McIntosh Experts Needed

I am currently contemplating another MC275mkvi to run as a pair of mono blocks. I am currently using one along with an Audio Research SP20 preamp, which by the way is an awesome combination. I use small Sonus Faber Minima Vintage speakers. What will I gain in sound quality? A friend told me that I would loose some of the sweetness of only one amp but would gain a bit more punch. He said it would sound more solid state than tube. What do the experts think ?
I tried with one MC275-V years ago. It sounded sweet and put me to sleep. I ran as a pair of mono blocks and I was awake and smiling. Lastly, I just bought a pair of MC601 and I found myself singing and dancing on the chair.
The choice is yours... whether you are going to bed or go dancing.
Mike,These MC275's are great when bridged so using a pair is recommended, I Think you will love the extra weight and solidity your system would achieve. Go for it.
A point to be aware of, if you would be connecting the SP20 to the amps via balanced connections: According to John Atkinson's measurements the SP20's balanced output impedance rises to 3460 ohms at 20 Hz (while being about 730 ohms at mid and high frequencies). The balanced inputs of the MC275mkVI are specified as having input impedances of 20K. Since the two channels are connected in parallel when that amp is used in mono mode (which is not the same as being bridged, btw, to make a minor correction to what was said above), I suspect that the balanced input impedance in that mode would be only 10K, which is not an ideal match relative to the measured preamp output impedance. For that matter, 20K isn't completely ideal either, being less than a 10:1 ratio.

Also, if you are driving your JL sub from the preamp's RCA outputs, and if (as is often the case) the preamp's RCA and XLR outputs are not independently buffered (i.e., driven from separate output stages), the sub's line-level input impedance of only 10K will worsen that situation considerably, and result in significant deep bass rolloff of the signals seen by both the sub and the main speakers. And JA's indication that the preamp's unbalanced output impedance is half of its balanced output impedance is suggestive of the possibility that the RCA and XLR outputs are not independently driven.

So before making this purchase, and assuming that I am correct in envisioning that you would have balanced connections to the amp inputs and unbalanced connections to the sub, I suggest that you ask McIntosh what the balanced input impedance is in mono mode, and ask ARC if the preamp's RCA and XLR outputs are driven by separate and independent output stages. If the answers are as I've speculated above, I would recommend against proceeding down this path.

Very nice system and setup, btw! Good luck. Regards,
-- Al
Al, thanks for the wise advice. I am using the single ended amp inputs as opposed to the balanced ones. I think they sound better, maybe for the reasons you suggest.
I'm with Beewax, I preferred 2 MC275's over 1 and prefer MC 601 monos over the 2 MC275s. Listen with your own ears, you really can't go wrong with any of these amps.
I also have two MC 275 mkV running mono for my top end on my Infinity RS 1-B's. I originally had only one for a week and then went with the two. The only real difference I have heard (and there is a caveat) is that with two there is more power. However, with only one the MC 275 is very powerful. Now the caveat....I do not listen to my system at extreme high level. I am very happy with the two!!!

RWD (Rick)
I used to run a pair of 275s. They're going to lose a little of that sweetness if you bridge them. It's all system dependent though. Sometimes a slightly more brisk presentation can be helpful, sometimes not.
Also, Almarg is right. Careful with that input impedence.
What's really strange is I don't remember the original MC 275 having such a low input impedence. I run a pair of MC60s on a high efficiency speaker and the input impedence is 500K.
I once heard a friend of mine who had this information directly from the tube guru Dissanayake who had suggested him to change the input tube 12AX7 on his Mc Intosh MC275 with another tube the E180cc and listen to the difference it makes.
Stereo or mono use it's the same, my friend is very happy of the change...
Best regards.