ELECTROPLAY SOUND FX PHASOR       amazing synthesizer soundtoy

The Sound FX Phasor is a very unusual lo-fi toy synthesizer from 1980 made in Britain by Electroplay. It is historically very important as the likely world first single-chip softsynth.
 

Beside 8 preset effect noises, it has a keyboard mode with synthesizer, featuring suboscillators with multipulse squarewave and freakish siren-like howling modulations. Particularly it can do sonorous organ-like bass notes and crunchy motor noises with simple decay envelope. The foil touchpad of the monophonic instrument has only 15 "white" keys (no sharps).

Remarkable is that it even precedes the famous Casio VL-1 by 1 year, and like the latter it can produce a variety of strange complex sound variants. The grainy lo-fi sound engine employs program loop synthesis and so may constitute the world first software synthesizer on a chip. But unlike VL-1 it is more centered on less melodic howling effects, and often resembles random glitch stuff in the style of Williams early electronic pinball machines, with strange techno sound loops those can include crackle, buzz and rough pulsing or bleeping noises. It was way ahead of its time.

But the user interface is awful. There is no sequencer, synth patches can not be saved and most obnoxious is that auto-power-off deletes the created patch (up to 31 key presses) after 46 seconds of idle. As a last warning it sounds a very low bass note during that you can quickly play a note to get another 46 seconds. It feels like an unfinished prototype.

The Sound FX Phasor has been emulated on MAME - yet with incorrect analogue volume envelope, but well enough to give an idea what this obscure synth unicorn sounds like.

main features:

• 15 foil keys (flats only, no sharps, Octave starts at '3')
• built-in speaker
• effect mode with 8 synthesized preset sounds {helicopter, telephone, ufo, police car, train, bee, racing car, boat}
• synthesizer mode with 6 parameters (2x pitch envelope, decay, square LFO, waveform suboscillator, noise waveform)
• monophonic main voice with grainy lo-fi timbres, complex multipulse squarewave suboscillator, analogue decay (capacitor envelope PWM), coarse digital volume envelope and howling digital pitch envelopes. Digital Envelope and LFO tempo is proportional to note pitch.
• no volume control
• CPU= "General Instruments PIC 1655A-522, 48-802, 8146 SAA" (28 pin DIL | PIC with 768 byte ROM, 32 byte RAM)
• auto-power-off (erases memory after 46 seconds)
• 6 cardboard overlays for 12 melodies (I only have 4).
• no jacks

The manual is a bad joke.

eastereggs:

• Switching to synth mode and pressing 2x "F" keeps parts of the last played sound (e.g. effect noise) in RAM.
• Typing too long numbers as synth parameter can make glitch sounds?? This thing behaves so wierd that it is hard to distinguish at all between bugs and features.
• shitshot: Undervolting (empty bateries) produce e.g. strange variants of the effect noises in wrong timbres. They sometimes set off randomly instead of the APO bass note.
• disable APO - grounding CPU pin 7 deactivates this worst plague, permitting to keep the synth patch in RAM.
• disable keyboard - pulling pin 6 hi turns all keys off.

notes:

The instrument has no volume control, so it always plays at medium volume (with fresh batteries somewhat loud), but battery life is still ok, which may be the miracle of 60 Ohm speaker. There is no mechanical power switch; it is powered on by pressing the effect (lightning) or synth (musical note) button, which sounds a Pong-like rough purring buzz (both have different pitch). All buttons make sound, which disturbs live performance. Worst is that after 46 seconds of idle it always powers itself off (sounding at second 43 a decaying very low bass note), which unfortunately deletes the currently created synth sound. This is particularly annoying because it has no display to write it down, typing it in takes up to 31 button presses (Casio VL-1 needs 9), and the synth programming is not straight forward and feels more like something circuit-bent and semi-random. Also switching to effect mode clears synth RAM. The box has a note "UK and foreign patents pending. Industrial Copyright 1980 (c) ELECTROPLAY.", but websearching that name only finds plenty of SM filth; possibly this was only a label of another company and quickly got changed by the sextoy connotation. A box tab is also marked "Reedecor", which was likely only the cardboard print company and shows no results either. Mine came without manual. Fortunately someone e-mailed me the photo; it turned out to be a brief single page instruction sheet that beside 3 sound examples tells not a scrap about systematic use of the synth, despite it lengthily explains the duration sensitivity of the "racing car" noise. Also the wording with some strange sentences and scarce punctuation sounds Engrish enough to raise suspicion wether this was a genuine British invention at all.

