Spectral Audio ProTone Service Manual

ProTone
MIDI Analog Synthesizer
Service Manual
CAUTION!
All instructions in this manual must be carried out by a professional who observes the valid safety regulations. In operation, they have got dangerous voltages in the instrument. Spectral Audio GmbH accepts no liability for personal injur y or m aterial damage.
Service Manual ProTone Page 1 of 20 © 1996-2001 Spectral Audio
1 Description of the Operating Elements 3
1.1 Sockets on the Rear of the Housing 3
1.2 Front Panel Controls 4
2 Functional Description 5 3 History of Series 7 4 Improvements and explanations 7
4.1 Sense of R174 and R175 7
4.2 Sense of C63 – C65 7
4.3 Sense of R174 and R175 8
4.4 Hum Problems 8
4.5 Increasing the Gate voltage to +12V 8
5 Adjustment of the ProTone 9
5.1 Digital PCB (MIDI to CV converter) 9
5.2 Analog PCB (VCO1 and VCO 2) 9
5.2.1 VCO1 9
5.2.2 VCO2 9
6 Digital PCB 11
6.1 Assembly plan 11
6.2 Part list 11
7 Analog PCB 13
7.1 Assembly plan 13
7.2 Part list 15
8 Mechanical part list 20
Service Manual ProTone Page 2 of 20 © 1996-2001 Spectral Audio
1 Description of the Operating Elements
Warning : Shock Hazard - do not open! Vorsicht : Lebensgefahr - nicht öffnen! Avis : Risque de choc Electrique - ne pas ouvrir!
230 V~
max. 500mAT
37 36 38 39 40 41 42 43 44
SPECTRAL AUDIO GmbH
Out
Out
Right
Left
Extern
Extern
VCO
LFO
Input
Input
0.7 Veff 0.7 Veff
Gate CV
5V:On
1V/Oct
0V:Off
MIDI Thru
ProTone
MIDI
IN
Serial No.
Made in Switzerland
1.1 Sockets on the Rear of the Housing
36. Power socket
37. Fuse compartment, fuse max. 500 mA, 250V type
38. Audio outputs right / left
39. External VCO input, switched on with switch (7)
40. External modulation input, selected with selector switch (22)
41. Gate input/output (dependent on the jumper setting inside the unit, standard setting: output)
42. CV input / output (dependent on the jumper setting inside the unit, standard setting: output)
43. MIDI Thru socket
44. MIDI IN socket
Service Manual ProTone Page 3 of 20 © 1996-2001 Spectral Audio
12 3
VCO 1
0
6
1
1
2
3
4
5
6
-
TUNE PW
6
5
4
3
2
1
0
SLIDE
4567
7
5
2
8
4
9
3
3
NOISE
4
2
10
5
1
11
0
12
6
+
VCO 2
0
1
1
7
8
2
2
9
3
3
10
4
4
11
5
5
12
SYNC
6
6
-
+
TUNE
3 2 1
3 2 1
EXT
3 2 1
89 11
6
5
7
8
4
9 10 11
0
VOL VCO 1
4
0
RINGMOD
4
0
VOL VCO 2
3
12
2 1
6
7
5
8
9 10 11
12
6
3
5
7
8
2
9
1
10 11
12
12 13 18 19
FILTER
6
6
7
5
4
0
CUTOFF RESONANZ
6
5
4
0
ACCENT
1410
7
5
8
9 10 11
12
7
8
9 10 11
12
ON
15 16 17 25 26 27
HIGHPASS
8
4
9
3 2
10
1
11
LOWPASS
0
12
KEY-
12 dB
FOLLOW
24 dB
20
SPECTRAL AUDIO
LFO
6
7
5
MIDDLE
LOW
RANGE
4 3 2 1
0
8
4
9
3
HIGH
2
10
1
11
0
12
FREQUENCY
6
5
7
8
4
9
3
10
2
11
1
0
12
DECAYATTACK SUSTAIN RELEASE
21 22 23 24
ProTone
RANDOM
NOISE
6
7
5
8
4
EXT.
