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DAC power supply - too much capacitance? soft-start?
DAC power supply - too much capacitance? soft-start?
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Old 8th July 2018, 09:09 PM   #1
Pegasus123 is offline Pegasus123  United States
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Default DAC power supply - too much capacitance? soft-start?

The Audiozen control board for my Soekris R2R dac has the option to add additional filter capacitors. Given the size allotted for capacitors I can add two 25v capacitors which range from 470uf to 11,000uf. So in other words up to 22,000uf.

At what point do I need to worry about capacitance being too much for a DAC? I'm concerned about pops, current spikes, etc.

Note: Disregard the soft-start in the title. I can't delete that with edit.

Last edited by Pegasus123; 10th July 2018 at 02:09 AM.
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Old 9th July 2018, 09:43 AM   #2
DF96 is online now DF96  England
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I cannot think of any good reason to use 22mF to power a DAC. Calculate the value to give low enough ripple, then double it.
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Old 10th July 2018, 01:04 AM   #3
Pegasus123 is offline Pegasus123  United States
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Well since this is DIY I have no problem with taking a sledgehammer to the problem. The cost difference in caps is equivalent to a McDonalds cheeseburger.

Not sure how to calculate necessary ripple. Would 22,000uf pose a problem in reliability, turn on surge, etc? If so what value max would you put?

I'll post the question in the venders forum but I trust the answer more here since this entire forum is dedicated to power supplies.
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Old 10th July 2018, 01:29 AM   #4
abraxalito is offline abraxalito  United Kingdom
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Don't lump all your capacitance together in one can. Distribute it into two or more units and provide some series resistance between the two. Ripple, most especially HF ripple will be attenuated better and in my experience the reduction of HF ripple correlates with improvements subjectively. Though reading again you say that the board is a control board - so is it purely digital? If so then I very much doubt you'll get improvements subjectively from adding more uF.
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Old 10th July 2018, 01:55 AM   #5
Pegasus123 is offline Pegasus123  United States
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It's a control board but the extra filter capacitors go before the DAC power supply. I'll try to distribute it across more capacitors then. There is the option of two big capacitors or four smaller.
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Old 10th July 2018, 09:30 AM   #6
DF96 is online now DF96  England
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Quote:
Originally Posted by Pegasus123
Not sure how to calculate necessary ripple.
In that case you are not in a position to determine what cap value to use.

Quote:
Would 22,000uf pose a problem in reliability, turn on surge, etc?
Possibly a surge problem. Possibly poor at filtering HF - so you get less ripple but more HF noise getting through.

Quote:
If so what value max would you put?
As I said, I would calculate what value I need for sufficiently low ripple then double it.

Generally in engineering, over-engineering can be almost as bad as under-engineering but the damage done can be more subtle.
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Old 14th July 2018, 01:25 PM   #7
lucpes is offline lucpes  Romania
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The resistance of (those small) transformer primaries is enough to ensure that you won't get a spike at start-up. The capacitors will progressively load up.
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Old 18th July 2018, 02:57 AM   #8
phase is offline phase  United States
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Is fairly common to have 10,000uf or more for the smoothing caps.
I have that in one dac, nearly 21,000uf in another, have been working fine with standard 3A diodes for years now with daily use.
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