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Overstayer MAS 8101

Stereo Analogue Distortion Processor By Bob Thomas
Published November 2016

Overstayer MAS 8101: Analogue Processor

In a market that seems, er, saturated with dedicated distortion processors, what sets Overstayer’s latest device apart from the rest?

LA-based Overstayer Recording Equipment describe themselves as “musicians and endless tweakers who design and build analogue recording equipment” — definitely my kind of people, then! Their small range of analogue stereo products (a mic/line preamp, a VCA compressor/limiter, a FET compressor/peak limiter and the saturation processor reviewed in SOS May 2014: has now been joined by the MAS (Multi Analogue Stage) Model 8101 stereo analogue processor. It’s designed to deliver the harmonic richness and the peak and transient compression characteristic of classic analogue recording chains.

The Box

In the flesh, there’s a vintage vibe to the MAS’s deep, 1U rackmount steel chassis. Its beige fascia is home to two totally separate channels, each of which features a number of controls: a three-position toggle switch for input selection, a vertical bank of three EQ buttons, a second bank of three switches to configure the harmonics circuitry, and input, wet/dry mix and output pots. These are joined by a quarter-inch instrument input jack and a four-LED meter ladder. A third three-switch bank with individual indicator LEDs switches the individual channels in and out of circuit, and turns the power on.

The rear panel carries a five-pin XLR connector for the external power supply, along with two sets of main L/R and auxiliary balanced XLR inputs and outputs. The latter enable you to connect the MAS in line with two separate stereo sources (or even four mono inputs) and to switch between them using the front-panel toggle switch. Although all inputs are separate, the aux output for each channel is a parallel of the main output, which means you get a fair amount of flexibility in how you integrate the MAS into your studio setup.

Lifting the lid reveals two identical channel PCBs, which are populated entirely by full-size components — there’s nary an SMD to be seen. What can be seen on each channel is a large white gobbet of what could, at first sight, be easily mistaken for mayonnaise, but which is in fact some kind of sealant that conceals a section of circuitry from prying eyes. The build quality is high, with resistor ladders being used on the mix and output potentiometers, the latter being stepped from zero up to an (unmarked) 11.


With the per-channel choice of either of two balanced XLR inputs, a front-panel unbalanced instrument jack and twin outputs, Overstayer’s MAS 8101 gives you plenty of flexibility in how you integrate it into your setup. In a DAW environment, the simplest approach could be to configure the connection with the MAS as one stereo and two mono hardware plug-ins. That would enable you to either patch it as needed in-line between mic pre and audio interface, or to your interface’s plug-in I/O.

There’s a wide range between where the MAS 8101’s multiple amplifier stages begin to have an effect on the signal and their clip point, and the LED meter displays this range. Perhaps reflecting the tape-like rounding-off of transients inherent in the operation of the MAS 8101, the meter illuminates from the top down, so the topmost LED indicates that low-order harmonic coloration and transient rounding are beginning to happen and, as the input level increases, the lower LEDs illuminate to indicate the rise in harmonic content and transient rounding.

The EQ and high-pass filter (from hereon HPF) are positioned prior to the amp stages and therefore affect the harmonics being generated. The HF EQ (+2dB at 12kHz) and LF band (+2dB at 100Hz) each have a fixed shelving response. The HPF is a fixed two-pole filter, with a resonant peak at its 50Hz corner frequency. Associated with the EQ is the Emphasis button in the second switch bank, which, when engaged, shifts the focus of its channel’s harmonic generation up into the middle and treble ranges, leaving bass frequencies unaffected.

Usefully, both the wet/dry mix and the output controls are stepped, allowing for simple stereo matching between channels. On the unit I was sent for review, the input control was continuous. Obviously, that’s less great for stereo operation (although its scale markings are probably sufficient to balance the two channels adequately), so thankfully there’s also a version available with a stepped input control — personally, I think that that’s the version I’d choose.

The two switches I’ve not yet considered are Dual, which puts a second discrete stage in series with the first, to increase harmonic complexity, and Second, which increases the amount of second-harmonic distortion.

On the rear are found the balanced input and output XLR connectors, and the power inlet, which interfaces with the included external PSU.On the rear are found the balanced input and output XLR connectors, and the power inlet, which interfaces with the included external PSU.

In Use

Only your ears can tell you if the MAS 8101 is doing what you want it to. Increasing the drive into it leads to more second- and third-harmonic distortion and transient rounding being produced, giving the impression of more body and level in the result. The profile of the harmonic distortion can be adjusted by using the EQ, HPF and Emphasis controls to change the frequency make-up of the signal being processed, and can also be made more complex by bringing in the additional processing stage via the Dual function. The Second switch can also be brought into play to increase the amount of second-harmonic distortion, either if you feel that the third harmonic has become overly dominant or if you just want more of the second.

How you configure the processing and the sounds that you can attain are completely dependent on the source being processed, your personal taste in harmonic distortion, and the amount of subjective increase in volume that you’re looking for. Some of the greatest drum sounds ever recorded came from the harmonic distortion, high-frequency roll-off and tape saturation ‘compression’ created by the tape recorders of the day being driven into the red by transformer-balanced consoles, and the MAS 8101 has this kind of effect pretty much down. I could push the unit quite hard with a stereo sampled kit before distortion became overly evident — and by that time transients were being rounded off wholesale and the sound of the kit had gained depth, body and apparent level. This was the point at which the mix control came into play, enabling me — just as I would with parallel compression — to dial back the effected sound into a blend that kept the dynamic feel of the original source intact but also added real weight and substance to the overall sound of the kit.

