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Old 28th January 2004, 11:34 PM   #1
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Question Actual capacitance on V+ & V- (gainclone)

Hi all,
I had a question about the recommended capacitance on the V+ and V- legs of the chip (say the LM3875...)

ASSUMING 1000uF as the value we are going to use (because the actual value is not part of my question), I will also be using a single transformer, single rectifier bridge to power a stereo set.

In this case, isn't he ACTUAL capacitance of the circuit at that point (pin 4 of the chip, for example) 2000uF??

Thanks for any response

see picture (section in question is RED):
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File Type: gif non-inverted topology-caps.gif (7.2 KB, 175 views)
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Old 29th January 2004, 01:22 AM   #2
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Theoretically it is 2000uF, but I wouldn't loose any sleep over it. Just put 1000u at each chip's supply pin and it will work fine.
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Old 29th January 2004, 01:24 AM   #3
hifi is offline hifi  Sweden
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Use separate diodes for each channel and they should be separated

/micke
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Old 29th January 2004, 01:45 AM   #4
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Thanks for the replies
Somehow my picture didn't make it through review.

Is there any particular reason to leave the "AC noise" (AKA ripple) in the V+ and V- all the way to the chip and then clean the power right at the end ?

I was thinking of including the filter caps in the power supply chassis and running ~DC (still somewhat dirty) to the amplifier chasses.

Is the idea that it filters out any accumulated noise as well? Does the ripple from these power lines introduce noise in the rest of the circuit?

I know, I know, I should just shut up and finish building one and then experiment...

I just like a firm basis in theory
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Old 31st January 2004, 01:02 AM   #5
GregGC is offline GregGC  Canada
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Quote:
Originally posted by Joshua Layne
Thanks for the replies
Somehow my picture didn't make it through review.

Is there any particular reason to leave the "AC noise" (AKA ripple) in the V+ and V- all the way to the chip and then clean the power right at the end ?

I was thinking of including the filter caps in the power supply chassis and running ~DC (still somewhat dirty) to the amplifier chasses.

Is the idea that it filters out any accumulated noise as well? Does the ripple from these power lines introduce noise in the rest of the circuit?

I know, I know, I should just shut up and finish building one and then experiment...

I just like a firm basis in theory
Read this please. (The first 3 pages at least)
http://www.analog.com/UploadedFiles/...8865AN-202.pdf
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