BiBer wrote: > seanadams;396704 Wrote: >> The wall wart and/or AC power connections have nothing to do with it. >> The problem is that the amp is placing no load on the input when it's >> not selected, and this allows SB3's output to drift away from 0V. Then >> later, when the connection is established, there is a thump while this >> capacitor charges back to the correct bias. >> >> You can fix it by attaching some high-value (100K) resistor each of the >> RCA signal lines. These could be connected inside the sb3, inside the >> amp, or perhaps on the cables. >> >> Maybe we should have included these resistors on our end, but it seemed >> to be industry practice not to. It is extremely unusual to have an >> amp/receiver that does not have them. > > I looked at the schematics of the amp and the line inputs go directly > into balance control (after passing through the relay switch). these > balance control are actually not in chain when centered. then the > signal goes to volume board which is just two variable 30k resistors. > so there are no resistors between the line and ground, i assume this is > what you meant. > > could someone please explain why the sb output drifts from 0V without > load?
I did that already... 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. As for adding a resister (or evidently even a coupling capacitor), I'll assume that the amps designers are after the best performance possible and omitted what they though were redundant components. That or they just wanted to look good on paper. If you add a resister, you will change the properties of the sound. But I doubt you will hear the difference if you keep the resistance high enough and the SB's capacitors do not allow a significant amount of current through. _______________________________________________ discuss mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/discuss
