Halcyon Miasma

Halcyon Miasma  ·  Source: Halcyon

Everybody’s at it. The CEM3340 is the chip to be reckoned with these days and the reissue of these classic lumps of silicon has made its way into a number of the synths we saw at NAMM. It’s the VCO behind the sound of synthesizers such as the SH-101, Prophet 5, Oberheim OB-Xa and Jupiter 6. You can pick one up from Thonk.co.uk for a tenner. Now Halcyon has put one in a Eurorack module, called it Miasma and stuck it on Kickstarter.


Halcyon kick off by saying something I don’t quite understand. They say “We just couldn’t find any currently available oscillators with the sound textures and capabilities that we wanted, so we had to design our own; and now you get to own one as well.” But then the whole point of this VCO is that it uses the CEM3340 – so they did find an oscillator. I’m confused! Maybe they are referring to the circuitry around the CEM3340? Who knows? I guess we just have to trust that they know what they are talking about.

Miasma is a dual oscillator module. The oscillators can be used together or independently. There are some interesting cross-modulation possibilities, as well as access to both hard and soft sync. Each oscillator has a triangle, sawtooth and pulse output, with sub-octaves 1 and 2 octaves below. Pulse width and frequency modulation is available and each oscillator can be stuffed into the other for some lively internal FM action.

There’s an internal mixer which routes the combined outputs of both oscillators to oscillator B’s output. This lets you easily setup fat, doubled or detuned voices from a single output. Or you can split them out individually once something is patched to the output of oscillator A.

By default the oscillators are soft-synchronised, but they can be separated into completely free running, independent oscillators by plugging something into the Sync B input. Each oscillator has it’s own 1v/oct input and so you have two independent voices.

It’s not a particularly pretty module at this stage, but they have packed in some interesting functionality. I really like the dual personality and versatility with how they relate to each other.


Early adopters can pick up a Miasma for $350 after which is goes up to $385. They are expecting to deliver in April or May.

This won’t be the last module we’ll see this year with a CEM3340 chip in it. Although in my view, it’s not just the chip that makes a classic synthesizer, it’s also the flow, modulation and shaping that gets applied to it. In a Eurorack module the VCO is at its most naked and without a lot of patching through a lot of other modules it’s not going to sound anything like the classic synths that are always mentioned.

More information

  • Miasma Kickstarter page.


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