Bottlehead Crack Output Transformerless Headphone Amplifier Kit

Bottlehead Crack 1.1 OTL Headphone Amplifier Kit

$369.00

The Crack is a legendary OTL (output transformerless) headphone amplifier kit, purpose-built for high-impedance headphones like the Sennheiser HD600 and HD650, as well as AKGs and Beyerdynamics. Its single-ended triode design delivers rich midrange, spacious soundstage, and a uniquely engaging tube character. Designed with first-time builders in mind, the Crack offers a fun, rewarding build experience—and sonic performance that rivals amps several times its price. Add the Speedball to elevate your Crack’s dynamics, clarity, and resolution.

The Crack uses a universal power transformer. International customers will need to supply their own power cord, but the kit can be wired for different voltages using instructions in our detailed manuals.

This product has a universal power transformer and can be used worldwide by following the wiring instructions in the manual. Please note that international customers will need to provide their own power cord.

Our kits do not come with a badge, but you can buy one here. Because of a weird quirk in Shopify's shipping, international customers will need to drop a request in their amp's order notes instead of adding one to cart.

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The Bottlehead Crack is a transformerless (OTL) headphone amplifier kit designed specifically for high-impedance headphones like Sennheiser, AKG, and Beyerdynamic models. With a straightforward, minimalist circuit that’s perfect for first-time builders, this Skill Level 1 kit can be assembled in just an evening or two, making it a favorite entry point into DIY tube audio.

At its core, the Crack uses a Bottlehead PT-10 universal power transformer and a proven C-R-C-R-C power supply layout originally made famous in the Foreplay preamp. This configuration—featuring ultrafast rectifiers and generous filtering—delivers a quiet, stable power source with ample headroom. The signal path is equally elegant: a 12AU7 dual triode directly drives a 6080 tube configured as a cathode follower, creating a clean, dynamic sound free of output transformers.

To keep the kit affordable, high-quality electrolytic capacitors are used for output coupling, but the design is highly tweakable. Builders can experiment with premium capacitors, alternative tube variants, and the optional Speedball Upgrade to elevate performance even further. Whether you’re chasing better tone or just enjoy hands-on experimentation, Crack offers endless potential for customization.

Affordable, approachable, and endlessly upgradeable—the Bottlehead Crack is a modern classic in DIY headphone amplification.

Product specifications

Tube Complement: One 6080, one 12AU7
Output Impedance at 8 Ohms: 120 ohms
Gain: ~15dB into a 300 ohm load (like a Sennheiser HD600)
Input Impedance: 100K ohms
Power Output: ~10V into a 300 ohm load
Assembled footprint (LxWxH): 13 in x 7 in x 6 in

Customer impressions

“For the HD650, this amp rivals pretty much anything else I’ve heard” 

“I auditioned the crack for a day with HD650s and was blown away.”

“All parameters checked out right off and it’s making the sweetest music I have ever heard and that’s just with a pair of ATH A700 phones.”

“I just got the 600 Ohm DT880 yesterday and can’t tell you enough what a perfect match these headphones are with the crack.”

“Although the headphones I’ve been using with the Crack (Sony MDR-SA5000, 70 ohm) are not an ideal match, they still show off the incredible sound quality of this little amp!”

“None of my other amps has done justice to the AKG K501s like the little Crack. It’s provided a richness of sound which nicely expands on the AKG’s strengths of soundstage and midrange performance.” 

“With “Nowhere Boy,” a new John Lennon biopic, the Bottlehead Crack amplifier and my old Sennheiser HD-580 headphones kept me totally absorbed in the film.”
“For those of you wondering about the new Crack amplifier, this is also very sweet and enticing set up. I think I heard the version with the extra add-on circuit. That was lovely with a variety of headphones, including the HD-800s. Ahhh.”

“the amp really sings now with the Etys, and with AKG K701s”

“This is now my favorite amp for my Sennheiser HD800s.”

