Owner`s manual
grace design m201
owner’s manual
11
Four standard sensitivities are supported in the m201 A/D converter: +18dBu = 0dBFS (14dB Head-
room) +20dBu = 0dBFS (16dB Headroom) +22dBu = 0dBFS (18dB Headroom) +24dBu = 0dBFS
(20dB Headroom).
The front panel interface features a calibration mode that allows precise adjustment of the A/D sensi-
tivity. To recalibrate one or both of the input sensitivity congurations, simply do the following:
1. Disconnect AC power from the m201.
2. Remove the 8 top cover screws using a #2 Phillips screwdriver. Lift the top cover o the unit and
set it aside.
3. Reconnect AC power to the m201 and turn it on.
4. Connect a signal generator to the A/D LINE inputs. Set the signal generator output to +4dBu @
1kHz (1.29V rms).
5. Turn on the m201 A/D converter and select LINE as the A/D input source.
6. To enter CAL mode, press and hold the INPUT SENS button for approximately 3 seconds. The nor-
mal operation displays will extinguish and the CAL indicator will begin ashing indicating CAL
mode is active. The current input sensitivity range (A) or (B) will be illuminated along with that
range’s current sensitivity calibration (shown as “dB Headroom” in the bottom left of the meter
display).
7. Press and release the INPUT SENS button to select the range (A) or (B) that you wish to calibrate.
8. Press and release the A/D SOURCE button to scroll through the 4 available sensitivities until the
desired setting is illuminated.
In calibration mode, the digital audio meter is congured such that the “0” position is the target
sensitivity level. The meter then indicates the current signal level versus this target sensitivity. The
meter will display a window centered around the target sensitivity with a +/- 0.4dB width (in 0.1dB
increments). When the sensitivity adjustment on the A/D converter is calibrated for the selected set-
ting, only the “0” LED will be illuminated. If the signal level is high, the 0 indicator will be illuminated
along with the error (in 0.1dB increments) to the right of 0. If the signal level is low, the 0 indicator
will be illuminated along with the error (in -0.1dB increments) to the left of 0.
On the m201 A/D module, trim pots are used to adjust the (A) and (B) ranges for each channel. Each
of these are labeled on the A/D module circuit board <gure 3>.
1. Locate the appropriate trimmer for the channel you wish to adjust. If the current signal level is
high, you need to decrease the A/D sensitivity. Using a non conductive tool, turn the appropriate
trim pot counter-clockwise to reduce the level until only the “0” is illuminated on the m201 meter.
If the current signal level is low, you need to increase the A/D sensitivity by turning the appropri-
ate trim pot clockwise to increase the level until only the “0” is illuminated on the LED level meter.
2. Once all desired calibration adjustments have been made, press and hold the INPUT SENS button
for approximately 3 seconds. This will exit CAL mode and return the A/D to normal operation. The
new settings are now stored until future changes are made.
3. Power down the unit, disconnect the AC power and reinstall the top cover.