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

Did you hear about the 3 engineers that walked into a bar?

You’d have thought the last 2 would have ducked.


Wouldn’t you know it…I got all resistances to check out good. All voltages were within spec. The LED’s even lit up beautifully along with the Tubes. All was well in the household…until…

I plugged in my Atrium and have officially damaged the left channel somehow. As in the left channel barely has volume compared to the right. Tested this out on my Jot2 and still has the issue…so yep.

I got a pop when plugging them in to the crack. Looking through the BHC forums I am reading all sorts of people who had to go back and reflow different points to fix this. The most typical is apparently on the headphone jack where the 2 black wires join. I’m in contact with their forums but of course I need to go through and do some reflow work first. First time soldering and first time reflowing…though the process seems easy enough to understand.

The not so simple process will be getting my Atrium repaired. My wife could tell right away when I came downstairs with a complete look of failure and defeat. Why do some lessons need to be so damn sucky to learn? I do wish there was a better test for this so I may have avoided this terrible problem before plugging in such an expensive set of cans. As an aside, I wasn’t sure if I did damage them so I plugged in my Porta Pro’s (on low volume of course) and wouldn’t you know it, they are fine.

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I’ve built a few amps and pre amps (some of my own design), and I won’t plug anything expensive into them before I’ve verified everything is fine with something I don’t care about.
I shorted the input of my Schiit Magni for going on 10 minutes straight (I realized afterwards) trying to debug an issue with a preamp, amazingly it survived.
I still own most of my first headphone setup, and that’s what get’s used for testing, headphone in question varies, but never more that a 6xx.
Still lesson learned, sorry to hear about the damage, hopefully Zach will work with you and it’s not too expensive a mistake.

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FWIW at this late date, I always always always turn the Crack’s volume to 0 before plugging in or removing my headphones. I even try my best to plug/unplug with the amp turned off. Headphones form part of the amp’s electrical circuit and TRS connectors briefly short out during insertion and removal.

See our own @Torq’s review of the now $2,850 SPL Phonitor X:

You MUST turn down the volume or, better still, engage the “mute” function when connecting/disconnecting single-ended headphones via the standard 1/4” (6.35mm) jack.

Your amp build may (or may not) be fine even if the Atrium is toast. I’d personally use my cheap Beyer 880 600 ohm (<$200) or Senn HD 6XX (~$200) for OTL amp shakedowns. They both sound decent on the Crack too.


Yeah, I did have the volume down to 0. Unfortunately that didn’t seem to matter in this case.

Believe me I wish I had other high ohm headphones but I don’t. I did use the porta pros on it and they were fine at low volume. Another reason I got so baffled by this.

I may just grab a used set of beyers…or who knows what. I compared my pictures of my work on the BHC forums and thought mine looked pretty good in comparison. Still it’s either a cold joint or the point where both black wires meet. I also need to double check the RCA jacks, especially the left channel.

Hard lesson to learn though not sure I even could have avoided it since I passed all pretests.

Hey on a side note, I love how my finished build looks with tubes in and all. I’ve got a damn nice paperweight for now!

Aw what a bummer! Looks like you just had rotten luck. You plugged in the cheap-o headphones first, and still got burned. I was looking forward to hearing your impressions too!

If it makes you feel better, I’ve heard from Zach that the vast majority of the driver replacements he does are from tubes and tube amps malfunctioning. It seems fairly common. This is the main reason buying directly from ZMF with that lifetime warranty has a high spot in my priorities. You just never know what could go wrong.

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Well that makes me feel a bit better. Still, I’ve learned as I just bought an 80ohm knockoff studio headphone on Amazon for 20 bucks…aka…crash test dummy ha!


If it makes you feel any more better, many of us have done this. One of my PortaPros has a dead driver on an amp build too.

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Not to be a smartass, but I’d take a dead driver on my Porta Pros over my Atrium right about now ha! Seriously though, it sucks to have happen to any piece of gear.

I’ve made some adjustments and reflowed some joints on the amp. Passed all checks once again. Now all that is left to do is see if it fries these HP’s coming to me on Friday. The big question is will I get up the courage to plug the repaired Atrium’s back into the amp if it tests out fine. That…I don’t know yet.

Many of us own the Senn HD 6XX or HD 600 – they are well matched to the potential of BHC. The 650/6XX and Crack is a longstanding endpoint for people who are not headphone fanatics. Reference sound.

Really sorry to hear about the Atrium. Hope you get something worked out with Zach for a quick/relatively painless fix.

I use my trusty 58x as a crash test dummy for every new tube in the BHC that needs to prove themselves. While not nearly as legendary as the 650, it’s a bit cheaper and I wouldn’t cry too hard if a driver blew. At 150ohm it’s high enough impedance that I’m often impressed with how good it actually does sound with tubes. I also like that I can easily drive it from an iPhone around the house.

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Yeah I will plan on getting one of the Senns here soon after things are up and running well. I now know how good of an idea it is to carry around some cheap cans for things like this.

I think the other thing I’ve learned through this process is to also check your DIY amps often. I’ve read through their forums of others who have used the Crack for a while only to one day have a short and same thing happened to their HP’s. Kinda scary, though probably not to someone who is an experienced builder.

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Alright, so 1st test has finally passed with flying colors. Currently I am listening to the BHC on my TYGR 300. The cheapa$$ headphones I ordered from Amazon were dead on arrival ha! No worries…the TYGR isn’t exactly cheap but still cheap enough to test with. Though not quite the type of HP to use with the BHC, I must say it sounds good! Everything is mellowed out and even the sibilance isn’t quite so bad.

The next part will be to add the Speedball upgrade, but I’ll give this a good few hours of listening time before I do that. No popping when inserting the hp jack which is a big step in the right direction. I get a bit of static on plug/unplug but hell that happens at times when plugging into my normal amps. Still, volume always cranked to 0 now when doing that to be safe as I can.

Picture for some pleasure: