Slider calibration
The slider maxima and minima are factory calibrated to follow approximately the decibel scale under the sliders.
If for some reason some of the sliders seem to be very different from the others, there is a way to recalibrate them.
Keep the HG-16 running, and the toggle switch in the “off” position. For the minimum value calibration, push all
sliders to the minimum position. Then locate a hole to the right of the
adjust 2
-knob. Under that hole there is a
small push switch that can be activated by pushing with a narrow stick. There should be a clear but low mechanical
click when pushing. Keep it pushed for a few seconds and release. Turn power off and on again. Then move all
sliders to their maximum positions, and repeat the same action. Now the sliders should better follow the decibel
scale.
The scale is very coarse, so more accurate values can be found, e.g. if you have a digital sound card with an
FFT spectrum display.
Note:
Each recalibration requires prior power reset, i.e. you cannot immediately redo calibration without turning
power down and up again, nor do successive zero and maximum calibrations without power cycling in between! Of
course, you first need to check the reason for the need to recalibrate. B
ecause the optical potentiometer sliders do
not have dust covers, prevent any debris from entering between them or inside the wedge-like opening in the sliders.
If there is dirt in the openings, use gentle vacuuming to clean them.
Tuning
HG-16 uses a precision 12 bit A/D converter to convert the VC note signal from the bus to the note value. Therefore
it stays well in tune, and normally tuning is not needed. However, if the input VC note value is inaccurate, HG-16
has means for compensating for the inaccuracies. The two common errors are:
1.
An offset error: each C note should correspond to an exact integer VC voltage value. HG-16 scale starts at
C1 = 32.70Hz which corresponds to an input voltage value of 0V. A constant difference from the integer
values along the scale will make an offset error.
2.
A scale error: the input should follow accurately the 1V/octave scale. If the scaling is incorrect, there is an
increasing difference from the correct note when going the scale up.
HG-16 has a front panel opening below the text
tune
.
Under it there is a trimmer for fine adjustment for
compensating possible input scale error. This is typically sufficient for normal situations. If not, there is a software
facility for adjusting both the offset and scaling errors. Errors can also occur in the pitch bend signal (
CV pitch
input), so they can also be compensated in software. This is described in the following.
Software tuning
For software tuning, turn the
mode select
-knob to position 15. The output signal amplitude is now controlled only
by the
volume
knob. Only sliders 1 and 16 are functional in this mode. When
slider 16
is fully down, you can
compensate for VC note errors. When it is fully up, you can compensate for errors in pitch bend and/or adjust the
pitch bend range. Start by moving both
slider 1
and
slider 16
fully down and connecting the output to a precision
tuner. Play C1# in the keyboard (not C1, because C1# allows you to observe both positive and negative offset
errors). The offset error can now be zeroed by turning
adjust 1
. Only the internal A/D offset is compensated, so the
adjustment range is small. For large offset error compensation, see the pitch bend offset compensation section later.
Next, play a high note, e.g. C5, and use
adjust 2
for possible scale error compensation. If no pitch bend corrections
are needed, you can now raise
slider 1
fully up. This move will burn the new calibration values to the nonvolatile
memory.
Pitch bend tuning
If pitch bend adjustments are needed, keep
slider 1
down and move
slider 16
fully up. Connect your pitch bend
signal source to
CV pitch.
Check that the pitch bend signal is inactive. Use
adjust 1
to compensate for possible
pitch bend offset. Activate the pitch bend signal and use
adjust 2
for adjustment of the desired range. Again, when
slider 1
is moved up, the values are stored in the nonvolatile memory.
Warning
: The sum of VC note and pitch bend offsets make the total note offsets. Therefore pitch bend offset can
also be used for compensating such large offset errors in the VC note signal that are out of its own adjustment
range. However, then you have to remember that when you disconnect the
CV pitch
source, the tuning is different.
Also, if you have adjusted the pitch bend offset, you have to redo the VC note calibration process described above.
Because during this tuning process it would be impossible otherwise to find out which offset is wrong, there are
additional means for hearing the difference: With zero or disconnected
CV pitch
bend, the output signal has both
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