Is Amp OK?
Have you got a CD player you can plug into the amp (turn amp's gain down first, play cd, raise gain, lots of volume?
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Is TT ok?
do you have another unit to temporarily try it? Take TT to a friends house? Take TT to Store (call, prearrange). IOW, is the TT's built-in phono output up to line level?
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McIntosh amps have a switch on the back, two optional input sensitivities which can change the volume out. Default is 0.75v; verify that,
TURN GAIN (volume) controls way down 1st, then try the other 2.5v setting. Play TT, Gain up slowly, Big or small difference?
from manual, page 16
https://cdn.shopify.com/s/files/1/0003/3275/9084/files/McIntosh-MC7270-Owners-Manual.pdf?v=1592943508
"INPUT SENSITIVITY Switchable: 0.75 volt or 2.5 volts-level control provided for higher input voltages."
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How Select Source?
Do you only have a TT plugged into the amp's input jacks, OR, do you have more than 1 source, and if so, how are you selecting which source goes to the amp's input jacks?
How high are you turning your GAIN (volume) controls?