I'm running into lots of questions.

1) When matching caps for the passive riaa, do I have to burn them in in any way before measuring?

2) What is the exceptional matching of fet's for? Why not simply matching after IDSS? What will I miss?

3) If some of the 9V accus are used to prevent the caps from switching + and - (see text on his homepage), how can I ever charge the accus safely?

4) One FET is used as a current source; has it the same IDSS, and if so, why?


That'll be lots of fun!
Rüdiger
 
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