Several customers have run afoul of the Adjustable Impedance feature - at least as it's currently designed/controlled - wherein they accidentally switch from the default impedance setting (#1 - 20k) to say setting number 2. No harm in that per se but if you switch the preamp to a setting number that hasn't been configured yet...you get...well....nothing. As in no sound at all. Zero. Zip. Nada.
This has a magical way of making our phone ring.
Cust: "Hi, my name is _______ and I recently bought your _______ preamp and it suddenly stopped working."
Me: "What do you mean it stopped working?"
Cust: "Well, there's no sound coming out."
Me: "Is it on?"
Cust: "Yes, it's on."
Me: "Are the displays working?"
Cust: "Oh yeah, everything looks and acts normally but there's no sound. And it was working great a moment ago. Sounds great by the way."
Me: "Are you at the unit now. Do you have the remote handy?"
Me: "Press the left button on the remote and tell me what number show up."
Cust: "Ok. Ah...2!"
Me: "Have you configured any of the impedance settings 2-5 since you first received the unit?"
Cust: "No. I was planning on messing with that next but I was enjoying listening to it and hadn't gotten around to it yet. And then it stopped working."
Me: "Ok. Press the down button on the remote to change the impedance setting back to 1."
Cust: "Heh! That fixed it!! It's back on! What happened? "
Me: "You'd accidentally switched from impedance setting #1 which is the default setting number and switched the unit to #2. Since #2 hadn't been configured yet, there's no attenuation table established so no sound comes out. Basically the unit is muted. If you switch it back to #2, then adjust the impedance level (1-99k), press enter, turn it off, and then run auto-cal, that will set up setting number 2. Same from settings 3-5. At that point you can switch back and forth between impedance settings on the fly with live music and home in on the optimal setting for your system. "
Cust: "Ok, great. Thanks."
Me: "You're welcome. Enjoy. Bye."