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Looptrotter Monster

FET Compressor & Valve Distortion Processor By Matt Houghton
Published February 2012

With a FET compressor/limiter and tube-saturation circuit on each channel, there's plenty here to dirty up your sounds. Get ready to mash with the Monster...

Looptrotter Monster

I'm a big fan of 'attitude' compressors. You know what I mean by that, of course. The sort of thing you can really spank a loop or drum bus with, twisting, mangling and otherwise abusing the source into something beautifully unrecognisable. Something you can use to take a clean, limp-sounding drum part and mash it into mojo-laden oblivion. So when a two-channel, 3U, FET compressor named 'Monster', with waspish warning livery, two chunky VU meters, a tube-saturation circuit and a mix control for parallel processing, was drawn to my attention, I could hardly resist the chance to put it through its paces.


I'll try not to dwell too long on the layout of this debut product from new Polish company Looptrotter, as it's large and spacious enough to see on the main photo. The paint job is the only thing about this device to scream 'marketing' to me: I'm sure that the colour scheme won't be to everyone's taste, but I get bored easily with understated grey or black boxes and I loved it! Despite the gaudiness, though, there are no gimmicks. Everything on the front panel serves a useful purpose, and there's space enough to get the fattest sausage-fingers in amongst the controls. The meters and legends are clear, and the knobs and switches seem to be of good, reassuringly solid quality.

Each channel comprises three sections: a switchable FET compressor/limiter (it's the same circuit, so you can use it in one or other mode but not both in series), a tube-saturation circuit and a master section, in which you can both blend the dry and treated sections to taste and set the master output level. The first two sections can each be bypassed independently, as can each channel as a whole (a true hard bypass, so signals are still passed when the Monster is sleeping). The two channels can also be linked, so that they work from the same side-chain signal and attack and release controls. The input and output levels, tube-processing controls, and mix and main output controls remain independent on each channel. Two VU meters are switchable to display either gain reduction or output level on their respective channels.

Easy Squeeze & Crunch

Looptrotter Monster

Designer Andrzej Starzyk says that he opted for a FET-based compressor specifically because this results in even-harmonic distortion. Think along the lines of an 1176 compressor, but with no transformers and fewer controls and you'll get the general idea. This is a fixed-threshold design: you have control over the input gain and output level, so rather than bring down the threshold, you boost the input signal. Other than the limiter option, there's no selectable ratio, as Starzyk wanted to keep things simple. Instead, the ratio increases the more the signal exceeds the threshold. The attack and release times run from 0.1 to 100ms and 15ms to 1.5 seconds respectively. There's also input- and output-level metering for the compressor section, via a pair of stacked LEDs.

The compressor is only half the story, though, and nice-sounding as it is in its own right, I get the impression that it's largely there only to give the signal a nice controlled, characterful squeeze before passing it on, via a discrete op-amp, to the tube-processing circuit — and it's this that really sets this device apart from other processors. From a user point of view, the tube section is simple. There's a saturation control (clockwise equals more saturation) and a '2nd Boost' switch, to put greater emphasis on second-harmonic distortion. With only those two controls, it's easy to arrive quickly at a satisfying sound. I was interested, though, to find out that for the tweakers out there, there are further controls on the inside....

Under The Hood

The internal layout is neat and tidy, with ribbon cables joining the various PCBs. You can see the two NOS 6N2P-EW tubes on the centrally positioned PCB.The internal layout is neat and tidy, with ribbon cables joining the various PCBs. You can see the two NOS 6N2P-EW tubes on the centrally positioned PCB.

Opening up the box (by unscrewing a generous15 screws!), I was confronted by a slightly emptier case than I'd imagined, even taking into account the need for ventilation. I suspect that everything could easily have been fitted inside a 2U rack case, but then that would have made the controls more cramped... and I'd probably have moaned about that instead!

The electronic circuitry is split in modular fashion across a number of PCBs, with a mix of ICs, and discrete and surface-mount components. The one tiny criticism I had on the review model is that some of the ribbon connectors between boards could have fitted a little more snugly: one had worked its way loose on the way to me for review. It was easy enough to fix, and it's also nothing a blob of glue during manufacture wouldn't have prevented, a recommendation Looptrotter say they may adopt on future units.

The tube circuits are based around two NOS 6N2P-EW vacuum tubes (one for each channel) that are described as 'military grade'. I wasn't able to make out the markings sufficiently well to decipher the brand, but Starzyk tells me that he chose these tubes specifically because of their longevity. To my ears, they sounded perfect for the job, although if a user prefers to use a more conventional ECC83/12AX7 tube, Starzyk says they can be swapped, as he has included a heater-voltage jumper to make this possible.

Hard To Beat

As is so often the case with boutique hardware, I found that it was possible to push things very hard and to create far more subjective loudness relative to the peak levels than I could with any plug-in or combination of plug-ins — and all without clipping my converters (as I sometimes like to do with drums, just to shave the tops off the transients without 'smearing' the sound).

My initial thought when slamming the drum-bus signal into the Monster was that the world might just about be ready for a '90s Big Beat revival! The combination of compression and tube distortion would lend itself to that sort of effect pretty well, not only squeezing the sound, but also giving it a pleasing sense of presence, or 'forwardness' that seems to be so in vogue these days.

