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neskor 11th April 2013 03:18 PM

Quad 22 interstage cap?
 
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I'm trying to restore my Quad 22 preamp.
On the internet there are two different schematics.
On first early version there is no input cap, interstage cap is 5000pF and output cap is 0.047uF.
In second (improved) version there is a input cap and interstage cap is now 820pF and output is 0.1uF.
Reason for input cap is known, output is changed probably to improve bass respone, but I don't know why this drastic change from 5000pF to 820pF for interstage cap?

DF96 11th April 2013 03:22 PM

In the later version has R26 been increased in value, perhaps to 10M so that the triode now uses grid current bias? That would explain a change in coupling cap, to maintain the same 20Hz rolloff.

neskor 11th April 2013 03:29 PM

They didn't change R26 in any revision, it was always 1.5M.

DF96 11th April 2013 05:03 PM

I can't believe that they intended a 120Hz LF cutoff. Is this section within a global feedback loop? That might explain it - the change could then reduce subsonic peaking.


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