The hardware is built around the GI PIC 1655A, which is a documented 8-bit microcontroller with only 512 word of 12-bit ROM and 32 byte RAM. It is running a monophonic software synthesizer resembling the famous "Gwave" sound engine of early electronic Williams pinball and video arcade games. Although it lacks their iconic bright phasing drone timbres ("Defender" start sound), it does plenty of different crunchy noise waveforms. Many are POKEY-like, but the timbre palette goes beyond that, including e.g. semi-metallic clangs like gongs and ringing bells. For a 1980 toy the thing is crazy. (To get an idea, a Speak & Spell had 16 kByte ROM, which is >21 times more.) With minor redesign, its software could have blown most early budget mini keyboards off the market. This is the same type of British low-cost miracle like the first Sinclair homecomputers. It could have been a game changer; under different circumstances UK instead of Japan would have created the VL-Tone.

The 8 effect noises ("Living Sounds") are strongly synthesized and buttons respond duration sensitive. (Most sound names were choosen by me, because there are only icons on panel buttons and the manual only mentions 2.) The "helicopter" contains noise with high pitched whine that grows louder and quieter. The "telephone" is electronic high pitched, somewhat like tyre screech. The "ufo" is a sequence of 3 fast siren-like noises; the last one fades silent. The "police car" sounds like 2 alternating organ notes. The "train" is a steam locomotive with rough hiss that turns faster and higher (quieter), followed by a realistic whistle (louder again). Also "bee" varies volume. The "racing car" is modulateable; it starts with loud reving up engine (low buzz), but holding the button makes it change gears and drive away (engine grows quieter). The "boat" (ship horn) toots buzzy, followed by a 2nd duller toot of its echo (told by manual - very artificial). Hitting the button quickly sounds for a default length (few seconds). Holding it longer plays them in a loop (some with algorithmic variations) until release of that button. The same 8 noises are as doublets (wired parallel) on the key buttons and thus can not be played melodically.

synthesizer parameters

Press the 'musical note' button and play a note on any key beside 'F'. The synth mode starts now with a primitive "guitar" preset sound (2-bit wannabe sawtooth). Its (anyway too short) decay gets truncated by key release, which seems to be the default behaviour in synth mode. Any synth parameter is edited by pressing "enter" (F button), typing any number (this sounds a blip) and pressing one of the 6 letter buttons. Each letter button (also F) sets a corresponding parameter. It is hard to figure out what they exactly do; depending on the parameter. While their range seems to be 0..255 (8 bit, typing bigger numbers wrap around, ignoring upper bits), typing more digits sometimes seems to do more complex things (which may be buffer overflow bugs). Parameters also interact with each others.

After switching on (note icon button), you need to first play a note before setting a parameter, else glitches occur, those however can be used to get different sounds. Apparently default values of the preset sound are only initialized when playing a note before setting any parameter. Particularly the octave of the main voice can strongly change, e.g. depending on which effect noise was previously played. Possibly such semi-random glitches made the designer give up any plans of describing synth parameters in the manual.

