Well Tzh21y, I don't know how you worded your inquiry to the McIntosh tech, nor did I hear his response. However, I'm a little suspicious of his words as you reported them
And I can tell you this: I'm right now looking at the McIntosh service manual for the MC275 Model IV (which I ordered from McIntosh after purchasing my amp) and the schematic clearly shows there is NO WAY for the balanced input signal to go through the V-1 tube (and on to the rest of the amp,) when the the input switch is in the BAL position. It's not a matter of whether I believe you. Frankly, I think there was some miscommunication going on when you spoke with whomever at McIntosh.
You can order a service manual from McIntosh for $10, or (now that the Mk IV is not a current model ;--) download a pdf version for free at this site (which I just tested for you): http://safemanuals.com/user-guide-instructions-owner-manual/MCINTOSH/MC%20275%20MK4-_E
OR! you can prove it to yourself by sliding the input switch on your amp to the 'BAL' position. I guarantee you won't hear anything out of your amp (which you WOULD if the RCA signal could get to the rest of the amp (via the V-1 tube) with the input switch in the BAL position.
Furthermore, you can 'double-prove' it to yourself by doing the reverse: unplug the RCA cables and plug in balanced cables (carrying a signal of course) and slide the input switch to UNBAL. Again, I guarantee you'll hear nothing out of the amp. The balanced input signal neither goes to, or through V-1. Why would it? There is absolutely no reason for it to do so when driving the amp with a balanced signal -- in fact, going through V-1 would actually screw up the balanced signal!
If you still think driving the amp single ended sounds better than driving it balanced (assuming you have balanced main outputs available on your preamplifier, and have made an honest A-B comparison,) then it has to be for one or another of the reasons I suggested previously, and you should investigate the cause. If, as you say, "others" feel the same way, then they should also investigate! As for balanced cables being a "waste of money" unless the amp has balanced circuit design, you are simply dead wrong! First of all, studios have been using XLR's since 'the dawn of time' because of their proven superior performance, regardless of the circuit design of the various equipment they use. And second, any conventional push-pull amplifier, be it SS or tube, requires a balanced signal in order to amplify! If you feed it a single ended signal, then you need to first create a copy (splitter) and then reverse the polarity of one of the copies (inverter) and then feed that BALANCED SIGNAL to the amp, or it won't amplify! This is what the V-1 (splitter/inverter) circuit does. Nothing wrong with that except it is a lower impedance input, and adds another layer of processing (and noise, and distortion) to the signal. However, if you are already supplying the amp with a balanced signal, the V-1 tube is not needed, WHICH IS WHY IT REMAINS OUT OF THE SIGNAL PATH WHEN DRIVING THE AMP WITH A BALANCED SIGNAL!
It would have been fun to listen in on your conversation with the McIntosh tech, just to discover where the miscommunication started. In any case, I stand by all my previous remarks regarding the basis for your BAL vs. UNBAL listening experiences. So there YOU have it! ;--)
their tech support told me that V-1 is definitely in the signal path when using balanced cables on the Mark IVCould he perhaps have meant "the V-1 tube is (still) in the SINGLE-ENDED signal path, even when you are using balanced cables"? -- which would be true. But the V-1 tube is definitely NOT in the balanced signal path. EVER! Further, "using balanced cables" has nothing to do with whether the V-1 tube is in (even) the single ended signal path or not. It ALWAYS is. It has to be. What determines whether the V-1 tube is in the (single-ended) signal path (before the signal goes to the rest of the amp) is the position of the BAL/UNBAL switch.
And I can tell you this: I'm right now looking at the McIntosh service manual for the MC275 Model IV (which I ordered from McIntosh after purchasing my amp) and the schematic clearly shows there is NO WAY for the balanced input signal to go through the V-1 tube (and on to the rest of the amp,) when the the input switch is in the BAL position. It's not a matter of whether I believe you. Frankly, I think there was some miscommunication going on when you spoke with whomever at McIntosh.
You can order a service manual from McIntosh for $10, or (now that the Mk IV is not a current model ;--) download a pdf version for free at this site (which I just tested for you): http://safemanuals.com/user-guide-instructions-owner-manual/MCINTOSH/MC%20275%20MK4-_E
OR! you can prove it to yourself by sliding the input switch on your amp to the 'BAL' position. I guarantee you won't hear anything out of your amp (which you WOULD if the RCA signal could get to the rest of the amp (via the V-1 tube) with the input switch in the BAL position.
Furthermore, you can 'double-prove' it to yourself by doing the reverse: unplug the RCA cables and plug in balanced cables (carrying a signal of course) and slide the input switch to UNBAL. Again, I guarantee you'll hear nothing out of the amp. The balanced input signal neither goes to, or through V-1. Why would it? There is absolutely no reason for it to do so when driving the amp with a balanced signal -- in fact, going through V-1 would actually screw up the balanced signal!
If you still think driving the amp single ended sounds better than driving it balanced (assuming you have balanced main outputs available on your preamplifier, and have made an honest A-B comparison,) then it has to be for one or another of the reasons I suggested previously, and you should investigate the cause. If, as you say, "others" feel the same way, then they should also investigate! As for balanced cables being a "waste of money" unless the amp has balanced circuit design, you are simply dead wrong! First of all, studios have been using XLR's since 'the dawn of time' because of their proven superior performance, regardless of the circuit design of the various equipment they use. And second, any conventional push-pull amplifier, be it SS or tube, requires a balanced signal in order to amplify! If you feed it a single ended signal, then you need to first create a copy (splitter) and then reverse the polarity of one of the copies (inverter) and then feed that BALANCED SIGNAL to the amp, or it won't amplify! This is what the V-1 (splitter/inverter) circuit does. Nothing wrong with that except it is a lower impedance input, and adds another layer of processing (and noise, and distortion) to the signal. However, if you are already supplying the amp with a balanced signal, the V-1 tube is not needed, WHICH IS WHY IT REMAINS OUT OF THE SIGNAL PATH WHEN DRIVING THE AMP WITH A BALANCED SIGNAL!
It would have been fun to listen in on your conversation with the McIntosh tech, just to discover where the miscommunication started. In any case, I stand by all my previous remarks regarding the basis for your BAL vs. UNBAL listening experiences. So there YOU have it! ;--)