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ash_dac 18th June 2005 07:33 PM

unregulated wallmart power supply cap size

I opened up an unregulated ac wallwart for my QED Digit dac today. (The wallwart contains a transformer, 4 diodes, and 1000uf noname capacitor).

The wallwart is 12V dc (500mA).

Can I safely replace the 1000uf cap with a 100uf cap ?

(I have some 100uf 25V Black Gate capacitors )

Kind regards,


jaycee 18th June 2005 08:57 PM

Sure you could, but you would be increasing ripple in the supply by reducing the rail capacitance. Better would be to add the Black Gates inside the DAC.

ash_dac 18th June 2005 10:54 PM


Thanks for the information.

I put two black gates inside the dac (I think one is for the regulator) and have been blown away by the change in sound :D .

Leave the 1000uf in there?

ps post title should have read walwart, and not wallmart :whazzat:

kind regards,


jaycee 19th June 2005 11:05 AM

Yep. The capacitance that makes the difference is in the DAC... you won't really get any improvement by adding capacitance to the inside of the wallwart.

paulb 19th June 2005 01:42 PM

But it will probably sound worse without the 1000uF. No need to remove it.

ash_dac 16th August 2005 07:56 PM


I picked up some rubycon mbz caps off ebay. 1800uf


Is it a dangerous to put low esr caps after a rectifier bridge of a PSU?



Stocker 16th August 2005 09:12 PM

Not at 1800uF. Add a couple of zeros to that number and you have a short-circuit at the end of your rectifier string for a second or two after power-up. 1800uF I tend not to think twice about, unless the transformer is rated for single-digits of volt-amps.

cerrem 17th August 2005 12:18 AM

If it is an input cap after the bridge....then this won't do much since the SMPS flyback ciruit will adjust it's duty cycle for input voltage variation...
If the cap you are refering to is a output cap..then you should not deviate from it's original value, you run the risk of putting the SMPS into instability and oscilation... The output cap and Load resistance provide a POLE that is compensated by the error control loop....move the cap, then you may move the POLE and make problems...
Unless this thing is UNREGULATED?? ::rolleyes:


Stocker 17th August 2005 02:21 AM

Re: unregulated wallmart power supply cap size

Originally posted by ash_dac

I opened up an unregulated


please refer to the title of the thread.

tade 17th August 2005 02:37 AM

We are snippy on this particular post aren't we?

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