Precalibration (or “PreCal”) is a method of normalizing the measurement and control electronics in the LDR3x.V2 so that each board behaves the same as any other board over the full volume control range. The PreCal process uses a set of 100 ohm and 100k ohm resistors that get plugged into the V2 board to give the V2 two known resistance points that are then used to apply correction factors when performing normal LDR calibration. The resulting stored PreCal correction factors increases the accuracy of the preamp controller.
Tortuga Audio performs precalibration on each V2/V2.1 preamp controller before shipping them to customers or using them in a preamp product. The results of the PreCal procedure are permanently stored in the board’s memory memory chip. PreCal should not have to be repeated, but since the V2 was introduced as a DIY product we are making the procedure available here for our DIY customers.
PreCal is a normal part of Tortuga Audio’s commissioning process for each LDR3x preamp controller starting with the release of version V2.1 of the LDR3x preamp controller board on January 5, 2015. If you already own an LDR3x.V2.1 board or any Tortuga preamp product shipped on or after January 5, 2015 your board/preamp has already gone through PreCal and repeating the process is not necessary.
If you own a V2 version of the LDR3x or any Tortuga preamp built with the V2 board, then your preamp will likely benefit from PreCal. PreCal only needs to be performed once.
It’s critical that you have a very clear understanding of how to identify the LDRs on the V2/V2.1 board.
The instructions assume you are facing the front of the board looking towards the back (top in the pic below) where the LDRs are located. Going from left-to-right, the 4 LDRs are identified as follows: RV4 RV3 RV2 & RV1. These identifiers are printed on the circuit board. The PreCal sequence is #1-RV3, then #2-RV4, followed by #3-RV1 and finally #4-RV2.
If you supply your own calibration resistors you will need to solder or otherwise attach them to 0.1″ square pin female sockets. To make you own we recommend using a typical 6 inch square pin female-female jumper wire, cut it in half, strip each cut end, and solder the wire ends to each leg of a resistor. You’ll need to do this for all 8 precalibration resistors. When done, each resistor will have a square pin female socket attached to each end of the resistor. The two square pin sockets will be used to plug each resistor into the 2 rear male header pins on each of the four LDR headers.
The table below describes each step in the precalibration procedure.
Powered by BetterDocs