Dual Differential / Balanced?
Well Ralph your explanation of misuse /improper application of "balanced " circuits would explain why I don't usually find them better sounding in many audio systems. Nonetheless single ended /unbalanced components can often sound fabulous. Superior implementation of either circuit type is mandatory. Charles, |
Thank you Ralph, I will keep reading more. I use fully balanced stages in low level amps without any ground reference. It has bandwidth of few kHz only, but full scale of the signal is in single millivolts. At the end A/D converter with differential input provides its own ground reference. I can see a problem with fully balanced audio amp design that has no reference to ground. Both outputs can be floating together since without output current or voltage difference feedback won't react to that. It needs ground reference somewhere or some kind of servo on common mode. Shield should never be used to carry signal but it was unfortunately common practice long time ago. Scope's coax is a good example of that. Scope with shorted leads, touching circuit under test, shows phony signal - since ground return path (possibly thru supply) causes current flow thru the shield, that input amp (referenced to scope's BNC GND) sees as a signal (voltage drop on the shield). Shield converts common mode to fake normal mode signal. My small Rowland has only XLR inputs - perhaps mature decision in class D amp, so I was not able to compare it with single ended RCA cable. I still can see substantial sound quality difference between decent XLR cable (AQ King Cobra) and very good one (AZ Absolute). I have to read AES48 standard, you mentioned. There was wonderful EDN magazine issue on that many years ago. Grounding and shielding is considered by many as black magic. |
Kkijanki, A friend of mine has the Atma-Sphere MP-1 preamplifier and the MA-1 amplifiers. With this fully differential balanced signal path he says he can hear differences between various brands of balanced interconnects. By the way his MP-1 sounds terrific mated to my Coincident 300b SET amplifier. Charles, |
Charles & Kijanki, see Ralph’s first post dated 3-22-2013 in this thread for a summary of what is necessary to make a balanced line-level interface insensitive to cable differences. And also for what I consider to be a compelling proof Ralph offers for his contention. But also note a question I posed a few posts later in that thread, and the answer Ralph provided: Almarg 3-27-2013 Atmasphere 3-27-2013I see that the MA-1 amplifier which Charles mentioned has a specified balanced input impedance of 200K. I’d imagine that one reason Ralph would have chosen to not provide a very low input impedance, such as the 600 ohm standard he refers to, is that most preamps made by other manufacturers would not be able to drive such a load with good results. Best regards, -- Al |
