future.retro XS Manual

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XS Synthesizer
Calibration Procedure

Table of Contents
Calibration Procedures
1. Calibrating the V/Oct CV OUTPUT
2. Calibrating the Scale of Oscillator A
3. Scale of Oscillator A Diagram
4. Calibrating the Octave Control of Oscillator A
5. Octave Control of Oscillator A Diagram
6. Setting the Overall Pitch of Oscillator A
7. Overall Pitch of Oscillator A Diagram
8. Calibrating the Pulse Width Duration for Oscillator A
9. Pulse Width Duration for Oscillator A Diagram
10. Calibrating the Scale of Oscillator B
11. Scale of Oscillator B Diagram
12. Calibrating the Octave Control of Oscillator B
13. Octave Control of Oscillator B Diagram
14. Setting the Overall Pitch of Oscillator B
15. Overall Pitch of Oscillator B Diagram
16. Calibrating the Pulse Width Duration for Oscillator B
17. Pulse Width Duration for Oscillator B Diagram
18. Calibrating Oscillator B’s Triangle Wave Shape
19. Oscillator B’s Triangle Wave Shape Diagram
20. Calibrating Oscillator B’s Sine Wave Shape
21. Oscillator B’s Sine Wave Shape Diagram
22. Calibrating WAVE C’s Ring Modulator
23. WAVE C’s Ring Modulator Diagram
24. Calibrating Envelope 1
25. Envelope 1 Diagram
26. Calibrating the Filter Pitch Tracking
27. Filter Pitch Tracking Diagram
28. Calibrating the Filter Cutoff Range
29. Filter Cutoff Range Diagram
30. Calibrating the Overdrive Noise Gate
31. Overdrive Noise Gate Diagram
32. Calibrating the Amplifier
33. Amplifier Diagram
Additional Testing Procedures
34. Testing the Glide Time
35. Testing the CV IN
36. Testing Oscillator A’s Fine Tune Control
37. Testing Oscillator A’s Wave Control
38. Testing Oscillator A’s Modulation Amount
39. Testing Oscillator B’s Wave Control
40. Testing Oscillator B’s Modulation Amount
41. Testing Oscillator B’s Env 1 Sweep Amount
42. Testing Oscillator B’s Frequency Control
43. Testing Oscillator B’s Frequency Sync
44. Testing the MOD W OUT
45. Testing the VEL OUT
46. Testing the LFO
47. Testing the Filter Types
48. Testing the Filter Modulation Amount
49. Testing the Filter Env 1 Sweep Amount
50. Testing the Filter Overdrive
51. Testing the Filter Velocity Amount
52. Testing the Amplifier Velocity Amount
53. Testing the Envelope 2 Shapes
54. Testing the GATE IN
55. Testing the GATE OUT
56. Testing the AMP IN
57. Testing the MAIN OUT
58. Trimmer Location Reference
NOTE: Due to the nature of the analog circuits used in the XS, the unit should be turned on for at least 20 minutes before the testing and calibration
procedure is performed. This allows the circuits to reach their typical operating temperature, and will provide a much more accurate results.
WARNING: Always disconnect the power of the unit when opening it up and making connections. Always be sure to ground yourself when handling
the exposed internal components of the XS PC boards, to eliminate the possibility of electrostatic shock to components. Failure to do so may damage
the unit beyond repair.

Step 1, Calibrating the V/Oct CV OUTPUT:
Connect the MIDI Out of your MIDI keyboard to the MIDI In jack of the XS. Using a 1/4” cable, connect the CV OUT jack to a voltmeter (positive terminal will connect to
the tip, ground terminal will connect to the shield of the connector). Controls shown in red must be set to the settings as indicated.
Play note C1 on the MIDI keyboard, and note the current voltage being output. Play note C6 on the MIDI keyboard, and adjust trimmer TR1 so the CV output is now +5v
higher than the voltage generated for note C1. Play note C1 again just to verify that it’s voltage has not changed since adjusting TR1. If it has, note it’s new voltage and then
play note C6 again to fine tune the output to +5v higher than C1. Voltage trimming should be accurate within 1/1000th of a volt.
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Step 2, Calibrating the Scale of Oscillator A:
Connect the MIDI Out of your MIDI keyboard to the MIDI In jack of the XS. Using a 1/4” cable, connect the WAVE A output jack to an oscilloscope (probe will connect to
the tip, ground terminal will connect to the shield of the connector). Controls shown in red must be set to the settings as indicated.
Play note C1 on the MIDI keyboard, and adjust the oscilloscope to display 1 period of the sawtooth waveform across the horizontal width of the display. Note where the
waveform ends, as this will be our reference when tuning the other octaves. Play note C2 on the MIDI keyboard, and adjust trimmer TR2 until 2 periods of the waveform are
displayed within the reference distance. Play note C3 on the MIDI keyboard, and adjust trimmer TR2 until 4 periods of the waveform are displayed within the reference dis-
tance. Play note C4 on the MIDI keyboard, and adjust trimmer TR2 until 8 periods of the waveform are displayed within the reference distance. Play note C5 on the MIDI
keyboard, and adjust trimmer TR2 until 16 periods of the waveform are displayed within the reference distance. And finally, play note C6 on the MIDI keyboard, and adjust
trimmer TR2 until 32 periods of the waveform are displayed within the reference distance.
Now play notes C1, C2, C3, C4, C5 and C6 on the MIDI keyboard, while doing so make sure that ends of these saw waveforms are lining up perfectly with one another, at
the defined reference distance.
While calibrating this control you can monitor the audio by connecting the Main Output of the XS to the input of your sound system if you wish to hear the adjustments you
make.
Alternative Method:
If you do not have access to an oscilloscope, you could substitute the oscilloscope with a digital frequency counter. In this method you would connect the WAVE A output
jack to the input of your frequency counter. And select the square waveform for WAVE A. Play note C1 and note the frequency generated. Play note C2 and adjust TR2 until
the frequency is now twice that of note C1. Play note C3 and adjust TR2 until the frequency is four times that of note C1. Play note C4 and adjust TR2 until the frequency is
8 times that of note C1. Play note C5 and adjust TR2 until the frequency is 16 times that of note C1. And finally, play note C6 and adjust TR2 until the frequency is 32 times
that of note C1.

