Can you use guitar pedals with an acoustic guitar?

Fishman publishes a 10 M ohm input impedance on this pedal, and that figure is the reason it belongs first in the chain. A piezo (under-saddle) pickup is a high-impedance source, and feeding it into a normal pedal or amp input — typically 1 M ohm — loads it down and takes the top and the body out of the sound. That is the harsh, brittle, quacking tone people blame on their guitar. It is usually an impedance mismatch, and this is the published specification that solves it.

The rest of the control set is aimed at the same instrument. There is up to 20 dB of gain to bring a weak pickup to a usable level, a sweepable low cut for the boomy low-mid resonance that feedback starts in, and phase inversion on a footswitch hold — the single most effective trick against feedback on a loud stage, because reversing polarity moves the frequency at which the loop builds. Fishman also publishes true bypass with a buffered bypass option, 24-bit conversion, 53 mA draw and a -100 dB signal-to-noise figure.

The cons are specific and worth knowing before you buy. There is no XLR output — Fishman lists 1/4-inch TRS in and out only, so this is a preamp and EQ, not a DI box that hands an engineer a balanced output. It needs 9 V external power and has no battery compartment, and no supply is in the box. And Fishman's own page is inconsistent about its own product: the copy describes four tone bands, the feature list says five, and the spec table publishes no band frequencies at all — so the exact voicing of the EQ is not a documented number.

Reverb is the effect an acoustic wants, because a plugged-in acoustic has had its room taken away from it — the pickup hears the string and the top, not the air around the instrument. The RV-6 publishes eight modes (Hall, Plate, Room, Spring, Modulate, +Delay, Shimmer and Dynamic), and the useful ones on an acoustic are the quiet end of that list rather than the dramatic end.

Dynamic is the mode worth knowing about: BOSS's description is a reverb that responds to playing level, which on a strummed acoustic keeps the reverb out of the way while you are playing and lets it bloom in the gaps. Stereo in and out plus an expression jack mean it also works as the last pedal before two amps or a stereo feed to a desk.

The downsides are the familiar BOSS compact ones. 95 mA is a real load and rules out sharing a daisy chain with other digital pedals, there is no way to save a setting so every mode change is a knob move mid-set, and the published three hours of alkaline life makes battery operation a non-plan. No adaptor in the box.

An acoustic has a wider dynamic range than an electric and a much sharper transient at the start of every note, especially with a pick. Compress it conventionally and you flatten exactly the detail that makes it sound like an acoustic guitar.

Blend is why this pedal survives the job: Keeley publishes it as a mix of compressed against dry signal, which is parallel compression. You can hold the quiet fingerpicked passage up to the level of the strummed chorus and still keep the pick attack, because the dry signal carrying that attack is never compressed. At 10 mA, all analog and true bypass, it costs almost nothing to have on the board.

What it does not have is an attack control, and the Release switch is a two-position switch described as tuned for single coils or humbuckers — magnetic guitar pickups. Neither position was voiced for a piezo, so you are choosing the one that sounds better rather than the correct one. Keeley publishes current draw but no impedance figures, which matters more than usual here: put a compressor before a preamp and you have put a 1 M ohm-class input in front of your piezo, which is the problem the preamp exists to solve.

Chorus on an acoustic is the effect that makes a single strummed guitar sound like a record rather than a person in a room, and the CH-1 is the cheap, durable way to get it. BOSS publishes four controls — E.Level, EQ, Rate and Depth — and mono plus stereo outputs.

The EQ knob is the one that earns it a place: chorus on an acoustic goes wrong by making the instrument sound glassy and synthetic, and being able to pull the top off the wet signal without dulling the dry one is how you avoid that. Stereo outputs into two amps, or into two channels at a desk, is where any chorus sounds best.

The cons: BOSS publishes no current-draw or impedance figure for this pedal, so you cannot budget it on a supply from published data. It is a bright, clearly digital-voiced chorus — if you want a warm analog bucket-brigade sound, that is the Small Clone, a different circuit. And no adaptor is in the box.

The entry to avoid, included because it is the mistake people make. A distortion pedal on an acoustic does not sound like a distorted acoustic — it sounds like a quacking piezo with hard clipping on top, and there are two reasons.

First, the pickup. An under-saddle piezo already emphasizes the attack and the upper midrange; clipping amplifies exactly that character. Second, the tone stack. The DS-1's single Tone knob scoops as it brightens, so the control you would reach for to tame the harshness removes what little body the signal had. Its 1 M ohm input is also a tenth of what a piezo wants, so the pedal is loading the pickup down before it does anything else.

If you actually want a dirty acoustic sound, the route is a magnetic soundhole pickup rather than a piezo, and then the normal electric-guitar rules apply. Overdrive vs distortion vs fuzz covers which category to reach for once you have a magnetic pickup feeding it.