3 2 1
0
WAVE
6
5
7
5
8
4
9
3
10
2
11
1
0
12
12
MODULATION
6
6
7
5
8
4
9
3
10
2
11
1
0
12
28 29 313032
MIDI ANALOG SYNTHESIZER
VCO 1
CUT OFF
VCO 2
9 10 11
7
8
12
9 10 11
PW 1
LFO ON ...
5
4
3
2
1
0
ENV MOD
PAN
6
7
8
9 10 11
12
­6
5
4 3 2 1
0
GROUND-
LEVEL
C
1
2 3 4
5
L
PAN
33
34 35
1
7
8
0
9 10
POWER
11
12
GATE / LEARN
1
2
LEARN
3 4 5
R
1.2 Front Panel Controls
VCO 1:
1. TUNE: Regulates the pitch of the VCO 1
2. PW: Pulse width of the rectangular pulse
3. Changeover between the signal types saw tooth, noise and rectangle
4. SLIDE: regulates the time balance of VCO 1 and VCO 2
VCO 2:
5. TUNE: Regulates the pitch of the VCO 2
6. SYNC: Synchronises VCO 2 with VCO 1
7. Changeover between the signal types saw tooth, external (input on rear of housing) and rectangle
Mixer:
8. VOL VCO 1: Volume of VCO 1
9. RINGMOD: Volume of the ring modulation of VCO1 and VCO2
10. VOL VCO 2: Volume of VCO 2
VCF:
11. CUTOFF: Cut-off frequency of the filter
12. RESONANCE: increases the harmonics at the cut-off point
13. Changeover between lowpass and highpass
14. ACCENT: Pulsed increase of the cut-off frequency and the volume
15. ACCENT ON Indicator: Lights when the accent function is switched on (MIDI Controller 65)
16. Determines the edge steepness of the filter: 12 or 24dB / octave
17. KEYFOLLOW: The cut-off frequency is influenced by the actual note
LFO:
18. RANGE: Changeover between three LFO frequency ranges
19. FREQUENCY: Setting the LFO frequency
20. LFO Indicator: Indicates each positive half wave of the LFO.
Note:
The eye recognises frequencies larger than 60 Hz as being static.
21. Changeover between symmetrical and asymmetrical LFO waveforms
22. Selector s witch for different LF O waveforms. By means of the m atrix presentation, there are a total of 9 signal forms available: sinus , asymm etric al sinus, triangle, s aw tooth, rectangle, pulse, r andom , noise and external (input on the rear of the housing)
23. MODULATION: Determines the strength of the LFO influence
24. LFO ON..: LFO assignment possibilities: VCO 1, VCO 2, PW 1, cut-off, pan (any combination possible)
Envelope:
25. ATTACK: Rise time
26. DECAY: Decay time
27. SUSTAIN: Hold level
28. RELEASE: Release time
29. ENV MOD: Influences the cut-off frequency with the envelope
Stereo VCA:
30. GROUNDLEVEL: Ground level of the unit. This also includes the volume increase influenced by the accent.
31. PAN: Regulates the relationship of the volume from the left and right-hand channel
Various:
32. LEARN Key; Switches the ProTone to the learn mode
33. GATE / LEARN indicator
34. Switch-on indicator
35. Main switch
Service Manual ProTone Page 4 of 20 © 1996-2001 Spectral Audio
2
Functional Description
The basic principle of the ProT one c orres ponds to the tried and test ed analog synthesizer principle with VCO, VCF, VCA, envelope generator and LFO. This principle is called subtractive synthesis. In order that the Pr oTone is suitable for MIDI, an additional MIDI to CV conver ter is necess ary which converts the MIDI signals into analog signals with which the VCOs, the filter, as well as the envelope generator are controlled.
