Boss AD-2 Acoustic Preamp Review

Released in late 2016, the AD-2 is one of the more compact acoustic guitar preamps available. It follows the familiar Boss form factor, being 73mm wide, 129mm deep and 59mm tall. This means that it will fit on standard pedal boards alongside your other floor wizardry, and gives it an advantage over its numerical big brother the AD-3, which takes up significantly more space. The pedal features a notch filter, ambience and acoustic resonance effects and a balanced line out in addition to the standard unbalanced output, making it the simplest pedal of this type available from Boss.

Input impedance is 10 M ohms which means that the pedal can accept passive piezo pickups directly with no need for an additional buffer in the signal chain. This would also allow the pedal to act as a backup in the event that your onboard preamp were to go down. Of course magnetic soundhole pickups will work fine too. The pedal features a buffered bypass which means that it will not pass signal if the batteries fail completely, but in my experience the pedal knows when the juice is about to run out and stitches off the effects in order to keep the buffer alive. Nevertheless an external power supply is to be preferred if at all possible. Battery life is stated to be 6 hours of continuous use. 

The pedal features two outputs which can be used simultaneously – an unbalanced output designed to be connected to other pedals or an acoustic guitar amp, and a balanced line out designed to connect to a mixer or recorder. This is effectively a built in direct box, and although the connector is TRS rather than XLR adapters are readily available (see image below) and the reduction in pedal size is worth it in my opinion. It also means that the pedal can be used as a transparent active DI box some of the time and the effects only switched on for certain songs, a useful feature to have.

Out of the box the signal to the outputs is the same, but the pedal can be programmed to output the ambience effect to only the unbalanced output, leaving the line out dry. This would be useful in situations where a front of house engineer would add reverb appropriate to the venue, leaving the musician to manage the level of reverb on stage. The process for making this change is simple and involves holding down the pedal, powering it up and then rotating the ambience control in order to select one’s preference. See video for a full demonstration.

The pedal is made in Taiwan and like all Boss compact pedals feels extremely robust and well-built. The knobs are plastic but turn smoothly and do not wobble on their shafts. They are shaped such that they are not easily moved and I find that in transport the settings usually stay put. Input and output sockets are metal and well-secured to the chassis. This pedal should give many years of trouble-free use. I tested this pedal for three months prior to this review with a variety of guitars and had zero reliability issues.

AD-2 controlsHow does it sound? To begin with, the bypassed sound is what you would expect from any high quality active DI box – quiet, uncoloured and true to the original sound of your instrument. Stepping on the pedal to engage the active circuitry immediately changes the sound, even when the knobs are all set fully counter clockwise, something that I have learned to expect from Boss acoustic pedals. The sound become slightly ‘bigger’ which to my ear implies that a small amount of compression is being applied, and possibly some EQ.

Of the three controls, two are very straightforward and the third much less so. The ambience knob adds a room or chamber-type reverb to the sound. As the name implies this is a relatively short reverb that simulates a smaller acoustic space. The range of adjustment is very well chosen, and even with the knob fully clockwise I never felt the sound became unnatural.

The notch filter is pretty standard equipment on acoustic preamps and is designed to act as an anti-feedback tool, reducing the frequency at which the feedback is occurring without sucking the life out of the rest of your sound. I don’t play at high stage volumes so have never needed to use this, but it might come in useful for those who play in louder contexts. It can also be used as a sweepable cut-only EQ control although this is not its primary purpose. For me, it lives permanently at the OFF position.

And now the Acoustic Resonance knob! The copy in the owner’s manual states that this control “…adds the natural resonance of an acoustic guitar that’s often lost by the pickup of an acoustic-electric guitar.” This sounded like marketing hype to me, so I paid particular attention to this control during the testing process, listening very carefully to the effect that it had on the sound and using several guitars with different types of pickups – several Takamines with their multi-element palathetic piezo systems, a Breedlove Atlas with a very basic undersaddle piezo element and finally my GS mini with an installed LR Baggs Lyric microphone. After all of this, I can say quite categorically that this control is NOT a ‘resonance’ control in the conventional sense. Instead, it appears to me to be more of a dynamic EQ feature, possibly coupled with some compression. Here’s what I found:

  • From off to the 9 o’clock position the control acts as a mid-cut, and I find this is where it is most usefully employed.
  • From 9 to 12 o’clock the reduction in the mids continues, and in addition some treble is added.
  • Beyond 12 o’clock, and especially past the 3 o’clock position, the control adds bass and also seems to compress the signal.