Step 2, Oscillator A Scale Calibration:
Playing C1 on MIDI keyboard Playing C2 on MIDI keyboard Playing C3 on MIDI keyboard
Playing C4 on MIDI keyboard Playing C5 on MIDI keyboard Playing C6 on MIDI keyboard

Step 3, Calibrating the Octave Control of Oscillator A:
Connect the MIDI Out of your MIDI keyboard to the MIDI In jack of the XS. Using a 1/4” cable, connect the WAVE A output jack to an oscilloscope (probe will connect to
the tip, ground terminal will connect to the shield of the connector). Controls shown in red must be set to the settings as indicated. The control shown in green is the one we
will be adjusting. It may also be helpful to connect a digital tuner to the FILTER OUT jack to verify these octaves are in tune.
Play note C1 on the MIDI keyboard, and make sure the OCTAVE control for Oscillator A is set to its “0” setting. Adjust the oscilloscope to display 1 period of the waveform
across the horizontal width of the display. Note where the waveform ends, as this will be our reference when calibrating the other octave divisions. Now select the OCTAVE
“1” setting for this control and adjust trimmer TR3 so that 2 periods of the waveform are displayed within the reference distance. Select the OCTAVE “2” setting for this
control and adjust TR3 so that 4 periods of the waveform are displayed within the reference distance. Select the OCTAVE “3” setting for this control and adjust TR3 so that
8 periods of the waveform are displayed within the reference distance. Select the OCTAVE “4” setting for this control and adjust TR3 so that 16 periods of the waveform are
displayed within the reference distance. Now you can rotate the OCTAVE control quickly through settings 0 through 4, while doing so make sure that ends of these wave-
forms are lining up perfectly with one another, at the defined reference distance. If not, you may need to make slight adjustments to TR3 so that the waveforms are generat-
ing perfect octaves.
While calibrating this control you can monitor the audio by connecting the Main Output of the XS to the input of your sound system if you wish to hear the adjustments you
make.
Alternative Method:
If you do not have access to an oscilloscope, you could substitute the oscilloscope with a digital frequency counter. In this method you would connect the WAVE A output
jack to the input of your frequency counter. And select the square waveform for WAVE A. Play note C1, and set the OCTAVE control for Oscillator A to its “0” setting, and
note the frequency being generated. Select the OCTAVE “1” setting and adjust TR3 until the frequency is 2 times the frequency produced by the “0” setting. Select the OC-
TAVE “2” setting and adjust TR3 until the frequency is 4 times the frequency produced by the “0” setting. Select the OCTAVE “3” setting and adjust TR3 until the fre-
quency is 8 times the frequency produced by the “0” setting. Select the OCTAVE “4” setting and adjust TR3 until the frequency is 16 times the frequency produced by the
“0” setting.

Step 3, Oscillator A Octave Calibration:
Octave control set to 0 Octave control set to 1 Octave control set to 2
Octave control set to 3 Octave control set to 4

Step 4, Setting the Overall Pitch of Oscillator A:
Connect the MIDI Out of your MIDI keyboard to the MIDI In jack of the XS. Using a 1/4” cable, connect the WAVE A output jack to a digital frequency counter (probe will
connect to the tip, ground terminal will connect to the shield of the connector). Controls shown in red must be set to the settings as indicated.
It is essential that you set Oscillator A’s OCTAVE control to the “0” setting, and Oscillator A’s FINE TUNE control is set to its mid position (indicated as “0”). Play note C1
on your MIDI keyboard and adjust trimmer TR4 until oscillator A’s frequency is 32.703 hertz.
While calibrating this setting you can monitor the audio by connecting the Main Output of the XS to the input of your sound system if you wish to hear the adjustments you
make.
Alternative Method:
If you do not have access to a digital frequency counter, you could use a digital tuner to verify that the pitch is indeed in tune.
Or you could audibly compare the pitch generated to that of another audio source which is known to be in tune. Although this method may not prove to be as accurate.
When using this method it is better to try and match the highest playable frequency.
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Step 4, Oscillator A Overall Pitch Calibration:
or
Playing note C1 on MIDI keyboard, and Octave switch set for 0, tune oscillator to produce 32.703 Hz

Step 5, Calibrating the Pulse Width Duration of Oscillator A’s Square Wave:
Connect the MIDI Out of your MIDI keyboard to the MIDI In jack of the XS. Using a 1/4” cable, connect the WAVE A output jack to an oscilloscope (probe will connect to
the tip, ground terminal will connect to the shield of the connector). Controls shown in red must be set to the settings as indicated.
Set Oscillator A’s OCTAVE control to its “0” setting, and the WAVE A control to the Square wave shape. Play note C1 on your MIDI keyboard and adjust the oscilloscope
to display 1 period of the waveform across the horizontal width of the display. Adjust trimmer TR5 until the both the high and low portions of this square wave are equal in
their durations.
While calibrating this setting you can monitor the audio by connecting the Main Output of the XS to the input of your sound system if you wish to hear the adjustments you
make.
Alternative Method:
If you do not have access to an oscilloscope, listen to the Main Output of the XS while adjusting TR5 until the square wave produces a nice hollow sound.
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