The Matinee Organ (Part 6)
A complete electronic organ to build at low cost
PART 6: Rhythm voicing, Final effects and output circuits, Explanation of controls
The outputs of the rhythm unit from ICs 21 and 22 as shown in Figure 40 are fed to the rhythm voicing circuits shown in Figure 42. These outputs go high to trigger the relevant instrument. The characteristic sound of the bass drum, low bongo, conga drum, claves and high bongo are all produced by versions of the same type of circuit.
For example, when the input to the low bongo is low, the circuit is just prevented from oscillating as set by RV21. When the input pulses high, TR22 is triggered into oscillation. The incoming pulse is given the required duration by C80 and R295 and then fed to the complex network that determines the characteristic frequency and envelope of the sound required. In this circuit (and the conga drum) a second preset, in this case RV20, is provided to adjust the length of the resonating period and thus the overall tonal quality of the instrument. The output is then mixed with the other four circuits and fed via C121 to the rhythm volume drawbar RV18.
The white noise required for the cymbal and snare sounds is produced from the reverse biased junction of TR29 whose collector is not connected. This noise is fed via C104 to the base of the amplifying transistor TR27. This transistor is turned on when any one of the three inputs to snare and cymbals is triggered by the rhythm unit. In the case of short cymbals, for example, the pulse from the rhythm unit is level-shifted by TR30 and lengthened by TR31 and C112. The pulse also controls the two filter circuits around TR28 and TR34 which give the characteristic tonal quality of the instrument with a rapid attack and a decay time set by C103, C113 and C115.
RV27 controls the overall level of the white noise and RV26 controls the level of the snare white noise only. Note that when the snare drum is triggered, not only is the white noise triggered, but the high bongo is also triggered. The outputs of the two filters are coupled via C111 and C120 to the rhythm volume drawbar RV18.
The outputs of all the circuits so far described are connected to the inputs of the master mixer shown in Figure 43. There are two signal paths through the mixer; the main path carrying flutes and/or strings which can be switched through the wah, reverb and rotor circuits and a "strings direct" path which allows the strings to bypass the wah, reverb and rotor circuits.
Figure 43 shows S19, "strings direct", operated and in this condition the collector of TR55 is high and IC17 a and d are on (and therefore b and c are off). The strings from the upper and lower manual are therefore connected to the strings balance control RV47 and mixed together by R569 and R570 and then go to the final output pre-amp via R581.
The flute voices from the upper and lower manuals are connected to the main path and if S19 is not operated (i.e. IC17 b and c are on), the strings will be mixed with them and the composite signal connected to the main path via the balance control, RV46.
The lower manual main path is connected via R576 to the premixer IC46a. The upper manual main path, however, is connected via S34a, the wah on/off switch and R575 to IC46a. Thus the manual and auto wah only operate on the upper manual. The output of IC46a now goes to the reverb circuit.
If S34, wah on/off, is operated and S35 released (auto), the upper manual main path is connected to the wah bandpass filter TR52 and associated components. The signal is amplified at mixer TR53 and reconnected to R575 via S34c. The auto wah envelope is triggered from the upper manual envelope shaper TR45 via S34d and S35c to TR51 which shapes the pulse. This signal controls the feedback of the bandpass filter.
If S35 is operated (manual), the foot pedal becomes a manual wah control and- the volume function of the pedal is replaced by preset RV48. The upper manual envelope trigger is now disconnected from the wah envelope shaper and replaced by the foot pedal via S34b and S35a to the bandpass filter.
The reverb circuit is shown in Figure 44. The input from the premixer, IC46a (Figure 43), bypasses the reverb driver amp IC38 via R396 and R402 if the reverb drawbar RV34 is fully in. If the reverb drawbar is fully out the bypass line is connected to ground via the wiper of RV34, allowing the signal to go to the spring line driver power amp IC38. The output from the spring line is amplified by mixer IC39. In addition, C140 and R401 provide a high frequency bypass to give a more natural sound at full reverb. The output of IC39 is connected to the rotor on/off switch S17a.
With reference to Figure 45, S17 is shown in the off position, in which case the rotor is bypassed by R412 and returned to the final mixer C230 in Figure 43. With the rotor switched in, a percentage of the signal is connected to IC30 which is a series of phase-shift filters and another part of the signal passes to the rotor output via C64 and R251. The remainder of the input signal passes to IC32a and b which are phase-shift filters running 180° out of phase with IC30. The outputs of IC30d and IC32b are re-mixed with the direct signal and are then connected through S17b to the final mixer C230 in Figure 43.
