Does a DI Box improve the sound of Piezo Pickups into an Acoustic Amp?

Channel reader Will sent a comment a while back proposing that if one found piezoelectric pickups in acoustic guitars too brittle sounding that the use of a DI box between the guitar and the amp would improve things. So I decided to test it out.

The results are shared in audio files below but for the TL;DR crowd, my answer is a firm possibly. It really has a lot more to do with the piezo pickup than anything else, but there is a subtle capping of brittle tone and a nominal increase in low end when a DI box is used.

Getting Started

For this to work, your guitar amp needs to have a balanced XLR input that can handle Mic level input. Most do, so that is possibly not an issue.

I prefer to use a parametric EQ with a notch filter for acoustic guitars in general but to remove their impact from the equation, I did not use one for these tests. My preferred option is the Source Audio EQ2, but I have briefly tried the LR Baggs Parametric EQ and thought it good as well.

If the scenario is a stage show where the acoustic guitar is going to a PA, I will always use a DI box, both to provide a better signal over long cable length and because PAs do not have preamps tuned for acoustic guitar.

In the studio,. I may run the piezo output direct to the interface, but if there is a long cable run involved, I will put a DI box at the guitar and run a balanced XLR back to the desk.

My Setup

The guitar I chose was my Martin SC-13E. It is a lovely guitar to play, but I have never liked the sound of its built in piezo pickup. When I have used it for recording in the past, I have always used one or two microphones instead of the piezo pickup output.

The amplifier used was my AER Compact Slope 60. After testing a number of acoustic amplifiers, I have found that AER amps deal with piezo outputs best as far as my ear is concerned. The tone stack was neutral and the internal effects were disabled.

For the DI box, I used my Radial Stagebug SB-4. This is a DI box designed specifically for use with piezo pickups and I will always recommend a piezo specific DI.

I used an extra long (25’) Ernie Ball guitar cable for two reasons. The longer the guitar cable, the more tone it saps, which a DI box can help with and because I wanted to have the guitar in front of the desk while the amp was in another room.

For the last two examples, I added an MXR Studio Compressor. This pedal is based on their implementation of a circuit to be like a UA 1176 compressor. The attack and delay were set to the mid point and the input and output levels were set to deliver unity gain. The compression ratio was set to a very light 4:1 compression.

I connected the XLR output of the AER amplifier directly to a balanced input on my Clarett+ 8pre and sent the signal direct into Logic Pro. Typically when recording acoustics, I like to use a professional channel preamplifier, my favourite being the Avalon VT-737sp, but I did not use it this time wanting to keep the signal from the piezo as native as possible.

Example Sounds

The following example is as follows;

#1 - Martin SC-13E into Radial SB-4 into AER Slope 60, output to Clarett+ 8pre

#2 - Martin SC-13E into AER Slope 60, output to Clarett+ 8pre

#3 - Martin SC-13E into MXR Studio Compressor into Radial SB-4 into AER Slope 60, output to Clarett+ 8pre

#4 - Martin SC-13E into MXR Studio Compressor into AER Slope 60, output to Clarett+ 8pre

Whichever you prefer, if any, is entirely up to you.

Wrap Up

I did hear a subtle difference using the SB-4 over not doing so. It’s not enough of a difference to warrant spending on a DI box for this scenario, but as it doesn’t hurt, I will use it. When I added the compressor, the difference was reduced in my perception. I am also still convinced that I could have cleaned up the brittleness with the EQ and without the DI. LR Baggs in facts makes an EQ with DI out if you want both in one place.

Whether you always use a Piezo DI is your choice. I found no harm in doing so, and while I would not demand one for guitar to acoustic amp use, the fact that one is, in my opinion required, for connection to a PA or for longer cable runs in the studio, makes this a simpler decision.

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