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Old 8th January 2007, 07:37 AM   #1
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Default PS Decoupling question

An amp I am working on has two output transformers connected to the same B+ supply. The final PS cap, a 10uF Solen, before the transformers is probably 12 inches away. I was thinking about, very close to the transformers, adding some small resistors, and another cap, one for each side, to make the PS slightly more split. So, the current version is on the left, and the proposed is on the right.

I am sure this is fine to do, but I am looking for suggested resistor and cap values. Voltage is right where it should be, so i don't want to drop much voltage with the resistors. I was thinking in the 20R range. Current draw is about 25mA per side. B+ ripple is very low as the PS is regulated. Is 0.1uF fine for the caps, of should I use something larger than that?

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Old 8th January 2007, 08:52 AM   #2
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Default Re: PS Decoupling question

Quote:
Originally posted by dsavitsk
An amp I am working on has two output transformers connected to the same B+ supply. The final PS cap, a 10uF Solen, before the transformers is probably 12 inches away. I was thinking about, very close to the transformers, adding some small resistors, and another cap, one for each side, to make the PS slightly more split. So, the current version is on the left, and the proposed is on the right.

I am sure this is fine to do, but I am looking for suggested resistor and cap values. Voltage is right where it should be, so i don't want to drop much voltage with the resistors. I was thinking in the 20R range. Current draw is about 25mA per side. B+ ripple is very low as the PS is regulated. Is 0.1uF fine for the caps, of should I use something larger than that?

Thanks

I would agree with the local caps, but not the resistors. They would effectively isolate the Solen and cause lf signal-dependent ripple on the B+.

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Old 8th January 2007, 08:53 PM   #3
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Agreed, 0.1uF caps at the OPT B+ terminal would be a good idea but the resistors would not.
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Old 8th January 2007, 09:08 PM   #4
lndm is offline lndm  Australia
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If my purpose was to give isolation between the two output stages, I would ensure the final cap could supply them on its own. If the 10uF is appropriate in your case, why not buy a second Solen, and buy a second one of whatever is before it (choke, resistor) to create two independent L-filters.
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Old 8th January 2007, 09:49 PM   #5
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Quote:
Originally posted by lndm
If my purpose was to give isolation between the two output stages, I would ensure the final cap could supply them on its own. If the 10uF is appropriate in your case, why not buy a second Solen, and buy a second one of whatever is before it (choke, resistor) to create two independent L-filters.
I think this is what I was intending to do, more or less, except by adding a stage. And, I think it means that rather than a 0.1uF cap, I'll need something larger, which was really what the poorly worded question was getting at. The 10uF is plenty large for both sides, so I think I'll try some 5uF solens I have around and see how that goes.
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