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Old 30th December 2003, 08:17 AM   #1
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Default Are these good places for bypass caps

Are the capacitors in the picture good places for bypass caps to get rid of high frequencies? Possible ways to remove any chance of occsilation? Plus just clean up the signal a bit.
Thanks for any help.

-David
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Old 30th December 2003, 09:16 AM   #2
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Hi David,

In short, possibly, no and no.

The 0.01u on the input will provide a low pass filtering (RC) effect with the source's impedance. However, this will vary from source to source. A low pass input filter may be useful to remove the ultrasonic noise produced by sigma delta CD players and may also remove some low r.f. interference which may be required in some locations / setups. If you want to create a well defined lpf then place the capacitor after the 1K input resistor. You should also make this cap value smaller. See Mark Hennessy's site for an example.

http://www.mhennessy.f9.co.uk/

The 0.1u top right is across two ground points and therefore has no effect. This might be better placed across the +/- power supply pins of the IC.

The 0.01u bottom centre appears across the load. This isn't helpful and may actually help in creating oscillations. If you are worried about oscillations created by the interaction of the amp and the speaker cables/speaker, then you can use a Zobel network on the output (R&C to ground). An output series inductor can also be used, as can a low value output series resistor (0.1 to 0.2 ohms).

James
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Old 30th December 2003, 10:47 AM   #3
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Woops, yes I meant to apply the capacitor across the V+ and V-...not across GND...was to busy looking at what was convient to draw rather than what actually made sense.
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