[jbreher]

OK, I'm floundering. Any help would be appreciated.

Seems my assumptions above on how one is to calibrate the Pre are incorrect.

First, while enabling the OSC and enabling INS on a channel does route the OSC signal to the output. However, using this routing, the Trim pot for that channel has exactly zero effect on the output as monitored on the DB25. Accordingly, from my naive viewpoint, the ability to route the OSC signal to each channel's outputs is useless for calibrating the Pre itself.

I can't imagine digi would have implemented a feature that has no use, so I must be confused about something. Perhaps its utility is to calibrate something (e.g. an ADC) downstream? But even so, such utility is hampered by the fact that the OSC level (on my admittedly possibly compromised unit) is somewhat below the manual spec. What am I missing?

Next, I envisioned/postulated the following cal mechanism. I used a TRS to route the OSC signal to each channel's line input in turn. I set the measured channel to line, and 0dB gain. I was gratified to learn the the Trim pot in this case did indeed affect the channel signal output at the DB25.

Figuring that 0dB gain indicated on the GAIN/PARAM display corresponds to an actual 0 dB gain from Line input to DB25 output, I tweaked the Trim pot to make the measured signal level at the DB25 equal to the measured signal level (when unloaded - maybe a small error introduced?) at the OSC TRS output. Or very close - approaching this level, channels stop changing level with additional pot rotations.

At the point that the pots stop affecting the output level, I measured the following unloaded Vrms levels:
OSC TRS: 1.184
Channel outs - 1.171 to 1.183, with the low reading being quite the outlier.

I'll consider this good enough for the work I'll be doing, unless I've made some error in procedure.

Anyone want to comment on how I went about this?