IC31 contains six elements that are used as voltage-controlled resistors which, when changing value, alter the phase relationship between the inputs and outputs of each of the six op-amps in the signal path to give the characteristic swirling sound of a mechanical "Leslie"-type rotor.
IC43a and b and TR20 form a voltage-controlled oscillator that runs at one of two selectable rates: 1Hz and 7Hz. The rate is selected by S18, rotor fast/slow. When changing between fast and slow and vice versa, R265,6,7 and C70 give a slow transition to simulate more accurately a mechanical rotor.
R275 feeds the ramp oscillator output to IC31 by DC blocking capacitor C72. R275 also feeds the signal to an inverter formed by IC33, whose output is fed to IC31 via DC blocking capacitor C73. RV52 applies a bias voltage to IC31 but when adjusting you will note that the change takes place after a delay, due to the charge or discharge time of C72 and C73. This ramping input to IC31 controls the resistance change in the elements and thus the rate of phase change in the signal.
Figure 43 shows IC46b which is the final mixer. All the signals previously described are mixed together here and applied to pin 6 of IC46b. The output is connected via the potential divider R583 and R597 to the swell pedal (unless manual wah is selected) and then to the master volume control RV50.
Figure 46 shows the main power amp. IC16 is an IC power amp type TDA2030, giving around 15W output into 4 ohms. Pins are provided on the main PCB that may be connected (using screened leads) to an external power amp or the line input of a hi-fi amplifier should additional power be required. The output of IC16 is connected via C201 to a headphone jack for connection to a pair of stereo headphones and then to the main loudspeaker. This completes the description of all the circuits in the Matinee organ.
The following text in conjunction with Figure 47 describes and identifies the switches and controls fitted to the Matinee Organ.
1. 16' Organ Bass drawbar. The deepest sounding pedal voice. In auto mode this stop is inoperative.
2. 8' Organ Bass/Auto Bass drawbar. A similar pedal voice to 16', but one octave higher. In auto mode this drawbar sets the volume of the auto bass line still using the 8' Organ Bass voice.
3. Sustain drawbar. Gives a fully variable delay on both Organ Bass voices. In auto mode sustains the auto bass line.
4. 8' Bass Guitar drawbar. A pedal voice designed to simulate the characteristic sound of a bass guitar. In auto mode this stop is inoperative. Any of the pedal voices can be used together, for instance to simulate a string bass use the 16' Organ Bass with Sustain and a small amount of 8' Bass Guitar.
5. 16' Flute accompaniment drawbar. The lowest harmonics in this voice have been removed to make it more useful as an accompaniment voice. In auto mode this stop is inoperative.
6. 8' Flute/Piano Vamp accompaniment drawbar. When the Vamp button is pressed, this drawbar sets the volume of a vamping piano sound.
7. 8' String/Guitar Vamp accompaniment drawbar. When the Vamp button is pressed, this drawbar sets the volume of a vamping guitar sound.
8. 4' Flute accompaniment drawbar. This stop is inoperative in auto mode.
9. 4' String/Countermelody accompaniment drawbar. In auto mode this drawbar sets the volume of the countermelody. Note that in auto mode all accompaniment voices are 8' only.
10. Sustain accompaniment drawbar. In auto mode this stop is inoperative.
11. Rotor on/off switch. Controls an electronic rotor effect, but has no effect on pedal or preset voices.
12. Rotor fast/slow switch. Changes the speed of the rotor effect with the advantage of slow transition as with a mechanical type.
13. Strings Direct switch. When operated, any string voice bypasses the reverb, wah and rotor effect. When playing with a combination of string and flute voices and rotor on, a pleasing effect can be obtained with this switch. For the best effect set the string drawbars to about half the setting of the flute draw bars. In auto mode this switch has the effect of enhancing the vamping guitar voice.
14. Vibrato on/off switch.
15. Vibrato Delay switch. When vibrato is on, this switch has the effect of delaying the onset of vibrato after a first key is pressed on the upper manual only. This effect is best used with a single solo voice when it helps to achieve a sound closely resembling an acoustic instrument being played.
16. Vibrato Rate drawbar. When vibrato is on, this drawbar varies the speed of the effect.
17. Vibrato Depth drawbar. With vibrato on, sets the depth of the vibrato effect in the overall sound.
18. Rhythm Volume drawbar. Sets the level of the drum accompaniment.
19. Presets Volume drawbar. Sets the volume of the banjo, accordion, harpsichord, piano and percussion stops.
20. Banjo Repeat drawbar. Controls the rate of repeat of the banjo and percussion voices. There is no repeat when drawbar fully in.
