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9 of the Best Compact and Medium Format Schumann PLL Style Harmonizer Fuzz Pedals

Beetronics FXFuzzGrendelGuitar Synth and SequencerIdiotBox FXMammouth MachineMantic EffectsModulated FuzzModulationOddball FuzzOscillating FuzzParasit StudioPedalPCBSunsine AudioWraa Defects+-

Just over a year ago I did a piece on ’9 Cool Phase Locked Loop Synth Harmonizing Oscillating Fuzz Pedals’ where I focused on the original Schumann PLL and the larger format full-feature/full-range replicas of said pedal. This included the EarthQuaker Devices Data Corrupter - which was on my wishlist for quite a while but I never ended up getting - for reasons which I will explain. There were a couple of pedals I overlooked in that overview - one which had relatively recently been discontinued, but which still has its fans to this day - the Broughton Audio PLL. Also just soon after I published, Glou Glou released their own Four Voices version of the format with 4 separate banks of filter controls. I’ve added those two to my original article per above link so you can view all of the key contenders for full-feature PLL replicas in one place.


This article however was inspired by the relatively recent arrival of my Beetronics Swarm PLL Harmonizing Fuzz - which essentially takes the key aspects of the Schumann PLL and miniaturises them to fit within a more compact and simpler to use form factor. I was immediately wowed by the Swarm, but then thought that it must have some competitors in the compact PLL stakes - and hence this article was born. In the process of researching and writing up this article I have now acquired the entire left-hand column of those pedals featured - namely the Beetronics FX Swarm, Mantic FX Flex Pro LE White and PedalPCB Mini Heterodyne Receiver. All of those should be in my hands and fully tested by the time this article goes live (or not depending on slow-moving customs clearance and lousy Parcelforce or Royal Mail processing rates).


Contrary to what seems to be the case in general with PLL pedals - none of these are yet discontinued, while some are somewhat hard to get hold of. I feel though that this is as solid an overview as the original full-featured version - and between the two you should get a pretty comprehensive idea for what is out there, and what may suit your own needs.


Often in writing these articles I make acquisition decisions during the process of reviewing and writing up my findings. On this occasion though I feel I probably have all the PLL’s I need before I fully complete this feature, and in the format that best suits my own preferences. In working with a variety of Glitch style granular synthesis/looper pedals I finally realised that having too many controls can be as much of a curse as a blessing - and particularly in the area of being able to easily replicate your favourite tones/settings - if you need to tweak dozens of knobs and switches - it’s going to be problematic dialling things in a second and third time. So I really appreciate the length these pedal builders have gone to in order to simplify the PLL experience sufficiently so that I can use it to the best of its and my capabilities.


As mentioned, I considered the EQD Data Corrupter for the longest time, but in the end decided it was just a little on the large side for me. So when the Beetronics Swarm was announced I was delighted - as I already had a latent requirement that needed satisfying. I had foolishly though overlooked the equally impressive Mantic Flex Pro which had already been out for a number of years and which I actually covered quite a while back in my ’16 Weird and Wonderful Guitar Noise Pedals’ feature but then sort of forgot about. I quickly realised the error of my ways and had soon bagged one of the newer white limited editions.


I was also eyeing up the Grendel Drone Commander Classic for a while, but decided that there were probably a few too many options there, and its larger size and larger price had some say in it too. My third acquisition in the end was the fortuitous discovery of an assembled Mini Heterodyne Receiver - a DIY Kit pedal, but one which had been expertly put together by Flint Amplification. This was the most compact extended-range version I came across - so I decided that this should be part of my Tone Library also.


Obviously there are a number of simpler choices here - like the Wraa Glitchwave One Knob PLL Synth Fuzz and increasingly rare assembled Parasit Studio Raygun Youth Chaos Fuzz. Or the more readily available Idiotbox Lost Ark and Sunsine Audio Harmonic Decoder. Finally. I came across the Mammouth Machine Cobra Commander which rounds up this overview sort of - and which is cool too, but probably a little too close to the Mantic Flex Pro format to warrant my adding it to the collection.


I’ve kind of decided that I may actually still add a Wraa Glitchwave One Knob PLL at some stage - as I’m fascinated by how it squeezes all that PLL Harmonizing goodness into just a single knob control. I would probably also pick up a Raygun Youth if I came across a good looking one in decent condition - these are assembled DIY Kits and therefore exist in various random versions - some considerably ’rougher’ than others.


