Oops - hit the post button too early!

The wave at the transformer output looks like:

_ _ _ _ +V
/ \ / \ / \ / \
\_/ \_/ \_/
-V

The wave at the rectifier output looks like:

_ _ _ _ _ _ _ _ +V
/ \/ \/ \/ \/ \/ \/ \/ \ _
0V

3) A smoothing capacitor smooths the pulsed double frequency into a steady DC at the RMS value of the wave.

The key thing is how the rectifier keeps the capacitor 'reservoir' topped up.

They're made out of diodes, and diodes conduct current in only one direction, so they only conduct when the voltage on the capacitor is lower than the voltage at the transformer output.

This difference is the 'ripple' of the supply. It's a bad thing. It increases the more current you draw from the capacitor, and decreases with bigger capacitors (they lose a smaller proportion of their charge before being topped up).

So, for a given current output, a bigger capacitor gives you a more stable supply, with less ripple.

Here's the problem, though. A big capacitor still only has the time where it's at a lower voltage than the transformer to be topped up. This means that it pulls a HUGE current through those diodes (actually only two at a time). That's why they're so big.

So here's the point:

A linear power supply, in the process of working, converts your relatively smooth 50/60Hz voltage into absolute horror of a current. It sits their doing nothing, then pulls all the current it needs in about 5% of the available time.

If it helps, think of a reservoir with a dam at the low side. Water (current) is allowed to drain out of the dam at a steady rate. The faster the water drains out, the more the 'loading'. Now top up the dam to its full mark once every minute, but you only have 5 seconds. You'd need to throw in a lot of water!

(A bigger capacitor is a wider and longer reservoir - might be time to stop stretching this metaphor!)

A normal linear PSU couldn't give a rat's about the quality of the mains, because it looks bloody awful anyway as its converted. That's what the caps are there for. (Mind you, spikes can get past at times).

But then again (as a mate of mine who designs BIG power supplies says). Imagine what is happening to the mains for the rest of your equipment whilst the power amp is pulling those big pulses from the supply. I think that's one of the arguments that one of the manufacturers of conditioners uses. It's there to protect the rest of your kit from the mess that the power amp is making of your supply. Then again, if they also use linear power supplies, then they also are isolated from a lot of the noise.

Personally, I think I'd need to upgrade a hell of a lot before I get a conditioner. And I'd be thinking of getting a posh mains cable when the local electricity board use OFC for their network :-)

Having the power amp on it's own spur from your distribution box might help, though.

Or even - having all of the delicate electronics (analogue, DACs, clock sources) on the smooth side of the supply, in the same box. I reckon that Bob Stuart might be on to something with these active speakers! :-)

Just another couple of pence. If I add these up, I'll be ablew to get that 568 I keep promising myself!

End of sciency bit!

Cheers,
Mark.

861v8, DSP5200, DSP5200HC, DSP5000mk2, UHD722, MF10, Prime, Prime PSU