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Sequis Motherload

Dummy Load & Speaker Simulator
Published July 2005
By Dave Lockwood

Sequis MotherloadPhoto: Mike Cameron

Using a combination of dummy load and speaker simulator lets you record your favourite valve guitar amp at full tilt without disturbing your neighbours. The trouble is, none of the designs so far have managed to sound close enough to a real speaker. Could this be the one that finally nails it?

The Motherload, a combined dummy load and speaker simulator, was originally launched a few years ago as a two-channel unit in a 2U chassis. It offered a reactive (as opposed to purely resistive) dummy load, like a real cone driver, and a series of sophisticated passive filters designed to replicate the response of a typical guitar speaker. It worked, in so far as amps were happy driving it, and it certainly didn't have the choked, gutless sound of most other passive speaker sims. What it did have, however, was some of the fizz and grit in the 5-6kHz region that real loudspeakers are so adept at getting rid of to give us what our ears have become attuned to as a 'proper' distorted electric guitar sound. Responding to feedback from guitar players and recording engineers, UK-based Motherload designer Rick Cawley, manufacturing under the Sequis name, continued to refine the filter stages until he came up with this, the 'new improved' Motherload, reborn as a single-channel 1U chassis, with a sound to make even the most sceptical sit up and take notice. (Original Motherload owners can get their units upgraded to the latest spec by contacting the manufacturer.)

The Design Challenge Of Speaker Simulation

Most of the sounds we think of as classic electric guitar tones are the product of two primary components; the distortion produced by a valve output stage driven into clipping, and the inherently bandwidth-limited response of a guitar speaker. Take away the latter, and the former does not sound 'nice' at all, full of fizzy upper-harmonic trash that leaves single notes and especially chords sounding harsh and unmusical — OK, I know there are styles of music where the sound of a DI'd fuzz box is appropriate, but for most people this is the audible equivalent of sucking a lemon. It was only ever the inherent low-pass filtering of guitar speakers that made the first forays into distorted sounds seem at all attractive, throwing away the less harmonically related overtones and leaving us guitarists with the richer, punchier, more interesting sounds that we have come to love.

But therein lies the challenge for designers of speaker simulators, because the top-end response of a guitar speaker in a cabinet exhibits some quite complex behaviour that is not easily replicated with electronics. Pioneering designs in this field from the likes of Groove Tubes (the SE and SEII), Palmer (the now almost legendary PDI03 and the current PGA04 model), and Hughes & Kettner (the Red Box series) are all noted for their somewhat less characterful and slightly darker tonality, shaving off the dreaded crackle and fizz at the expense of much of the life and soul of the sound (in my opinion, at least; 'your mileage may vary...'). Feed any of these boxes a maxed-out, ultra-distorted signal and they can sound quite authentic, but give them a valve amp just on the edge, where so much of the subtlety and expressiveness lies, and the top-end filtering is always too much.

At the other technology extreme, digital products like the Line 6 Pod range (and its many derivatives) use physical modelling DSP to simulate the tonal characteristics of the entire guitar system's signal chain from preamp to power amp to loudspeaker/cabinet to the microphone that picks it all up. This offers both great convenience and flexibility, but whatever your opinion on the sound of the products in this category, for some players there will never be a substitute for the touch-sensitive feel and sheer sonic vocabulary of a real valve amp running at sweet-spot volume. No problem if you've got a large recording space, well insulated from your neighbours, but for most people's home studios, something a little more controlled is more of a necessity than a luxury.

Premium Hardware

The latest Motherload, like the original model, is still an entirely passive device, which means it contributes no noise of its own to the signal path, taking the full speaker output of an amp and attenuating it to line level, passing it through multiple filter stages designed to replicate the response of a typical guitar speaker. Of course, passive filters can only cut, rather than offering the boost/cut option of active filter stages with gain. However, with so much signal to, effectively, 'throw away' (a guitar amp's speaker output can be pushing 20 Volts, whereas the eventual line output from this unit only requires around one or two Volts) the Motherload is able to use multiple 'lossy' passive filter stages to achieve the necessary response. Nevertheless, it is still quite a design feat to offer the degree of effective control available from the Motherload front panel using just passive filtering.

The Motherload is beautifully built, both inside and out: the pots feel just right, the switches and preset trims are all positive in action, and the load resistors, custom-wound components, and heavy-gauge wiring inside all serve to give you confidence in entrusting your amplifier's precious output stage to this device. It's not cheap, of course, but you can certainly see what you are paying for.

