The Guitar Tone You May be Missing

Guitar toneIf you have a couple of spare dynamic microphones in the bottom of your gig bag, you may not realize that they could be the key to your guitar tone.

This article will give step-by-step instructions on how shape your electric guitar tones by modifying a Shure SM57 and SM58. I’ve also included a video that demonstrates the first two (and most popular) modifications at the Lumen Audio recording studio.

You Don’t Have to Sound Like Everyone Else

guitar tone champIf your a guitarist, then you’ll know the pursuit of finding your tone. We spend years trying out different pedals, pick ups, and switching out tubes, but do we ever give our microphones the same attention?

Maybe your band made your last album at a recording studio here in Asheville and used an expensive microphone on your amp, but when you play a gig you settle for a 100 dollar SM57. This leaves you with two variations of your guitar tone: you have a “studio” guitar tone, then a “show” guitar tone. Back and forth, back and forth!

What if you were able to shape the gig-worthy 57 to better match your tone so that you have one mic that worked well with your guitar tone, weather or not your at a gig or in the studio? There’s tons of options, let’s dive in.

“This is great for smoothing out the top end. I personally can hear a big difference in the 5k range. It’s hard to describe, but the high end sounds less aggravating and piercing.”

The Mods

I’ve counted five modifications that I have tried. We’ll start with the most common ones. If you choose to do these modifications, do them at your own risk.

Mod 1:

guitar tone transformerA very popular modification to the sm57 and sm58 is to remove the transformer from inside the handle of the microphone. You have to be able to do some basic soldering to disconnect the wires going into the top of the mic, and also the wires at the XLR connect at the base of the mic.

The bottom portion of the microphone is then boiled in a pot of water for about 5 minutes and it frees up the glue that holds in the transformer. The transformer comes out easily and new wires are run from the XLR connector to the receptacles on the inside of the mic. This process takes about 20 minutes if your new to electronics.

Mod 1 Uses:

The sound of this mod is a big step. You’ll notice it most in a crunchy rhythm guitar, in that high end is shaped in a totally different way. It tends to emphasize certain parts of your tone in a different way than a stock SM57. This also will ad more low end.

A precaution: You’ll need 10 dB more of gain from your preamp as the transformer was helping to boost the signal. You will also need to be careful to not to expose this microphone to phantom power. The transformer protects the mic and without it, you could ruin the mic if your not careful. This could make Mod 5 more appealing if your going to be playing out.

Mod 2:

guitar tone sm57Most don’t ever think to take off the round pop filter from a sm58, but once you do, it looks close to a 57. It takes all of 10 seconds and you have a new variation of that mic. And no, it doesn’t sound like the regular 57 or the 58 with the grill placed back on.

Mod 2 Uses:

This mod is great if you have a thin guitar tone. The diaphragm of the mic is closer to the front of the mic. You can see in the picture (right) that the seam just above the red tape is higher up than the other two 57s. The whole front of this mic is indeed shorter.

This means that when you place this mic on the grill of your guitar cabinet, your getting the dynamic diaphragm closer to the speaker inside. This means more proximity effect and a thicker sound. In addition the diaphragm of the isn’t partially blocked by the wind screen, so it’s more prone to wind gusts from vocalist, but for guitar amps this may let in more high frequencies. Paired up with Mod 3, this could be a really nice combo.

This video compares the first two mods with a stock SM57 on three different guitar amps: ’62 Brown Deluxe, ’65 Princeton Reverb, and Reissue Bassman ’59. Each of the mics are in the same position and distance to the guitar amp. This means that the 58 is not positioned as close as it could have been to take advantage of the proximity effect mentioned above. The capsules of each mic are in phase with each other so it’s “apples to apples”. Thanks to Dr. Q’s for helping make this experiment possible.

Mod 3:

Asheville Recording StudioThe third modification starts with a bit of historical knowledge of recording technology. The sm57 is an old design, and historically not all preamps were designed at an input impedance of 1200 ohms. Many preamps had an input impedance much lower when the SM57 was first introduced in the field.

The impedance will shape the sound of the microphone, as the increased tension on the diaphragm causes it to overreact and resonate.

The modification is done by soldering a 840 ohm resistor across the hot and cold wires of the inside of an XLR connector, and caused your preamps to have an input impedance of about 500 ohms.

This mod can be done in the connector of a microphone cable, or in the mic itself in the lower handle portion just before the red and blue wires terminate with the XLR pins. If you modify a mic cable, you can use this cable on any dynamic mic that you’d like and alter the sounds of those microphones as well.

Mod 3 Uses:

This is great for smoothing out the top end. I personally can hear a big difference in the 5k range. It’s hard to describe, but the high end sounds less aggravating and piercing. If you layer tracks using this mod, the slight change in it’s sound will add with each track you layer, and become more apparent in your guitar tones.

Mod 4:

guitar tone princetonThe ring around each of the sm57s is a important function of how the microphone works. These vents are responsible for the polar pattern of the microphone. Sound comes in these vents and hits the back of the diaphragm and through a very natural matter of physics, the microphone doesn’t hear what’s behind it.

This pick up pattern is called a “Cardioid” pattern and it has a thicker sound than a mic that picks up from all angles such as a EV635a. (proximity effect is not present on omnidirectional mics, and Figure 8 mics having the greatest proximity effect)

Mod 4 Uses:

If you have a muddy guitar sound, try adding a small amount of electrical tape to this vent that goes around the top of the mic. You can fine tune the amount of this vent that you leave open, and by doing so you’ll be tuning the amount of low end that your capturing in the mic.

Mod 5:

guitar tone new xformerYou can upgrade the transformer in your sm57 or sm58 if you’d like. These can be hard to find, but are sold at Mercenary Audio online. They cost a shade less than the microphone itself, but it does turn it into a new mic. The sound is much smoother and even across the board. Some say it turns the sm57 into the sound of an sm7 which is a grade higher in quality.

Your First Steps to Completing Your Guitar Tone

Before you start tearing apart your microphones, you should considering the kind of guitar tone that you have coming from your amp. Is it a creamy distortion sound, or a pointy blues overdrive type sound played by a Stratocaster?

Make sure you are happy with the sound that is coming from the amp, then begin to consider how the tone of the microphone will complement your tone.


Hello, my name is Ryan Earnhardt. I am a personal mentor to audio engineers, and a debt free studio owner, Lumen Audio, located in the mountains around Asheville NC.

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