Phil Leigh wrote: > The way I would approach this is to disconnect all except the SB. If no > thump, then connect each item one at a time (keeping the SB connected) > and see when the bump appears. > > The SB is NOT grounded to mains earth, it floats. One additional test > is to disconnect the power supply from the SB (but keep the SB > connected to the amp), wait for 5 minutes and see if the thump is still > there. If it is DC on the SB outputs, this test will make it go away. > >
Phil's last idea above is a good one. If that is the case, I suppose, as unlikely as I think it is, electrolytic capacitors can age. However I don't think slimdevices has been around long enough to have sold equipment that old. Most amplifiers, by design, try to operate in a linear area of a transistor's range. That usually means there is a DC component to the output when all is quiet. To normalize this to 0 volts (a standard procedure to simplify the design of amplifiers) large capacitors are added in series between amplifier stages. Even if they age and leak it's not much of a problem as the input impedance of the next state is usually low enough to maintain the DC voltage necessary so that the next stage will operate properly. But, if the input impedance is low enough almost any capacitor will eventually leak enough to allow the DC components on both sides to be equal. And aged capacitors will probably leak more or "faster" then new ones. I am almost sure my Sony amps mute the output momentarily when switching sources. I think they are common STR home theatre amps. I have no idea how most amplifiers are built. But if I designed one I would always terminate the inputs regardless if they were switched in to ensure the coupling capacitors would filter out the DC component. I also like the momentary muting feature if in fact that is what my amps are doing. To analyse this much more would require someone who has actually fix this problem to give suggestions or to use test equipment to monitor the voltage at the amp's input when you hear the thud as well as the current leaking through the audio cable when all is quite and you are sourcing the SB. Say, you are not using the phonograph input on the amp are you?? All bets are off if that's what you are doing. ...good luck _______________________________________________ discuss mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/discuss
