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!

Lachlan Fennen Written by:

Facilitator, training design consultant, blogger / writer and amateur photographer


  1. Keevin
    December 12, 2012

    Thanks for the write up of the Bottlehead Crack. I was considering it when researching amps for my HD650. But in the end thought I’d start with a Little Dot MkIII. The HD650 certainly pairs well with tube amps. I’ve heard it with a Violectric V100, and found that a bit too clinical compared to the tube amps I tried (LD MkIII, ALO Pan Am, Schiit Valhalla).

    Maybe one day when I build up the courage to build my own amp, I might take this on.

    • December 13, 2012

      I can recommend it for a fun pastime and also will give great sound. Can’t comment on the performance compared to the Little Dot, but it’s always fun to try something new.

  2. Henry
    January 11, 2013

    Good review, I am thinking of getting this for my HD650. Did you buy one with Speedball upgrade? Is the 240V transformer separate unit?

    You surely done a nice job with the wooden shell, I like the rustic colour, did you stain it using normal wood stain?

    I am surely interested to get one of this just waiting for another person to join to save additional cost.

    • January 11, 2013

      Thanks for reading!

      I didn’t get the Speedball. There is a really slight background hum that’s really only audible when you’re listening for it and I think adding the Speedball might rectify this – I plan to get it in the future, but was interested in getting the stock kit and getting to know it before upgrading.

      The 240V transformer is a different version of the normal unit they put into the kit – i.e. it’s built into the kit (and looks exactly the same as the 110V one from what I can tell) – it’s the dark grey cube at the back of the amp with the curved metal top.

      Thanks for the compliment on the wood finish. I used Black Japan stain and put it on lightly and irregularly. I also sanded it a little irregularly in between staining and varnishing (and in between coats of varnish). I used a satin varnish.

      Good idea on a group buy. Good luck!!

  3. January 13, 2013

    Can anyone recommend a good DAC to go along with my Crack w/speedball?

    I was thinking the Schitt Bifrost.

    • January 13, 2013

      I have heard good things about the Bifrost, but haven’t used it myself.

      I’m really happy with my Audio-gd NFB-5.2 which is a DAC/amp combo (selectable line-out/HP out allows easy switching between the 5.2 solid state amp or the Crack). Audio-gd make dedicated amps too so you could check them out.

  4. Harney
    July 13, 2013

    Fantastic write up Lachlan….

    The only reason i ended up here was that bottleneck have a offer on this weekend buy it & get the speed ball free and if you ask me that is a real bargain ..& now just needed some more feedback on it and your writeup made my mind up so thanks to you and there offer i have got one but the wife is going to be a little pissed with me mind you.. i was looking at the crack a while back last year & after spending weeks researching valve amps i was going to buy it but due to work never go t round to it until i received an email from bottlehead regarding there offer and guess what i could not say no …who wouldn’t..there going to power my 650’s with high end rme converter 32 bit 192 khz….kind regards sy

    • July 15, 2013

      Glad I could help, Sy!

      I have no doubt you’ll love the pairing with the HD650s. Did you get the early offer with the included tubes?

      • Harney
        July 15, 2013

        Not sure yet but i sure did order early so i will have to wait and see….either way i am sure i will be happy as this is my 1st tube set-up coming from solid state …

  5. Don Dagohoy
    August 12, 2013

    am planning to have this kit also but am here in Riyadh..
    just worried I can’t finish the assembly coz’ of missing parts..
    it’s shipped completely right?..
    meaning everything such as the board, transformer, tubes, wooden box, etc.
    and all you have to do is just solder, etc?..

    • August 13, 2013

      That’s correct Don. They ship everything you need.

      The only issue you could strike is if you accidentally damage a component (like I did) and have to get another one. I imagine Bottlehead would help you out with replacement parts if needed or you can source them locally. This is only an issue if you damage something – otherwise they provide everything you need (except solder and tools).

  6. […] time ago I built the Bottlehead Crack amplifier and reviewed both the build process and the resulting sound. After thoroughly enjoying the Crack for over a year, I decided it was time to enjoy the next step […]

  7. Brian
    November 18, 2013

    What RCA cables are you using there?

    • November 18, 2013

      They’re some old (but good) Tara Labs cables from my old speaker / car audio setup (can’t remember which).

  8. […] in my headphone and speaker setups. It has paired beautifully with both of the amps I have tried (Bottlehead Crack and Bottlehead S.E.X. – review coming soon) and with all the headphones I’ve tried. To […]

  9. […] on over at Head-Fi. Some of you will have read my review of the assembly and performance of the Bottlehead Crack DIY tube amplifer and you might have also read my assembly review of the Bottlehead S.E.X. […]

  10. Simon
    September 24, 2014

    Nice write up. Thanks.
    My kit arrived today. (QLD)
    Just a Q on tubes.
    I’m not very knowledgable on tubes
    You state “I found that the combination of the Mullard 6080WA and RCA Cleartop 12AU7 tubes provide the sweetest sound” (aren’t these both the output?)
    But later “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.”

    Is it that you accept (prefer) the loss of ambiance and space.

    Thanks for any clarification


    • September 25, 2014

      Hi Simon,

      The 12AU7 is essentially an input tube while the 6080 controls the output.

      The reason I chose less ambience from the RCA Cleartop is because it was nicely balanced by the Mullard 6080WA. 2 Mullards were too much of a good thing and got a bit thick sounding at times, especially with warmer headphones (e.g. HD650s). The Cleartop’s clarity and the Mullard’s warmth and ambience made a perfect pair.

      Thanks for asking to clarify!


  11. Simon
    September 25, 2014

    Thanks Lachlan.

    I’m away at work. (The kit arrived the day I left…) I can’t wait to get home and begin construction.
    It will be difficult not to rush as I’m so keen to hear it.
    I have HD650s.


    • September 27, 2014

      Awesome! Take your time with the build, enjoy the process (and the finished product) and check out the Head-Fi and Bottlehead forums if you need any help.

      Good luck!

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