To see if I could achieve anything like a similar result in the plug-in world, I experimented with a range of both tube- and FET-compressor emulations, and dedicated tube-processor emulations. I was certainly able to get some very pleasing sounds in this way — and I was reminded just how good-sounding some of these emulations are in their own right — but I wasn't able to create the same sort of feel and presence that I could with the Monster, particularly at the more extreme settings. This was especially the case when mashing drum loops, but it was also true of later comparisons on guitar and synths.

Of the two, the tube saturation sound was far harder to get close to than the compression character. The biggest difference was that it took me ages to get close using plug-ins, whereas it took a matter of seconds to inject exactly the right amount of attitude using the Monster.

Axe Murderer?

The two NOS 6N2P-EW valves used in the tube circuit.The two NOS 6N2P-EW valves used in the tube circuit.

While it perhaps seems extravagant to lavish thousands of poundsdollars on a guitar distortion box, it would be remiss of me not to try such a processor on electric guitar. There's no instrument-level input, but if you're looking for a modern and present distorted guitar sound at mixdown, this beast would deliver all I could imagine ever wanting from it — and in a very controlled way. I was able to go from simple dynamic-range control, with little distortion, through to crushed-level, super-saturated tube distortion.

Because of the degree of control, I was able to create some surprising, yet rather useful effects. For example, I fed two identical guitar takes (a mono track multed in the DAW) through different channels of the Monster. As well as rewarding me with the bite and 'forwardness' I'd anticipated — all of which was pleasing in itself — it proved a fantastic way to generate different harmonics on each channel. This, in turn, enabled me to create a real sense of stereo width from that humble mono track. With some compression, the saturation cranked up on the right and a little less on the left, and with the mix set to 50 percent on the left and 100 percent on the right, the sound opened up in a truly delightful way, rewarding me with a convincing, tight double-tracking effect, combined with all the forward, biting goodness that this unit can impart. Pure filth! Feeding the signal back into the DAW and through a Brainworx stereo widening plug-in gave me a huge, dirty, wide guitar that in all honesty I was probably a little too proud of. A guitarist might kill me for doing that to their sound, but if the Monster were in their own hands they might love it: it certainly gets the thumbs-up as an 'axe' murderer!

Souped-up Synths

The rear panel of the Monster includes side-chain inputs and outputs and unbalanced monitor outputs, as well as the usual audio I/O on balanced XLRs.The rear panel of the Monster includes side-chain inputs and outputs and unbalanced monitor outputs, as well as the usual audio I/O on balanced XLRs.

Given its performance on guitar, it was no surprise that the Monster proved equally adept at squeezing, crunching and otherwise abusing various synth sounds. I ran a number of sources through it, both analogue (a Roland Juno 6) and soft synths, basses, leads and pads. The thing with synths, of course, is that the sounds are what you make them, and this makes the nature of any mangling difficult to put into words. However, I was certainly able to breathe some life and warmth into some rather limp and tired-sounding preset patches from my DAW's bundled synths. I could also easily scramble sine waves into something altogether more audible in a mix. Yes, you can use the compressor, and yes, you can easily add a tiny bit of tube colour just to impart some warmth... but, as with guitars, this thing is most at ease taking a sound and turning it into something much more abrasive.

Vox Box

Finally, as I often use tube compressors and limiters to bring out the breathiness and strained nature of some rock vocal parts, I wondered if the Monster would serve in that capacity too. It's certainly capable of broadly 1176-ish compression. The lack of ratio setting was frustrating in this context, although the blend control made up for it to an extent, and I found that I could also use a combination of compression and tube drive to get the effect I was looking for. However, although I'd probably be happy to press the Monster into service on vocals, there are better devices for this application. In any case, it seems a shame to 'domesticate' the Monster in this way!

Monster Monster?

Looptrotter's debut product is a snarling beast of a processor that's one of a kind. Like the paint job, the effect won't be to everyone's taste, and it won't get used on every source — but if you work in rock, pop, electro or any one of a whole range of urban genres, I can't imagine you not finding a use for it and being happy with the results! This thing is dripping with a dirty, distorted character that's quite literally music to my ears. Balancing that with the more mundane yet useful features, such as matched components on each channel and detented, I have absolutely no hesitation in recommending that you audition this processor.


There are many compressors out there, and many tube processors too, but nothing that I can think of does exactly what the Monster does, and certainly not in one box — so to achieve similar effects, I'd be thinking of pairing various other devices together. A Universal Audio 1176 used with an LA2A would give you more flexibility in some ways, and would be capable of some broadly similar sounds, but it wouldn't give you everything the Monster can offer. You could perhaps throw into the mix some of the Thermionic Culture tube processors, or the more general sound-mangling capabilities of the Chandler Germanium, Empirical Labs Distressor and the Evol Audio Fucifier. These can be very rewarding devices in their own right, but again, will not be quite the same.


  • Unique sound.
  • Good control over the tube distortion.
  • Wet/dry mix control.
  • Capable of interesting effects that you wouldn't at first expect.


  • The compressor would benefit from having more user-tweakable controls.
  • I can't justify lavishing the required sum on one... yet!


Looptrotter set out to make the Monster original and they succeeded. It's a refreshing take on the outboard compressor and distortion box concept, and it's capable of spewing out some truly twisted textures. Though they're obviously not its primary intended purpose, the Monster is also suitable for rather subtler applications.


£2400 including VAT.

KMR Audio +44 (0)20 8445 2446.