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Old 11th April 2013, 03:18 PM   #1
neskor is offline neskor  Serbia
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Default Quad 22 interstage cap?

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?
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Old 11th April 2013, 03:22 PM   #2
DF96 is offline DF96  England
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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.
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Old 11th April 2013, 03:29 PM   #3
neskor is offline neskor  Serbia
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They didn't change R26 in any revision, it was always 1.5M.
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Old 11th April 2013, 05:03 PM   #4
DF96 is offline DF96  England
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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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