• pitch envelope (A, B)

This produces siren-like effects by a triangular pitch envelope. Parameter A sets the vibrato speed by changing the pitch envelope steepnes (0=fastest, 255=slowest). B apparently sets the upper and lower ramp limit, i.e. changes the bounds between that the triangular pitch envelope ramps up and down with the rate selected by A, which makes the vibrato simultaneously deeper and slower (0=shallowest, 255=biggest amplitude). At high depths the pitch will wrap around and thus low note start at a high pitch ascending further until wrap point and continue ascending from the lowest pitch to the max and return to lowest vice versa. Regard that A defaults to off (no vibrato) and thus must be set to make B take effect. But both must be set 0 to disable pitch envelope again.

Pressing the note icon button always resets A and B (removes pitch envelope). Then press 2x F (do not play a note) to keep parameters C..F of the previous sound.

• decay envelope + suboscillator (C)

This modifies the volume decay envelope. I haven't fully figured out the details. Apparently the decay switching frequency for the analogue decay circuit also acts as a suboscillator (e.g. bass) that may decay at different rates (pulse density modulation). Parameter C seems to particularly change the lowest level (like "sustain" in ADSR) to those the oscillator decay during held notes. Values >15 make it decay fully, and higher values decay faster. 0=no decay (plain continuous tone). 255=both decay fastest. Values in between seem to make the suboscillator decay slower and/or less low than the main oscillator and affect its pitch, which adds a buzzy zippernoise-like additional tone. It may be that the step width and -position of the decay get controlled this way.

Regard that while the default preset sound contains decay (C=255?), the first manual change of any parameters disables decay (sets C=0?), thus it needs to be set by hand if you don't want a continuous tone.

Normally the tone immediately stops by key release, although sometimes (using parameters A, B?) a short delay occurs. I don't know if there is a hidden parameter for this or just a glitch. (In opposite to this, the 8 preset sounds of effect mode can run a few seconds without holding a key.)

• square LFO suboscillator (D)

Parameter D sets a frequency ratio to modulate the main voice with a 1:1 square LFO at 100% depth, i.e. it chops the tone on and off with a selected fraction of the note pitch. (0=off, 1=fastest, 255=slowest). Low ratios (high frequencies) fall into the hearing range and so act as a suboscillator to produce a bass voice. E.g. 2 sounds an octave lower. Higher ratios make a purring buzz (like missing the ball in "Pong", or clangs from the Namco game "Bomb Bee") while even higher ratios make the tone toot on and off with a tempo proportional to the note pitch. Apparently this edits the waveform on a deeper level than a simple LFO, because combined with E and F it can turn the tone much lower and buzzier. So it may be that it inserts a blank piece into the waveform by halting the oscillator instead of muting it during zero.

• waveform suboscillator + volume envelope (E, F)

Parameter E and F do the same, thus the same sound is produced with both values exchanged. So I conclude that internally they may be arguments of an addition, multiplication or XOR to produce the resulting waveform and envelope. Setting at least one of these 0 or 1 disables the suboscillator. Regard that E defaults to off and thus must be set to something else to enable this suboscillator.

Parameter E/F add an at least 1 octave lower suboscillator with selectable waveforms that modulates the resulting tone with buzzy multipulse textures approximating linear volume envelopes. The modulation depth is 50% (unlike the the square LFO) and it has different timbres (0=off, 1=off, 2=on, 3..255=waveforms or noise). With E and F set to the same value and other than 0 or 1, the volume pulses high and low (square LFO similar like parameter D). Like D, small numbers produce bass voice; a bigger number pulses slower. When both values differ by 1, a kind of beat frequency modulates it with falling pulse duration envelope. Bigger differences make it beat faster, which may hint that the output is derived from a phasing process, which would explain the name "Phasor". Depending on the values, the pulse duration envelope can be falling sawtooth shape (difference 1), but gradually becomes faster and then triangular to irregular if the difference between E and F is set higher. Unlike parameter C, this envelope speed is proportional to the note pitch. Tones with low E/F difference can sound like hemisync bleeps of old mindmachines (of course here mono). Some high values can produce LFO-like tekkno sound loops those add rhythmic crackling or switch the suboscillator rhythmically on and off.

