Hohner KS 49 midi multipulse squarewave synth with analogue filter & realtime programmable accompaniment RAM CARD

This keyboard from 1987 (embossed case date stamp) is the Hohner version of the Casio HT-700 synthesizer. Casio called its synthesis engine "Spectrum Dynamics" (SD) synthesis, but basically it is nothing else than the user programmable version of Casio's historical "Consonant Vowel" synthesis engine, which mixes 2  multipulse squarewaves with independent volume envelopes and which is famous for its warm and very sonorous droning bass organ timbres. The HT-700 was likely designed as a successor to the great Casio MT-400V (see CT-410V) and thus also employs a real analogue synth filter (low pass with cutoff/ resonance control) and stereo chorus. But additionally it has programmable sample based rhythm & accompaniment - and this all controllable through MIDI with 2 part timbrale sound. It sounds too great to be true - isn't it?

Unfortunately the thing is far less exciting than the feature list suggest, since for a serious synth the entire instrument sounds disappointingly cold, thin and digitallic; it resembles rather a Bontempi GT-759 than the much warmer sound of Casio's earlier "consonant vowel" keyboards. The problem may be that the HT-700 keeps its digitally controlled synth filter and stereo chorus ICs always in the signal path (even when not in use), while older keyboards either lacked them or could completely bypass them through a mechanical switch. (Late 1980th ghettoblasters often had similar sound problems with their fancy looking and cheaply designed equalizer or reverb units.) But this gives the sounds also a cheesy lo-fi appeal that reminds to typical C64 sounds, and the thing can do a lot of wonderful multipulse squarewave organ timbres those remind to classic Atari POKEY sounds (but without the complex noise effects and special tone scale), and some waveforms even include that small dose of distortion that is necessary to make polyphonic squarewave musics sound really good.

There are 40 preset sounds, of those 20 can be overwritten by the user. The preset sound and rhythm set is different between Casio HT-700 and Hohner KS 49 midi; at least with my KS 49 most preset sounds are quite unrealistic, but realistic timbres are anyway no great talent of this hardware. A special Ram Card (Casio RA-100, now hard to find) can be inserted to store 20 additional user presets and user rhythms etc., but there is no MIDI sysex feature to backup data elsewhere. The percussion is made from medium resolution samples; they resemble the Casio MT-520 drum section but sound thinner, brighter and knock less woody. The bongos e.g. sound here more like drumming with fingers on the floppy aluminium foil lid of a yoghurt cup. The preset accompaniments of the KS 49 sound quite cheesy and many are over- orchestrated; their chord timbres overuse filter wahwah effects, which makes them rather resemble cheap no-name FM tablehooter accompaniments than realistic instrument timbres. Fortunately the fingered accompaniment at least accepts also non- standard key combinations beyond establishment chords, and the rhythm programming mode can be abused as a tekkno drum computer (although the percussion sounds rather boring for this and can not be routed through the filter).

There is only a single common synth filter used for all main voice polyphony channels, but a 2nd filter exists for the also editable accompaniment voice on the left keyboard half. All synth parameters and tempo are selected and set through 2 buttons and a dial knob. Unlike the endless rotary encoder of other digital synths, the dial here turns a normal potentiometer, thus the value jumps to the current pot position when touched, and you have to turn it all way back and tweak the previous value when you only want to change a parameter a little; a normal number keypad would have been far less awkward here. Also the LCD only shows parameter numbers (0..95) instead of names. At least you can nicely abuse this dial as a realtime sound control for a previously selected parameter (e.g. filter cutoff), which often makes grainy zipper noise and can be also used for granular timbre change effects. But it takes many seconds to assign a different parameter to it, which disturbs live play. There is also a pitchbend-, but no modulation wheel, and synth parameters can not be accessed through MIDI.

main features:


  • polarity protection diode added, power supply jack polarity corrected.
  • notes:

    Strange is why Casio released their HZ- and HT- series SD synthesizers at all, since their own phase distortion synthesizers could do all the same sound effects and many additional ones with a much higher timbre quality. I doubt that SD synths were built for a lower manufacturing cost, since at least my Hohner KS 49 midi (identical with Casio HT-700) contains a very complex hardware with multiple stacked PCBs and many discrete components, that doesn't look in any way cheaper or easier to manufacture than the PCBs of my Casio CZ-230S phase distortion synth. Adding a similar simple parameter editor to the latter would not have increased cost much, and also the additional accompaniment would have been only a matter of ROM software. Nowadays the HT synths have their own fandom by their electronic squarewave sound, but when they came out in 1987, Casio certainly did not design them as a dedicated special purpose instrument for such customers, since there was no market for such sounds anymore upon a time where most people rather threw their outdated Commodore C64 computers out in favour for a new Amiga.

