xlr vs rca

Yes, very true. A lot of people post that don't have any idea what they are talking about.

The circuit Almarg described consists of 2 amplifiers or series of amplifiers one of which amplifies the inverted signal and the other the non-inverted. They can indeed be completely separate until applied to the speaker.

A differential circuit of the type used by Atmasphere consists of 2 tubes that share a common connection; the cathodes of the tubes. This is sometimes referred to as a long tail pair. It is difficult to explain circuit theory in a forum such as this but rest assured the 2 signals do interact in a differential amplifier. Applying a signal to either input will cause current to flow in both tubes. The circuit amplifies the difference between the signals, hence the name. It does not amplify any signal which is the same i.e. it rejects any common mode signals. If the 2 halves were separate and did not interact the circuit would not work as intended.

You can google it for more info.

Lew, thanks for the kind comments. Herman is more knowledgeable than I am concerning the type of balanced architecture he referred to, and I will defer to his comments. Perhaps my reference to fully balanced architecture should simply have said that it maintains a balanced pair of signals throughout its internal signal path.

On a separate note, one thing I neglected to emphasize in my post is that besides providing rejection of noise (in the sense of high frequency hiss and buzz), a balanced interface is much less susceptible to low frequency hum problems. Shadorne alluded to that, and the paper he linked to explains why.

Basically, since the chassis of single-ended equipment is connected to ac safety ground, to signal ground, and to the shields of single-ended interconnects connected between components, any offset in ac safety ground potential between the two components will cause an extraneous 60Hz current to flow through the shield, in common with signal return current. As Shadorne points out, the magnitude of the resulting hum will be dependent on the resistance of the path through the shield, and therefore on the particular interconnect.

If the interface between the two components is balanced, that becomes a non-problem, since the conductors for signal current and signal return current are separate from the shield of the cable. That is true whether or not the components are "fully balanced."

Regards,
-- Al

With the large amount of excellent SE gear it is hard to argue that balanced is inherently better in a home environment even though those that make it and use it would disagree.

SE gear is cheaper so it must be better - the savings can be used towards gold plated RCA connectors and ground loops are rare in the home... ;-) LOL

Herman, I guess I should have phrased my question differently. I am aware of the Atma-sphere dual differential topology and how it works; I am just not aware of any other way to do it with tubes. Perhaps I should have asked how can you do it differently with tubes, and who (what company) uses other than a differential topology to achieve true balanced operation with tubes? Also, in any "balanced" design, an early stage, have to split the signal into positive and negative halves? It seems to me that at least the phase-splitting step is easiest to achieve with a differential topology. Downstream from the phase splitting, I get that additional differential topologies may not be necessary. Sorry that this is somewhat OT, but it's interesting, at least to me.

Lewn,

Also, in any "balanced" design, an early stage, have to split the signal into positive and negative halves?

A phono cartridge can output a differential signal and most if not all modern DAC chips have differential outputs so no split is needed. It can start out that way.

I am just not aware of any other way to do it with tubes

you simply build 2 amplifiers in one chassis like stated earlier and one amplifies the + signal and one amplifies the minus. I don't know how all of the balanced manufacturers approach the problem but you can certainly do it that way. I did look through BAT's website and they make no mention of differential circuits. Perhaps they use them but don't talk about it?

Shadorne,

I'm afraid I don't follow. The balanced builders are just as likely to use gold plated connectors as the SE crowd. As for ground loops, take a look at my system. The phono is balanced into the pro box but it is converted to SE by transformers at the output of that box and is SE from then on. I run 107dB efficient horns with SET tube amps and even with the phono turned up I have to my ear up near the speakers to hear any kind of noise. No hum, no ground loops and I am biamping.