[Pampero]

The insertion loss is the same for both channels so it never occurred to me it could be the cables. Noise doesn't seem to be a problem but it would be interesting to solve the crime. i'm familiar with the 6dB loss that occurs going balanced to unbalanced which is why I mentioned it. I'm not nearly so smart that I won't take your usual excellent advice but I hope I have the basics covered. I was the JBL pro rep in the Pacific Northwest for 32 years, retired in 2010. Also Pacific Northwest AES chapter chairman three years running. Which doesn't make me smart but I'm older than you so be appropriately respectful! Hi Mom!

You're right of course. Voltage measurement would be definitive. I've been cheating by using the meters on the amp and preamp and a test disk with the necessary tones and noise designed specifically for this job. I have unity gain when going straight from the preamp to the amp. I drop 6dB patching in the crossover which I can make up using the mix pot. BTW, the disc is available from Barry Ober and it's tailored to this task. Actually I don't really think of it as a cheat, more like a shortcut. It's a fine sounding crossover no noise, no weirdness so as a practical matter it's not a big deal.

In any case I enjoyed fumbling my way to a 90Hz tuning of the crossover last night. After this, 80Hz. The experiments will continue until the patient is cured or dies.