Korg DL-50
A strings-and-synth hybrid with a joystick instead of a pitch wheel, and two output paths that let each half of the instrument go its own way.
Overview
Korg's own documentation calls the DL-50 the Delta, and describes it as a polyphonic synthesizer paired with a strings section under one 49-key C-to-C keyboard. The two halves are not layered into a single voice — they are separate signal paths with their own outputs, and that separation is the whole design argument. Owners can run the synth through one amp and the strings through another, or feed each into different effects, which is the kind of routing flexibility that mattered on stage in an era when a gigging keyboardist was often juggling two instruments to get the same result.
The synthesizer side is built around draw-bar-style slide controls for 16', 8', 4', and 2' plus white noise, feeding a 24dB/oct voltage-controlled filter and an ADSR envelope generator. Five signal generators are listed in the spec section, and the filter offers both bandpass and lowpass modes with a keyboard follower that can be switched in or out. Contemporary coverage of the period's synth accessories, such as Modern Recording (November 1980, p.32), noted the growing range of synthesizer controllers and accessories reaching the market alongside instruments like this one.
To the left of the keyboard sits a joystick, and it does more than pitch bend. Pushing it handles pitch bend and vibrato depth, while the noise modulation depth is also under joystick control — and the manual notes that on the polyphonic synthesizer, the joystick modulates the VCF. That last part is the interesting one: filter modulation from a performance control, on a polyphonic instrument, is a different playing experience than bending a single monophonic voice. A separate modulation generator handles vibrato depth and speed, and there is a tune control covering ±100 cents plus an octave switch for up or normal.
The envelope section is more complete than the panel's slide-control layout might suggest. Attack, decay, sustain, and release are all present, with a VCA envelope mode and a trigger mode switchable between single and multiple triggering — the difference between an envelope that retriggers on every key and one that holds through a legato line. Filter depth and filter mode (bandpass or lowpass) round out the synth voice controls.
The strings section shares the keyboard but keeps its own identity, and the manual is direct about the intent: the same keys give realistic strings alongside the polyphonic synth. Because the two sections have separate outputs — labeled Synthe and Strings — each can be processed independently, which is the practical reason the design exists. Mix outputs are provided in both high and low level, alongside a headphone output. There are also external inputs for VCF frequency modulation (−5V to +5V) and a trigger input, plus a trigger output, so the DL-50 can be tied into a larger rig rather than sitting isolated.
One service note is worth flagging for anyone who works on these: the manual's adjustment section states explicitly that the DL-50 strings synthesizer does not operate on the Hz/V system. That matters for anyone assuming compatibility with the CV/Gate conventions of other Korg gear from the period — the DL-50 sits outside that scheme, and the documentation says so up front rather than leaving it to be discovered the hard way.
Calibration is documented in the usual Korg service style. Tuning is set with a trimmer while playing C3 against a frequency counter, then checked across C1 through C5 to confirm release time stays consistent key to key. The joystick gets its own procedure: with the filter modulation switch off and the FM switch on, the FM depth control is adjusted so that pushing the stick fully right on C1 raises pitch to G1, and a trimmer is set so that pushing fully left on G1 drops pitch back to C1 — repeated twice to settle it. Filter cutoff and resonance have their own trimmers and a described oscilloscope trace to match. The parts list is complete down to transistor types (2SA733AK, 2SC644R, 2SK30 GR) and ICs (AN6551, LM324N, TL072, LM13600), which is the kind of documentation that keeps a forty-year-old instrument serviceable.
Physical details are sparse in the record. The unit is listed at 10kg, and accessories included a dust cover and connection cord. Dimensions appear in the spec table but the excerpt is truncated, so no figure is quoted here. Production years are not documented in the available material, and no original list price appears in the sources on hand.
eBay Listings
As an eBay Partner, we earn from qualifying purchases. This helps support our independent vintage technology research.