    The sound engine of the HT-700 was far inferior to the CZ synths; e.g. while the CZ synths can do a lot of different hiss timbres by "noise modulation", the noise generator of the HT can not change its fixed hiss timbres (except through the monophonic synth filter), and its noise pattern has always a tremolo with about 6Hz in it, which is likely caused by a too short shift register loop pattern (like with certain Atari POKEY noises). The main voice oscillator of the HT-700 can generate 32 different basic "DCO" waveforms, those all seem to be based on filtered multipulse squarewave. Any of the 32 basic waveforms seems to be made from 2 layered suboscillators those each generate a multipulse squarewave with independent envelope, but the internal parameters of these suboscillators can not be set directly, but only the 32 resulting basic waveforms. While most of these are simply static squarewave tones with different multipulses run through different filter capacitors, there are also special ones. E.g. number 6 is pure noise, some others mix that noise with a squarewave tone and 23 even automatically slowly grows brighter by crossfading between 2 suboscillators in the classic "consonant vowel" manner. Also some others contain quick timbre changes during their attack phase to approximate mallet, flute or picked string instruments, but they always keep their multipulse squarewave appeal. Just disable the filter (set cutoff=31, resonance=0), set chorus to 0 or 1, select a squarewave with simple envelope and voila - you get the nicest historical videogame music timbre; in some waveforms even the typical mild distortion is there, that gives polyphonic squarewave music the classic Atari VCS2600 appeal. The programmability of the accompaniment voice (left keyboard section) is far more restricted than the main voice (only 16 basic waveforms, less parameters), and annoying is also that the octave range of the oscillators can not be changed, because their pitch is too high to create really low bass sounds. The bass voice of the accompaniment can not be edited at all.

    Like with the CT-410V, the sound generator itself is mono and only post- processed by the stereo chorus, which adds to the main and accompaniment voice a cold sounding detuned chorus that reminds to My Music Center timbres; unlike the stepless slider of the CT-410V it can be set only to 3 panning/ vibrato speeds or turned off (but apparently always stays in the signal path), and the chorus setting is here part of each preset sound. Strange is that my Casio MT-800 and MT-520 sound much warmer despite active stereo chorus, thus possibly it is only the synth filter or even a poorly designed power amplifier that ruins the sound of my KS 49. Despite the data entry dial also the resolution of some other parameters is quite coarse, which appears especially unnecessary with the rhythm tempo setting. Instead of the awkward tempo/ entry dial, Casio should have better used the semi- OBS buttons as a keypad to type in parameters. Likely at least the analogue filter and chorus section of the the HT-700/ KS 49 can be easily upgraded with external potentiometers for better realtime controls, and I expect that like with my CT-410V there are many other things changeable through circuit bending. (I haven't analyzed the hardware closer yet.) Very unusual for Casio hardware is that the buttons of my KS 49 employ instead of rubber contacts metal cap switches, despite these tend to be less reliable (like known from the infamous original Atari VCS2600 or Spectravideo Quickshot I joysticks, those contacts often cracked apart or slid away under their adhesive film cover on the PCB). A bit confusing is also that the accompaniment control buttons {single finger, fingered, off} don't work so long any keys are held (likely a bug related to semaphores because a double press on "fingered" or "single finger" toggles the key split point).

    On the internet is a lot of info available about the Casio HT-700, thus I won't describe its operation and features in detail here.

