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




Part of my decision to go with paint vs. stain is my complete ineptitude when it comes to anything wood-related (not that I am much better with any other material if power-tools are involved).

Another part, and a major one at that, was Dan’s (Doc B.) “Neothoriator” amp. Which is entirely gorgeous, and very red. Sounds sublime … not to mention absolutely effortless. If I had somewhere to put it I’d buy it on principle. And beyond that, I may have to buy it anyway, as it’s in the top-two headphone amplifiers I’ve heard period.


Whats the approximate build time on a bottlehead crack? I thought about getting a kit over the summer but jumped on a rare chance to get an original Starving Student kit instead.


For mine … as someone very proficient in electronics builds …

30 minutes or so to attach all the hardware/sockets and transformer to the chassis. Then another 2 hours, maybe 2.5 hours, for the actual wiring/component build and the necessary voltage and resistance checks.

You could put the base together in 10 minutes, and with it all taped-up and glued, use it to assemble on while the glue cured out. And then finish the base afterwards (by far the longest “wait time” of the build).

Assuming no mistakes, and meticulously following the build instructions, I would expect that even a first-time builder could do it in 8 hours or less with no trouble at all. Though it was a fun build, so I would be inclined to take my time with it … especially if it was a first-build.


Thanks. No real space to put one anywhere, but I’ll consider getting one next time they have a sale on it.


Pretty O/T, but would you say the est. build time of a Mainline might be any different for a DIY noob? Thinking that one’s a better fit for my stable of transducers, haha. I’ve had a few projects under my belt, mostly CMOY and O2 amp builds, but I still believe myself firmly entrenched in noob territory.


That’s the challenge with wood, and a reason to respect the craft:

  • Natural defects = obvious
  • Not enough sanding = obvious
  • Rounded off corners = obvious
  • Dirt = obvious
  • Cut too short = obvious with no fix possible
  • Cheap stain = obvious

But, this often goes unnoticed because there are so many perfectionists who gravitate toward it.


Primary disclaimer: I’ve not built a Mainline myself.

I would, based on what I can find online, say it is substantially different to the build time for a Crack, regardless of whether you’ve built kits before or not.

I would also say that, looking at the build, I would want to employ two different irons/hand-pieces in it’s assembly vs. the one that seems to be optimal for the Crack. A low-wattage micro-pencil for the PCB work and something like the Hakko FX-8801 for the major connection points.

Anyway, I would not expect to complete a Mainline build in one sitting one a first attempt. The only way I can refine that estimate is to build one … so I’ve just added one to my order …


Glad to have been a precipitating factor in that…?

I’m admittedly fairly set on eventually getting a certain amp that I basically wrote a love letter to some time ago (despite her belonging to someone else, sob), but the relative difficulty with which I can get one has me eyeing alternatives at around the same price point. Add to the fact that I miss tinkering with things and I find myself on the Bottlehead landing page, bemoaning the fact that most of their offerings seem primed for high-impedance cans.

I feel no guilt over what I’ve done, please do have fun with that build, haha. Also, I understand you’re quite busy so I won’t ask for impressions with your TRX00. Not any time this year at least :stuck_out_tongue:


@Torq getting this on the right swim lane. I tested with nothing hooked up and it is silent up until the last 25% -30% of the volume when hum begins? I will say when listening to music I cannot hear the hum…but I never get it that loud lol. I’ll try and reflow the solder joints here next weekend when I get back from my trip.

I’m looking forward to chatting tomorrow and seeing your BHC in person!


Complete the BH trifecta! Build a SEX!


The S.E.X. is the one I want to build next! such a cool looking amp…


And speaker amp. Bonus.


Very nice. I am now going green with envy.:grin:


@Torq Listening to my BHC with my HD800…complete silence all the way to max volume nothing connected…I am thoroughly confused by this…I am now using my El DAC with it. Just plugged in the Clears, and with nothing connected I get the hum again…plug in the El DAC nothing playing complete silence all the way through to max volume. I’m going to blame space magic…“the wizard came from the moon!” Well enough playing around…time for bed…Long flight tomorrow (I’ll post my new flight setup once I get a chance).



The difference in behavior between the HD800 and the Clear is down to their significant impedance difference.

I’ve found with many tube amps, especially OTL designs (which are built to work with higher impedances cans - and not simply for tuning purposes) like the Crack, that hum that is not present with a higher impedance load shows up with much lower impedance cans.

So not hearing it on the HD800 in either situation isn’t surprising - that’s operating at the right impedance for the Crack’s design.

As to why you don’t get the hum with the EL DAC connected, but do with it not connected, suggests you may have a grounding issue - and when connecting the EL DAC you may be getting a better ground via it. The remedy for that is two fold in this case … one - make sure all of the bolts/screws/nuts are properly tightened (and you want them very tight). and two, reflow all solder joints that go to ground.

Also, I’m assuming you didn’t get any paint on the underside of the chassis plate? If you did … you have to make super-sure that you fully removed any that’s on/around the various screw/bolt/jack connections so that those points all hit ground correctly, as the chassis is part of the ground path.


@Torq, I started playing with this some more the, whine only happens when I have the RCAs plugged in otherwise inky black silence… I’ll keep at it, I quickly checked all the solder points but I still need to tighten all the bolts, and double check to make sure paint isn’t interfering. I do notice that with the weird build up noise is gone after reseating the tubes. Also when music is playing the whine is not audible. Man I love the sound out of this thing. Any suggestions for alternative Tube amps, or next level up from the BHC? Just curious, I still need to put the speedball on.


Ok, found the problem… it was of all thing the RME ADI-2DAC RCA out. I switched to El DAC and whine gone. I need to go to bed now…desk is covered in cables…and audio gear…need to clean…but first…sleep… lol…will revisit tomorrow and try and isolate the RME ADI-2DAC to see if that helps…

Edit: couldn’t not figure this out before sleep…brain won’t let me… and I re-seated all the cables on the RME ADI-2DAC and voila no whine…the odd part is I did that before switching to the El DAC, but this time I completely removed all outputs and then plugged in only the RCA…no whine…then plugged in the balanced outputs and…no whine?? I guess we’ll never know :wink:

and now to bed with me!


Sure … though prepare for some sticker shock - as the Crack 1.1 is not only a very solid unit, but has a significant built-in price advantage courtesy of being a kit!

And remember in most cases if you go with an OTL design you will typically need to stick to high-impedance headphones in order for a) the amplifier to operate correctly and b) avoid a very loose/bloomy (sometimes bloated) bottom-end.

For a start, there are the other models in the Bottlehead line-up, and then some other interesting pure-tube (no tube-hybrids) are, in ascending price-order:

Massdrop x EC ZDT Jr (or Laconic Night Blues Mini), Woo WA6 or WA6-SE, Feliks Elise, DNA Sonnet 2 (discontinued), Amps&Sound Mogwai, DecWare Zen Taboo MkIV, Eddie Current Zana Deux S (discontinued).

From there, things get very expensive, very quickly.


It could be marginal cables/connectors - particularly if they run anywhere near a PC with a windowed-case. Or it could just be oxidization on the connectors (plugging/unplugging usually clears that up enough to fix it, but “Deoxit” works better). Or it could be gremlins.


@Torq - Put the speedball in yet?