[sueata1]

Hey Guy's,,,I have 2 Mac 275's and would like to run them configured for Mono.....
The Mac manual is very vague about this,,,,
Does anybody have an idea to help out with the wiring

Thanx a lot and happy listening,,,Mel

[richidoo]

Manual for Original amp: http://www.berners.ch/McIntosh/Downloads/MC275_own.pdf   Page 8

Manual for Reissue amp: http://www.berners.ch/McIntosh/Downloads/MC275_MK4_bro.pdf   Page 11

These don't seem too vague?   

Connect the L and R outputs together in parallel using wire jumpers. That means connect the positive to positive and negative to negative. You will have to make up your own jumpers from a length of wire, 16ga minimum. This is paralleling both amplifiers together as one, sharing outputs. Then connect the speaker to the Left posts in correct polarity. You will have jumpers and speakers both connected to the left posts.  Using spades on the jumpers might allow better tightening. If using bare stranded wire, twist speaker and jumper wires together at left posts.  Switch the amp to mono to make it share the inputs too, then connect source to the Right input marked mono.  Say a prayer and turn it on...

+    >>>>        +       >>>>      +
Speaker     Left side         Right side
-    >>>>        -        >>>>      -

You can experiment with which output taps you prefer, by changing all the amp connections to the respective Left and Right 4ohm or 8 ohm taps.

Double check everything before you turn it on!  Don't cross polarities between right and left amps! Keep negative to negative and positive to positive all the way across.

Let us know how it sounds!

[mgalusha]

Mel,

The first question is do you have a preamp with full differential output? Running in mono it needs a balanced input. If so it's pretty simple.

Connect your speaker to the left channel of the amp as normal except us the next higher impedance tap. For a 4 ohm speaker use the 8 ohm connection. Now connect a jumper from the negative of the right channel to the negative of the left. Do the same for the positive using the same impedance you are using for the speaker, example is 8 to 8. Set the switches to Bal and Mono and connect the preamp output to the right input jack. Repeat for the other channel, being sure to use the right input on each amp since they are running in mono.

The current manual you can download from McIntosh has a better drawing than mine, which is from 2004. Current manual: http://www.mcintoshlabs.com/downloads/product_manuals/mc275arom01.pdf

Rich beat me to it. The one thing to keep in mind is the impedance. Because the channels are in parallel the output tubes will see 1/2 the expected impedance, so using the next higher taps is suggested. That said, experiment and as Rich said, let us know how it sounds. But please don't tell me I need a second one.