Preamp Output and Power Amp Input sensitivity - mismatch?

My amp is a Mcintosh 2505. I see on the specs the input sensitivity is .5V

Would it be bad to hook it up to a preamp, say a McIntosh C37, that has output sensitivity at 2.5V? Or a C31v that has output at 1.5V? Should the output from the preamp match the amp?

 

Ideally yes.
Otherwise you can overdrive.
An atteniator like IMG which is adjudtable would take care of that
In suc cases hooking the two together is best option.

 

A preamp has its own attenuator that allows you to match its output to the amplifier, so you can achieve any playback level between silence and amplifier overload. It is the volume knob.

 

That input sensitivity spec is with the GAIN controls turned fully clockwise.

Setting the GAIN controls at 12:00 will provide 2.5V input sensitivity which would be ideal for most McIntosh preamplifiers. Personally I find the 2:00 setting works best with my McIntosh MX113 or MX110 tuner preamplifiers - both of which are also 2.5V with 90 dB speakers I use most of the time. You may choose to adjust higher/lower depending on which provides you the best S/N for lowest noise floor depending on the speaker sensitivity.

McIntosh designed these earlier amplifiers to be compatible with the widest range of output voltages among the various preamplifiers that existed at the time, some of which had voltages that were quite low.