On oscilloscope the phasing/beating waveform has only 2 volume levels (about 50% and 100%) made from 2 mixed long multipulses. In total the audio is mixed through resistors from 4 digital pins, but the 3rd pin seems to not affect beating and the 4th is pulse density modulated decay envelope control, that also acts as a suboscillator. The logic analyzer reveals that only pin 16 outputs a complex repeating multipulse of falling PWM pulsewidth, that apparently intermodulates with plain squarewaves from pin 17 and 13.

The values seem to have no logical order, thus likely rather technical than ergonomical reasons. E.g. 2, 3, 4, 6, 8, 9, 12, 15, 18, 21, 24, 27, 30, 32 add harmonic overtones, while 5, 7, 10, 11, 13, 14, 16, 17, 19, 20, 22, 23, 25, 26, 28, 29, 31 produce disharmonic noises. I suspect that the bits control an RNG algorithm like shiftregister feedback noise. Sometimes the same value even seems to randomly produce different timbres, so the internal state may produce varying bit loops when ratios are not prime and the random seed differs. Generally many sounds resemble POKEY (the famous Atari chip), but tend to be less disharmonic and have no detuned bass problems, so the frequency resolution is likely higher. Apparently it also fails to produce fully atonal hiss (except as part of effect noises). So its relation to POKEY is more like that of Phase Distortion to FM; despite similar principles, the character of the timbres and its parameters can substancially differ and make of it a unique sound source.

Also Parameter D affects the timbre and makes it even buzzier. So strongly detuned low notes can produce e.g. motor noises or tekkno drones. It may be that this function similar like noise modulation in phase distortion synths. Parameter B seems to also affect pitch of both suboscillators, hence high values can turn the tone even lower and produce more extreme noise when combined with waveforms of E/F.

Parameters D, E and F interact with each other in complex ways those can produce long tone and noise loops. I suspect that bit patterns of different lengths get XORed with each other or something similar, so they need to be treated as a whole. The tempo of everything they do is always proportional to the note pitch frequency. So the ascending pitch of the siren effect by parameter A and B can result in an accelerating throbbing statccato when pulsed by the LFO parameter D.

• octave prescaler

This seems to be an internal parameter that can not be set directly. But you can change the base octave of the synth by playing an effect noise, switching to synth mode and pressing 2x 'F', which leaves residues of the previous sound in RAM including the octave setting. Hence entering parameters C, D, E, F manually (A and B reset anyway) will now make them sound in the octave of the previously played effect noise.

• internal sounds

The "guitar" default preset is set automatically by playing a note after power on. It resembles the parameters (A=0, B=0, C=255?? , D=2, E=0? F=0?), but the tone is 1.5 octaves lower during attack, thus C and possibly A and B seem wrong. After power-on, pressing 2x "F" (enter) instead of a note prevents this and so keeps parts of the previous parameters in memory. When the last sound was the APO bass, it adjusts the synth to a very low short crackling buzz sound (A=0??, B=0??, C=255, D=255?, E=120?, F=255?). I find no obvious identical settings, because changing one parameter apparently resets others to "sane" values. This confusing behaviour was likely done to need less typing for popular synth patches.

The effect noises seem more complex than what can be manually done with synth parameters. Although I haven't fully researched details, I suspect that those "Living Sounds" contain additional preprogrammed fast envelope sequences. They are not supposed to be editable nor played on note keys, but when previously an effect noise was played, switching to synth mode and pressing 2x "F" keeps residues of it in memory. But only the "police car" timbre stays fully intact as an organ tone. The "boat" turns into a low organ tone, which lowest playable note is somewhat higher than that ship horn. Of the "ufo" part 1 and 2 (release button to stop) produce a fast purring noisy tone, but part 3 a surprising disharmonic semimetallic buzzing clang. From the "train" remains only a high organ beep (so its rough hiss noise is likely out of reach); "telephone" becomes the same. The "bee" turns into a buzzy kind of e-bass; stopping later makes it duller. Also "racing car" turns into a buzzy decaying bass. The "helicopter" becomes a (heavy metal chord?) noisy and buzzy low synth bass; if stopped later, the result is less buzzy with decay. The results can be a little random, likely depending on the exact time when the Living Sound gets stopped. But they can not be stopped at their begin at arbitrary spots (not even with "on" buttons) which hints that they occupy full CPU capacity with nothing left for sensing other buttons. The stop behaviour varies with the noise; e.g. "train" and "boat" need 1 second to recognize stop, while others stop faster.

