990 noise measurement

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DAN_000

Well-known member
Joined
May 22, 2005
Messages
104
Location
Ganimedes
I finished some 990´s based on original jensen schematic, I tested in api312 premp style topology replacing 2520.
I do some measurements and I found in the case of 990 there are more noise floor (aprox 4 to 6 dB tested by carefully audtioning) compared to 2520.
Tested with nothing connected on input

I used the following componets on board:
APC75101 cinemag input
api 2503 on output
LM394CH for differential input stage of opamp
1N4148 diodes in opamp
+24-24 opamp voltage


My questions are:
Should I test in another way?
990 needs to change R-C feedback values in api topology for reasonable noise level?
is LM394CH the right component?

Thanks!
 

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