unregulated wallmart power supply cap size

ash_dac · 18th June 2005, 07:33 PM

Hi,

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,

Ashley.

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

Hi,

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

.

Leave the 1000uf in there?

ps post title should have read walwart, and not wallmart

kind regards,

Ashley.

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

Hi,

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

see:- http://www.rubycon.co.jp/en/catalog/...inum/e_MBZ.pdf

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

Regards,

Ashley.

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?? :

Chris

Stocker · 17th August 2005, 02:21 AM

Quote:

Originally posted by ash_dac
Hi,

I opened up an unregulated

Ashley.

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?

18th June 2005, 07:33 PM	#1
ash_dac diyAudio Member Join Date: Jan 2005 Location: UK	unregulated wallmart power supply cap size Hi, 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, Ashley.

16th August 2005, 09:12 PM	#7
Stocker diyAudio Member Join Date: Dec 2003 Location: Austin	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. __________________ Jesus loves you.

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18th June 2005, 08:57 PM	#2
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	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.

18th June 2005, 10:54 PM	#3
ash_dac diyAudio Member Join Date: Jan 2005 Location: UK	Hi, 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 . Leave the 1000uf in there? ps post title should have read walwart, and not wallmart kind regards, Ashley.

19th June 2005, 11:05 AM	#4
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	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.

19th June 2005, 01:42 PM	#5
paulb diyAudio Member Join Date: Jun 2001 Location: Calgary	But it will probably sound worse without the 1000uF. No need to remove it.

16th August 2005, 07:56 PM	#6
ash_dac diyAudio Member Join Date: Jan 2005 Location: UK	Hi, I picked up some rubycon mbz caps off ebay. 1800uf see:- http://www.rubycon.co.jp/en/catalog/...inum/e_MBZ.pdf Is it a dangerous to put low esr caps after a rectifier bridge of a PSU? Regards, Ashley.

17th August 2005, 12:18 AM	#8
cerrem diyAudio Member Join Date: Jun 2005 Location: San Diego, CA	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?? : Chris

17th August 2005, 02:37 AM	#10
tade diyAudio Member Join Date: Feb 2005 Location: Ralieigh nc	We are snippy on this particular post aren't we?