    While most preset sound names on Casio HT-700 correspond to many of the Casio CZ-230S presets, on the Hohner KS 49 midi several sounds are different; some of them differ even so much (e.g. "plunk extend" vs. "psycho", "pearl drop" vs. "harmonium") that it is unlikely that only the control panel names were changed, although some of them may be only in different order. With Casio HT-700 the presets are:

    The Casio HT-700 has a black case and also some control panel names differ among Casio and Hohner ("tone"/ "melody tone" = "poly voices", "chord tone" = "arr. voices", "tone edit" = "voice edit", "control" = "total control", "rhythm pattern" = "rhythm", "bass pattern" = "bass", "chord pattern" = "chord", "casio chord"/ "chord"/ "accomp" = "arrangeur", "chord/ operation memory" = "sequencer", "main volume" = "master volume").

    Generally the preset sounds are not really realistic; in the bass range many sounds turn into a more or less buzzy, sonorous purring drone, which is a characteristic style element of squarewave based instruments. When a key is trilled with sustaining sounds, each new note occupies a new sound channel, which produces a great phasing sound and volume increase effect although this eats up polyphony. The semi- OBS preset sound buttons have each a LED and respond nicely fast; pressing them retriggers the notes of held keys with the selected preset sound, which can be used for live play tricks. The "piano" has to much presence with a thin bass and slightly dull treble range. The "harpsichord" is a multipulse timbre with a nicely sonorous (although unrealistic) bass range; "clavinet" (Hohner invented that thing) is the same without sonorous multipulse. The "jazz organ" (resembles Bontempi GT-770 "circus organ") has a percussive attack and strong fast 6Hz square vibrato and chorus vibrato, but it fades thinner and generally sounds ridiculously thin and creaky despite sonorous multipulse bass range. The "brass" is a cold tooting electronic chorus tone with semi- percussive attack, which resembles the famous Casio SA-series "brass ens". "strings" employs the same timbre with slow attack, long sustain and 4Hz tremolo; unlike the latter it sounds astonishingly realistic. "wow brass" is a "brass" variant with filter meow effect and -tremolo; it turns bright and dull again and reminds to typical cheap FM synth brass sounds. "synth celesta" is bright squarewave musicbox timbre with nicely sonorous multipulse bass range and 4Hz tremolo. "celesta" sounds more massive and resembles more an unfiltered squarewave pseudo- piano. "magic flute" is a dull flute (or wooden organ pipe) with a small dose of chorus; the dull bass range resembles a grainy very low resolution sine wave sample. "harmonium" has an additional 2 octave higher overtone and thus sounds brighter. "harmonica" is a sonorous reed organ timbre (resembling sawtooth wave) that fades slightly thinner. "vibes" is a bright vibraphone timbre with long sustain made from filtered multipulse squarewave; "soft bells" sounds slightly brighter and shorter. "e-piano" is a duller "vibraphone" variant with only short sustain. "wah-brass" is a quickly dull fading dry filter sweep timbre with fast 6Hz tremolo; it resembles much rather a funky e-bass than a brass timbre. "crescendo" resembles a harp or dull xylophone layered with a louder and brighter fading synth strings timbre with fast 6Hz tremolo and some sustain (nice pad sound). "fantasy" has here nothing to do with any Casio sounds of that name, but sounds like a water drop in a cave layered with a short dull flute or xylophone tone (multipulse timbre) with sustain (that is slightly shorter with held notes). "psycho" is a sort of upward howling and brighter growing US police car siren, that with held key stops after 4 howls (about 3s), but slowly fades duller and fades away (while it keeps howling) when the key is released earlier. "storm" is an eerie wind noise that hisses brighter until key release (or 2s) and then duller using a filter sweep while it fades away with very long 10s sustain. There is also some chorus and a continuous 4Hz tremolo in it (caused by the poor shift register noise generator), which sounds very much like a typical classic analogue 1960th or 70th SF movie sound effect. Its fixed pitch unfortunately ignores the played note, but pressing multiple keys causes a dramatic volume increase and opens the (monophonic) filter again each time.

