The Logan String Melody designed by Ing. Giuliano Costantini for Logan was a portable keyboard produced in two versions from 1973 to 1982. Manufactured in Italy, it was sold under both the Logan brand name and re-badged as both a

Hohner Hohner Musikinstrumente GmbH & Co. KG is a German manufacturer of musical instruments, founded in 1857 by Matthias Hohner (1833–1902). The roots of the Hohner firm are in Trossingen, Baden-Württemberg. Since its foundation, and though known ...

and Vox product. The Vox version was called ''The String Thing'' but still featured the Logan brand name on the back of the case. The keyboard consists of four octaves split into two nearly equal sized ranges. In each of these ranges a combination of three string sounds can be mixed using faders labelled ''Cello'', ''Viola'' and ''Violin''. Each string sound is pitched one octave apart. In addition to the separate sets of faders for the string sounds, each range has a sustain and release fader. The lower range also features a simple

monophonic Monaural or monophonic sound reproduction (often shortened to mono) is sound intended to be heard as if it were emanating from one position. This contrasts with stereophonic sound or ''stereo'', which uses two separate audio channels to reproduc ...

synthesiser that is controlled from using faders labelled ''Bass'' and ''Perc''. On the first version, there is a button labelled ''Orchestra'' that has hard wired settings and disables the faders for the string sounds. The second version, the ''String Melody II'' introduced in 1977, added more buttons for further hard wired settings.

Technical

It came in a heavy wooden case and weighed 23 kilograms. It has full

polyphony Polyphony ( ) is a type of musical texture consisting of two or more simultaneous lines of independent melody, as opposed to a musical texture with just one voice, monophony, or a texture with one dominant melodic voice accompanied by chords, h ...

with a

variable-gain amplifier A variable-gain (VGA) or voltage-controlled amplifier (VCA) is an electronic amplifier that varies its gain depending on a control voltage (often abbreviated CV). VCAs have many applications, including audio level compression, synthesizers and am ...

for each key and a BBD (

bucket-brigade device A bucket brigade or bucket-brigade device (BBD) is a discrete-time analogue delay line, developed in 1969 by F. Sangster and K. Teer of the Philips Research Labs in the Netherlands. It consists of a series of capacitance sections C0 to Cn. The stor ...

) ensemble effect that gives it the distinctive string synthesizer sound. Sound production begins at a high frequency

square wave A square wave is a non-sinusoidal periodic waveform in which the amplitude alternates at a steady frequency between fixed minimum and maximum values, with the same duration at minimum and maximum. In an ideal square wave, the transitions b ...

generator, then flows to the

frequency divider A frequency divider, also called a clock divider or scaler or prescaler, is a circuit that takes an input signal of a frequency, f_, and generates an output signal of a frequency: : f_ = \frac where n is an integer. Phase-locked loop frequency ...

, a

Mostek Mostek was a semiconductor integrated circuit manufacturer, founded in 1969 by L. J. Sevin, Louay E. Sharif, Richard L. Petritz and other ex-employees of Texas Instruments. At its peak in the late 1970s, Mostek held an 85% market share of the d ...

MK50240N

integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...

for the highest octave. These top octave frequency dividers were commonly used in electronic organs of the period. The lower octaves are divided by nine 7-stage SAJ210 dividers. The square wave passes the variable-gain amplifier built as a

CV/Gate CV/gate (an abbreviation of ''control voltage/gate'') is an analog method of controlling synthesizers, drum machines, and similar equipment with external sequencers. The control voltage typically controls pitch and the gate signal controls not ...

and a pulse conversion. Then the sound travels to the mixer, the ensemble effect, a presence filter and the output stage. The monophonic bass sound available on the lower half of the keyboard has no variable-gain amplifier but has a

low-pass filter A low-pass filter is a filter that passes signals with a frequency lower than a selected cutoff frequency and attenuates signals with frequencies higher than the cutoff frequency. The exact frequency response of the filter depends on the filter des ...

. The percussion bass is low filtered and has an attack of 30ms and a decay of 700ms, with no release. A simple gate variable-gain amplifier is used with a 47µF capacitor, and the filter is behind it. The ensemble effect consists of two modules – a dual low-frequency oscillator and the triple

delay-line oscillator A delay-line oscillator is a form of electronic oscillator that uses a delay line as its principal timing element. The circuit is set to oscillate by inverting the output of the delay line and feeding that signal back to the input of the delay l ...

. The low-frequency oscillator puts out 0.6 Hz and 6 Hz mixed together as a tri-phase of the low-frequency oscillation to the delay-line oscillator. The delay-line oscillator consists of three TCA350 circuits – a chain of 185 MOS double transistor stages, which samples the audio signal, which is then modulated ( FM) by the dual LFO so the output samples are shorter or longer. I noticed in the version different technologies for the dividers: Before the mostek divider, there was a dozen master oscillator bank for each chromatic tone. And early versions have transistor octave dividers instead of the SAJ210. The BBD was available in 3 cases: Type X (DIL14) in early String Melody I, type Y (DIL8) as standard in all string melodies and type Z (metal can). The device shown in the picture is the one from ''trouby''; it has an switchable input-jack beside the presets to use the ensemble effect for external signals. This photo (original or edited) must not be used as picture for selling activities.

References

{{Reflist String synthesizers