21. Reverb Depth drawbar. Sets the depth of the reverb effect in the overall sound. Has no effect on pedal or preset voices.
22. 16' Flute solo drawbar.
23. 16' Cello solo drawbar.
24. 8' Flute solo drawbar.
25. 8' String solo drawbar.
26. 8' Clarinet solo drawbar.
27. 4' Flute solo drawbar.
28. 4' String solo drawbar.
29. Sustain solo drawbar.
30. Tempo control. Adjusts the speed of the accompaniment rhythm.
31. Balance control. Sets the relative levels of the upper and lower manuals.
32. Master Volume control. Sets the final output level of the whole organ.
33. Waltz switch.
34. Jazz Waltz switch.
35. Slow Rock switch.
36. Country switch.
37. Swing switch.
38. Rumba switch.
39. March switch.
40. Tango switch.
41. Disco switch.
42. Funk switch.
43. Reggae switch.
44. Cha-cha switch.
45. Bossa Nova switch.
46. Samba switch.
47. 5/4 switch.
48. Group Select switch. Selects the second variation of each rhythm. An interesting effect can be created by switching between rhythms whilst playing a tune.
49. Downbeat Indicator. On 5/4 time only, flashes on the last and first beat of each bar.
50. Beat Indicator. When autostart selected, rhythm speed can be gauged whilst organ is silent prior to playing. Note that when rhythm stop/start and auto stop/start are both released, this lamp may remain on depending on the point at which the rhythm was stopped.
51. Rhythm Stop/Start switch. With this switch selected and auto stop/start not selected, the rhythm starts immediately on the downbeat and remains running. See also 52.
52. Auto-Stop/Start switch. Note that this switch has nothing to do with the automatic mode, but simply provides automatic stopping and starting of the rhythm unit. With this switch selected and rhythm stop/start not selected, the downbeat and beat lamps function but sound is only heard when keys on the lower manual are pressed. Also the rhythm always starts on the downbeat. When all keys are released on the lower manual the rhythm stops at once. However, when the rhythm stop/start switch is also selected the rhythm will continue to the end of the bar after the last key is released on the lower manual. Also in this condition, beginners may find it an advantage that the rhythm unit continues running whilst changing chord. Should you wish the rhythm unit to start playing when you press a lower manual key and continue to run, then it is necessary to start playing with rhythm stop/start and auto-stop/start selected and then release auto-stop/start shortly after beginning. Then the rhythm can be stopped in the usual way by switching the rhythm stop/start switch off.
53. Auto Accompaniment on/off switch. When this switch is selected the function of the lower manual changes. If any single key in the lowest octave is pressed, an 8' chord with that key as the root note is generated (or the most left key if more than one key is pressed). The second octave repeats this function and the chord is the same, not an octave higher. Note that whilst not normally used in auto mode, the right-hand two octaves do repeat the sound of the last key, played in the lower octaves. The volume and tonal quality of the chord is set by the 8' Flute and 8' String accompaniment drawbars. Also when this switch is selected the normal pedal function is cut off (but see 69 and 70). When rhythm stop/start and/or auto-stop/start is also selected, the countermelody is available (see 9) and auto bass is available (see 2).
54. Vamp on/off switch. This switch only functions if rhythm stop/start and/or auto-stop/start is also selected. If auto accompaniment is off, then any manual chord played will be vamped and if auto accompaniment is on then the automatic chord will be vamped.
55. Memory on/off switch. If auto accompaniment is off, then all last notes played on the lower manual will continue to sound after key(s) released. If auto accompaniment on and rhythm stop/start and/or auto-stop/start are selected, the countermelody is memorised and if vamp is on, the vamping chord is also memorised.
Important note: when memory has been used with auto accompaniment it is important to switch memory off before auto accompaniment is switched off, otherwise a discord may be generated.
56. Preset Voices Cancel switch. This switch releases any previously pressed preset voice switch and must be selected if no preset voice is selected otherwise the upper manual may not sound at all.
57. Banjo Preset Voice solo switch. (See 19 and 20.) Note that this stop must be played by lifting all fingers from the solo manual before playing the next note or chord.
58. Accordion Preset Voice solo switch. (See 19.) Note that this stop must be played by lifting all fingers from the solo manual before playing the next note or chord.
59. Harpsichord Preset Voice solo switch. (See 19.) A longer sustain can be achieved by holding down the note. Remember that this stop must be played by lifting all fingers from the solo manual before playing the next note or chord.
60. Piano Preset Voice solo switch. (See 19 and 73). A longer sustain can be achieved by holding down the note. This stop must be played by lifting all fingers from the solo manual before playing the next note or chord.
