AmpRX BrownBox Review

AmpRX BrownBox Review

Throughout my years of recording, gigging, and touring I would notice a strange occurrence. My amps seemed to sound different from night to night. At the time, I mostly attributed this to the varying acoustics from room to room. I also thought the warm-up time of the tubes could be influencing the tone of my amp

Soundchecks at gigs are usually pretty short. There isn’t a lot of time to experiment. It’s often a hit-it-and-quit-it situation. Not much time for exploration. 

Earlier this year I saw a product called the BrownBox. It’s a device designed to adjust the voltage going to your tube amp. This made me think a bit. I hadn’t really considered that the amount of voltage feeding your amp could change your tone

I also found out that voltage can vary from outlet to outlet. It can even change intensity on the same outlet throughout the day. In my Brooklyn apartment the voltage can go anywhere between 119v to 126v. That’s quite a difference!

A Solution


The BrownBox is a step-down voltage attenuator. Meaning, it can take the voltage down, but not up. If you’re getting 126v out of the wall, you can reduce it to 117v. But you can’t take 117v coming out of the wall and convert it to 120v. 

The BrownBox is a step-down voltage attenuator.

Amp Spa

So what’s all the hubbub? It turns out that your tube amp’s tone changes depending on the voltage it’s getting fed. I have found that higher voltages result in more headroom, but the tone is more sterile. This was a light-bulb moment for me. 

Brown Box with a Vox AC15

Brown Box with a Vox AC15

Those nights that I didn’t like the tone of my amp? Turns out it was a venue that was running higher voltage from the wall. It wasn’t the amp warming up (although this also can drastically change your tone). It wasn’t the room acoustics, either. 

The biggest culprit was the voltage. Since using the BrownBox, my tone has been a lot more consistent. I find that I prefer the sound of my amps with the output between 117v-120v. 

Most modern amp builders test their amps at 120v. Amps are designed to handle a variance in voltage, but that doesn’t mean the tone doesn’t change. What’s more, it’s been said that running an amp at a higher voltage can wear tubes and other components down more quickly.

More Tubes

Effectrode Tube Drive

Effectrode Tube Drive

It wasn’t just my amp I was having inconsistencies with. I have some tube guitar pedals. I’m quite fond of pedals from a company in England called Effectrode. Their Tube Drive and PC-2A (tube compressor) are staples on my pedal board. 

Since there are actual tube circuits in these pedals, they also react to voltage variance. Some nights I would play and the Tube Drive would sound harsh. Other nights it was warm. I marked my settings down, so I know they didn’t change from night to night. 

Since I’ve been connecting my pedalboard to the BrownBox, my pedals have been completely consistent. 

One thing that’s been interesting is monitoring the voltage across the country. I’ve been touring a lot with Sister Sparrow and The Dirty Birds as well as Amy Helm. We’ve been jumping all over the U.S. and Canada. Let me tell you—voltages are all over the map. 

Testing 1,2,3

I decided I wanted to run some tests with the BrownBox. I reached out to my friends at Grand Street Recording in Williamsburg, Brooklyn. They have quite a nice selection of vintage tube amps and know how to capture them. It was the perfect place to document our voltage experiment. 

For the purpose of this test, we only used vintage amps. The voltage coming out of the wall at Grand Street was not only consistent but naturally in the range I prefer, between 117v-119v.

So for this test I didn’t get a chance to hear the amps above 120v. I can tell you that amps over 120v have more headroom and are louder but are also (to my ears) more sterile. I prefer a little warmth and forgiveness from my amps. 

As with all things tone-related, taste is subjective. The sweet spot for one player won’t be sweet for the next. 

In addition to changing your tone, more voltage can more quickly wear out your tubes. Controlling the voltage going to your amp will extend the life of your tubes. 


Let’s listen to some sound clips using a Fender 1952 Reissue Telecaster with Florance Pickups:

Brown Box with a vintage Fender Tweed Deluxe

Brown Box with a vintage Fender Vibrolux

Brown Box with a vintage Gibson GA-2-

Brown Box with a vintage Marshall Combo

Do you hear a difference? Do you have a preference? It’s possible your preference may change depending on the amp you’re using. 

Neil Young

Neil Young

Someone recently told me about a Neil Young documentary. In this film, his guitar tech says that Neil can accurately guess the voltage of a venue as soon as he plugs into his amp. 

Everybody Knows this is Nowhere

Everybody Knows this is Nowhere

This makes sense to me. He’s been playing that Tweed Deluxe for ages. There probably isn’t a detail he can’t discern about that amp. 

Upon further research, I found that Neil likes his amps at exactly 120v. I can get down with 120v. Over that, my guitar tone antennae start sending warning signals. I still prefer 117v, though. 

One for One

Patrick from AmpRX (and inventor of the BrownBox) informed me that when you employ a tube amp as part of your tone structure it’s critical to keep in mind that every extra volt going into the amp can increase internally between 4v-6v, depending on your amp’s power transformer/rectifier combination. 

This will skew the dynamics of the amp and is not a one-for-one correlation. 


Using Backline Guitar Amps

I can tell you that using the BrownBox has made using backline amps easier for me. Even with the varying models of Vox AC30s, the consistent voltage creates more of a through-point between amps. It’s for this reason that the BrownBox goes in my flight case at all times. 

Power Strip


My BrownBox has two available outlets. Others have one, three, or more. You can use a power strip with your BrownBox, but you have to pay attention to the draw. The limit to my BrownBox is 500mA. 

Before you start plugging all your gear into it at one time, read the power requirements for each piece of gear. Do the math and then proceed. Yeah, I know I just said “math.” 


BrownBox’s construction is high-quality and proprietary. There really isn’t another product like it. You can’t buy the transformers used in the BrownBox off-the-shelf. It’s a unique piece of tone-shaping gear. One I’ve come to rely on. 

Mark Marshall at Grand Street Recording in Brooklyn, NYC

Mark Marshall at Grand Street Recording in Brooklyn, NYC

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