THC Recursive Machine

I was a bit surprised when I couldn’t find any discussion of the Recursive Machine from The Human Comparator.

It hits alot of marks for my own interest, since I abandoned eurorack, but miss some patachability. Also, the combination double pt2399 and Belton reverb brick, lends itself to alot of feedback experiments.

Anyone here have any experience with this thing?

The instrument is DIY only, battery powered and contains:

2 x vco
2 x vca
1 x vcf
1 x distortion
1 x digital spring reverb
2 x pt2399 delay
2 x lfo
1 x mixer
1 x speaker


I’ve been using one for a few months, and like it a lot. It’s a unique instrument with a lot of possibilities. I love the timbres I’m getting out of it. Unfortunately, they’re only available as pcb/panel/frame sets, so it takes some work assembling all the parts and doing the (tight) build. It’s a lot of circuits in a small package, so I would have preferred a larger version, but once you get used to it, it’s reasonably playable.

It’s at the intermediate level of diy builds–the pcb is deceptively small, but you’re building a full synth. Mostly through hole, but a non-trivial number of SMD components. THC had some aesthetic ideas that go against the grain of sensible diy design, but anyone who’s built at least a few modules or other types of kits can likely finish a successful build.

The strengths are the interesting normalled signal flow with multiple feedback loops, and the dual PT2399 delays. There’s some similarities to the Make Noise Strega, but the RM allows you to break any normalling and patch the complete signal flow any way you like.

Here’s my first track made with the RM. It’s 90% one recorded pass, with a a small number of samples from other recordings added in post.


I’m in the middle of building mine. For me it fits that sweet spot between the cool feedback machines from the like of Ciat-Lonbarde, Meng Qi, and even the Make Noise Strega in a more straightforward package. Cheaper and DIY, which is a plus for me, though I know for some that’s either not an option or just a turn off.

Am looking forward to processing it through my Norns Fates as well.


Thank you for the thoughts! And the sound example is great, i love the grittyness and that feedback tone.

I’m not so concerned with the DIY part, as I’m quite experienced.

How do you find the stability of the jacks? Do they seem solid when patching around? My first and only worry when I saw the design, was breaking a jack one day.

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Just ordered my kit from Thonk! Hope to contribute to the discussion soon!!


Just received my kit from Thonk yesterday, waiting on mouser parts.

Looking at the small trimmer pots and picturing it when heavily patched I’m wondering if the small pots plus lots of cables makes it a bit testing to tweak ?

Thanks! The jacks are solid–with all the tabs soldered, they’re secure on the panel. I’ve noticed they’re somewhat stiff though–hopefully they’ll loosen a little with use. You could always order a couple of spares if you’re worried.

Well, the front panel is a dense field of jacks and pots, but some of the normalling can be controlled with pots, so even minimally patched, you have a lot of interesting feedback and signal flow loops with controls.

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Have to agree with this. If memory serves these jacks are the same as the ones on the Dreadbox Antiphon which I built a while ago. In use they are a lot more durable than they look and are fun to patch. At first though as @Hovercraft says they are stiff.

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THC just posted this concept for the next iteration of the RM–the recursive apparatus. wow.


Teenage Engineering meets Grendel Drone Commander. I can work with that!


I saw this just before Christmas and was almost tempted. It looks very good and I’m a fan of compact self contained battery powered things. Cheap is very good for me, and I’m comfortable with through hole DIY (not sure about SMD yet) But I decided to start getting into the AE Modular format instead, so I probably won’t be going Recursive anytime soon.

Very appealing project though, glad to see this thread as I couldn’t find much on it when I researched it before.

Ah damn. I just sold my Push 2 on Friday, to fund two kits from thonk, and now they are all sold out.
Guess I can order from multiple sources instead though.

Just received my pcbs today! I don’t have the sockets so I can’t tell exactly, but it looks like threaded metal pots fit the foot print ok. Anyone else considering this? Could allow it to be panel mounted or set in a metal enclosure


I was thinking about a front panel as well, but would go for long trimmers instead, and then trimmer knobs on them.

I feel it would kill the usability even more and make it hard to navigate, depending on which knobs you can get. I think the layout is pretty dense already.

I’ve been able to resist building one of these so far but if there was a front panel option I think that would put me over. Metal shaft pots will definitely work (assuming the height of the base is similar to that of the jacks). You could then use befaco micro knobs with T18 splined pots. Ideally there would be footprints for the jacks to also be one of the threaded shaft styles but maybe that’s not possible/practical with the jacks used here. Drilling holes in the pcb to put in spacers is possibly an option if there is space between the traces and hardware, though this solution would be last on my list! All that said, I do appreciate that this was designed to be lean (on your budget) and mean.

Anyone using one of these that is also knee deep in euro? Is this binging new things to the table (sonically or even inspirationally being self-contained, etc.)?

The RM is an instrument, rather than a collection of functions–so I think it offers something unique, regardless of the other gear you own. The normalled signal flow with its nested feedback loops lead in interesting directions, but don’t constrain you, since the connections can be broken. I love playing with it as a self-contained instrument–there’s enough present and absent to be satisfying and challenging.


That’s the impression I’ve been getting, thanks.

The “version 2” [[don’t call it a comeback]] Recursive Apparatus you posted the instagram link to above looks interesting, too. No patch points visible from the photos and looking at the signal flow diagram/spider web I’m seeing several possible points to tap outputs from. The substantial speakers also reinforce this one as being its own thing. Love the field test equipment aesthetic of it, which I hope stays with the final design.

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yeah bit worried about this given the tight layout. @addamm’s suggestion of t-18 pots with befaco micro knobs is what I’m investigating rn. Still waiting on my mouser order to compare the height of the body of the jacks and pots.

Did a quick check around mouser/digikey doesn’t seem to be an obvious threaded replacement for the jacks. They are specially designed switching jacks with multiple poles, looking at the schematic this appears how the normalized path works.

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Here’s a comparison with an Alpha B10k pot and the jack’s from mouser. There’s quite a difference in height.

If the t-18’s are the same height you would probably need washers to bring the height of the pots up plus a real thin panel to get some torque on the threading. Can’t really say it’s doable to be honest.

*Just remembered there are potentiometers with more threading such as these Alpha 9mm Long Pots – Vertical – Thonk – DIY Synthesizer Kits & Components