So yesterday I found my left channel was playing 6db lower than my right channel. Time for some troubleshooting. Switched output from preamp to poweramp, and now right channel is lower. Conclusion 1: poweramp is not the problem. Switched input from DAC into preamp and now left channel is lower. Conclusion 2: preamp is not the problem. Changes digital source into DAC. Nothing changes - digital source is not the problem. Changed DACs, same problem. DAC is not the problem. Connect poweramps directly to DAC, problem disappears - DAC is definitely not the problem. Switched input into preamp again - low level channel inverts. Now I'm really puzzled. What is the problem. Took me an hour to figure it out. What was the problem?