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In Reply to: RE: poly cap posted by sherod on July 01, 2016 at 11:55:40
OK, in the metric system going from micro to pico means you move the decimal point 6 places to the right filling in the missing places with 0s.
The ceramic is clearly marked .0047, moving the decimal point yields 4700, which is indicated on the schematic.
I read on one of the threads that a ceramic capacitor can maintain its capacitance better at RF frequencies. Could this be why H/K put it at C3 on the MPX board? Just wondering...
Yes that's absolutely true, that's why you typically don't muck with the cap type in the front end, the key being RF frequencies, figure 100MHz for FM. Now once you hit the IF stage the frequency drops to 10.7MHz and then into the composite stage at about 55KHz which is where C3 lives, so no there's no good reason to use a ceramic there. More a cost and availability reason than a technical reason. IMHO
I see you put a poly cap at C15 on the MPX board. Besides that location and C3 are those the only locations you feel benefit from a film cap upgrade? I was curious where C15 was in the signal path?
C15 is part of the stereo switch filter, and on mine it was already a film cap. I did check for value, should be the same on yours.
...just as what is in the deemphasis. I haven't checked for value but was wondering if that location was critical for the sound.
No, not at all.
I have some polystyrene caps on order to put in that location.
I understand now and will measure and order accordingly. Sorry for bugging you so much. Even though this thread seems to be a private conversation between you and me, maybe someone else will see it and the info can help them out.
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