NAMM 2025: “Increase and decrease voltage with volt by volt precision”: AmpRx launches Brownie – a voltage optimising power supply to make your tube amp perform at its best (and maybe help you finally nail Eddie Van Halen’s ‘Brown Sound’)

NAMM 2025: AmpRx has unveiled Brownie, an voltage optimising power supply that’s designed to give your tube amp exactly what it needs to perform at its best.

Now, AmpRx has made voltage attenuators for tube amps before. Its Brown Box series offered an over-the-counter remedy for those looking for Eddie Van Halen’s ‘Brown Sound’, the chance to dial in their own Variac-reduced voltage, run their Marshall head on 10, and apply an MXR Phase 90 to taste.

Brownie can do that, too. But this is different, because Brownie is the first of its kind that allows you to dial in exactly the voltage you need, allowing you to increase or decrease “with volt by volt precision” the supply to your tube amp.

This means that you know exactly what power is being fed into your amp; it will be consistently the same, whether you are playing in Rio de Janeiro, Berlin or Slough. Ask any touring musician – or better yet, ask their guitar tech – and they will tell you that on one night your amp might sound incredible, or on another there’s something missing. That is often down to the voltage.

Image 1 of 2

Kirk Hammett from Metallica caused a bit of a stir when he told Total Guitar that Marshalls sounded better when you ran them in the UK.

“You plug a Marshall straight into the wall in London and it will sound 30 per cent better than the same Marshall hooked up to the wall in America,” he said. “It’s everything to do with the voltage. And it would drive me crazy because it would sound different from show to show!”

Joe Bonamassa backed him up on that. And that is one example where the Brownie could help, allowing players to dial in the exact voltage night after night.

AmpRx promises not only a consistent sound and performance from the tube amp in your life, but also says that feeding it the correct voltage consistently can extend the life of your gear.”

The design is simple, too. There is one knob. There is a digital display screen. You can decrease the voltage in 1V increments, increase it in 3V and 5V increments. And there are 2A and 4A fuse options to match your guitar amp.

Introducing the Brownie by AmpRx - YouTube

Watch On

Brownie is compatible with modern and vintage tube amps alike. It is hand-wired in Nashville, TN, available now, and it is priced $299.

For more details, head over to AmpRx, or, if you happen to be visiting the Anaheim Convention Center, you can see it in person at the AmpRx stall at Show Booth #5630.