Yamaha's kind of ERCO: Zero Distortion Rule "ZDR" (M50, M70, A520)

[tiefbassuebertr]

Yamaha's kind of ERCO: Zero Distortion Rule "ZDR" (M50, M70, A520)

How works the circuit from the attachement (power amp section of the IA "A-520") ?
What is the aim of the diode network between in- and output of the output butter stage?
Where I can find hints of the winding parameter and the appropriate core material behaviour for a ZDR transformer

I have find only this threads in this case:
http://www.diyaudio.com/forums/solid-state/55164-yamaha-ns-m-50-a.html
http://www.diyaudio.com/forums/solid-state/89023-bob-cordell-interview-error-correction-343.html (post #3424)
Yamaha M-70 vs. M-80 - AudioKarma.org Home Audio Stereo Discussion Forums

 

[wahab]

The diode network will limit the current to 3A, but only
on the negative going of the signal.....

Are you sure that C163 is not connected to Tr111 collector ?..

"Zero THD" like will mostly arise from tremendous NFB ratio,
since the design is a 3 stages voltage amplification..
So much gain available that they managed to insert the
tone controls in the NFB loop...

 

[tiefbassuebertr]

The diode network will limit the current to 3A, but only
on the negative going of the signal.....

Are you sure that C163 is not connected to Tr111 collector ?..

Yes (see attachement). The complete Service Manual you will get about "hifi engine"
Thanks for the advice regarded the diode network

 

[tiefbassuebertr]

Which other brands uses this kind of error correction?
And where I can find hints of the winding parameter and the appropriate core material behaviour for ZDR transformers?