Calibration? "User controled event." What's it for? How do you do it? And what could go wrong?
Randy
Auto-calibration (AutoCal) is an inherent feature of our 3rd generation LDR preamp controller referred to as the LDR3x.V2 or "V2" board. The LDRx and LDRxB are built around the V2.
AutoCal is a self-contained software/hardware based system that provides for the recalibration of the individual LDRs to ensure that the preamp maintains its left/right channel balance over the full attenuation range. LDRs are not like pots or fixed resistors. They are analog devices that in some respects have characteristics of tubes insofar as their performance can drift over time as they age. AutoCal corrects for this...if it happens...and if it's needed. It may not. AutoCal addresses one of the key issues of owning an LDR based preamp over the long haul and as such is more of an insurance policy than a frequent necessity.
AutoCal is explained in more detail in our online documentation which can found here:
http://www.tortugaaudio.com/documentation/#document-22You can put your unit through AutoCal by pressing the Enter/Center button on the Apple Remote while the preamp is turned off. The cycle typically lasts about 10 minutes. Each LDR is run through 70 calibration steps so it takes 4 x 70 = 280 steps to complete the process. AutoCal status is displayed with left diplay indicated which LDR is being calibrated and the right display showing the current step. Results are permanently stored in EEPROM memory and used by the premap each time it's subsequently turned on and used. Rerunning AutoCal will overwrite the prior results.
What can go wrong? Probably nothing. We've found AutoCal to be highly reliable once the unit has successfully gone through its initial AutoCal cycle and we do that with each build before we ship. My marketing approach is tempered by my engineering mindset and I will never tell anyone that something is totally foolproof or infallible.
AutoCal is there if you need it otherwise you can ignore it. How do you know if you need to run AutoCal? Noticing that the stereo balance has shifted off center is the most likely indication. It's also possible for an LDR to go bad....like a tube can go bad. They're plug-in replaceable. Put in a new one, rerun AutoCal and you're back in business. This is rarely required but it's there if you need it. A small percentage (< 1%) of the LDRs in our V1 design needed to be replaced. So we made them replaceable in the V2. So far, 0% of LDRs in our V2 design have gone bad.
If one of a matched set of tubes goes bad you usually have to replace them all with a new matched set. With our V2 design you only replace the one LDR that went south and then let AutoCal match them all up again. Cool beans!
