All this passive pre amp does is to attenuate the volume and switches among different inputs. No power needed.
This passive preamp use a 4-port, 3-position switch. All channels' ground signal is switched with the main signal. The grounds of each channel are isolated, therefore ground loops between equipments are eliminated. Also, the noise from one source cannot get into another.
I bought this 23-step 4 deck volume switch from www.my3c.net, cost is NT$690, it comes with 90 Dale 1% resistors and a aluminum knob. It is a lot cheaper then other switch I could find on the web. This is a 100k ladder type switch.
The interconnect wires are shielded twisted pairs, with the shield connected to the ground at the source end.
The sound? Very transparent, I think it does not has any sound of its own because there are only resisters and wires between the input and output.
Also check out my OPAMP balanced preamp.