Pedals are listed alphabetically by brand as usual:

Beetronics FX Swarm - $249 (


I latched onto this as soon as it was announced - as mentioned in the intro - I had already done research into PLL, and had all but decided to get an EQD Data Corrupter at one stage - before deciding that unit was a little on the large side for me. So when the Swarm came along it satisfied a latent need and I ordered one as soon as the pre-orders opened. I very much classify this within the Fuzz category and despite its 7 knobs and rather obtuse legends - Queen (Harmony Level), Drone (Sub Harmony Level), Species (Harmony Interval x 9), Flight (Frquency Modulation Response), Sting (Frequency Modulation Rate), Workers (Fuzz Level) and Master Volume - you actually get used to how it works pretty quick. I get great tones out of this pretty much wherever I point the dials - and some really cool quirky wobbly oscillations in there too which I love - particularly the ones that occur on the sort of trail decay. This is actually a really well thought out pedal which you can easily spend a day experimenting / having fun with. I so enjoy using this that it triggered my need to get a couple of more examples from this genre. Obviously as with all PLL's this is for more adventurous players - and not all of the output will work well within a band mix - but there should be plenty here for everyone.

Grendel Drone Commander Classic Pedal - $369 (


I can't exactly recall how I came across this one, but it was under solid consideration for quite some time. It has 9 dials here in 3 columns - each followed by a couple of toggle switches as follows : Osc 1, Osc 2, 1 Mix 2, Osc 1 Switch, Osc 2 Switch | LFO, Shape, 2-4-8-16, Envelope Switch, LFO Switch | Filter, Pulse, Volume, Shape Switch, Filter Switch. Certainly an interesting proposition and does everything you need it to do - but I already had the Swarm, and decided that I would rather get the Mantic Flex Pro and PedalPCB Mini Heterodyne Receiver in addition. I might still come back to this one day - although its form factor is really on the too-large side for me, so perhaps not.

Idiotbox Lost Ark PLL Octave Glitch Synth - $99 (


I've featured Idiotbox a couple of times on this site - they do a number of slightly quirky pedals - so it's fitting they have their own PLL variant. The Lost Ark is an elegant simplification, while I'm not that enamoured with the 8-bit artwork. You get Frequency, Filter, Out, Octave 1 and Octave 2 dials - and that's your lot. Possibly not quite as interesting as some of these other ones - but the results are still rather pleasing.

Mantic FX Flex Pro Limited Edition White - $255 (


So I featured this pedal initially in my piece on 16 weird and wonderful noise boxes - but then somewhat overlooked it and forgot about it for a few years! Fortunately the Swarm actually rekindled my interest in the Flex Pro - and I now have one of the newer white ones as pictured. I am so glad I acquired this as it's every bit as great as the Beetronics Swarm. It's control topology is somewhat different to the Swarm - they both take just a little bit of getting used to - there's not so many dials here that you don't quickly enough figure out what roughly everything does. For the Mantic Flex you have 6 dials - Level (Output), Focus (Attack), Pump (Envelope Speed), Mix (Dry/Wet), Filter (6 x VCO/Range Sizes) and Rate (LFO Modulation); then two toggle switches under the protective bar - '$' (Decay Length - up = longer) and '&' (Attack/Sensitivity - up = slower), and finally dual footswitches with the left one the On/Bypass and the right on the LFO Activation. It's a tweakers' pedal just like the Swarm above and is equally fun to use - they overlap to a degree, but they are each their own thing too!

Mammouth Machine Cobra Commander PLL Harmonizer - €200 assembled ( [DIY Kit / Assembled]


This was actually the last one of these I came across (albeit not alphabetically) to round out my selection of 9. Mammouth Machine is one Jérémy Stoz of Belgium who is principally a DIY Kits creator - but also offers those in fully assembled format - like this Cobra Commander PLL. You get 6 knobs on this unit - Gate (DC Bias), Frequency (Oscillation Frequency), Blend (Mix between Fuzz and Harmonizer), Volume, Octave Selector (+/- 3 Octaves), Intervals (Intervals of 3rd & 5th Harmonics). This is a pretty cool take on the format - but I don't believe it gives me anything really in addition to my Swarm and Flex - which I feel are slightly more capable.

