ARC Reference 110 vs older ARC amps eg VT150

And how does it sound, in your opinion?

How does the VS110 sound? Very nice, if rounder and less transparent than ARC's balanced amplifiers.

A Richard Vandersteen preference, which I agree with, is to get two VS55's and run them as balanced monoblocks. Very cool.

Sorry if I'm missing something - how do you run two VS55's as balanced monoblocks?

Each VS55 is normally a stereo unbalanced amp. To convert a VS55 into a mono balanced circuit requires that you have a balanced preamplifier and make two special set of "Y" interconnects.

Lets look at one channel for this example. Coming out of your preamplifiers right balanced XLR output, your cable would have to be terminated with a female XLR at the preamp end and then two RCA's at the destination end, which would plug into the two RCA inputs on your VS55. One RCA would represent PIN 2 (non-invert) & Ground, while the other RCA would represent PIN 3 (invert) & Ground. Balanced connections used to be more commonly terminated this way (two RCA's rather than an XLR).

Now your VS55's left channel circuit will carry the non-inverted leg of the balanced signal, while the right channel circuit will carry the inverted leg of the balanced signal.

The last thing you need to do is properly connect the speaker wire to the outputs. You will no longer be following the normal connection practices as labeled on the back of the amplifier. Here's what you do:

First tie the two 4 ohm taps together with a piece of wire. Then connect your right channel speaker (+) wire to the "Right" channel 0 ohm tap and then the negative (-) wire to the "Left" channel 0 ohm tap. Viola! You now have a 100 watt, truly balanced mono amplifier.

Warning: this really works well with speakers that are 8 ohms and don't dip too much below that. It's not a good idea with lower impedance speakers. For example, it works very well with Vandersteen Quatros which never go much below 7 ohms.