Bottlehead Crack OTL AMP (Kit/DIY) - Official Thread


Bottlehead’s basic headphone amplifier kit, the “Crack”, is probably the most well known, and best regarded, kit-based/DIY headphone amplifier there is. It is an all-tube output-transformerless (OTL) design, intended to pair with high-impedance headphones, such as the Sennheiser HD6XX line.

It’s an excellent sounding little unit, with good potential for modifications (indeed Bottlehead themselves offer optional upgrades, such as the “Speedball” constant-current-source power-supply modification.

I know several forum members, including @Darthpool and myself are building these, so I figured I’d put up a thread for what I’m sure will be a lively and on-going discussion about this lovely little amp, how it sounds, building it, modifying it and what tubes people are enjoying with theirs (I plan to post an illustrated build-log).

And this is something you’re interested in, don’t let the fact that it’s a kit put you off - the instructions are extremely detailed and very easy to follow, and there are no tiny, fiddly, joints to solder.

Bottlehead crack
DAC/AMP Upgrades and Sidegrades Discussion

So far I’m having a blast with the B.Crack…what a fun amp… this is what I was looking for when it came to learning what different amps/DACs could do. The Crack just wow…really hard to put it into words, so many subtle things and not so subtle things that it does to the music that all add up to a WOW while listening to the different headphones in my collection. I’ll have to do a rundown soon… I’ll cross post with the 58X thread that I did a quick impression with the 58X and even quicker Fostex PH x00. Listening on the CA Cascade at the moment and actually even better of a listening experience to both the 58X and PHx00. I am noticing a trend…every new headphone is better than the last lol… maybe it is the fact the B.Crack adds different sound then I’m used to, to each new headphone I plug in. This is making me happy


picture with flash… I actually have the El DAC off to the side now to hide some of the cables…I might have to re-configure how I have this all setup…it gets very hot in that lil cubby with the El DAC (gets surprisingly hot for a DAC) and the Bottlehead Crack (very hot, tube glow for the win…also this winter will make excellent hand warmers).


HD700 and the Bottlehead Crack are I think almost the perfect combo at this point in my listening (caveat HD800 is still my preferred headset to pair with). It has a fullness and warmth that I didn’t realize it was missing (HD700). For lack of a better term the B.Crack adds a “musicality” to the Senn line. It allows them to keep the analytical reference they are known for and just adds a layer of Care Bear Stare to them lol. And…the daughter is now pulling on me wanting to play… I’ll add more to this thread later on… =)

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The only thing I’ve never enjoyed about the bottlehead aesthetic is the vertical wire ports. Is there a way to build these with ports in the back? That way I can hide all my pesky wires.


You can get right angle adapters, or custom wire it, all sorts of options really.


You could certainly modify the build to relocate the power-input, the RCA connections and the headphone socket.

The electrical part is fairly simple.

The harder parts are a) finding suitable IEC socket, RCA jacks and TRS connectors that can be mounted through the case (which is much thicker than the top-plate), b) cutting the case so that you can install them (the stock parts are all panel-mount, so won’t really work for that application) and c) you need blanking pieces, or a new top-plate, for the build so avoid having four holes in the top of it.


So it would be a custom case / woodworking job. Not too terrible.


Indeed … and many have done it. The electrical side is really just extending the connections and maintaining the same time of cable run (braided, twisted or straight) while not passing those cables any closer to parts they were originally separated from. Well, and finding parts to fit the new case.

For me … I know that if I take power-tools to wood myself, one can generally rely on the end result being a pile of blood-soaked wood-shavings, a run on bandages, and the invention of several new forms of profanity.

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Haha sounds about right. You know what they say, Perfect is the enemy of good.


I’ve built the original Bottlehead Foreplay, sweet little pre-amp right out of the box.
I’ve been thinking of another build. Sounds like I need to get over to the BH site, and return my forums name from the abyss (Same name I think, Lotek.)


I built the crack and added the speedball right away so I can’t compare the 2 versions. I discovered some cold and poorly soldered joints during playback and got those squared away. I actually found it only marginally better than my Project ember and mcth.

I decided to upgrade the pot to a stepped smd resistor one from Valab on ebay. (very well built) The build went true to form, I melted the insulation on 1 rca input while removing the wire. I ordered a couple more and said what the heck and ordered a Triad choke. While reading choke threads I read that occ wire is highly regarded so I ordered some 24 gauge from VH audio for the rca to the pot.

I put it all together at once so I can’t say what the difference maker was but my crack has improved a great deal. It is much quieter, better separation, just way more musical than before. I actually really enjoyed the Die Walkure cd I ripped. It was a bit cluttered before and I couldn’t hear what all the fuss was about. The amp doesn’t make any noise with no signal and pot turned to max anymore. Just dead silent. Everything I listen to is just much clearer and dynamic.

I won’t be looking at caps or tubes for a while but I may consider occ wire for the rest of the signal path. Apparently 24 gauge is fine for everything but the green wire.

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Bottlehead is having a 15% off sale through this Friday the 14th September on a bunch of gear.

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Just love the expression . :wink:

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Every time I turn on my “Darkness” lol I just fall in love with it! Sure some of it might be because I built it…but truly after listening to lil amps here and there or even from my phone most frequently this past week, I finally sat down at my home desk and turned on my bottlehead crack and threw on the HD800SDR mod and just… blown away…I’m now listening with my Elex and it isn’t quite the same, the airiness that the HD800 has just makes it an almost magical experience…maybe I’ll throw the HD58X on next…ooh maybe the HD700 after that…hmm…or go to bed and be bright eyed and bushy tailed for work tomorrow…did you hear that? I think it was my HD800 calling to me…ok maybe another song or two… =)


Your a lucky man. I bet that your HD800 just sings plugged into your Crack!! :grin:.


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Sorry, this hasn’t come across quite as I had intended. I am being sincere when asking how much better your HD800 and more interestingly your HD700 now sound through your BHC. I have a certain affinity for the HD700 (I owned it until I got my HD800) it gets a lot of hate but I really liked it. I just can’t imagine what the BHC does for the sound. I mean it should in theory improve the sound (sound interpretation being subjective of course) as it does certain other headphones in Sennheisers lineup.


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I’m a big fan of the BHCrack and the Sennheiser line, especially the HD700 and HD800, both get nice boosts in my opinion, when paired with it.

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I suspected as much. The BHC seems to be a special pairing with Sennheiser headphones. I’ve got to get to listen to one sometime. Thanks.


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