Crackatwoa Headphone Amplifier Kit

Crackatwoa is a premium evolution of the beloved Crack amplifier, positioned between the original Crack and the flagship Mainline in both performance and price. Designed for high-impedance headphones (200 ohms and above)—including the Sennheiser HD600/650/800 and higher-impedance Beyerdynamic models—Crackatwoa delivers enhanced sonic refinement, more input flexibility, and superior upgrade potential.

At its heart is a direct-coupled circuit based on the Crack, but upgraded with C4S active loads (as in the Speedball) and shunt voltage regulation via dual 6AQ5 tubes. This more sophisticated power supply, supported by a larger power transformer, results in a quieter background, greater bandwidth, and tighter bass control. The addition of three switchable RCA inputs provides convenience for users with multiple audio sources.

The standard volume and balance controls are precise and practical, and users can optionally upgrade to a high-end stepped attenuator system—similar to the BeeQuiet used in the BeePre and Mainline—for dramatically improved resolution and natural vocal presentation.

The chassis is twice the size of the Crack, allowing ample room for expansive upgrades like oversized output coupling capacitors. The built-in balance control also addresses common low-volume channel imbalance found in some potentiometers, making this a more refined listening experience right out of the box.

Crackatwoa offers a rich blend of precision, power supply sophistication, and customization flexibility—making it the ideal next step for audiophiles who love the Crack and want more.

“I completed building the stock Crackatwoa last evening and have been enjoying listening to it. It’s character with both the ZMF Auteur and HD800S ideally matches my preference. It’s transparent in the presence region, noticeably tighter in the bottom end than my Crack/Speedball and delivers explosive dynamics. Truly a keeper! Over the next couple of days, I’ll do some tube rolling. A few weeks from now (or when the spirit moves me), I’ll build and install the Two Quiet upgrade. And, some time after that, I will probably install a pair of 100 uF Clarity CSAs I’ve got set aside. I’d be remiss if I didn’t, once more, thank the Bottlehead crew — Doc, Paul and Eileen — for your comprehensive and methodical build instructions and support. As with my two previous builds, I find the process immersive and therapeutic. Can’t wait to build my next kit(s)! Be well, Joe”

“I’m totally intoxicated by the sound of my recently completed Crack-a-two-a. There’s an immediacy to the sound, which fosters a real emotional connection for me. I’ve rolled a couple tubes and settled — for now — on a mil-spec Sylvania JHS 6189-12AU7WA in the input-tube position, NOS Chatham Electronics 6080WB with slotted graphite columns in the output position and a pair of NOS GE 5-star 6005s in the shunt-regulator spots. The overall character is one of crystalline clarity, airiness and silky smoothness in the mids and highs with well-rounded, incisive, punchy and robust low end when called for. So glad I made the decision to purchase this fine amp! And on top of that, there was the bonus of being able to immerse in the build process.” Joe

“My first full weekend off since July, and the Crack-A-Two-A just happened to show up on Friday. What better way to spend my time off than building a new kit. The build went pretty smooth, and I had no issues during the resistance and voltage checks. It powered up perfectly first time, and sounds great. Like the Crack but much more resolving and refined. It’s the perfect pairing for my HD-800s.” -Rocketman248

Crackatwoa vs. Crack

“…the difference is in your face, its really obvious. The bottom octave is unmistakably extended down, the lower notes that were crushed together and now added freq spectrum with all the different tones and their own dynamism that comes with the extra range. The noise floor is lower, their is noticeable silence between notes that with the crack just wasn’t as black, and with that the low level information can be heard so clearly, its just wow, its good. The other thing that is really noticeable is the tightness around notes, there is no flabby reverb or sliding into sharp notes, its just neat and tight. The mid range and vocals. I am listening to The Tennessee Waltz (allan Taylor & Chris Jones, TAS 2008 ex Stockfish) and its like your ear is hard up to the end of the mics, its uncanny. The little intonations in the voice, the playing around and tapping on the strings between and after notes, you hear it. Its smooth and tight and feels accurate. The tones and intonations in the tones and voices are fully heard. Its not quite front row feels 5th row, just back at row 5. The other uncanny thing is it just seems at ease and a clear step more relaxed than the crack, the crack always feels its struggling to keep up the 2 is a body builder lifting a ten pound weight.” -netosullivc