Spectral Audio Neptune User manual

Neptune
Service Manual

Contents
1 General Note......................................................................................................................................................................3
2 Manual Changes................................................................................................................................................................3
2.1 Having pulse-width modulation (PWM for the rectangular wave on OSC1..OSC3.................................................3
2.2 OSC3/LFO sync with OSC1 or OSC2........................................................................................................................3
2.3 Even faster envelopes.................................................................................................................................................3
2.4 Increase the tuning range for OSC1..OSC3................................................................................................................3
2.5 General in/outputs.......................................................................................................................................................3
3 Assembly plan Analogue Print..........................................................................................................................................5
4 Assembly plan Digital Print...............................................................................................................................................6
5 Adjustment.........................................................................................................................................................................6
5.1 Adjustment of 12.000 V Supply.................................................................................................................................6
5.2 CV slope adjustment...................................................................................................................................................6
5.3 Osc1............................................................................................................................................................................6
5.4 Osc 2...........................................................................................................................................................................7
5.5 Osc 3...........................................................................................................................................................................7
5.6 Filter............................................................................................................................................................................7
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1 General Note
Fully schematic is not supported by this manual. If you think you really need to receive it, please write to
[e-mail] .
2 Manual Changes
2.1 Having pulse-width modulation (P M) for the rectangular wave on
OSC1..OSC3
2.1.1 OSC1
remove U01 pin 13 from round (it's connected on both side of pcb, so you have to heat up the pin with the
solder gun and pull the pin out)
2.1.2 OSC2
remove U11 pin 9 from round (it's connected on both side of pcb, so you have to heat up the pin with the solder
gun and pull the pin out)
2.1.3 OSC3
remove U12 pin 9 from ound (here it's more easy, just on bottom side you have to cut the connection to the
Via)
The free pin is now the input of a DC voltage in the range to have pwm 0..50%.
2.2 OSC3/LFO sync with OSC1 or OSC2
For this, connect a 470pF to Base (middle pin) of T03 (OSC2) or T01 (OSC1).
2.3 Even faster envelopes
To increase even more speed of E 1 (Volume), you may solder a resistor in the value of 100 Ohm down to 10
Ohm parallel to R118. For the VCF Envelope use R100. Both may be result in some click noise because of the
low rise and decrease time of the Envelope.
2.4 Increase the tuning range for OSC1..OSC3
It is possible to reduce the value of R001 for OSC1, R022 for OSC2 and R128 for OSC3. Its standard value is
1M5. Decreasing its value may also mean to decrease of R002, R021 and R129 to have the reference note in
the middle of the Tune Pot. To learn another Reference Note over MIDI is another solution but this decreases the
note range.
2.5 General in/outputs
2.5.1 Oscillators
The easiest way to get the signals of the Oscillators are the switches SW02, SW03 and SW11. Amplitude is 0 to
+12V. Same for the noise generator.
2.5.2 Envelopes
These signals can be taken on ENV MOD potentiometer for the filter envelope and on the Volume potentiometer
for the VCA envelope.
2.5.3 Filter
The Filter input is at C18 and its output is U07 pin 8. Control voltage is applied to the Base of T05 and R073.
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2.5.4 Distorter
The filter output is directly connected to the distorter/fuzzer selection input. Remove pin 8 from U07 from the
solder pad (leave it in the air and connect R105 to it). The remaining pad is now the input for the distorter/fuzzer
selection.
Output is at U15 pin 14.
2.5.5 VCA
Input is R176 (sold it away from the output of U15 pin 14). Output is pin 12 from U06 and at the output jack on
the rear side. Control voltage can be applied to the volume potentiometer.
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4 Assembly plan Digital Print
5 Adjustment
Keep the following sequence.
5.1 Adjustment of 12.000 V Supply
Connect a precise DVM to C12 and round (i.e. from a potentiometer mounting pin) and adjust R19 to 12.000V
after a warm-up phase of at least 30 minutes.
5.2 CV slope adjustment
Connect a precise DVM to the output jack of CV. Adjust R15 to 3.00V between C1 – C4 (input over MIDI).
5.3 Osc1
The offset for VCO1 is set with R003 and the oscillator slope with R008. Nonlinearity in the upper frequency
range is adjusted with R014.
Proceed as follows to make the adjustment:
1. Set the MIDI reference note to C1 by pressing the learn-key.
2. Press key A3 and set the VCO1 frequency with offset trimmer to 220.0 Hz, measured with an exactly
frequency meter.
3. Press key A1 and set the frequency to 55.0 Hz with oscillator slope trimmer.
4. Repeat steps 2 and 3 until frequency values are stable.
5. Press the key A5 and set the frequency to 880.0 Hz with nonlinearity trimmer.
6. Repeat steps 2 to 5 and re-adjust if necessary.
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5.4 Osc 2
Same as above but with R020 as offset, R026 as oscillator slope and R039 as nonlinearity correction. Do it first
with Oct switch in 16' pos and correct later the Nonlinearity pot with Oct switch in the highest position until no
beats are hear able to Osc 1.
5.5 Osc 3
Same as above but with R127 as offset, R132 as oscillator slope and R142 as Nonlinearity correction. Do it first
with Oct switch in 32' pos. Now all frequencies are half the value of the above. Correct later the Nonlinearity pot
with Oct switch in the highest position until no beats are hear able to Osc 1.
5.6 Filter
Put it in self resonation (start of). Set key follow switch to 100%. Measure the generated frequency and set
Cut-off pot to 100Hz with C1 at MIDI input. Input now C4 at MIDI and adjust R152 to 800 Hz. Repeat if
necessary.
~~~
Have fun!
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