SI T-Amp: getting rid of PSU hisses and hums

[Livino]

Hello all,

I'm using a Sonic Impact T-Amp coupled with a pair of JBL Control 1 (CM42, the 6-ohm version - nice impedance match), with a variety of sources (SoundBlaster X-Fi, CD Player, etc.). Great sounding little set-up.

I ended up buying two different power supplies for the T-Amp: a 12V 2A switched-mode PSU that looks like a flimsier Nokia phone charger, and a big heavy linear PSU that looks like a metal box with a transformer in it (13V stabilized, also 2A).

Each of these PSUs has its problems: the $35 switching thingy produces an audible hiss at high volumes (if I put my ear to a speaker, but I think it may influence sound quality anyway).

The $50 linear supply, well, it looks more powerful, but causes a hum (also at high volumes if you listen close to the speakers). I think it is a 60Hz hum but I'm no specialist.

What I'd like to know is: which one is the most appropriate type of PSU for the T-Amp? And, more importantly: how do I get rid of the hisses or hums these power supplies produce? Can I do anything about them?

(with the linear supply I though about an "isolator module" thing that I use to compensate the lack of grounded outlets for my computer equipment. I basically isolates these components from the rest of the stuff I have plugged in. The manual says it should eliminate speaker hum in multimedia systems but I'm not that's the case).