NotaBotYet - Howler Monkey PRO Headphone Amplifier

How do you top the best sounding headphone amplifier ever designed? (OK, that is just our opinion, but it was really that good!) Well, after we went back to the  drawing board, worked out a lot of math formulas (only to remember how much we did not like calculus all that much), then we erased the drawing board out of frustration because we realized something: the internal design was already too good to mess with.

We decided not to improve upon perfection (again, our opinion!) and focused on the physical aspects. The result isn’t a replacement for the original Howler Monkey—it’s a sibling with a different purpose and audience.

A while back, a drummer friend of ours—who played in a well-known industrial rock band from the ’90s (we’ll keep the name to ourselves)—wanted to try the original Howler Monkey. Since it was built for broadcast studios, we had to rig up some RJ-45 adapters to make it stage-friendly. He got it working and called it “unreal” driving his SE535’s (with some other colorful language we’ll leave out for the sake of family-friendliness… but all positive).

But there was a problem: the original was designed to mount under a studio counter—not exactly ideal for a drummer mid-set, or live sound, or recording studios. That was our cue to evolve.

Meet the Howler Monkey PRO

The Howler Monkey PRO isn’t a replacement—it’s a fraternal twin with its own mission. Purpose-built for live sound and recording studios, it delivers the same precision and reliability as the original, but in a rugged, portable form.

• Inputs: +4dBu balanced stereo via dual ¼” TRS jacks or RJ-45
• Build: Durable 12-gauge aluminum chassis
• Mounting: ¼-20 threaded mount-point for mic stands, drum kits, or clamp mounts
• Jacks: Genuine Neutrik ¼” TRS for maximum durability

Why “Howler Monkey PRO”?

Just like the original, the name comes from one of the loudest animals on Earth. Adult howler monkeys can hit nearly 140 decibels and be heard from 3 miles away. While they thrive in Central and South America, the Howler Monkey PRO is right at home on stage or in the studio.

Then we added “PRO” to the end.  Whether you think that stands for “Production-Ready and Overengineered,” or “Precision Roadie Optimized,” it really just means that this is the next level and has “Precision Rockin’ Output!”

But with so many headphone amp choices out there, why use the Howler Monkey PRO?

We’ve used countless headphone amps in broadcast studios over the years. We also performed engineering test and measurement as well as listening tests on many popular brands.   Some were great. Some were awful. Some were amazing—but ridiculously expensive.

What we noticed? Impedance matters.

Most modern headphones—like those from Sony, Beats, and Shure—have lower impedances (32–44 ohms). Many amps on the market struggle with these, either distorting at moderate volumes or failing to deliver enough current changing fast enough to avoid harmonic distortion. Others can’t handle high-impedance headphones. And since headphone impedance varies across frequencies, poor amp design can color the sound.

The Result.

Every component in the Howler Monkey PRO was carefully selected to provide the highest possible quality audio performance while keeping the device affordable. (Seriously, we could have gone crazy here, but decided against hand-matched gold-plated germanium FETs!).

Instead, we focused on what matters: clean, powerful, reliable sound—whether you’re in the studio or on the road.