Most-likely it's an amp.
First off we need to know what amp you have (tube? transistor?)
If you have a tube amp you'll definitely know it's a tube(s)
If you have SS amp and can reach an output transistors, you should check-compare its temperature on different channels.
Replacing transistors in SS amp is a-bit more tougher and may require tuning and matching. Often you would want to replace output transistors on both channels especially if you can't find right replacement.
If you connect only faulty channel, you may hear clipping even on low volume while the one non-faulty will play OK.
First off we need to know what amp you have (tube? transistor?)
If you have a tube amp you'll definitely know it's a tube(s)
If you have SS amp and can reach an output transistors, you should check-compare its temperature on different channels.
Replacing transistors in SS amp is a-bit more tougher and may require tuning and matching. Often you would want to replace output transistors on both channels especially if you can't find right replacement.
If you connect only faulty channel, you may hear clipping even on low volume while the one non-faulty will play OK.