How to Choose an Acoustic Preamp Pedal

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What is an Acoustic Preamp Pedal?

An acoustic preamp pedal takes the relatively low output of your guitar’s pickup system, and increases the signal level so that it can be plugged directly into a sound system, recording device, or power amplifier. Another way to look at it is that a preamp pedal is basically the same as the preamp section of an amplifier, usually offering gain controls as well as EQ or tone controls.

While the core functionality of a preamp pedal is to convert the signal (from unbalanced instrument-level to a balanced line-level signal), most preamp pedals offer you more functionality in the way of built-in tuners, compression, FX loops, EQ, feedback suppression and more. This is why choosing the right acoustic preamp pedal is so important — you could potentially replace extraneous pedals from your rig, or open up new sonic possibilities with acoustic effects chains.

Why Do I Need an Acoustic Preamp Pedal?

The output of your acoustic pickup is a low-level signal that needs to be increased substantially to properly integrate with other audio electronics. Most recording interfaces feature an instrument-level input that you could plug into, but sound mixers and multi-channel recorders generally use line-level and mic-level inputs. If you connect your acoustic guitar directly to these, the result is a weak, indistinct signal, and probably a noticeable amount of noise. You may have used a direct box (DI) to solve this issue before — direct boxes and preamp pedals can both solve the problems of connecting your acoustic guitar to other gear, but a preamp pedal will give you more control over your sound as a musician.

Can an Acoustic Preamp Pedal Replace a DI Box?

Yes, an acoustic preamp pedal could eliminate your need for a direct box both on stage and in the studio. While a preamp pedal is not the same thing as a DI box, it achieves the same goal (a low-noise balanced signal that you can connect to sound systems and recording devices) but gives you much more control over your sound. Look at it this way — a DI box will serve the technical function of allowing you to connect your guitar to mixing boards and recording interfaces, with good fidelity and extremely low noise even over long cable runs. An acoustic preamp pedal will allow you to do exactly the same thing, but can also give you additional features like EQ, feedback control, compression and so on.

DI boxes can solve all sorts of problems for guitarists and sound engineers alike, which is why so many variations of them exist. If you’re a live sound engineer that needs to be prepared for live performances, you should definitely have some good direct boxes on hand — you’ll need them sooner or later. But if you’re an acoustic musician looking for just one box to give you maximum control over your sound, you’ll be much happier with an acoustic preamp pedal.

Acoustic Preamp Pedal Inputs and Outputs Explained

At minimum, an acoustic preamp pedal will have a 1/4-inch instrument input, and a balanced output either on XLR or possibly 1/4-inch TRS. Most will be equipped with XLR, ready to connect to a mixing board or microphone input on a recording interface with a standard XLR microphone cable. A balanced TRS output can be connected to a TRS line-level input (make sure to use a TRS cable and not an instrument cable), or to an XLR input with a TRS to XLR cable.

In addition to the balanced output, some preamp pedals may have an amplifier output as well — this allows you to split your signal to an amp on stage for personal monitoring, while also sending your preamp signal directly to the sound system.

If your preamp pedal has an effects loop, you will have a 1/4-inch “send” or “FX out” (to connect to the input of your effect pedals), and a 1/4-inch “return” or “FX in” (to return the output from your effect pedals). The effects loop is an instrument-level signal path, so use standard 1/4-inch TS instrument cables. It’s also possible that your preamp pedal may have one single 1/4-inch connection for the effects loop send and return — this requires an easily-acquirable 1/4-inch TRS to dual 1/4-inch TS adapter cable, which may or may not come with the preamp pedal itself.

What is an Effects Loop, and Do I Need One?

If you want to add acoustic effects pedals to your sound, it’s a good idea to look for an acoustic preamp pedal with an effects loop. You would connect effects pedals like delays, reverb and modulation to the preamp’s effects loop (instead of creating a chain of pedals before and after the preamp). This allows your dry acoustic signal to pass through without any processing, and you can balance the sound of your effects separately from your core acoustic tone.

If you don’t plan on using effects pedals, but you do use utility pedals like a tuner, compressor, or looper pedal, there is no benefit from connecting those to an effects loop. Tuners and compressors work best at the start of the signal chain anyway, and placing a looper pedal after your preamp will allow you to create loops with your carefully crafted preamp tone.

Understanding Feedback Suppression on Acoustic Preamp Pedals

Many acoustic preamp pedals offer some solution for fighting feedback — the loud howling sound that occurs when your acoustic guitar begins resonating in response to loudspeakers or floor monitors. Below are the most common types of feedback controls you’ll find on acoustic preamp pedals, but make sure to consult the product manual for detailed info on how your specific preamp pedal works.

Filter-based Feedback Control

Often labeled “Notch” or “Filter”, this type of feedback suppression allows you to target the specific frequency that is most likely to cause feedback. The filter lowers the volume of the problem frequencies, reducing or eliminating the possibility of feedback. The most effective way to use filter-based feedback control is with a sound check — you’ll need to approach feedback and then adjust the filter control until you hear the growing feedback subside. The good news is that the problem frequency is mostly based on your specific instrument size and shape, so you probably won’t need to adjust the frequency control again unless you change to a different instrument.

“Phase”- and Polarity-based Feedback Control

Usually a switch labeled “Phase” (technically it’s polarity), this control actually inverts your guitar signal’s waveform — positive becomes negative, negative becomes positive. So, what does this have to do with fighting feedback? When feedback begins, you want to shut it down immediately, and flipping the Phase switch can potentially stop feedback instantly — note we said potentially.

Depending on where you are in relation to the loudspeakers creating the feedback, inverting your signal phase could cause the offending frequencies to cancel themselves out, or it may not make much of a difference at all. It’s definitely not a fail-safe solution, so we recommend experimenting during sound check — if you’re approaching feedback, just flip the phase switch to see if it makes a noticeable difference. If it stops the impending feedback, that’s great. If not, that’s totally normal too — move on to filter-based feedback control. Even if the phase switch helps stop feedback, that may change when you move around stage — it’s more effective when you stay in a consistent position relative to the sound system.

Multiple Inputs and Multiple Channels for Multiple Guitars

Lots of acoustic guitarists bring two guitars for performance, whether it’s a 6-string and a 12-string, a nylon-string guitar and a ukulele, or any other combo of acoustic instruments. As you probably know, you should always mute your signal path when changing instruments (a tuner pedal makes this easy), but there is something to be said for the convenience of having two guitars plugged in and ready to go. Most acoustic preamp pedals are single-channel/single-instrument devices, but some preamp pedals offer dual instrument inputs for fast instrument changes. Keep in mind that dual inputs will usually run through the same signal path — if you want to have different preamp and EQ settings for different instruments, you’ll want to look for a dual-channel preamp.

Looking for more ways to take your acoustic tone to the next level? A studio-quality compressor made specifically for acoustic guitar!