12.
Calibrate your Laka.
(You will need a multimeter and 1V/Oct voltage source)
1. Power on Laka and allow it to warm up for a few minutes.
2. Use a multimeter on the DC Voltage setting to VREF and -VREF. Connect the black probe to
one of the terminals marked “-Gnd-” on the Exp1 header or some other circuit ground such as the sleeve
of a Thonkiconn jack, and monitor the voltages present at the test points marked “+Vref” and “-Vref”.
Adjust the corresponding trimmers marked “+Vref Adj” and “-Vref Adj” so that they are as close as
possible to 5.0V and -5.0V respectively.
These can be adjusted for other values but we highly
recommend the “stock” setting of +/-5V, both for the safety of other modules and playability of
Laka.
3. Put all four “Zero” switches in the downward (Zero) position and set all four “Offset” knobs to the Center
Detent position. Use your multimeter to monitor the output of Channel A while adjusting the rear trimmer
labeled “1” so that the output of the channel is as close to 0V as possible.
--The center detent of each pot will have a “range” of approximately 100-150mV which will
inevitably cause the output to change slightly based on various factors such as which direction it
is being rotated, so just do your best to center this “range” around 0V.
Repeat this step for the other Offsets. The rear trimmer labeled “2” corresponds to Channel B output, “3”
to C, and “4” to D.
4. Calibrate the channel Inputs. This can be done a few ways, depending on tools available:
-Set all Offsets to the center (null) position. Zero the channels which are not being tested by
turning the Zero switches to the down position. Patch a decently precise voltage output such as
the 1V/Oct output from a well-calibrated sequencer or precision voltage source into the Channel
A input and position the Channel A fader at full amplitude (all the way up). Patch Output A into the
1V/Oct input of the best-tracking VCO in your rack and use a frequency counter (such as the Hz
mode on your multimeter if it has one) to monitor the VCO’s frequency. Adjust trimmer “A” so that
an increase of 1V from your voltage source corresponds as closely as possible to an increase of
1 Octave (precisely double the frequency) as indicated by the frequency counter. This might
involve going through the octaves a few times to ensure tracking is good over at least 3-4
octaves. Repeat for the other three channels, with the trimmers labeled “B,” “C,” and “D”
corresponding to the appropriate Channel inputs.
The normalization from one channel to the next means that the signal patched to Input A does not
have to be repatched to test a different Channel, although due to the cumulative impedance of
each channel input, each channel should be switched to “Zero” when not in use to avoid
cumulative loading of the source signal, which may cause the input voltage to droop slightly and
throw off the calibration.
-Quick calibration: Patch your sequencer into the Channel A input and patch Channel A output to
the 1V/Oct input of your favorite oscillator and tune by ear. Repeat for the other three channels
until you are happy with the tuning.
5. All done! Enjoy your new Sequential Voltage Processor!
Thank you for building the Laka!
