The Benchmark is an excellent amp.
The thing driving the interconnect cable is where the difficulty lies in supporting the standard. Its pretty easy to do in an amplifier- you can do it with a differential input, which can be done with an opamp easily enough. But to drive the balanced line so that neither the non-inverted phase or inverted phase references ground (the interconnect shield)- that's a bit of a trick. How its done in studio equipment is with a small output transformer that has no center tap. It has a simple secondary winding that has one side tied to pin 2 of the XLR and the other side of the winding tied to pin 3. Pin1 is tied to chassis and no connection to the transformer whatsoever. This is done to prevent ground loops but it also prevents the cable construction from influencing the sound. However for the latter its not enough to not reference ground- the circuit also has to be low impedance. For many years the standard was 600 ohms but these days is a bit higher: if your balanced source is going to support the standard, it should be able to drive 1000 ohms without bandwidth or distortion issues.
We patented a way to do this that is direct-coupled, which to my knowledge is the only other way to support the standard. Any system that employs dual out-of-phase single-ended outputs has to reference ground and so does not support the standard.
Clearly a passive simply cannot support the standard- and so the interconnect cable will impose a coloration, and quite often one that varies with volume. With many sources that employ an output coupling capacitor, it can cause a bass rolloff if the volume is set to anything less than full. This does not happen with all sources, but if it works out that way, the choice of passive volume control will have no effect!
The thing driving the interconnect cable is where the difficulty lies in supporting the standard. Its pretty easy to do in an amplifier- you can do it with a differential input, which can be done with an opamp easily enough. But to drive the balanced line so that neither the non-inverted phase or inverted phase references ground (the interconnect shield)- that's a bit of a trick. How its done in studio equipment is with a small output transformer that has no center tap. It has a simple secondary winding that has one side tied to pin 2 of the XLR and the other side of the winding tied to pin 3. Pin1 is tied to chassis and no connection to the transformer whatsoever. This is done to prevent ground loops but it also prevents the cable construction from influencing the sound. However for the latter its not enough to not reference ground- the circuit also has to be low impedance. For many years the standard was 600 ohms but these days is a bit higher: if your balanced source is going to support the standard, it should be able to drive 1000 ohms without bandwidth or distortion issues.
We patented a way to do this that is direct-coupled, which to my knowledge is the only other way to support the standard. Any system that employs dual out-of-phase single-ended outputs has to reference ground and so does not support the standard.
Clearly a passive simply cannot support the standard- and so the interconnect cable will impose a coloration, and quite often one that varies with volume. With many sources that employ an output coupling capacitor, it can cause a bass rolloff if the volume is set to anything less than full. This does not happen with all sources, but if it works out that way, the choice of passive volume control will have no effect!