61. Percussion (4') solo switch. (See 19.) The repeat drawbar also operates with this stop although it would not normally be used with it. The stop produces a very fast initial attack and is best used to complement the solo manual drawbar voices i.e. with drawbars add switch also selected.
62. Drawbars Add solo switch. When selected, the upper manual voices on drawbars sound in addition to any preset voice selected.
63. Wah on/off switch. This only operates on the upper manual drawbar voices.
64. Wah Auto/Manual switch. When wah is on and this switch is not selected, wah occurs whenever a new key is pressed on the upper manual after all keys have been released. When wah is on and this switch is selected, the swell pedal becomes a wah pedal and the organ's output volume is now under control of the master volume only.
65. Headphone Socket. For use with any stereo headphone with a standard stereo ¼in. jack plug. When a headphone is connected, the main loudspeaker is switched off.
66. Solo or upper manual.
67. Accompaniment or lower manual.
68. Mains on/off switch.
69. Minor Chord. Changes any automatic chord to minor. (See 70. )
70. Seventh Chord. Changes any automatic chord to seventh. Note that if minor and seventh are pressed together, a minor seventh chord is produced.
71. Pedalboard. Only one note plays at a time and if more than one note pressed only the lowest one sounds.
72. Swell Pedal/Wah Pedal. Normally a volume control used whilst playing, but if wah is on and manual wah is selected, the pedal generates a wah effect when moved.
73. Glide/Piano Sustain switch.
Except when piano switch selected, the pitch of the whole organ is shifted down by one semitone. Normally used to create a Hawaiian Guitar effect e.g. with harpsichord and selected drawbar voices. When piano is selected, the switch sustains notes after the keys have been released similar to the loud pedal on a piano.
Since the original circuits and parts lists were prepared for publication, we have made many improvements. These, plus any errors and omissions, are given in the following lists.
Page 7. Parts list for master oscillator.
R370 should be 330k (was 68k).
R373 should be 470R (was 1k0).
R374 should be 47k (was 10k).
R375.6 should be 47k (were 4k7).
R607 should be 100k (added).
RV29 should be 10k (was 220k).
RV31 should be 10k (was 1k0).
C123 should be 3.3uF at 63V (was 10uF at 25V).
C126 should be 100uF at 6.3V (was 22uF at 10V).
C127 should be 33pF (was 100pF).
C128 should be 330nF (was 100nF).
Page 10. Figure 2.
Make all changes as for page 7.
R607 is in parallel with C126.
The two wires to S36 should be shown via PL6.
S20 and S21 should be S20b and S21b.
Add note: S20a and S21a unused.
S31d should be shown as a latchswitch.
Page 37. Text.
Just prior to heading "Organ Voice Circuits", the pulse is provided by C208 and R379 (not C212).
Page 37. Fig. 7.
Circuit around IC44 redrawn, see Figure 48.
C212 is in parallel with R485.
C213 is in parallel with R493.
C217 is connected between IC42 pin 8 and 0V, positive end to IC.
TP1 added at IC43 pin9.
TP2 added at IC43 pin 8.
TR45 emitter goes to R603 in preset voice circuit.
TR45 collector, R507, D148 and D149 junction connected to S34d in master mixer circuit.
Make all changes as for page 38 parts list.
Page 38. Parts list for upper manual.
R413-R417 should be 5k6 (added).
R418-R423 should be 1k0 (added).
R437 should be 22k (was 27k).
R473 should be 8k2 (was 47k).
R484 should be 10k (was 100k).
R485 should be 220k (was 470k).
R487 should be 470R (was 150R).
R490 should be 100k (was 10k).
R492 should be 1k0 (was 100k).
R493 should be 150k (was 470k).
R494 should be 10k (was 27k).
R500,502 should be 100R (were 2k2).
R501 should be 1k0 (was 8k2).
R503 should be 10k (was 8k2).
R505 should be 150R (was 100R).
RV35 should be 100k (was 10k).
C141 should be 10nF (was 3n3).
C142 should be 100nF (was 22nF).
C143 should be 100nF (was 68nF).
C144 should be 39nF (was 15nF).
C145 should be 470pF (was 330pF).
C147,8 should be 100nF (were 10nF).
C149 should be 120nF (was 68nF).
C150 should be 47nF (was 22nF).
C153.154 should be 100nF (were 10nF).
C156 should be 82nF (was 47nF).
C161 should be 820pF (was 1n5).
C164 should be 12nF(was 100nF).
C165 should be 12nF (was 22nF).