“As for the sound, with my Beyer dynamic DT880’s (600_ohm)….Super sweet!! highs are smooth airy & detailed, ….midrange is very organic, detailed and transparent,…… bass extends deep and detailed (no wanting for any additional bass with the DT880’s….BTW)… and the soundstage extends well outside my head….”

“What an amazing amp! Dead quiet, the bass has incredible slam and definition. Brushes against a drumhead are stunning. It does a better job with my HD-650’s than my K-702’s but not by much” 

“The Bottlehead Crack is a superb introduction into the world of DIY audio. The parts quality is very good, the documentation is truly excellent, the Bottlehead forums provide fantastic peer-to-peer assistance, and construction is very easy. The Bottlehead Crack is an outstanding first project for the novice
audio DIYer. The big win, however, is that once you’ve finished your build, you’ll have a fantastic sounding amp for your high impedance headphones. I simply can’t recommend the Bottlehead Crack highly enough, if you’ve got a yen to try a little soldering, this is the way to go. You’ll love it!”

Tyll Hertsens, innerfidelity  (Here is a marvelous video from Tyll of how to solder your Crack kit. Anyone can Here is a nice review on Head-Fi, from Bill Way
Black headphones on a white background

Addiction-worthy sound at entry-level prices

The Crack is the gold standard output transformerless headphone amplifier. It's world-renowned for its ability to drive high-impedance headphones like the Sennheiser HD 600/6XX/800S, ZMF Atrium, and Beyerdynamc DT 770.

Despite its reasonable price, it sounds better than amps that cost you twice as much. There's a reason audiophiles have been addicted to the Crack for over a decade.

Bottlehead Speedball 1.1 Upgrade for Crack Amplifier - Bottlehead

Make your Crack even more addictive with a Speedball

Our Speedball upgrade kit gives listeners tighter bass, improves treble extension, and enhances imaging without losing the signature warmth and smoothness of the original design. Most builders can assemble and install the Speedball in an evening, but you can prolong the fun by installing half of the upgrade first, then listening to the difference, and then adding the rest of the upgrade a little later. Don't worry: all of this is outlined in our detailed manual.

While we recommend building the Crack kit stock first and adding the Speedball later, remember: you get 10% off the Speedball when you buy it together with the Crack.

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Person using a screwdriver to attach hardware to a Bottlehead amplifier kit chassis plate.

Yes, you can do it!

Bottleheads have been assembling our kits for over thirty years. Every kit includes the parts and components you need to build the kit plus an incredibly detailed manual with step-by-step instructions and close-up photos. Check out this sneak peek into what every manual includes. We've also put together a handy list of the tools you'll need to bring along.

Need some assistance or inspiration? Check our user forums.

Just add tools

Bottlehead kits come complete with everything you need to assemble. We provide the wood base, chassis plate, tubes, hardware, wire, circuit boards, and electronic components. You just provide the tools and solder.

Check out this blog post to see what comes in every kit, and this handy list of tools and equipment you should gather before you begin.

Bottlehead Crack in the wild

Our customers start with the same base model kit and customize them to their specific tastes and style. Here are a few examples of Bottlehead Cracks our customers have built over the years.

Visit our forums to see what others have built and get inspiration for your very own Bottlehead Crack.

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FAQs

Please read our FAQs page to find out more.

Which tubes should I use?

We include a set of tubes with every kit so you're ready to play music as soon as you've passed your voltage checks.

We love it when you roll your own, too. You could use not only 6AS7s and 6080s, but also 5998s, 421As, 7236s, and maybe some others for the output stage, and the input tube could be changed to some other dual triodes like 6922 or 6CG7 with a little care taken to do the proper tube socket wiring for the heater pins - ask around in the forums for some help.

Can I put an output transformer on it and use it with speakers?

Hey, once you buy it, you can do anything you want to it! However we will suggest that we have kits that are much better suited to the purpose, like the S.E.X. kit.

Can you make me a custom version with multiple inputs, a selector switch and a stepped attenuator?

We created a kit for this once called the Crackatwoa, but it wasn't a hot seller. If we get enough interest we'd consider another run.

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