circuit bending details The Sound FX Phasor is built around the microcontroller "PIC 1655A-522" running a software synthesizer. It has a tuning trimmer for pitch adjustment. caution: The touchpad hangs on a short and flimsy foil cable, very similar like those in early Sinclair homecomputers. Although it is less delicate than the infamous Casio LCD foil cables, it may tear easily when removing the PCB. If necessary, the cable can be carefully pulled out of its PCB connector and later pushed back in, however repeated removal may scratch the conductive paint, and any sharp fold may crack it, thus better leave it in place. The 60 Ohm 0.25W speaker is wired to a single-endet darlington amp made of transistors T3 and T4. The APO circuit switches positive voltage to the CPU through T1.  In synth mode, waveform pin 13 (suboscillator and decay rate control) and 17 (main oscillator) output plain squarewaves, while only pin 16 outputs complex generated multipulse patterns depending on the synth parameters. (Unlike my expectation, the multipulse is not on another pin when swapping values of parameter E and F.) Rise on pin 10 starts the decay envelope. The pitch of the "guitar" default preset starts 1.5 octaves lower during attack. In noise effect mode also pin 13 and 17 can contain multipulses. Pin 15 only outputs waveforms in sound signals and "telephone". Likely the mixing at the base of power amp transistor T3 does some kind of analogue multiplication (distortion) that results in more complex phasing waveforms. Pin 17 seems related to parameter D, and by its high amplitude (lowest resistor) sort of chops the rest. keyboard matrix There are no eastereggs. The effect noise buttons are wired parallel to cipher buttons '0' to '7'. The 2 power buttons for effect and synth mode have own CPU pins outside the matrix.   22 23 25 24   CPU pin in 1 in 2 in 3 in 4 in / out   o G1 '0' helicopter o A1 '1' telephone o B1 '2' racing car o C2 '3' ufo out 1 19 o D2 '4' train o E2 '5' bee o F2 '6' boat o G2 '7' police car out 2 18 o A2 '8' o B2 '9' o C2 'A' o D3 'B' out 3 20 o E3 'C' o F3 'D' 'o' G3 'E' enter 'F' out 4 21 The input lines are active-low, i.e. react on GND. Any functions can be triggered by a non- locking switch in series to a diode from one "in" to one "out" pin. eastereggs: disable APO APO deletes the synth patch in RAM after 46 seconds of idle. To disable it, simply wire CPU pin 7 to ground 0V. Because the hardware consumes about 32mA when on (1uA during standby), install a power switch. There are multiple options for this beside the obvious one. To preserve the original warning bass note, you may place your switch into your line to pin 7 to reenable APO. Instead of a hardware switch, you might also install a non-locking button switch to pull down reset pin 28 to immediately drop into standby (no bass note, has no benefit). Add an optional power LED (e.g. at CPU pin 1 through 10k resistor to ground 0V) as a reminder to turn it off to conserve battery. disable keyboard Pulling pin 6 hi (normally wired to GND) disables the keyboard matrix outs and so disables all keys except power buttons. pitch control Clock rate is controlled by an RC oscillator at CPU pin 27 (capacitor to GND, resistor to positive supply voltage of the CPU). You may replace the 22k trimmer VR1 with an external pot or other pitchbend control. (It is not DC controlled, thus sensitive to RFI.) volume envelope control The analogue envelope circuit (parameter C) uses transistor T2 and electrolytic capacitor C2. Decay speed is controlled by a PWM signal (that also acts as suboscillator) from CPU pin 13 and start is triggered by rising edge of  CPU pin 10. Capacitor C2 (4.7uF) controls decay duration. Pulling pin 10 lo (through a resistor to avoid CPU damage) causes slow attack in all sounds. (This