From all of my listening, my best take on this control is that it is attempting to reduce the midrange honk/quack of your typical undersaddle piezo pickup. Whilst this is a nice idea, why Boss would call it an acoustic resonance control is beyond me, considering that it does not appear to add any resonance whatsoever… I have been unable to find a satisfactory sound with this control anywhere past the 9 o’clock position, and often run the pedal with it completely off. To my ear it just seems to suck the midrange out of the tone, which is most definitely not a good idea on acoustic guitar. Even on my Breedlove Retro OM, which has an extremely basic and quite mediocre-sounding undersaddle pickup, the tone was not significantly improved once the control was past 10 o’clock. The one guitar which DID seem to benefit from this control was a Taylor 400-series guitar which I tried at the shop before buying the pedal – that guitar seemed to sound best with the A.R. knob at 12 o’clock. Hmm! In any case, buyers should be aware that a) there is no ‘correct’ position for this control and b) there is no need to use it at all!

What else didn’t I like about the pedal? The lack of a stereo output! I personally like to run my acoustic guitars in stereo, and the dual left and right outputs on the AD-3 are one of my favourite features of that pedal. Especially when singing, I like to be able to pan the acoustic guitar left and right and have my voice panned centre – I find that this helps to separate the two signals and also makes the guitar sound much bigger, especially with some reverb and stereo chorus added. However on a pedal this size I can understand the lack of a stereo output and would rather have the balanced/unbalanced outputs that the AD-2 offers.

In conclusion, this is a very simple and straightforward pedal/preamp that combines high quality balanced and unbalanced outputs with a useful short reverb and notch filter. If I had to choose one word to describe this pedal it would be ‘subtle’ – the unit does not seek to change the tone of your guitar, rather it enhances what is already there. The exception to this of course is the acoustic resonance knob, which is something of a non-starter in my opinion, but others may find some use for it, especially if you like a very scooped, compressed sound. The relatively small size of the unit is also an advantage, fitting nicely in guitar cases and gig bags. The Boss AD-2 is definitely one to consider if you like simple, well-built and relatively affordable gear that will get the job done night after night, year after year.

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4 Responses

  1. Hi, thanks for this precise review but there’s still an information I’m missing personally… There is something I don’t get at all about this gear : it is said to be a preamp but no reviewer or even Boss in its description talks about GAIN at all ! Because a preamp IS meant to add substantial gain, right ? 😉

    So, my question is simple : since there is no Level control on this device what is the actual gain it applies to the sound of the guitar ? Let’s say for a soft effect with resonance knob around 9 o’clock ?

    Thanks alot in advance !

    1. Yes, it can be frustrating when manufacturers do not publish specific information on this topic, but I think very few people ask for it or even know what gain is. If you look at the specs of the pedal it has a nominal output level of -20dBu at both the output and line out sockets. This is actually pretty close to instrument level, so depending on your instrument/pickup combination, it may or may not provide any gain! Also the use of the word ‘nominal’ casts further uncertainty on their statement…

      The truth is that many manufacturers play fast and loose with the language and use the word preamp when referring to any pedal that has an instrument level input. Remember that we don’t know anything about the circuitry inside the pedal, so it may operate internally at a higher voltage but then step the signal down at the output to allow it to be connected to other pedals and/or a microphone output.

      To answer your question: depending on your guitar, pickup and preamp combination, this pedal may apply no gain or even negative gain to your signal! The only way to be sure is to connect your guitar to the pedal and then connect the output of the pedal to a voltmeter. Pretty useless answer I know, but in practice I have found that it is almost impossible to overdrive this pedal, and it’s output is suitable for connecting to other pedals and/or to the mic input of a mixing console. So BOSS may be vague with their specs but their pedals do perform well in the real world 🙂


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