Introduction
We recently acquired a Suzuki SX-500. If you are wondering what this has to do with Siel DK or Korg Poly-800 synth families, the SX-500 is a rebadged Siel EX-80 (the expander for the DK-80). For a little background, both the DK family (DK-70, DK-80, EX-80) and the Poly800 family (Poly-800, Poly-800II, EX-800) have similar styling, parameters, and unusual architecture, sharing a single filter between all voices (two filters in the case of the DK-80), so the amplifier feeds the filter (vs. the typical VCF->VCA architecture). FWIW, these DK synths are not siblings to the DK-600 and DK-700, which are related to the Siel Opera 6.
Superficial Comparison
The Korg EX-800 and Siel EX-80 (Suzuki SX-500) share a lot closer resemblance than just model numbers. They are both table top units of about the same size (although the EX-800 is metal vs. plastic), with similar buttons, knobs, and parameters displayed in the top half of the face. Both can be rack mounted with optional rack ear kits, although they would take a lot of rack space (5-6U plus cable clearance). Carrying the similarities further, both the Poly-800 and the DK-70 have strap pegs to be warn guitar style (keytar) and can run off batteries (6 Cs or 8 AAs, respectively). However, the DK-70 removable neck has a pitch ribbon and three control buttons (mod depth and assignable), while the Poly800 has the familiar Korg joystick (pitch bend, filter/pitch mod). Additionally, the DK family has a cartridge interface to store more programs and there is no bitimbral equivalent to the DK-80 in the Korg family.
Sound Source
As mentioned in the introduction, both families share a similar architecture, including additive square waves (4 harmonics) and single/dual oscillator modes. However, the DK family offers a saw waveform, while the Poly800 family can weight the square harmonics volumes in a saw pattern. The DK family can also weight the square harmonics in any pattern, since each square wave harmonic volume is variable (vs. on/off in the Poly800 family). Noise can also bypass the filter in the DK family.
Modulation
Both families share similar envelopes, featuring dedicated ADBSSR volume envelopes for each oscillator and the filter (shared by the noise VCA). However, the DK family has dedicated pitch and filter frequency LFOs (vs. shared). The DK family LFOs also feature initial and sustain levels (IAS envelope vs. Poly800 LFO delay) and selectable triggering. The DK family filter LFO waveform can be a triangle or square (pitch and Poly-800 LFO waveform is a triangle). Neither family offers VCA LFO modulation (tremolo).
Performance Control
Unlike the Poly-800 family, the DK family supports velocity (routed to amps and filter) and the sustain pedal can be assigned to the volume envelopes individually. The DK family dual track sequencer is real-time, while the Poly800 family single track sequencer is step-time.
The Guts (Components)
To find out how deep the similarities go between the Poly-800 and DK families, the circuit Components were also investigated. Both use 8 bit microprocessors and BBD style chorus, but so do most synths of that era. For filters, the DK family uses the SSM2045, while the Poly-800 family uses their usual NJM2069. However, the DK family does share processors (TMS700 family) with the Elka EK family (not a big surprise, since the Italian synth manufacturers seem to collaborate on synth technology). The DK family tends to use dedicated components for the signal and control path (polyphonic, noise, and oscillator generator ICs), while the Poly-800 family uses discrete components and software for the same functions.
Conclusion
While the similarities are significant, so are the differences. The Poly-800 family was very popular, due to their low price, while the DK family never became as common. A wild guess would be the DK family was a me-too product, since the Poly-800 was released a couple years before the DK-70, DK-80, and EX-80 arrived. The DK family have some significant advantages over the Poly-800, but before you go buy your own Siel Moog Slayer, note if it includes the external (brick) power supply, since the power supplies are uncommon (16VAC with 5 pin 90° DIN power connector, see pic).
BTW, you may notice the white switch above the filter cutoff parameter on the EX-800 pictured. That mod selects the two or four pole filter. Since the SSM2045 also has both two and four pole filter outputs, we will probably eventually mod the SX-500 too.
Part 2 (Deeper Dive)
The Korg Poly-800 and Siel DK families have a lot of similarities. This leads to the question, do they sound similar? The short answer is not really, due to their different filters. We have characterized and sampled the Suzuki SX-500 (a.k.a. Siel EX-80) and Korg EX-800 primarily to compare their filters. As a side note, editing the EX-800 was easier than the SX-500, thanks to the 3 LED displays (vs. 1 on the SX) and Bank Hold button.
