35
6.
Set VCO Coarse Frequency slider to minimum / left and Fine Frequency slider as closely as possible to
its mid-point, and VCO mode to audio.
7.
Connect VCO output to frequency counter.
8.
Ensure pitch bend and modulation wheel are centered/zeroed
9.
@0.000v/C1, adjust Freq Adj for 32.7hz, and @4.000v/C5, adjust 1V/Oct for 523hz. Repeat until no
further improvement is possible.
10.
Repeat for all VCOs.
VCF
As above, however:
1.
Remove all audio and CV inputs
2.
Set all audio and CV attenuators to zero
3.
Set Coarse Frequency to minimum and Fine Frequency to middle.
4.
Ensure nothing patched into KBD CV jack
5.
Increase resonance to full
6.
Measure frequency at VCF output jack
7.
@0.000v/C1, adjust Freq Adj for 32.7hz, and @4.000v/C5, adjust 1V/Oct for 523hz. Repeat until no
further improvement is possible.
The Gain, Offset, Freq Adj and 1V/Oct set points for the 4012 and 4072 filter cores are far apart. You can
expect to run through complete calibration (from both the ARP 2600 Service Manual and as above) when
swapping VCF cores.
Listening Test
1.
Baseline the VCO tunings (Coarse Frequency=minimum, Fine Frequency=center)
2.
On the VCF, reduce resonance to 0, and bring the Coarse Frequency control all the way up.
3.
Bring VCO1 up to full in the mixer of the VCF.
4.
Raise the input of VCO2 on the VCF to 80%.
5.
Play C1
6.
Adjust the VCO2 Fine Frequency control to tune with VCO1, eliminate any beating.
7.
Reduce the input of VCO2 on the VCF to 0, and increase the level of VCO3 to 80%
8.
Adjust the VCO3 Fine Frequency control to tune with VCO1, eliminate any beating.
9.
Raise the input of VCO2 on the VCF back up to 80%. Now you should hear all three VCO together,
in tune, at C1.
10.
If you have the luxury of both a MIDImplant and an external CV source, compare their base
frequency and how well they track up the keyboard. If you have properly calibrated their CVs,
you should hear little if any difference in their pitch tracking.
Play up the keyboard. You should not hear any objectionable amount of dissonance for at least four
octaves. You will hear beating as you go up, but it should not become fast, dissonant beating. If you do,
go back and refine the 1V per octave tracking adjustments. If you can make this work across six octaves,
you have done very well
–
this is difficult and / or impossible on some TTSH units.
PUTTING IT ALL TOGETHER
Only when you are completely sure all functions are working, should you install the panel.