is independent from the simulated PWM volume envelope of parameters E/F.) pinout PIC 1655A-522 The "General Instruments PIC 1655A-522" (28 pin DIL, "522"=software number of internal ROM) is the CPU of the Sound FX Phasor. Technically it is the 8-bit microcontroller PIC 1655A, which has 32 byte RAM and 512 word of 12-bit mask ROM containing a monophonic software synthesizer, featuring 8 preset effect noises and a user programmable synthesizer with 6 parameters (each 8-bit?). Because the chip supports no analogue ports, the audio signal is mixed from 4 digital pins through resistors. One of them is pulse width modulated decay envelope speed (that also acts as suboscillator) connected to an external transistor circuit with capacitor for the decay envelope. The "1983 PIC Series Microscomputer Data Manual" shows on page 175 the PIC1655A example application "7.3 Sound Generation Using a PIC Microcomputer" with source code and schematics for a similar toy with 8 effect noises, which however contains 2 melodies instead of the synthesizer, sounds are simpler and pin assignment differs. It apparently refers multipulses as "pulse trains". Most interesting is that one of its sounds is indeed refered as "Phasor"! (gun in space war games).   pin name purpose 1 /RTCC real time clock counter (wired to 2 | not used) 2 VDD supply voltage +5V 3 VXX out pins supply voltage in (wired to 2) 4 VSS ground 0V 5 TEST test mode (wired to 4) 6 RA0 key matrix out disable in (wired to 4) 7 RA1 /APO disable in (not used) 8 RA2 /effect mode power on in 9 RA3 /synth mode power on in 10 RB0 decay envelope trigger out (rising edge) 11 RB1 (not used | lo out)  12 RB2 APO out (hi when on) 13 RB3 decay envelope PWM + waveform out (synth square) 14 RB4 (not used | hi during "train" noise) 15 RB5 waveform out (signals, "telephone") 16 RB6 waveform out (synth multipulse) 17 RB7 waveform out (synth square) 18 RC0 key matrix out 19 RC1 key matrix out 20 RC2 key matrix out 21 RC3 key matrix out 22 RC4 key matrix in 23 RC5 key matrix in 24 RC6 key matrix in 25 RC7 key matrix in 26 CLKOUT clock out (not used) 27 OSC clock oscillator (capacitor to 0V, resistor to VDD) 28 /MCLR /reset The PIC1655A is the mask rom version of the eprom based PIC16C55. Both are very close relatives of each other and hence even have a similar rom dump mode, despite it is activated differently. With the documented PIC16C55 pin 1 needs to be set hi and pin 28 connected to programming voltage to make it output rom data bits at pins RB7 (msb) to RA0 (lsb) in a loop (controlled by clock rate, no address signals). The undocumented PIC1655A instead needs the TEST pin 5 pulled to 3V to start dumping, which after reset starts at address $1FF (reset vector) wrapping around from $000. So with some help I managed to dump the "Sound FX Phasor" rom. I had to desolder pins 6, 7, 15, 16, 17 and circumvent APO (pull base of T1 through 1k resistor to +BAT (behind diode)) to prevent powering off when 12 goes lo. I also wired a 100nF cap parallel to C6 to reduce clock speed (CLKOUT about 370Hz) to record the data (pins 6..17 = bits 0..11 | data sample rate set to 500kHz) without capacitive distortion. As expected, the 12-bit word repeats every 512 steps of CLKOUT. I also could examine some audio pin signals. (I had to remove the 100nF cap to run properly, which now needed 4MHz data sample rate to see CLKOUT properly.) Likely also any PIC16C55 programmer can be easily rewired to read a PIC1655A (beware of its programming voltage, that may be deadly to the mask rom version) by feeding 3V to TEST pin 5. That pin seems to accept voltages at about 1.4 to 3.7V to output rom data. Below 1.4 it gets distorted, while above 3.7 came garbage (may do something else, like dumping current RAM content for debug). Unlike newer PIC the 1655A is