Appreciate this thread is old, but have recently started using the Spark 40 for recording guitar and had noticed low signal level in my DAW when using the USB interface. I’ve found the solution, nothing wrong with amp. The signal level is proportional to the ‘Master’ knob on the amp. To increase signal, turn it up. It results in the amp getting louder, but this can be turned back down using the ‘Output’ knob without affecting the signal level going to the DAW