The raw material for the s ound is of f er ed by the VCOs (V or rectangular signal as well as the noise generator (f or effects such as wind and thunder sounds) . The width of the rectangular signal from VCO1 can be changed with the PW regulator (2). The narrower the rectangular signal (regulator turned to the right), the 's harper ' the sound. VCO 2 is synchronised f rom VCO1 with the SYNC switch (6). The tone will be interesting in this case when the TUNE regulator (5) of VCO2 is turned (or by modulating with the LFO VCO 2), which results in a typical "Sync-Sound".
By means of the external VCO input, other sounds can also serve as raw material. The ring modulator multiplies the signals of the two VCOs which markedly amplifies the beat (frequency difference).
Note:
When the SYNC switch (6) is switched on, no beats are developed and the ring modulator has
therefore no effect.
The SLIDE regulator (4) determines the time balance from one note to another and is valid for both VCOs. Afterwards, the signal flows through the voltage controlled f ilter (VCF=V
certain frequency ranges are suppress ed. The lowpass filter allows low frequencies to pass and suppr esses the high ones, the highpass filter lets high fr equencies through and suppresses the low ones. The frequency from which the signals are s uppr ess ed is c alled the limit or cut-off f r equenc y. With the ProTone, this is formed from various sources:
oltage Controlled Oscillator) in the for m of a sawtooth
oltage Controlled Filter), within which
1. CUTOFF frequency regulator (11)
2. ENV MOD regulator (29) (influence of the envelope on the cut-off frequency)
3. LFO
4. ACCENT regulator (14)
5. KEYFOLLOW switch (17).
With the KEYFOLLOW s witch (17), the cut- off fr equency increases on higher notes so that audible f requency bands always remain the same. The res onance forms a feedback of the output to the input of the filter and causes an amplification of the frequencies around the cut-off frequency.
The ACCENT regulator (14) s ets the s har e of the s econd envelope and affects the cut-off frequency as well as the volume. It is only active when the ACCENT indicator ( 15) lights, i.e., when the accent function is switched on via the MIDI controller 65. The accent f unction is always active when the unit is switched on. By means of the MIDI controller 65, it is now possible, as with the TB 303, to give individual notes an accent (value 127) or to take an accent away (value 0). For this purpose, the corresponding control value must be sent in the sequencer, timed either before or with the note.
Before the signal leaves the ProTone, it arr ives at the VCA (V the ProTone in stereo form. Here the input signal is multiplied with a contr ol signal. In this way, the volume can be influenced by a control signal which comes from the envelope generator and the MIDI converter. The volume of the ProT one is c ontrolled with the GRO UND LEVEL regulator ( 30) as well as via the MIDI c ontroller EXT (7). Additional to this level is the s hort-ter m increas e through the acc ent func tion. The panor am a (volum e relationship of the left-hand to the right-hand signal) can be set with the PAN regulator (31). The LFO is particularly developed with the ProTone. Using its signal, the pitch from VCO1 and VCO2, the pulse width of the rectangular signal from VCO1, the cut-off frequency of the filter as well as the panorama can be modulated with the LFO ON ... switches (24).
oltage Controlled Amplifier) which is available in
With switches (21) and (22) select ion can be m ade between 9 diff erent signal f orm s. By means of the external LFO input on the rear of the housing, it is also pos sible to use any other signal for modulation. To do this, switch (22) m ust be turned completely to the right. A microphone, etc , must be connected via a pre-am plifier as this is a high level input. When the external inputs of the ProTone are used, the ProTone must simultaneously receive a note command (the same MIDI channel) in order that something is audible.
The envelope generator determines the chronological sequence of the volume after receiving a note command. The MIDI to CV converter then gives out a gate signal (+5V) with which the sequence of the envelope generator begins. The gate signal rem ains at +5V until the 'note off ' com m and com es, i.e., the key is
Service Manual ProTone Page 5 of 20 © 1996-2001 Spectral Audio
released. The parameter s of the envelope can be set with regulators (25) to (28) . How the envelope should be imagined is described later on in the glossary.
Service Manual ProTone Page 6 of 20 © 1996-2001 Spectral Audio
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