Chosen Solution
The left surround channel is very quiet compared to the other channels, I have checked with other speakers - it is definitely the amp channel. Any idea what to check?
Your Marantz receiver has automatic speaker setup and equalization called Audyssey. It uses a microphone to measure your room and set speaker levels. If the Audyssey setup program hasn’t been run yet or if the setup procedure had measurement errors, then one or more of your speakers could have the wrong levels set by the receiver. I’d start by running the Audyssey setup program again, even if you’ve run it already. Place the measurement microphone centrally in your listening room at about ear-height. If there are still issues after running the Audyssey setup, then you can manually adjust the individual speakers. The receiver’s setup menu will allow you to set individual speaker volumes, and you can even play a test tone through each speaker to see how they compare. If you set all the speaker levels to how you like them and one speaker still seems very quiet then there might be something wrong with the receiver’s software that would require professional repair.
