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In Reply to: The distortion consequences of GNFB posted by 6AS7_6SN7 on May 13, 2017 at 09:55:36:
Is that eliminating the three high gain small signal tubes (12AX7s) for low output-Z medium Mu and more linear tubes, allows you to significantly lower total NFB, without any shift upwards in OPT-Z into spkrs.Loop NFB around the OPT stage also proves to be a good idea. Moves opt-Z even lower, and it still sounds nicer.
Noting of course that the OEM St20 is highly regarded on the niceness front.
Given that by the 1980s most OEM St20s would have been in need of a re-cap, I figure I am very lucky to have got them as a swap for a St60 which I was given.
'Not a LEAK any more?' WGAS! I don't.
Here's a 'systems' thought - 'It depends."
Also, please comment on this thread re strapping my two modded St20s - as mono-blocks - into QUAD 63s.
8 ohm taps would give me a 4 ohm 'mono' tap. Using the 4 0hm taps would give a '2ohm' tap.
Should I simply try both ways?
The mods we did are covered in 'Reviews'. Both amps will be in pentode mode and both now have 4 x 4 470uf 400V 105deg. caps, bypassed.
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
Edits: 05/14/17 05/14/17
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Follow Ups
- My experience in re-thinking a classic 'high NFB' PP amp - LEAK St20 - Timbo in Oz 18:17:23 05/14/17 (0)
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