Sequis MotherloadPhoto: Mike Cameron

The controls are far from self-explanatory, especially as many of them are rendered inactive in all but the Custom position of the six-way Preset selector switch. Presets one to five offer a spread of basic tonal characteristics corresponding to a range of viable front-panel control positions, with an increasing mid-range peak as you go up through the settings until you reach preset six, which by contrast has a significant mid-range scoop. The top-end roll-off point of each of these presets can then be individually fine-tuned using screwdriver-adjusted trimmers. The response of these filters is actually quite complex, for example position one has a -3dB point at 5kHz and a -6dB point at 5.6Hz, whilst position six is -3dB at as low as 1.8kHz, but the -6dB point is still up at 4.2kHz. Their primary function is to let you tune out fizzy harshness within distortion without at the same time depriving the signal of the degree of brightness necessary to still sound 'right'. In preset mode, the only other active front-panel control is the Line Out level pot.

The other front-panel controls come into play in Custom mode (preset zero). First up is a six-position Filter control which replicates the action of the screwdriver trims, followed by a pair of Resonance controls: Resonance Plus offers five preset amounts of resonant band-pass, ranging from 60Hz in position one to 2.6kHz in position five; and Resonance Minus is a band-cut filter, switchable from 600Hz (position one) to 1.7kHz (position five). Used separately or in combination, these controls have a more significant effect on the overall character of the sound than the Bass, Mid Shift and Treble controls that follow. Dialling both Resonance knobs to their neutral setting allows you to hear the subtler effects of the other controls rather better. The Bass control really means bass here, behaving more like a console low-frequency shelving EQ than a guitar amp's bass control. It is very effective at simulating the thump of a real speaker driven hard without muddying the audible part of the signal, so long as there is already enough low-frequency energy in the signal, but it won't do anything to warm up an already thin, brittle guitar sound from the amplifier.

The Treble control gently determines overall brightness, from quite low in the mid-range up to the Motherload's overall upper cutoff point. Although I never set it below halfway, I also never found myself wishing for more range either. That leaves Mid Shift, which is the most subtle of all and yet in some ways the most useful, once you've got everything else set to your satisfaction. It appears to move a minor mid-range peak up and down the middle of the spectrum, but the audible result is rather more complex than that, suggesting perhaps that there is a complementary mid-range dip that moves with the peak. Sonically, the effect is rather akin to moving a mic to very slightly different positions in front of a speaker cone — not as obvious as just 'brighter near the centre dome, warmer near the edge', for it still preserves fundamentally the same tonality and also doesn't affect overall level. It is more like the tonal change you get from slightly varying the mic's angle in front of the cone: very useful when you get to the final stages of nailing the tonal focus of a particular guitar sound.

Sequis MotherloadPhoto: Mike Cameron

Round the back, the Motherload offers a nominal 8Ω dummy load input (rated 100W RMS), a speaker Thru connection, and a highly attenuated (2.5 percent of input) speaker output governed by a rotary control. A send and return pair offers patch points for effects to be inserted prior to the speaker simulator's filtering. There is a significant loss around the loop, so it should really only be used with devices with plenty of I/O level range that also won't add much in the way of noise: I can verify that it works fine with a TC Electronic G Major and a Rocktron Intellifex. In practice, it seems that with any reasonable input level there is always enough signal available at the output, which is taken from either a balanced 600Ω TRS jack (uncontrolled) or an XLR governed by the front-panel level control.

Richter Control Speaker Attenuator

Sequis MotherloadPhoto: Mike Cameron

Sequis also offer the Richter Control — an attenuator, with no speaker simulation, for simply knocking down the volume of a loud valve amp. This allows you to turn your amp up, to get the output stage distortion that guitarists love, but independently turn your speaker down to precisely the volume you want. The front-panel control varies from 6dB attenuation, which equates to a subjective loudness of just over half the unattenuated level, right down to no output. Significantly, the Richter Control manages to maintain a consistent sound at all attenuation levels, whereas most competing products in this area get progressively less real as their output is trimmed back. A dedicated output is provided for feeding into a Motherload, connecting to the loop return — in other words after the dummy load and before the filters.

Is It Live Or Is It Motherload?

