1100a² #2

One channel of amp distorts when the volume is turned up. It's goes from clean to distorted around ½ power.

The voltages across r206, 207, and 208 are identical to the voltages across r306, 307 and 308.

Audio remains clean at c304 a and c201
 

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This is the amp (green)that when turned up would start to distort before I made the bias stop working.

The other amp (tan) was distorting at anything outside of 15-30hz. Replacing a single .1 ohm resistor seems to have fixed it.
 

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I'd like to see if disabling the protection circuit will make a difference. It's somewhat risky but this is an odd problem and we need to eliminate some of the circuit. Removing D305 and D307 will disable it. Be careful, all semis tightly clamped to the heatsink, be ready to power down if there is a problem.
 
Yes. When the distortion is present. Remember to measure the voltage on the collectors.

What you have to remember is that when the shield has voltage on it for one channel, that feeds the other shield so if the other probe is plugged in and laying on the bench, it won't be safe. Only plug in one channel when you're connecting the shield to something other than ground.