UcD / Hysteresis,
what's the difference?
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
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
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
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
It is clear that class-d
with the inherently low PSRR requires quite good powerful, stiff supplies with
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.