Parameter Comparison
The Korg Poly-800 family envelope parameters have twice the granularity, compared to the Siel DK family (32 vs. 16). Envelope attack and decay also have twice the range on the Poly-800 family vs. the DK family, although they do not exceed the DK max time of ~6s until the last 3 values (29-31), maxing out at 13s. However, the reverse is true for envelope slope and release, since the Poly-800 family uses identical values for all rates, while the DK family slope and release are much slower, maxing out at ~20s.
The LFO rates both start at around 0.3Hz, but the maximum LFO rate for the SX is 10Hz, while the Poly800 family top rate is 25Hz. The max delay times for the Poly800 and DK families are similar (1.24s and 1.55s respectively), although the DK can ramp the delay (via initial and final level parameters) and has dedicated LFOs (vs. Poly800 shared LFO).
To save all of those parameters, the DK family offers 10 user editable presets (it also has 40 non-editable presets). While that sounds paltry compared to the Poly-800 family 64 editable presets, the DK family also supports memory cartridges, which can hold another 50 presets (RAM or ROM). Be aware that memory storage is relatively important to these families, since all of the DK family members and the original Poly-800 family member do not support MIDI SysEx (System Exclusive). So, a computer can not be used to edit or transfer presets in most cases.
Oscillator Comparison
The Poly-800 family has a range advantage, since the oscillators can be shifted an octave up or down. Additionally, the two oscillators can have different waveforms, while the DK family oscillators share a common waveform. The saw and square waveforms for both families look similar, but not identical:
| Model | Key | Saw | Square | Square (all harmonics) |
|---|---|---|---|---|
| EX-800 | C1 |  |
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| SX-500 | C1 |  |
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| EX-800 | C6 |  |
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| SX-500 | C6 |  |
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The SX-500 higher frequency waves are more rounded off, probably due to the filter. Surprisingly, the EX-800 additive saw looks closer to a saw (in the higher keys) than the SX-500 dedicated saw.
Filter Comparison
The SX-500 filter cut-off tops out at 20kHz, while the EX-800 filter tops out at 25kHz. While that may not seem to matter (since human hearing does not usually exceed 20kHz) it does color the SX-500 noise: SX-500 noise bypassing VCF, SX-500 noise through VCF . However, when an envelope modulates the EX-800 filter at full depth, it actually sweeps up to 40kHz, which explains why the EX-800 filter sweep sounds like it tops out faster (since half the range is above our hearing threshold): EX-800 filter sweep and resonant filter sweep, SX-500 filter sweep and resonant filter sweep.
Admittedly, the noise used on each synth has a different spectrum. The EX-800 is closer to white noise, while the SX-500 is closer to pink noise: EX-800 noise, SX-500 noise (VCA), SX-500 noise (VCF) . However, using the same noise source for both samples would have required modifying both synthesizers (which we will probably do eventually). So, here are the same filter sweeps, using all square wave harmonics as sources (C1 fundamental): EX800 filter sweep and resonant filter sweep, SX500 filter sweep and resonant filter sweep.
SX-500 Chorus
The detune (Detune Fine) caused some confusion, since it is also active in (single oscillator) whole mode (i.e. causes beating when one key is played). Could the SX-500 really have 16 oscillators (vs. 8 in the manual)? The answer was partially evident when the detune depth is at maximum ... the beating sounds like a flanging or phasing effect. In reality, "Fine Detune" is the chorus delay time control, but it is disabled when "Chorus" is enabled (i.e. "Chorus" switches to a preset delay).
EX-800 Filter Slope
As also mentioned in the previous comparison post, both the Korg EX-800 and the Suzuki SX-500 have 4-pole filters (24dB/octave). However, the 2-pole (12dB/octave) output is available on both ICs. Here are the two outputs with the filter set to 2kHz: 2-pole and 4-pole
Verdict
The major differences are relatively even ... While the DK/SX family lacks an octave range, it does have dedicated LFOs for pitch and filter and variable harmonic volumes. The lack of dedicated waveforms for each oscillator make most of the DK synths (except the DK-80) dual mode nothing more than an interval generator. The Poly800 family's better resolution/range for some parameters is irrelevant unless really slow envelopes or LFOs are needed. Similarly, DK family's more versatile sequencer is irrelevant when most musicians will use a software based sequencer. The DK family is velocity sensitive, but most of the Poly-800 family support MIDI SysEx (Poly-800II and EX-800, not the Poly-800), so that winner depends on the application.
While major similarities (and differences) abound, the Korg Poly-800 and Siel DK family filters are different enough to give them each a unique sound. So, there is no clear winner, just two similar families.