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TDA7294 with SRPP front end.
TDA7294 with SRPP front end.
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Old 13th September 2017, 05:15 AM   #11
lcsaszar is offline lcsaszar  Hungary
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Omitting C8 will drop the gain.
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Old 13th September 2017, 02:11 PM   #12
stocktrader200 is offline stocktrader200  Canada
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Join Date: Jan 2008
Location: Calgary
The 12au7 in SRPP mode has a gain slightly less then the mu of the tube.
I think the 12au7 is around 20 - 25
the IC has a gain of 33 as drawn in the schematic
you can input the tube stage via a 22k resistor on the inverting pin of the IC along with the grounded NFB resistor increased to 1.5k . This gives a gain of -1 so that the amp will now be non inverting as well
this would leave the circuit gain entirely to the tube stage

Last edited by stocktrader200; 13th September 2017 at 02:13 PM.
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Old 14th September 2017, 01:53 AM   #13
nigelwright7557 is offline nigelwright7557  United Kingdom
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Location: Carlisle, England
Originally Posted by lcsaszar View Post
Omitting C8 will drop the gain.
Yes I will omit C8 and reduce 7294 feedback resistor to 4k7.
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