fortunately unprotected. SeanRiddle mentioned that the PIC1650A instead needs 5V at TEST and RA3 pulled lo to dump rom. Because this PIC supports no interrupts, the whole program is one big loop. The chip is Havard architecture (separate code and data path) with fixed size 12-bit instructions (containing an operand) and fixed execution time, which makes it very crash resistant and effective for simple waveform programming. By shitshot behaviour I would not have guessed it to be a softsynth. But Havard likely also implies that it can not accidentally output its ROM code as waveforms. Likely the code can be easily adapted to a newer flash based variant like PIC16F57. So theoretically it may even be possible to install it with a bugfixed/more ergonomic upgrade of the code inside the original instrument. The unused pin 7 disables the annoying APO so long it is pulled lo. Pin 17 goes hi only during the "train" effect noise and nowhere else (may be dead code from older software, or planned to switch a filter or light effect for a different toy). Pin 6 (wired to GND) disables the keymatrix out pins when pulled hi (i.e. no keys except the 2 power-on buttons work). Powering on with both pin 8 and 9 pulled lo starts in noise effect mode. Also pulling APO resistor from pin 12 hi (turns supply voltage on) during standby starts noise effect mode (hence can not be used to continue from standby with intact synth patch in RAM). Pin 11 stays always pulled low. Strange is that pin 1is wired hi trough a separate wire bridge (not PCB trace) despite pulling it lo has no effect; likely a prototype version used the eprom version PIC16C55 which uses this pin for eprom write mode. Pin 10 rising edge (pull low and release) retriggers the analogue decay envelope. Holding pin 10 lo (through a resistor to avoid CPU damage) causes slow attack in all sounds. Tones from pin 13, 15, 16, 17 are mixed through resistors to form the tone waveform. (pin13=R10 5.6k, pin 15=R13 68k, pin 16=R14 12k, pin 17=R15 1k). But pin 15 is only used during few sounds (button blips, power-on beeps, APO warning bass, effect noise "telephone"), so only 3 bits remain for the synth waveform, mixed from in synth mode 2 squarewaves and a complex multipulse. The result is routed through the analogue decay circuit. The pulse width(?) from pin 13 controls the analogue decay rate (synth parameter C); the frequency is a fraction of the note pitch and additionally acts as a (often bass) suboscillator.

The instrument has no built-in demo melodies (so it keeps its tiny rom for more interesting stuff), but in its bottom a compartment for originally 6 musical score card overlays. They contain each 2 short songs to be manually played on the touchpad by pressing coloured circles and other symbols on its keys.

(web photos of missing cards)

With my specimen 2 are missing (song names seen on internet photos).

1. London Bridge | Old Smokey
2. Twinkle Twinkle Little Star | Polly Put the Kettle On
3. Pop Goes the Weasel | Oranges and Lemons
4. Old MacDonald | Mary Had a Little Lamb
5. Yankee Doodle | This Old Man ? [missing]
6. Mulberry Bush | When The Saints ? [missing]

questions: Did they sell separate overlays e.g. with synth sounds? Was the case designed for something else (e.g. a handheld computer barcode scanner)? Were any other kids toys released with the brand name "Electroplay", or was this just a label by another company?

The Sound FX Phasor seems quite rare. Likely it did not sell well because of too many quirks and unobvious operation. If Kraftwerk would have got his hands on it, everybody for sure would name it in the same sentence with Speak & Spell. Another awesome complex sound toy was Tyco - HotKeys.
 

removal of these screws voids warranty...
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