C212 should be 100pF ceramic (added).
C213 should be 120pF ceramic(added).
C217 should be 1000uF 6.3V axial (added).
C221,2 should be 3n9 ceramic (added).
C237-C241 should be 220pF ceramic (added).
Page 38. Figure 8.
D76 and D77 are removed and replaced by R603. The junction of R603 and C167 is also connected to the emitter of TR45 in the upper manual circuit
Figure 7. On IC45, pins 9 and 10 are linked, pins 13 and 14 are linked and pin 6 is connected to -6V.
Lower end of RV17 should be connected to 0V (not -6V).
The wipers of S27a and S33b should be shown connected to -6V (not 0V).
R509 shown connected between KPS rail and -6V should be shown connected between TR46 emitter and KPS rail.
C227 should be between IC45 pin 6 and 0V.
C215 should be between IC45 pin 8 and top end of RV17, positive to IC.
C224 should be between IC40 pin 14, R510 junction and top of S32b (was shown linked).
C226 should be between TR44 emitter and -6V.
TP3 added at IC45 pin 8.
Make all changes as for parts list page 39.
Page 39. Parts list for preset voices circuit.
R411 should be 390R (was 47R).
R509 should be 270R (was 1k0).
R521 should be 22k (was 39k).
R526 should be 680R (was 1k0).
R537 should be 270R (was 560R).
R540 should be 47k (was 100k).
R541 should be 5k6 (was 12k).
R553 should be 10k (was 22k).
R554 should be 10k (was 4k7).
R603 should be 47R (added).
C171,174,180 should be 22uF 10V axial (was 470uF 16V).
C177 should be 47nF carbonate (was 100nF).
C215 should be 2.2uF 35V tantalum (added).
C224 should be 15nF polyester (added).
C226,227 should be 100nF disc (added).
TR50 should be BC548 (was BC108C).
S31 should be latchswitch 4-pole (added).
Page 39. Text.
In last paragraph before heading "preset voice circuits", C166 charges via D149 and R505 (not D19).
Page 25. Fig. 16.
R2 should be 4k7.
R3 should be 2k7.
R4 should be 5k6.
The 4-pole latchswitch mentioned in the text should read '2-pole latchswitch'.
Fig. 23. In connections to PL1, pins 1 and 2 are transposed.
Page 28. Parts list banjo repeat circuit. R390 should be 68k (was 33k).
C130 should be 1uF carbonate (was axial).
Page 29. Fig. 24.
Make all changes as parts list page 28.
Page 34. Figure 34.
PL1 and SK1 connections to pins 1 and 2 transposed.
TP7 added to IC3 pin 9.
Page 35. Parts list for pedalboard circuit.
RV124 should read RV12.
Page 33. Figure 39.
There should be no vertical line connecting the 0V line under C22, C23 etc. and the junction of R109, R110 and the junction of R111, R112.
There should be no vertical line connecting the 0V line under C28, C27 etc. and the junction of R122, R123 etc. C220 should be connected between IC14 pin 11 and -6V and not between pin 9 and -6V. On IC15, pins 9 and 10 are linked and pins 13 and 14 are linked.
TP4 added at IC15 pin 8.
TP5 added at IC14 pin 8.
TP6 added at IC14 pin 9.
Page 36. Figure 40.
On IC24, pins 1 and 2 are transposed and pins 22 and 23 are transposed. Pins 18 and 20 should be shown connected to -6V and pin 21 should be connected to -1V, IC29, pin 3 should be connected to -1V and pins 4 and 12 should be connected to -6V.
Page 38. Parts list for lower manual.
R120, 213 should be 4k7 (were 390k).
R126, 132 should be 390k (added).
R202 should be 1k (was 10k).
One final item that we have omitted to mention previously is the strapping required as shown in Figure 49. The EPROM is preprogrammed with 30 rhythm patterns and this strap is required in order that the downbeat light functions correctly. The strap required might be different if the chip contained different rhythms. Maplin can provide charts for you to fill in if you wish, to write your own rhythms for use with the Matinee and they will program a chip for you at a small charge.
Maplin have set up a technical enquiry desk for Matinee constructors, so if you have any technical problems with your Matinee organ, please telephone (Contact Details) and ask for Matinee technical enquiries. A very reasonably priced organ stool is available from Maplin to go with the Matinee. The order code is XB95D and the current price is £29.50.
Now that the organ is built, we are sure many of you will be interested in our special offer set of books that will help you learn to play the Matinee. An excellent set of books that will guide you to greater enjoyment of this superb instrument. Finally, may we wish you many happy hours at the keyboard.
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