Dual Differential / Balanced?

Kijanki,
Thanks for your interesting and informative comments here. Listening confirms many of your points regarding real life sound quality. I appreciate the theoretical advantages of differential balanced circuits. Coincidence or not some of the very best sounding Amplifiers I've heard were simple unbalanced circuits with RCA  cables. As you and Al  point out  implementation is a very major factor. 
Charles, 

thanks so much for the replies, I'm learning a lot.

sorry for the lack of circuitry knowledge, most of my info is based off of forums like these and it seems the way people describe balanced is tossed inconsistently, I just got schooled though!

I thought the RDC 7.1 had a balanced design because the dacs are dual differential PCM1704, and because BAT had a hand in developing.

The matching Integra research/BAT RDA-7 power amp I know is fully balanced, so I assumed that they would make the pre/pro to match

I've had McCormack/Pass on my mind, how are the classe balanced input?

also does anyone know how good the circuitry is on the emotiva XPA-1? it claims fully balanced and looks impressive

thanks

Al, I agree, that was invalid point - double DF doesn’t make much difference in most cases. As I stated in my older posts speaker’s impedance is mostly resistive and it is in series with back EMF reducing max possible DF to about 1. As long as amplifier doesn’t destroy it too much it is OK. Some of Ralf’s amps had DF<1 sounding fine.

You are right that I assumed two independent amps in differential mode - that’s different from balanced. In order to make identical gain stage in each amp they have to reference each other (like in the first stage of instrumentation amp) instead of being ground referenced. In that case amps aren’t really independent as I thought they should be. Noise rejection in such design should be great but it is not worth extra expense IMHO. Single ended amps with balanced inputs might have great noise rejection as well, while better components can be utilized for the price of fully balanced design.

Charles1dad, Thank you.  I often engage in discussion with Al or Ralph to learn more.  It is difficult to understand why particular architectures are being implemented since it is often fueled by demand.  I like to understand technical merits of design but sound is the only proof.

I won’t even comment on the issue of instability because you can find it in any FAQ/primer on fully balanced design, but it appears that you question my notion that connection with XLR cables is not always the best. Experience of many people on this forum was that RCA connection sounded better than XLR.

That is true, please consider though that there is a standard for balanced operation, of which about 95% of high end audio ignores.

The result of not adhering to the standard is that you may well get inferior operation. When balanced line is done properly (and can be done with single-ended circuits, the Ampex 351 tape machine being an excellent example) the result is that the interconnect cable ceases to be a part of the system sound. A common example of an audio company not adhering to the standard is any ARC balanced preamp. The standard calls for ground to be ignored at the input and output- it is for shielding only. But the ARC preamps put signal current through the shield of the interconnect, which causes the construction of the cable to suddenly become critical. The result is that the cable might have an audible fingerprint when used with such a preamp (and I’m not picking on ARC beyond example, this is a very common situation with many balanced products in high end).

So suddenly something that is supposed to eliminate cable interaction doesn’t; IOW the balanced cable is going to editorialize just like a single-ended cable, which IMO makes me wonder ’why bother?’ As you pointed out, others do too.

IME, audiophiles obsess over interconnects and for good reason- they often sound different and often one sounds better than another in their system. I’ve experienced this a lot; I’m not one of those engineers that thinks this is all some sort of audiophile fantasy!

But the fact is, if you can get the interconnect cable to not editorialize, it will result in better sound. So far the balanced line system is that solution. That is why I mentioned the AES file 48; even though I’m not a particular fan of the AES in general (lots of the types of engineers I just mentioned tend to hang out with that otherwise august group), the definition that is file 48 is rather handy and succinct. Unfortunately unknown or misunderstood by the majority of high end audio.

So yes, there are many on this forum that think RCA connections sound better out of experience, I’m just pointing out that is happening due to the balanced system not being executed correctly (which BTW, also means that the length of the cable is irreverent). That is why there is even a debate in high end audio about the benefits of balanced!