    Additionally there are 20 overwrite able default user preset sounds, those original names I don't know because I only have the downloaded Casio HT-700 version of the manual. Thus the following names were chosen by me where the Casio names don't match. "piano 2" is a bit brighter than 1. "marimba" is a bit too dull. "pipe organ" is the well known multipulse timbre that simulates a metal pipe organ rank; this one has long sustain and sounds a bit thin. "strings 2" has a faster attack and more mids than 1. "wow brass 2" resembles 1 but grows only dull. "harp" sounds ok with some chorus. "koto" is a bright picked string that fades duller during attack (like intended) with some sustain/ chorus. "double reed" is a dull rather thin reed organ timbre with some chorus. The "clarinet" is ok with some chorus. "fantasy 2" sounds like a thin harp layered with a howling flute that slowly fades silent and has short sustain. "honkytonk piano" sounds like "piano 2" with howling detuned chorus vibrato. "vibraphone 2" sounds duller than 1. "violin" sounds fairly realistic with some chorus. "synth-strings" sounds like "strings" with a small dose of detuned chorus vibrato. "synth trumpet" is a buzzy squarewave trumpet timbre with percussive attack and sustain. "mandolin" doesn't ring and has a percussive metallic treble range like a toy piano; the mids rather resemble a mandolin or small harp. "sitar" is a bright picked string with chorus and sustain; the buzzy mids are rather a decaying synth brass timbre (made from sawtooth waves?). "slash reed" is a thin and squawky reed organ(?) timbre, which scratchy attack phase somewhat resembles a saxophone. "synth-guitar" is a thin picked string timbre, which fades duller by a filter sweep (like an e-guitar wahwah effect); it has no sustain and immediately stops by key release. "storm 2" resembles 1 but starts bright instead of dull and sounds thinner and less spectacular.

    The preset accompaniments of the KS 49 sound quite cheesy and many are over- orchestrated; especially their chord timbres overuse filter wahwah effects, those resemble 1970th funk "wokachika" sounds. The accompaniments and rhythms are programmable and there is an additional bass track with a fixed monophonic e-bass sound. Nice is that the rhythm programming mode can be also abused as a tekkno drum computer, although the percussion sounds boring. Like with a Yamaha "custom drummer" mode, a template pattern repeats in a loop and you can add individual percussion in realtime through keyboard keys (press simultaneously leftmost ">" key for loud accent notes). Holding the "record/ delete" button simultaneously with a particular percussion key deletes the corresponding percussion track from the user pattern only for that duration the key is pressed, which nicely permits small changes in the running pattern. Pressing "record/ delete" with stopped pattern clears the entire pattern. Unfortunately the thin drums can not be routed through the synth filter (the old Casio CT-410V still could do this). The accompaniment sound depends on the currently selected preset rhythm (also with rhythm off). Annoying is that despite in fingered chord mode the left keyboard section can be expanded to the entire keyboard half, it can not be used as a real 2nd main voice, because it transposes any played notes into a single octave and always attempts to hold chords so long any key in that section stays pressed. Also the maximum chord volume is a bit too low as 2nd main voice. Running rhythm always starts the automatic accompaniment and can not be combined with manual chord mode (e.g. as a 2nd main voice) - outsider keyboards like Antonelli 2495 were much more versatile here. The programmable accompaniment also only accepts 8 standard chords, those are entered in a strange way through the rightmost 8 white keys.

    A HT-700 variant without editable parameters was released as Casio MT-600 (similar case without LCD and entry dial). Casio also released an 61 fullsize keys variant of their HT-700 as Casio HT-3000, which had an additional modulation wheel (that may be also addable to the HT-700 and KS 49 as a hardware easteregg); a light grey version of it was released as Hohner KS 61. I read that the same SD sound generator was also used in the electronic guitar Casio DG-20. The flagship of the HT-series was the Casio HT-6000 (61 fullsize keys), which had a more versatile synthesis engine (4 suboscillators per sound, ring modulator etc.). Another (much simpler) midsize keys synth with halfway similar digital ice- age sound is the Elta KE-491.

    questions: The original Casio HT-700 had a different preset sound set than the Hohner KS 49 midi. Is there a different ROM inside (which IC?) or is this just caused by a jumper or fixed matrix diode (like with Casio MT-540 variants) on the PCB? Which other behaviour differences between original Casio instruments and their Hohner versions are known?

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