Measuring battery voltage won't necessarilly tell you much, if its a small drain. What i'm saying is that if you measure the current being drawn while the ignition is off (current that runs the clock, keeps keyless entry on standby, etc), it should be too low to be detectable. So if you read any current with your amp plugged in, there'* a problem. Don't try measuring current with the ignition on---most meters are fused at 10 amps, and the ignition may draw close to that much, i dunno.

i let the car sit all weekend and i measure the battey wit out the amp fuse plugged in. and i got 12.22v does thar sound good cuz it fired right up with no heasataion.