Updated May 19. 2007


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UcD / Hysteresis, what's the difference?



The setup

I used an old DVD player chassis for the amp. All 4 amps running from the same PSU having 2 x 4700 uF and two 18V AC transformers.

The speakers are connected to Speakon outlets, to make switching the speaker cables a lot easier. (I can only recommend this type of connection, it quite cheap, foolproof and as good as any high end speaker bindings!)

I played the same music on both amps, switching between the two a number of times.

The UcD seems to be more susceptible to heterodyning, producing a high pitched sound (made by the difference between the PWM frequency in the two amps).

By careful wiring, this can be reduced to a bare minimum, but it is clearly detectable by putting your ear to the speaker.


So what's the difference?

Well it's not that easy to conclude. Sometimes I wonder how Hi-Fi magazines can come up with a description on how this amp sounds compared to the other. They regularly compare to something they tested months ago, describing pros and contra as if it where scientific facts!!

The fact that the two amps have a bit different gain, makes it a bit more difficult to judge the difference, to make a real good comparison you should have a real A/B set up, where you by flickering of a switch could switch between the two amps and correctly adjust the gain, while still sitting in your chair. .... well there is a project for later :-)

Overall I'd say that there is very little difference between the to configurations. They both sound really good, leaving not much to be desired. I'm sure that a much better and more powerful PSU, would have made both sound even better and lowering the hum to nothing.

It is clear that class-d with the inherently low PSRR requires quite good powerful, stiff supplies with low ripple.

Compared to my old faithful LC-Audio "The End", (ULC circuit, 2 x 180W, running from 2 X 800VA toroids, with 4 x 22.000 uF RIFAs), it seems that both class-d amps sound a little more restricted, less free, less spatial, less roomy. Maybe it's just that I have now come to know this sound as "correct", but the difference is more notable, than between the two d-amps. On the other hand I think the treble was a bit less distinctive, maybe less "harsh" on the small d-amps (not that it is at all harsh on the LC-Audio amp).

So I'll keep my old for now, and start constructing a d-amp where the focus is best possible, and not as cheep as possible.

Is this little amp worth building? Definitely, yes. It gives a good platform for trying out class-d, it will be easy to upgrade it and experiment with. So yes try it out, if you want to go full DIY ..... otherwise bye a Hypex.