unregulated wallmart power supply cap size

[ash_dac]

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]

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]

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]

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]

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

 

[ash_dac]

Hi,


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

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


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





Regards,


Ashley.

 

[Stocker]

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]

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]

Hi,


I opened up an unregulated

Ashley.

please refer to the title of the thread.

 

[tade]

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

 

[Stocker]

I'll break your neck if you call me violent!

Does it bother anyone else just a little when a question is asked that the OP answered *twice* in the first post?

 

[cerrem]

Stocker...
I guess you missed the last line in my post when I jokingly put in the embarassed look... I kind of realized late in the post what the deal was....
Doesn't matter you getting all worked up over this, since Jesus loves my anyway

Chris