4 or 8 ohm to drive 6 ohm speakers for the MC2255

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Try both and use whichever gives you the best results. If the amp runs unusually hot with them connected to the 8 Ohm taps, then go to the 4 Ohm taps so that you don't sacrifice reliability.
 
Yep try them both and go with the tap that sounds the best. After several a+b comparisons I decided the 8 ohm tap sounded best for my 6ohm speakers.
 
Hmmm; after reading Mac's take on this I think it's time to try out the 4 ohm taps on my new amps. The 8ohm tap sounded best on the old ones so I never tried the 4's on the new ones.
 
Of course speakers are not simply 6 ohms or 8 ohms or 4 ohms. The impedance goes up and down with frequency. There should be an impedance sweep graph somewhere to show you what the impedance curve looks like. Pay close attention to what the impedance values look like below 200 Hz. If that area is mostly above 6 ohms, then running off the 8 ohm tap shouldn't be a problem. If that area drops quite a bit below 6 ohms in places, you may want to stick with the 4 ohm tap. Evenso, I'd probably go with what sounds the best, unless its getting too hot on that tap.
 
The idea is to use the tap closest to the impedance likely to be seen the majority of the time with a given speaker. Exact matching at all times is obviously impossible.

-Purely for sake of discussion, wouldn't PG spring into action should a mismatch occur, ie: a 4 ohm speaker connected at the 8 when driven to the point where distortion exceeds 1 - 2%? :idea:

Secondly, Ron Evans is quite explicit on this point in the Mc book, "A [McIntosh autoformer amp] will double down too..." (like a DC amp when so connected) which would seem to be in direct conflict with McIntosh's official warning that output would be reduced....:idea:
 
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62caddy said:
The idea is to use the tap closest to the impedance likely to be seen the majority of the time with a given speaker. Exact matching at all times is obviously impossible.

-Purely for sake of discussion, wouldn't PG spring into action should a mismatch occur, ie: a 4 ohm speaker connected at the 8 when driven to the point where distortion exceeds 1 - 2%? :idea:

Secondly, Ron Evans is quite explicit on this point in the Mc book, "A [McIntosh autoformer amp] will double down too..." (like a DC amp when so connected) which would seem to be in conflict with McIntosh's official warning that output would be reduced....:idea:
Click to expand...
Obviously an internal conflict between the engineers knowing the full capability of the product and marketing’s decade old purveying message about the autoformer / operating temp / reliability.
 
Thanks to this thread I swapped my speaker cables from the 8ohm taps to the 4ohm taps on my mc1201's. It was a very easy change to make and I immediately noticed one hell of a difference for the better:banana:. I have no idea why the 8ohm tap sounded better vs. the 4ohm tap on my mc2500's but it sure does not work that way on the 1201's with the same 6ohm speakers. :dunno:
 
Speakers don't have a constant impedance curve. 2255 are very robust units. They are some of the last Mac SS power amps designed to be used at 110 % 24 hours a day 365 days of the year. So I would connect the speakers to the 8 ohm tap. If you find the heat sink becomming hard to touch change the connection to 4 ohms. If heating persist place a small whisper fans on top of each heat sink separated by non conductive isolators. If the power guard lamps flash before the meters indicate 200+ watts you have issues. 2255 has a very well defined signature, but that said they aren't hard either. They were my preferred HF horn amp driving Big Altec JBL and Klipsch horns. Loud clean clear with no signs of fatigue. They worked well with ML-4C, Concert Grands, ADS , Martin Logan and Magneplannar speakers. If you need big power for low impedance dips I prefer the MC 7200. Lets say you want to drive 3 pairs of power hogs. The MC7200 is the definite answer.
 
motorstereo said:
Thanks to this thread I swapped my speaker cables from the 8ohm taps to the 4ohm taps on my mc1201's. It was a very easy change to make and I immediately noticed one hell of a difference for the better:banana:. I have no idea why the 8ohm tap sounded better vs. the 4ohm tap on my mc2500's but it sure does not work that way on the 1201's with the same 6ohm speakers. :dunno:
Click to expand...
Elaborate so that we all may benefit.
 
^^^^^^^Ok; first thing I noticed was increased bass. I was playing Pandora and Johnny Cash's version of Ghost Riders in the Sky came on at the same time I finished the swap. I brought it to a steady 120 on the meters and WOW! I've heard that song several times but I never heard such a low end. Next thing I noticed is the 3D soundstage my sda's are noted for became much more pronounced. There's a rock solid and very pronounced image now right, left and especially center with an increased amount of "air" around the instruments.
I'm still amazed that swapping those taps has given me all those improvements. Next it'll be on to the mc2255 as that's running 6ohm speakers on the 8ohm tap to. I'm hoping for likewise improvements but I'm really not expecting quite as much.
 
damacman said:
Better yet, ask for a demonstration of that.
Click to expand...
That would be the proper thing to do. I was thinking at first I may have had a loose or dirty connection but that was not the case. It could be amp specific on how much change there is in the taps to. Thinking back I remember very little if any change at all when I tried tap swapping on my 2100's.
 
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