Conrad Johnson ACT2 against Audio Research Ref 3

"I am surprised that you even heard any sound at all."

I'm not. It comes down to how ARC has implmented the SE input signal. As with the LS5 that started it all with ARC, the design here is a truly balanced implementation. Only ARC has since added SE input and output connections. The question is how do they support SE signals:

1) Is the SE input converted to a balanced signal through a phase-splitter circuit which then runs the signal "balanced" from then on; or 2) Does the SE signal simply run through the "+" phase of the balanced design from input to output? My guess is the former as ARC is a big proponent of the balanced topology. In the former case, the SE/Bal switch would do nothing more than "activate" that phase-splitter stage. In the latter case, the SE/Bal switch would simply ground the input of the "-" phase just like an adaptor would do if using an SE source on a balanced-only connection like the LS5. In both cases, there is a signal on the "+" phase as the ARC products are non-inverting.

And then the output: 1) is the SE output simply the "+" phase; or 2) is there an additional stage that brings the two phases together for a SE output? The benefit here is using both phases throughout but at a cost of adding that final stage to produce an SE output.

In any of these cases, with balanced cables, the sound will come through just fine with the "+" phase and the "-" phase possibly having no signal. But this is no different than when I used an adaptor on the LS5 to run a SE power amp; the "-" phase was simply not being used.

Knowing exactly the implementation here would give the user a better idea as to the benefits, or more likely, the losses, of using the SE inputs or outputs vs. the balanced connections for a more "pure" sound.

John

Excellent points John. I will call Leonard at ARC when I have a minute. I will post his answers here.

Simply put......The deficiency that Guido heard was a human error based on his activating SE and not balanced outputs on the Ref 3. It has nothing to do with a fully balanced system. Having said this however I rest assured that Guido is going to love his Ref 3 as I do.

Just spoke to leonard at ARC:

Ref 3 is a truly differential design. No splitters/inverters are used to simulate balanced operations. Two 6H30 tubes are used for the positive signal, and two for the return signal. If the Ref 3 is switched to SE operation through the remote control, a relay switch is activate which turns off the return signal on the XLR connectors and takes the 6H30 tubes responsible for the return signal out of the active circuit. Leonard suggests that if single ended operations are desired, the user should employ RCA ICs instead of balanced ones. However, he confirms that turning off the balanced signal on XLR, or using RCA connectors will still result in a 'good' sound with a predictable loss of 6DB of gain. This 'good' sound will however be noisier, slightly flat, and pinched, if compared to the sound of Ref 3 in a fully balanced configuration.

One further note, according to Leonard, the 6550C tube employed on Ref 3 is in fact an original SED Wing 6550 manufactured in the St. Petersburg plant, rather than the lesser pseudo-Svetlana equivalent.

Please note that in the previous post I should have been more specific: instead of 'sound' I should have specified 'Ref 3 sound signature'. The reason of course is that the actual sound is a function of all components. As such, we can't make a categorical statement about how best to run the Ref 3--single ended or balanced. It will all depend on the rest of the system.