[goodguys]

Hi thanks for reading.

I built a simple psu for my amplifier, consisting of a 12v 15 amp transformer, followed by a bridge rectifier, then a 47,000 uf cap.

There was noise coming through the speaker so i inserted another 47,000uf and the noise went down. Then I kept inserting caps, the noise kept lowering, until i reached 135,000 uf and the noise disappeared completly, using six caps in total.

I figured 135,000 uf was the perfect value so i took out the six caps and replaced with a single 150,000uf cap which is the closest value i could find, but some of the noise came back.

Why is the noise returning. Is it because the first cap smoothed the ac from the bridge rectifier, the second cap smoothed a little more, until it reached the sixth cap and was further smoothed to clean out the ripple totally, something a single cap cannot do.

Or is it the six caps being paralled connected had lower esr and esl values which aided the smoothing process.

From this is it possible to build a power supply with just one smoothing cap or is this going too far.

The reason i am trying to use a single capacitor in the power supply is the more caps i put into the psu the more the sound changes, becomes inaccurate when compared against a single cap.

Caps add a certain colouration of their own, the more caps the more the colouration, the more inaccurate the music sounds.

Searching around i've read a ton of threads wherein people say things like elna caps sound different / better than nichicon, nichicon sound different to panasonic, panasonic sound different to mundorf. There too much evidence to think i am making a mistake or imaging it.

Just am disliking the sound of multiple caps and all the different colourations messed up the experience for me. Sorry for being so picky.

I think what is happening adding caps in 'bypass' with each other ends up with each cap's frequency impedance being added to the mix, in the end i ended up with a filter with multiple poles - almost like a EQ. That also varies with temperature, model range (capacitance) and the model/make build etc depending on the cap. I suspect this is why the sound is being coloured. The treble goes down considerably compared to using a single capacitor.

What do you think i should do next, why is a single cap not effective against lowering the 50hz ac mains noise compared to a bank of caps. Can anything be done about this, or will i be forced to use more than one capacitor. What do you think about going up in capacitance value, i am on 150,000uf at the moment.

Many thanks.

[Speedskater]

You just need a better amplifier design.
Once the supply is at about 10,000uf, it should be good to go. Above that it's in rapidly diminishing returns territory.

[Speedskater]

You might be ably to improves things with a very old fashioned, cap - choke (inductor) - cap, pi filter.

[FullRangeMan]

Maybe you could be interested in the inductive (no caps) PSU from Bartholomeo Aloia, if you find something on the web please inform us.

[HAL]

Using a parallel combination of a 10000uF electrolytic cap, 100uF polypropylene film cap and 1uF stacked ceramic cap should help with the capacitor for the power supply as each cap has limitations to its overall frequency response.  Each of those types will have a frequency response that is good over a different frequency range and better than a single cap as the parasitic components of the device take over the response.  A parallel large value resistor can further damp any peaking response if needed. 

Good luck with the power supply design.

[FullRangeMan]

For hi-fi audio use caps should work full for better performance, if they are working half full or so there will be constant refill operational and drawbacks.