Parasit Studio Raygun Youth Chaos Fuzz - c£120 assembled when available ( [DIY Kit / Assembled]


I've covered Fredrik Lyxzén's Parasit Studios before - his Into The Unknown Guitar Synthesiser Deluxe in particular. Similar to Jérémy Stoz at Mammouth, Fredrik is actually principally a maker of circuit PCBs. Where the Raygun Youth is a fully assembled pedal made with that PCB which is still available on the Parasit Studio store - but there aren't any assembled models available right now. They occasionally crop up on - but depending who assembled - the look and quality of assembly can be fairly diverse. Generally though this is heavily simplified 3-knob derivation of the PLL. You get a 4-way mode selector - Stun | Kill | Incinerate | Degenerate (That last setting would be better as Obliterate!), then Level and Disorder control dials - with the latter manipulating the frequency modulation. I think it's quite a cool pedal - and if a decent example found its way onto I may well be tempted. Looks like these had their heyday quite a few years ago now though.

PedalPCB Mini Heterodyne Receiver Analog PLL Harmonizer / Fuzz - c£146 assembled ( [DIY Kit / Assembled]


PedalPCB is a similar operation to Parasit Studio - specialising mainly in pedal circuit PCBs. It has two PLL circuits - the Mini Heterodyne Receiver and the Super Heterodyne Receiver - which is the one demo'd in the above video while I have the Mini version as pictured! This is another pedal I came upon in my research - a fully assembled Mini version by Flint Amplification - and courtesy of The Mini Heterodyne Receiver is the most compact extended range version of the smaller PLL pedals. It has 6 dials and 3 toggle switches in 3 sections / columns. Sub (Sub Octave Level), Sub Interval (Octave Interval x 8), Sub Root Switch (Subdivided Frequency - Unison/Oscillation Root) | Square (Fuzz Level), Modulate (Modulation Rate), Modulation Mode Switch (Portamento/Vibrato Modulation) | Osc (Oscillation Volume), Oscillation Interval (Interval of Frequency Multiplied Voice x 8), Oscillation Root Switch (Root of Frequency Modulated Voice - Unison/-1/-2). I felt that this version complemented my Swarm and Flex Pro nicely - and they together make quite a formidable trio all-in-all.

Sunsine Audio Harmonic Decoder PLL - $165 (


This builder seems to be more like Meris or WMD - making Eurorack modules as well as pedal equivalents. Currently a very compact range - Origami Orgasm Wave-Shaper Module, Harmonic Decoder Module (PLL) - and then Gold or Silver accent Harmonic Decoder Pedals (PLL). This is another simplified PLL derivation with just 3 dials - Frequency, Depth and Volume, and then an Envelope/Control Voltage toggle selector. It does the job perfectly well - though for some odd reason my preference in the 3-knob stakes is Parasit Studio's Raygun Youth take - possibly there is something in the naming of those pedals too!

Wraa Defects Glitchwave One Knob PLL Synth Fuzz - £80 assembled ( [DIY Kit / Assembled]


Something about this UK-made One-Knob PLL really appeals to me - had I known about it sooner I would most definitely have included in my piece on 'One Knob Wonders'. As expected - you have just the one dial to effect the changes - would love to see the control circuit on this. It produces exactly the kind of tones you might expect from a PLL - but with slightly less control over exactly how those tones are generated/shaped. These are really cool and affordable pedals - available as a £10 PCB or fully assembled for £80 - I will likely have one of these too before long!

Final Thoughts

Before getting stuck into the summing up I thought I would give the Subdecay Harmonic Antagonizer and Lastgasp Art Laboratories Lluna some honourable mentions - as while they are Not PLL types, they sort of get you into vaguely similar territory.


In terms of my conclusions then - I feel this is as good a selection as any for the format - and depending on how simple or complicated you want to get - there are options either way here. The Grendel box is pictured somewhat smaller than it actually is in relation to the others - it probably falls into the same camp as the EQD Data Corrupter in terms of just being a little too large to be practically useful within my rig.


I feel that the 3 ones I've already acquired are the best matches here to my own preferences and requirements - and I'm delighted what they deliver - and the differences in each one's approach. As mentioned above I will almost certainly get a One-Knob Wraa Glitchwave - while if a decent looking Raygun Youth Chaos Fuzz turns up on I might just consider that too.


I obviously love fuzzes and squelchy synthy sounds - so the PLL format is a match made in heaven for me really. You yourself will need to decide whether you like this effect and will use it regularly - and therefore which unit here best serves your needs. In terms of picking an overall favourite here - I can't really split it between the Swarm and the Flex Pro - each has its advantages and I love them both dearly! The PedalPCB MHR ain't half bad either!

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Stefan Karlsson
Stefan Karlsson
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