The Emphasis function produced the expected mix of unaffected bottom end and harmonically-enhanced mids and above, much as you’d get from putting a high-pass filter in a compressor’s side-chain. I did notice that I could drive the analogue stages harder in this mode before things started getting over the top, so there are obviously additional creative opportunities available using low-passed, high-passed and band-passed tracks to feed the MAS 8101.

Connecting a bass guitar to the instrument jack again made for interesting experimentation, its sound gaining weight and note-to-note volumes being evened out without requiring any dedicated compression while tracking, although if I were to take that result to a mix I’d probably run a few decibels of light compression across it just to tighten it up that little bit more. The MAS 8101 also turned out to be well suited to the more mid-range-biased signals from an electric guitar; it’s capable of a very believable, clean-to-crunchy tube-amp sound if need be. With vocals, this type of processing can often be a bit too much of a good thing, but it’s still possible to get some lovely effects by backing off the wet/dry mix to the point where you can’t really hear the distortion, but you miss it when it’s not there.

Across a full mix, the MAS 8101 is as effective as it is on individual tracks and, as with those, the results will depend on the source material and your sonic desires. The transient-rounding compression effect can certainly knit a mix together, although finding the appropriate balance between the amount of that apparent compression that is needed, the level and profile of the harmonics being generated, and the mix with the dry track is the real trick — when you get it right, the result can be quite stunning.


The MAS is one of those pieces of outboard that’s bound to put a smile on your face — it certainly did on mine! Its easily controllable ability to both introduce harmonic distortion and round off transients does add an analogue-type character to signals passing through it. Personally speaking, I felt that the MAS was at its best with the Emphasis function engaged, letting the low end pass through virtually unaffected and giving me more headroom when driving its analogue processing stages with mid and upper frequencies.

Although the MAS is relatively expensive, if you want to have the effect that it produces on your tracks I can’t think of a better, more controllable way of achieving it in the analogue domain. No matter what style of music you work with, it will give you something that you won’t find elsewhere. I highly recommend it — and lust after it!


If you’re into tube gear, the more expensive Black Box Analog Design HG-2 might float your boat. Overstayer’s own Saturator NT 02A is also a worthy alternative and, for those of us with smaller budgets, there’s the Looptrotter Sa2Rate and Elysia Karacter to consider. There are a number of analogue tape simulators too, such as the Rupert Neve Designs Portico 5042 and Roger Mayer 456 Stereo, and for those who can solder, DIYRE’s Colour system is well worth investigating.

The Nature Of Distortion

There’s little mystery in the hooking up of the MAS and neither is there much in its operation, or at least there isn’t once you’ve appreciated how to control what it does. Before you get there, it might be worth a gentle recap of how distortion is generated in an audio signal as it passes through the hypothetical analogue recording signal path of preamplifier/EQ/channel amplifier/mix bus/multitrack tape recorder. There’s not the space here to explore this subject in depth, but you’ll find enormous amounts of detail on this subject online and in various textbooks if you feel the desire to get granular about it.

There are two kinds of distortion created in the above signal path — linear and non-linear. A linear distortion, such as the phase shift in an EQ circuit, is a distortion that increases as the frequency rises, but that does not result in any new frequencies being added to the original signal. Non-linear distortions, on the other hand, add new frequencies to the original signal in the form of its harmonics. Of course, in music these non-linear harmonic distortions are introduced deliberately (otherwise an oboe would sound like a flute, which would sound like a pure sine wave, and a Les Paul into a Marshall stack would sound exactly the same).

The gain of any given device, such as the tubes and transistors in our hypothetical recording signal path, will vary with the current passing through it, the voltage across it and its internal temperature. In our recording path, this means that audio signals are being amplified by devices whose gain is being constantly changed by them — with the result that the gain in the path is non-linear and the signals are therefore distorted. If the source is a simple 1kHz sine wave, the distorted output from the signal path will contain the fundamental 1kHz frequency plus a series of harmonics of varying amplitudes — 2kHz (second), 3kHz (third) and so on — and it’s a situation that obviously increases massively in complexity when an audio signal containing multiple frequencies at multiple amplitudes is being amplified.

As musicians and engineers, we like the sound of the two low-order harmonics and their interactions. Our preferences are, quite naturally, entirely personal — my own take is that the presence of second harmonics makes music feel warmer and that third harmonics give the music a more dynamic feel. Of course, too much of either (or both) of these can result in negative impacts, as does the presence of any audible quantity of higher-order harmonics — which is why electronic design engineers have spent inordinate amounts of time over the last century or so designing harmonic distortion out of audio equipment and why, perversely, musicians and engineers have spent significant sums on software and hardware putting low-order harmonic distortion back in — which brings us neatly back to the Overstayer MAS Model 8101!


  • Delivers a great old-school analogue sound character.
  • High degree of control of the harmonic profile being generated.
  • Transient rounding evens out signal levels to produce a perceived increase in volume.
  • Intuitive operation.


  • It isn’t exactly cheap — though that’s not to say it doesn’t offer impressive value!


An intuitive, effective, stereo analogue processor that imparts a distinctive character to signals passing through it by generating low-order harmonics and rounding out transients, in a highly controllable manner reminiscent of classic analogue recording chains.


£1620 including VAT.

KMR Audio +44 (0)20 8445 2446

$1495, or stepped-control ‘Rotary’ version $1795).