Comparing the Motherload output directly to a guitar speaker is always going to be somewhat misleading; the real comparison that needs to be made is with the sound of a guitar speaker miked up and heard only over studio monitors. Recording guitarists are all too familiar with the scenario where you tweak your tone to perfection in front of your amp, stick an SM57 on it... and then wonder where all your sound went when you listen to the playback of what you just recorded. Standing in front of a cranked guitar amp, you are in fact hearing very little of the direct sound that the mic is picking up, and you are certainly not hearing it from two inches away from the speaker cone! Reflections from the floor and any adjacent walls, plus the natural attenuation of high frequencies that occurs just with sound waves propagating in air over any significant distance, all serve to both colour and warm the sound. In comparison, a close-up SM57 or Sennheiser MD421 will always seem rather sterile and harsh, and if you are using a lot of distortion, you can even get a bit of crackle and fizz in there too — yes, real speakers do fizz sometimes, you just can't normally hear it! The fact is, close-miked guitar speakers always need a bit of work, whether that be a second mic, a more distant 'room' mic, a bit of artificial 'dimensioning' from reverb or delays, or just plain old EQ.

Switching directly from a dry SM57 three inches from the speaker to the Motherload output set to 'neutral' (everything at 12-o'clock in Custom mode) on a medium crunch tone, the sound of the latter is actually slightly deeper, although a little less complex in the mid-range, but still identifiably the same amp. Advancing the Motherload's Treble from five to eight and dropping the Filter setting to three/four allowed me to get rid of a hint of grit that was creeping in on harder struck notes. Advancing the Bass control fully or going to the first setting of the Resonance Plus control actually made the Motherload sound bigger at the bottom end than the speaker/mic signal path, but there seemed to be no tweak I could make to match the speaker's slightly recessed mid-range character. I settled on a Resonance Minus setting of three, taking out some 1.1kHz as the best compromise between the clean tone's requirements and the lead voicing; the former always benefiting from a hint more 1kHz dip.

I certainly wouldn't say that the Motherload sounded in any way fake or wrong; it just sounded like a different, rather more smooth speaker. In fact, the more distortion I dialled in from the amp, the more I actually preferred the mid-range of the Motherload on single-note lines. At these settings there was a just hint of fizz audible in crunch chords when listened to in isolation, but certainly not in the context of a track. Thickening the upper mids with a smooth-sounding, symmetrical clipping pedal, like a Tubescreamer, masks this to the point of insignificance, to my ears, just as it does with a real speaker.

Returning to the miked speaker after 15 minutes or so of listening to just the Motherload output, I am struck by just how brittle and hollow it now sounds. There's a distinct mid-range 'hole' that I immediately feel I want to fill out with EQ, although the urge to do so goes away as soon as I play along to a track. One tweak I invariably apply to a close-miked guitar speaker signal is a hint of fairly dark-sounding stereo room reverb just in the monitoring, to give a more natural sense of scale when playing. Applying this same process to the Motherload actually makes me want to open up the top end a bit: experimenting with both the Treble and Filter controls, I ended up consistently preferring the sound with the Filter on two or three and the Treble backed off to five or six, rather than Treble wide open and the Filter clamped down hard at five or six, as I had initially dialled up.

Sequis Motherload vs Line 6 PodXT

Sequis MotherloadPhoto: Mike Cameron

Comparing the Motherload/amp combination to a PodXT, with all its effects switched off, I could actually get the PodXT to sound pretty close. Surprisingly, there was often more fizzy/crackly top in the PodXT signal, but the characteristic real-speaker mid-range dip was already there, and the bottom end was comparable, although the Motherload was better at really deep 'thump' frequencies, so long as they were present in the source. The thing I could never match was the clean-to-distorted range of the real amps. Most of these could go from warm clean to singing distortion just on the guitar's volume control, whereas the PodXT always needed a gain tweak to get either end just right. Plugging the PodXT into the filter stage of the Motherload, switching off the PodXT's cabinet simulation, and using the effect return input actually improved some of the PodXT sounds, to my ears, whilst failing to match others. This could be a useful strategy for anyone who needs the versatility and immediacy of the PodXT, but who isn't quite convinced by the sound. Where it works, it seems to shave off a bit more of the high top end than the Pod's own cabinets, somehow leaving what remains sounding far more focused, and just more convincingly real, especially if you then apply room simulation after the Motherload output.

The original Line 6 Bass Pod proved even more successful, with the Motherload invariably providing a more usable recorded bass sound than the Pod's own cabs, to my ears, with a smoother, more extended bottom end. One thing to watch out for when connecting a unit like the PodXT in this way is that the Motherload chassis is not grounded, for safety reasons, and the PodXT chassis isn't grounded either. This can produce a lot of noise pickup in some situations, for which the only cure is grounding the PodXT chassis. I did this by connecting the other output to my mixer, but connecting both sockets sends the PodXT's output into stereo mode — not ideal if you are using any of the PodXT's stereo effects, as you'll only then be recording one side. A shallow self-tapping screw into one of the mic stand adaptor holes on the underside of the PodXT crocodile-clipped to something earthy (like the sleeve of a jack lead coming from your mixer perhaps) seems to solve the problem completely, although this isn't recommended if your PodXT is still under warranty.

