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Bottlehead Crack – “The Review”


Recently I posted a review of the construction stage of my Bottlehead Crack amplifier. The amp’s been in action for a few weeks now and I’m ready to share a review of my impressions.

I’m not going to start with the normal list of specifications for the Crack because it’s so variable due to the massive range of modifications you can make to it. What does matter are the following details:

  • Tube driven amplifier for headphones
  • Designed for high impedance headphones (ideal with Sennheiser and Beyerdynamic cans)
  • Buckets of power


The Bottlehead Crack is a DIY kit sold by Bottlehead in America. It costs around $350 fully shipped to Australia and takes a couple of days to put together if you take your time, but could be completed in a day of assembly, committed soldering and testing.  If you want to know how easy it is to build one of these for yourself, you can check out the build post here: Bottlehead Crack – “The Build”

For $350, this amp is simply incredible. To put it into perspective, the Crack performs on par or better than products like the Woo Audio WA3 (~$580) and Schiit Lyr (~$550). Because of its DIY nature, you can get brilliant performance for a very low price. On top of that, building it yourself means you know what’s going on inside and can easily add to it and improve it either on your own or using the add-n “Speedball” kit from Bottlehead.

Tubes, Glorious Tubes

Crack0010The Crack uses 2 tubes in its design – a small 12AU7 model at the input and a larger 6080 model to provide the output power. Don’t worry if you don’t know what that means, I didn’t either when I started. Actually, I still didn’t know even after I had finished building the amp – it’s only been in recent days of research and reading up on the great Bottlehead Forum that I’ve learned more about it.

Using tubes means two things. 1 – the sound from the amplifier is smooth, liquid and magical. 2 – it’s very easy to adjust and upgrade the sound by simply swapping tubes.

The 12AU7 and 6080 combo that’s supplied with the Crack do a great job. The sound from the Crack was an instant and significant upgrade over the output from my Audio-gd NFB-5.2 and it’s not a slouch.

After building and listening to the Crack for a while I became curious about upgrading the tubes (or valves as we call them in Australia). This was compounded by some minor issues with the supplied tubes which likely resulted from the trip from America to Australia.

I found a local supplier called Evatco who were able to offer a selection of replacement options. I ordered a Mullard 6080WA, a Cleartop RCA 12AU7, and a Mullard ECC82 which is an alternative to the 12AU7. After a bit of playing around, I found that the combination of the Mullard 6080WA and RCA Cleartop 12AU7 tubes provide the sweetest sound and the upgrade only cost around $50!!

Sound Quality

This is why you’d bother buying an amp in the first place. This is what matters and it’s where the Crack really delivers.

Crack finished +MullardsI’m running my Crack (yes, plenty of humour available with this amp) from the line outs of my NFB-5.2 which is connected to my laptop via USB and is running 96kHz / 24-bit sound. My headphones of choice with this setup are the Sennheiser HD650s. Admittedly, the choice of headphones is simple given the need for high impedance headphones with the Crack, but more on that later.

The most immediate characteristics of the Crack’s sound are openness and smoothness. The sound is liquid and creamy, but never slow or veiled. It’s just real. The music flows out of the Crack like it would flow straight from the instruments. There’s space and depth and separation between the instruments, but again it’s delivered naturally – nothing artificial.

I had heard talk about analogue sound being smoother and more natural, but had never really paid much notice. Moving from the solid state sound of the NFB-5.2 over to the Crack immediately showed me why analogue sound has such avid fans.

I’m not suggesting that tube amplifiers will always outperform solid state because there are some truly amazing solid state amplifiers out there, but they cost a whole lot more than this $350 gem. I feel pretty safe suggesting that you will not find a better amplifier for the same dollars as the Crack. In fact, I think until you’re spending in excess of $700-800 on solid state, you will have trouble finding better sound.


Without realising it, I somehow didn’t expect high levels of clarity and detail from the Crack because of its simple  and analogue design. It certainly surprised me.

It’s not analytical in its sound like a solid state amp might be, but there’s no lack of detail and the beautiful separation of different sounds and layers means you can really enjoy the music and the details, not just pick the music apart to hear separate details.

Sound Signature

The Crack’s sound is basically neutral, but perhaps slightly warm. It doesn’t add significant colouration to the sound that I can hear, but it does bring out the extended bass more than my NFB-5.2. The Crack makes the bass from the HD650s sound fuller and meatier, but it doesn’t make the sound significantly warmer overall, just fuller at the bottom end.

Top end sparkle and air is still great, mids are well-balanced, liquid and smooth, and the bass is full and solid, but not forward of other frequencies. Overall, I think it seems a little warmer because everything is so smooth.

Of course, the signature can change with a simple swap of tubes (valves). The Cleartop RCA 12AU7 I bought makes the sound a bit leaner and brighter, but does so at the expense of ambience and space within the music so it’s all a matter of personal preference.

I guess the key here is don’t decide on the Crack because of a sound signature because that’s adjustable with simple tube swaps.

Overall Presentation

2012-12-06 18.22.50This is the smile-inducing part of the Crack’s sound. I don’t feel like the Crack dramatically enlarges the soundstage of the HD650s, but it’s placement and layering of sound is flat-out holographic. Individual instruments and sounds are perfectly separated and spaced around the soundstage to a degree that’s surprising at times and almost enough to make you look over your shoulder or second-guess if you’re alone in the room!

All of this adds up to a sound that’s fun, addictive and realistic. It’s probably not an amp for people who like to dissect music and analyse recordings, but it is definitely an amp for anyone wants to really enjoy their music in a way they might not have previously. The Crack brings music to life in all it’s amalgamated glory. The music is presented as a whole, magical soundscape, not a series of analytically correct, but unrelated parts. It’s been quite a revelation to me and has me subscribed to the benefits of high quality amplification.

A Note About Headphone Impedance

HD650 open boxThe design of the Crack results in a high output impedance. In layman’s terms, this means that it doesn’t work particularly well with low impedance headphones.

Most headphones on the market are low impedance (<100 ohms) which means the Crack is not a good match for the majority of headphones on the market. Not that it sounds awful with these cans – it actually still sounds quite good with my 70 ohm Ultrasone HFI-680s, but it’s not ideal because the amp doesn’t have as much control over the movement of the drivers when the headphone’s impedance is too low.

An amplifier relies on impedance to control and limit the movement of the headphone drivers. If the headphone impedance is less than or close to the amplifier output impedance, it’s ability to stop (or dampen) the movement of the driver is reduced and can result in lower sound quality.

Where the Crack really excels is with 250 ohm and 600 ohm Beyerdynamics and with 300 ohm Sennheisers (among other options). It consistently receives rave reviews when paired with HD650s, HD800s, T1s, DT880s, etc.

Closing Statements

If you own or are thinking about owning some high impedance headphones and want to get the most out of them without spending $1000+ on an amplifier, have a serious think about the Bottlehead Crack. It’s easy to build (and fun), and will easily give you the best headphone experience that $350 can buy! Add to that the ability to tinker, upgrade, swap tubes and generally customise your amplifier and it’s an amazing bit of kit – get you one!