MXR M81 Bass Preamp: First Impressions and an adventure in going direct.

Since taking up bass guitar in 2000, I can trace a gradual evolution in my attitude towards the bass amp. In the beginning, I saw it as an integral part of my tone, and was reluctant to even connect to the PA system, believing that bass and drums should come directly from the stage. During this period I had some fairly massive bass rigs, including a Gallien Kreuger 700RB-II 2×10 combo which was 700 watts and about 30 kilos/66 lbs, and a truly spectacular preamp/power amp/cabinet combination consisting of an Acme Low B4, an SWR Grand Prix and a Crown CE1000 running in bridge mode for 1,100 watts. In hindsight, this was a time when I didn’t know what I didn’t know.

As time passed and I grew as both an amateur musician and a professional sound engineer, I learned the hard truth that the best way for musicians to serve their engineer and audience is to keep the stage levels reasonable, especially in small venues. I can’t remember who it was who wrote that the hardest assignments for sound guys are the loud gigs in small clubs, not the ones in stadiums! This, combined with the advances in PA systems over the past 20 years have led me to seek out smaller and smaller bass amplifiers, culminating in my recent purchase of a Hartke HD25 – just 25 watts into an 8″ speaker!

This tiny amp, despite having more than enough volume for the playing situations I typically find myself in, lacks both a direct out as well as any kind of semi-parametric midrange EQ. I found myself using a normal active DI box and then adjusting the EQ on the mixing console, leaving the EQ on the amp set almost completely flat. I do a lot of playing in one particular venue which is relatively badly behaved when it comes to the bass frequencies – anything below 100Hz will quickly become muddy if turned up too loud. In fact, I often find myself putting a 12db per octave high pass filter on the bass signal at around 80Hz, and then boosting 200Hz – this adds body to the sound while controlling the low end at the same time. This process led me to the realization that what I needed was a DI box with EQ – no more and no less.

And so, enter the MXR M81 Bass Preamp:

MXR M81 Bass Preamp

This is, literally, a DI box with some very useful additional features:

  • A footswitch which allows you to quickly compare your sound pre- and post-EQ while playing your instrument! I find that this switch is most useful when setting up the EQ during practice or rehearsal – I leave the pedal on all the time during gigs.
  • Both input as well as output level controls – the former allows you to boost the signal from your bass before it hits the EQ section (very useful for passive basses) the latter sets the overall output of the pedal when it is engaged. Together, these allow up to 30db of clean boost.
  • Both a quarter-inch as well as a full-sized XLR output, which is essential for quick and fuss-free hookups without requiring the use of adapters such as on the Boss BB-1X. An additional benefit of this is that it allows the pedal to be powered by phantom power from the mixing console, removing the need for batteries or a separate 9V power supply. Thank you, MXR!
  • A pre/post switch allows the XLR output to be switched pre-EQ whilst the 1/4″ output remains post-EQ. So if you have additional pedals in your signal chain, the M81 can be used as a signal splitter, sending a clean/dry signal to the FOH console which is then mixed in with the wet (post-FX) signal by the sound engineer.

Now what about the EQ section itself? I’m pleased to say that MXR have absolutely nailed this part of the pedal: the Bass control is set at 40Hz, the frequency of the open E-string on bass guitar. Boosting this control adds warmth and fatness, cutting it controls a boomy or muddy sound. The Treble is set at 4kHz, right where the harmonics of the instrument live. Boosting this brightens the sound without making it clanky, cutting it darkens the sound without making it wooly. MXR have clearly chosen these frequencies with bass players in mind, rather than settling for the more typical 100Hz low and 10kHz high. And of course, the priceless midrange! MXR have chosen the range of this control perfectly, with nearly every marked frequency position being useful for one application or another: boost 250Hz to add ‘punch’; boost 400-500Hz to add ‘growl’; boost 800Hz-1kHz to add ‘bite’. And it’s not just about boosting: cutting 400Hz can make a P-bass sound more like a J-bass by reducing its signature midrange bark; cutting 600Hz is great for slap. Of course, all of this will depend on your specific bass, strings and hands – the above observations come from using it in conjunction with my 2013 Fender American standard precision.

In terms of the sound quality, I’m pleased to say that the M81 is equal to my Radial DI boxes, specially the industry-standard J48. In other words, effectively silent in real-world situations. The only area in which the MXR unit comes up short is its inability to lift ground when running on phantom power – because the ground lift switch on this pedal disconnects pin 1 on the XLR connector, it effectively switches off the phantom power supply when engaged. The Radial units get around this issue by lifting ground inside their power supply instead – very clever.

The MXR M81 has drastically reduced my need for a bass amp. At home, I use it to connect my bass to my USB audio interface and thence to my studio monitors when practicing. This is very helpful when it comes to playing along with thing like backing tracks, recordings, Spotify tunes – anything that comes off my desktop computer. Being connected in this way also means that I’m set up to record into my DAW at the press of a button.

Gig-wise, this little green box has given me the courage to leave my bass amp at home for the first time in more than twenty years. Now, I need to state that I have only done this ONCE at time of writing, in a very familiar venue which I knew had a good PA system and where I was able to control my monitor mix directly through an app on my tablet. This particular event I was playing bass, singing and also controlling a pedal-actuated drum sequencer. Not bringing an amp meant that I was able to dispense with my hand-cart and extension cords. Everything else fit into a small backpack and the front pocket of my bass gig bag. I monitored everything – bass, drum machine and vocals – through a single Community 10″ co-axial monitor wedge. And it sounded GREAT! There was something very natural and organic about hearing my bass in the context of the monitor mix, rather than having it come out of a separate speaker. I used the EQ on the M81 exclusively, never needing to adjust the 4-band fully parametric EQ on the venue’s SQ7 digital mixing console.

In conclusion, more than being a well-built, easy to use and great-sounding product, I believe that the MXR M81 bass preamp has the potential to change your mind about going direct – it’s certainly made a believer of me!

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