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Re: Need to upgrade my McIntosh 2105

Jim,

Your MC2105 was designed in the late 60s. The design was dependant on the transistors which were made at that time. To assure reliability the amp had low voltage rails, +35 / -35 volts. the way to make a transistor last is to lower the rail voltage and use more of them, all other things being equal. Other parts of the reliability package were thermal and current draw monitoring protection circuits and the output transformer which allowed the output stage to be set up for maximum linearity and let the autoformer match the speaker load.
This series of amps MC2100, 2105, 2300, MC250, etc. was a success and powered many a band and dance club troughout the 60s and 70s.
These design principles are still used by McIntosh but we are about five generations down the line as far as output transistors go. Your amp was bandwidth limited due to the original transistors where moderm Mc amps are rated at half power @ 100 KHz and actually do more.
If you put new power supply and replaced the two signal caps your amp would sound like new but still be a 2105. A new Mc amp will have more extention on the top and bottom, be much quieter, and in comparison be transparent.
The output transformer is flat at 100 khz and has a greater bandwidth than any output transistors. The modern autoformer will still allow the linerazation of the output stage while delivering full power into 2, 4, or 8 ohms. See if your local dealer will let you audition a MC202 or MC352 with your speakers.
If you want to stay in the used market look for a MC7270, MC150 or MC300.
Many seem to prefer the tube Macs with maggies and the MC275 reissues or the new MC2102 will work fine.

Ron-C


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