"This One Goes Up To Eleven..."

Ditching the real-speaker reference altogether, I found myself drifting towards some rather different settings on the EL84-based Cornford Hurricane amp that was forming the basis of most of my testing at this stage. Master volume went up to max, input gain to the amp's usual seven/eight sweet spot, bass backed off a bit more than usual (just under 50 percent) to take out the beginnings of 'flubbiness' in the distortion, mids up a bit more (eventually to maximum), and treble backed off a hint — say, 60 percent rather than my normal 75 percent. I now had a fat, singing lead tone that would clean up to warm and clear when I backed off the volume control, with a crunch stage somewhere in between. Above all, the amp felt entirely normal when playing; warm and dynamic when backed off and either edgy or smooth, according to how I attacked it, when flat out. With a hint of audible space added via a room reverb in the monitoring it was easy to forget there was no speaker and mic in the signal chain. Opening up the front-panel filter setting all the way with this amount of distortion brought back just enough fizziness to diminish the illusion of reality, confirming just how effective a job it does when you get the right setting for the sound you are using.

Testing across a variety of amps confirmed my feeling that the Motherload/amp combination needs to be regarded holistically — settings that work well into a speaker don't necessarily translate directly into recording well with the Motherload. My MkIV Boogie displayed its best characteristics with its master on maximum, intermediate (channel) masters as near to maxed as channel balancing would allow, and front-end gains backed off to about 60 percent — a condition I have certainly never run it in on gigs. The change in character from the harder-sounding preamp valve distortion to sweeter output valve distortion is immediately evident, and allows you to back off the treble and push the mids a little, making the sound rounder and more musically satisfying.

Although speaker differences had obviously been removed from the equation, the distinct character of each of the amps I tried still came through; my little Fender Deluxe sounded sweet and singing (its valve rectifier 'sag' helped a lot here with the feel), my little 6W single-ended Cornford Harlequin still did its lovely Fender/Vox hybrid thing, and with no lack of level out of the Motherload in spite of its diminutive output. I found I could get a usable sound out of all of them, but I could also make some pretty ugly noises when I failed to get everything right. You have to be prepared to work with the Motherload, but the more you do the more you will find within it.

Sequis MotherloadPhoto: Mike Cameron

On the whole I'd say recording with the Motherload takes about the same amount of tweaking as painstakingly optimising the position of a mic in front of a speaker, although leaning over and turning the Motherload's controls is obviously a bit more convenient, and once you've got it right, it's a lot easier to recreate next time! The sound requires precisely the same amount of post-processing as a close-miked cone driver (indeed, many of the same processes worked for me) to achieve a recorded signal that sounds natural and that will respond to effects and EQ in the normal way. The one tweak that I consistently applied to the Motherload signal that I don't normally do to a speaker was an EQ cut, about half an octave wide, centred around 1kHz, which just seems to sit the sound into a recording rather better. Setting the Resonance Minus control to number three will get you somewhere near, but an external EQ as well seems to be the optimum solution.

With large wound components on board and passive circuitry, the Motherload needs careful siting in the studio: at least one and preferably two rack units' distance from any power transformers, or it will hum; and if you are planning on using it with single-coil pickups, you need to get it at least an arm's reach away, or it will squeal at high gain settings. I didn't hit it with anything more than 85 Watts, but it didn't get unduly hot at any stage and I didn't manage to get the overload warning light to come on.

A Real Alternative For The Discerning Player

Having checked out a Motherload in its earliest form, the performance of this latest version was a real surprise — products don't normally change this much from one incarnation to another. Whilst I would hesitate to say that it sounds exactly like a miked speaker cab, I certainly can say that I believe it provides a viable alternative that will satisfy even the most discerning of players. Matched with an appropriate amp and the right settings, it makes for a 'silent' recording system that retains those elements of a good electric guitar sound that matter most to me. The Motherload manages to pull off the trick of retaining just enough top end to sound right without allowing fizziness to creep in, whilst no previous speaker simulator even comes close to matching its capacity for authentic bottom-end chunk. I can pay the Motherload no higher compliment than to say that I kept finding myself just playing through it, for hours on end, when I should probably have been doing something else — an activity I actually engage in all too often, but normally only when real speakers are involved!

If you're one of those people who is entirely happy with the sound of a digital amp simulator or guitar amp software plug-in, you probably don't need this; if you are happy with the sound of your valve amp with its master volume really low you probably won't see the point of it. For the rest of us, recording authentic electric guitar sounds in a home studio environment just got a whole lot easier.

Published July 2005