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



I really hope they drop this again…
I also really like the look of the Fireflies, but at the end of the day I love my BHC. Which makes me want to try more tube amps :grin:. I’ll probably do the speedball soon and start tube rolling soon also…so much fun to be had, so little time


If the tube says GE on it, skip it.



It’s built - I just haven’t installed it yet.

I still want to do some “before” measurements, as well as record the output for some test tracks so I have a primitive way to compare before/after. Plus … lack of time …

Though I may just skip all that and wait until my 2nd Crack 1.1. arrives, and keep one stock and one with the Speedball.


I think I’ll go after the S.E.X. as the next Bottlehead build…


Well, back home and listening on the BHC and no more whine… I think it was Gremlins, as the weird build up noise is gone also! I must say the BHC is such a joy to listen to (yes I’m biased, I have no qualm saying it…I put it together and put my own little spin on it, therefore it is special to me) I highly recommend anyone who has the chance to build one do so! Well I think it’s time to take it apart and start the process of putting the speedball on…


It could also just have been a tube taking longer than normal (I don’t know how many hours you have on your BHC now) to settle/burn in. Some never do and either are perpetually noisy or exhibit other spurious issues.

That can be an interesting situation for people that are new to tube amps and/or new to a specific tube/amp. If you get a tube with issues from the outset, troubleshooting can be a bit of a pain. You need to give them time to burn-in to see if it’s an actual issue or not. And if there is an issue, and you decide to replace a tube to fix it, you will likely have to go through the burn-in process with the new tube to see if that did fix the problem.

The problem with that comes when the replacement tube winds up being one with issues as well! Fortunately it’s a rare occurrence - but it is a frustrating one when it happens.

Which is one reason why people that focus on tube amps tend to keep known-good tubes around, even when they no longer specifically need them (e.g. they’ve sold the amp that used them). It makes for a much quicker path to validate the performance of an amp and to do troubleshooting/comparisons later on!


@Torq thank you, I need to buy more tubes for tube rolling soon lol. Update right before I unplugged everything in prep to put the Speedball on…the whine came back on both the El DAC and the RME ADI-2DAC, I can consistently get it to go away by unplugging everything and powering down then plugging it all back in, but it will apparently find its way back to the whine. Hopefully with new tubes and the upgrade to speedball will fix the issue. Otherwise I’ll be forced to pick up a S.E.X. sooner than later lol…


Did you ever reflow all the solder joints?

I know you “checked” them, but I’m not sure what that actually entailed.


I didn’t, I figured it would be the perfect time to do that when I updated to the speedball…


would love to try one of these out…the devout following and DIY appeal…the top end models, what sort of off the shelf tube amps would you compare them to for sq?..just wondering how far they punch beyond their price points. only tube hp amp i had was the mapletree ear+plus hd.


One of the challenges with comparing to off-the-shelf “tube” amps, is that there are not that many of them until you get well into four-figure pricing. Most of what’s available for under $1,000 are tube-hybrid models, which have very different characteristics in terms of what they’ll pair well with and how they sound.

Just taking the stock-build of the Crack 1.1, and assuming you stick to pairing it with high-impedance dynamic cans, then it’s on a similar level, sonically, to things like the EC ZDT Jr, Woo WA3 and WA6, the LittleDot amps up to about the Mk 6. That’ll change a bit if you stray from high-impedance dynamics though, with things like the WA6 and EC ZDT Jr. being notably more appropriate for efficient planars and other, low-impedance, cans.

The Crack 1.1 wins out in terms of overall tubey-ness, lucidity, liquid-mids and stage over almost all the relevant hybrid models, including the Vali 2, MCTH, the entire Garage 1217 line-up, Valhalla 2 and even the Lyr 3, though those other amps all have various, sometimes quite significant, benefits over the Crack 1.1. as well (e.g. the Lyr 3 is more transparent, far more powerful - it’ll drive pretty much anything, and has more slam and low-end control).


cough @torq speedball cough


Won’t be long now …

My 2nd Crack 1.1. kit arrived a bit ago and I’m going to put that together (in a more restrained finish), and then install the Speedball in that unit and do direct comparisons. I just need a free afternoon with nothing else distracting me to get that built and burning in.


I put in a RCA chrome dome 6sn7 with adapter yesterday. A very nice upgrade over the stock tube and a Psvane 12au7 (probably still needs break in). Get a nice tube and an adapter from Garage1217 and you will be good to go. Verified that it is a drop in replacement at the bottlehead forum. All sorts of upgrade and replacement info there. I added a stepped pot from Valab and a choke and both made an improvement. Don’t think I will go down the capacitor rabbit hole for a while , if ever.


Having heard special caps + special bypass caps + special-diode-board-thingy + choke in one Crack -vs- my stock Crack, I couldn’t help but think that the “improvements” were more for the Uber-Detail orientated crowd, where the possibility of placebo is thrown out the window and any perceived improvements were worth doubling or tripling the cost of their amp.

It’s kind of a “Damn the torpedoes, full speed ahead!” type of thing.


It’s all incremental for me. No travel on the pot before it’s too loud too quick with channel mismatch. Valab makes a nice stepped pot. While waiting for the slow boat I observed the choke was really cheap so 1 more in the bucket. Nobody wants my Ember/tubes and adapter so I figure what they hey and gave it a try. 6SN7 put to good use.All inexpensive upgrades. Still have to put resistors in to pre attenuate and be able to use more of the pot. The capacitor upgrades are more expensive. Maybe pcx will have a sale, who knows? Jeb’s well documented upgrade path on the excellent SBAF thread helped to fuel my fancy.


Going to be building a Crack for a friend. Might be doing a CrackATwoa along side it for myself. Any interest in a build log/photo journal?


Always interested to see something built. I haven’t done one myself so it’s all helpful in the end.



At this rate, you’ll beat me to doing mine! :wink:


Woah there… I never said I’d be putting in a Speedball. You still owe us that! :stuck_out_tongue_closed_eyes: haha