cliveb;573632 Wrote: > I have absolutely no knowledge about the Electrocompaniet amp, but what > you describe sounds like some kind of protection circuit is kicking in, > and I do have a hypothesis.... > > First, the background. You're connecting the SB3's unbalanced output to > the EC's XLR input. Probably the SB3's signal is going to pin 3 (or 2), > and its ground is going to pin 2 (or 3). Pin 1 on the XLR (the ground > on the EC) is probably only connected to the screen of the cable, and > the screen isn't connected at the SB3 end. This configuration is fairly > typical for driving a balanced input from an unbalanced output, and the > difference between pins 2 and 3 is what the balanced input regards as > the signal. > > Now, under normal circumstances, the ground from the unbalanced source > will be 0V, because the source component (eg. preamp, CD player, etc) > has its ground plane connected to the mains earth. But the SB3 has a > floating ground, and (using the stock PSU) there's quite a lot of > ripple on its ground plane. This means that what's going to pin 2 (or > 3) of the EC's input isn't 0V, but some very small amplitude mains > frequency ripple. Because it would be treated as signal and get > amplified, it would result in quite loud hum. If you connect the SB3 > output direct to a normal balanced amp that accepts whatever it's > given, loud hum is preceisely what you'll get. (The reason you don't > get this hum when you connect an SB3 to a normal unbalanced amp is > because the ground planes of the SB3 and amp are connected, and so the > ripple gets shunted to earth via the amp's mains earth connection). > > Conjecture: Perhaps the EC amp is detecting this unacceptably high > level of hum and refusing the power up, in order to protect your > speakers/hearing. An experiment to try would be to try connecting the > screen end of the RCA-to-XLR cable to the ground at the SB3 end. This > will shunt the ripple to earth via the EC's ground (assuming that the > EC's ground plane is connected to mains earth). Alternatively, connect > a wire between the SB3's ground plane and mains earth (a suitable place > to access the SB3's ground plane is the outer ring of its COAX digital > output).
It goes beyond my understanding a little bit, but it sound promising. As I imagine, this could be either the problem you describe, or some strange ground level difference between SB3 left and right channels, but I cannot imagine how this could happen. I'll try to connect the grounds. The amp have the ground connector on the rear panel, like most amps used to have (I think mostly for turntables). Can I just connect this to SB3 coax outer ring, or could I break anything? Could it have any negative effect on either EC or SB3? -- azaz44 ------------------------------------------------------------------------ azaz44's Profile: http://forums.slimdevices.com/member.php?userid=21080 View this thread: http://forums.slimdevices.com/showthread.php?t=81664 _______________________________________________ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/mailman/listinfo/audiophiles
