A New JX-style DCO Polysynth - JX2044

The past few years have been incredible for analogue Polysynths. 15 years ago, outside of small boutique instruments - it seemed like the Prophet 08 was the only game in town. Whilst it's a deep and bold-sounding CEM design, what happens if you wanted a more Roland-y experience? Jupiter and Juno prices have increased year upon year, leading many to explore Roland's more-affordable JX instruments and, in the case of Kiwitechnics, even upgrade their feature sets. Many of these synths are now seen as classics in their own right.

The JX8p, a big grey slab of 80's synth - offers a number of unique tones via Sync & AM cross-mod, so we were excited to hear of a brand new design that is essentially a JX on steroids. We spoke to developer Adamstan about his new prototype, but first - a few specs:

• 2 DCOs per voice based on JX-8P, but with addition of PWM.
  DCO A features sawtooth, pulse and noise, while DCO B has triangle on the last switch instead. Waveforms can be switched independently and mixed.
• Cross Mod (AM) - the same circuit as in JX-8P
• 3 ADSR envelopes per voice, with shape switchable between exponential and linear, RTZ switch and adjustable keytracking (with note number affecting envelope speed relatively to C4 (60).
• 3 LFOs per voice with seven waveforms - triangle, sine, square, rising ramp, falling ramp, random and noise. LFOs can be switched to mono mode, or work polyphonically with adjustable keyboard tracking, which is very useful e.g. for PWM patches
• 4 pole resonant low pass filter built around CoolAudio's V2044 chip. Filter can self-oscillate and also has adjustable keyboard tracking.
• Filter FM using DCO B as a source.
• 1-pole master HPF per part similar to the one in JX-3P

 

Initially I tried to use BBD-based chorus, using MN3207 chips, but it was too noisy even for me, so I decided to switch to digital FX.
 

Each layer has its own FX processor with following blocks:

• Resonant filterbank with two modes:
  • VP-330 "Human Voice" section emulation (with two presets)
  • Polymoog resonator emulation

 

• Stereo Chorus with three presets - "JX Slow" and "JX Fast" corresponding with "I" and "II" settings from JX-8P, and the third mode is "Stringmachine", which uses three delay lines modulated with dual phase-shifted LFOs.
• 4 stage phaser
• Delay / Reverb - switchable between the two. Delay has its own modulation LFO with adjustable rate and amount. Reverb output also can be pitch-modulated.

The addition of Filter FM, more modulation & FX to the 8P's classic sound seems pretty exciting. Thought it must be said, the 2044 has quite a different character to the IR-3R05 filter chips of the original. No matter, you can buy an original for not too much money - this should be seen as a new design with classic inspirations. It certainly sounds beautiful!

Paulee: Wow, creating an analog poly synth is a huge undertaking, right? Did you start off with simpler projects, like perhaps a single voice?

Adamstan: This is actually my fourth (or third-and-a-half) synthesizer project. However, as weird as it might seem, I started my adventure in synth building already with polysynths - and, if memory serves, the only thing I made before was one tube amp  I built my first synth in 2008, for my EE graduation project. I wanted to do it for some time, and the direct inspiration was repairing SIEL Opera 6 with heavily damaged digital board after battery leakage. That required me to understand how it is supposed to work in order to fix it. That first synth was 5 voice with dual VCOs, ring modulator and Moog ladder VCF - you can see it here:

Then in 2016-2017 I built two iterations of the next project, where I used different VCO design and replaced Moog VCF with 2-pole multi-mode SVF. The first version was 6 voices, while the second one was 8 voice bi-timbral:

Paulee: The JX-series synths were perhaps seen as a "lesser" polysynths in the original 90's analogue revival, but now the 3P, 8P and 10 are heralded as classics. Why did you choose the JX8p as the basis for your design? What inspired you to marry the 2044 filter with this design?

Adamstan: I always liked the '80s pop sound, and I'm big fan of analog emulations of bread'n'butter sounds as well as lush, warm pads - and JX8P, not to mention JX10 excel at that. I also really like the quite unique sound of JX8P's "Sync 2" mode, which combines sync and that quirky ringmod (or rather AM). I found out that I couldn't replicate it on any of my VCO synths. So it was time to get something JX-ish. But they are big keyboards, and not as available as I'd like  And as for the SSM2044 - there we come back to the aforementioned SIEL synth that was my initial inspiration for synth building. I eventually sold it, and regretted it ever since, missing the lovely 2044 sound. Some time ago I bought the module version - also suffering from battery damage. But I gave up on rebuilding it, and decided to build new synth that would combine those two - especially considering that we now have brand new inexpensive 2044 chips from CoolAudio.

Paulee: Have you implemented resonance compensation or are you staying true to the sound of the 2044 as is?

Adamstan: No resonance compensation - just raw 2044.

Paulee: Are there any design ideas you tried that didn't pan out, or sound good?

Adamstan: I had to give up on analog chorus, because the noise was a bit too much... It also took me some time to find good levels for pre-filter signal, so it wouldn't sound too weak and wimpy, but I also didn't want to drive the filter too hard, because then it started to sound too harsh, and lose that elegant tone that I'd expect from a synth having "JX" in its name.

Paulee: I personally love Filter FM - perfect for chewy pads and vocal tones. Many CEM-based DCO synths had this - but *not* the Roland's - why include it here, and was it difficult to implement?

Adamstan: I also like Filter FM (as well as standard digital FM, with DX7IID being my main synth) - and frankly it was relatively easy to implement, requiring just few additional components - so here it is. I actually added it in the second revision after playing a bit with initial version that didn't have it.

Paulee: Do you think it's important for synths to include onboard FX as you've chosen here?

Adamstan: Without a doubt chorus is essential part of JX sound. Since I had to give up on analog one, I decided to make use of the processing power available, and add other useful bits - delay and reverb was natural, but then I thought "what else could I do that would provide some interesting sounds?" - and finally ended up adding phaser and resonant filter bank. Even if they're useful just for a few patches - I like those patches :D

Paulee: What format (keyboard/module/rack) will the proposed synth take?

Adamstan: I'm aiming for rackable (5U) desktop. It's my dream to make a keyboard as well, but I cannot afford it for now. Perhaps later, if the module does well enough to bring in some money needed for developing keyboard version.

Paulee: How will assigning modulation destinations work?

Adamstan: Modulation assignment system is mostly ported from JX8P. So there is amount control at each destination - like, there is a slider for ENV>PITCH, ENV->FILTER, LFO->PITCH, LFO->FILTER etc etc like on the JX, and then when you call up the edit menu for oscillator or filter, you can select one of the available sources (ENV1-3 or LFO1-3) for that destination. So that's the equivalent of EG select switches found on PG800 programmer.

We look forward to hearing more tones from the JX2044!

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