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

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.

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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:


Got a Bottlehead Crack already built with the Speedball mod and stock tubes (the big one says “GE” on it, not sure what the small one is). Been primarily using it with my HD6XX paired with the Bifrost 2/64 with Apple Music. I tried some tube amps before at CanJam NY, but that’s not the best listening experience for source gear, but it did make me tube curious. Otherwise, my primary amp is the RebelAmp, which is marvelous, and outperformed all the lower end amps I compared it to (Atom Amp, Zen Can, Magni+); I even bought a Piety thinking it would dethrone the Green Monster and save me desk space based on how people fell over each other praising it, only to be disappointed by how harsh I found the treble on it.

The Crack on the other hand been an amazing experience. At first when I plugged the headphones in and started listing, I was completely transported, just getting a 3D experience of euphoric sweetness that carried me away. I made comments here like “I understand how the 6XX could be endgame now” and meant it.

After a few days of listening for many hours a day, I started to notice that after a few hours I started getting this “drowning” feeling, like it was just too much richness swamping me. When I described it to someone else in the community, he compared it to having too many rich desserts in one sitting, and I think that checks out. The sound is still startling, especially when I first start listening, but after a while it becomes too much.

So then I switched back to the Rebel and it was like, “oh yeah, this is still great”. Though the soundstage and positioning are reduced, there’s a sharpness to the notes that the Crack seems to round off. And the “euphonia” effect on the Crack almost seemed like a gimmick in comparison.

The obvious thing to do is to try some new tubes in the Crack, and they’re on their way now–on recommendations from online I ordered two GEC CV4079 with a CV4079 adaptor, and a Clear Top 12AU7A. I’m very curious to see what they do for the sound. But they’re coming from Britain, which for some reason is a haven for tubes, so it might take a while.

It does feel like though there’s some kind of middle ground to be had between the Rebel and the Crack, some that adds a bit of “glow” to the notes and the 3D effect of the Crack while preserving the “cleanliness” of the Rebel and not making me feel like I’m drowning after continuous listening.

An obvious option (besides tube rolling) would be the Schiit Valhalla which is relatively affordable and known for having a much “cleaner” sound. Another option might be the Schiit Lyr+ which, unlike the Crack or the Valhalla, could theoretically replace the Rebel amp entirely, but it’s not a full tube implementation so I’m not sure if it’d be a case of being halfway SS, halfway tube, and great at neither. (I wish I lived closer to the Schittr so I could just try them out.)

From there though, options get much more expensive. The Bottlehead Mainline is supposed to be clean sounding, but I’d have to get it prebuilt (I’ve never used a soldering iron in my life and I’m not starting now) and since it’s $1400 just for the kit and however much more for the build, well, that’s a completely different class of money and I’m not sure I’m willing to pay that much. At that price point there’s some other options as well, the Feliks Echo, the LTA MZ2, the Quicksilver. And from there you start looking at stuff like the DNA Starlett, the Zana Deux, the Dragon Inspire IHA-1 and start thinking “you know maybe I could save up for that”.

And it’s a little crazy. I do have an Atrium coming, so this isn’t just for the 6XX. And I couldn’t believe I paid what I paid for the Atrium. I’m still digesting it, but I fell in love with it at CanJam.

But in terms of amps, I already have the Rebel and every headphone I have sounds wonderful on it already, so what am I doing to myself here? But there’s this sense that headphones like the 6XX and the Atrium are “supposed” to be on tube amps, they’re what sound the best. (I’ve also heard that they sound better on balanced solid state, which has me eying things like the Burson Soloist 3XP and going maaaaybe.) But I’m very ambivalent at this point. If I were sane, I’d stop now and settle for tube rolling the Crack. Maybe I will. At any rate I’ve resolved not to buy anything more for a bit and let things settle instead of rushing from one product to the next. If nothing else it’s been really cool to experience the Crack sound, and get some sense in a proper listening environment of the kind of thing that tubes can do.



How much do you want to pay for it to sound different?

Is different enjoyable?
Or do you enjoy the music even more than the sound?

This wisdom brought to you by a guy that has been seriously considering blowing 5 figures on some new speakers. Eventually.

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Thanks for the writeup.

I never liked the sound of my factory cylindrical power tube (GE 6AS7GA) on the Crack. To my ears it’s rough and range restricted, and it suppresses the highs. I quickly switched to a modest Svetlana 6N13S Coke bottle tube and the presentation became much more natural to my ears. I’ve tried several other cylindrical power tubes and they all resembled the GE, while the sound of my other Coke bottles resembles the Svetlana Coke bottle. So, I’d personally get a Coke bottle tube and stop.

To my ears the input tubes (12AU7s) fall into a few broad categories, and their character is mostly determined by the size and physical shape of the metal parts inside. Be aware that some current production tubes appear to come from the same factory and have different labels – their builds and qualities are indistinguishable.

To my ears, a smaller mass of metal inside tends to be brighter while a larger mass tends to be deeper and/or warmer. Some (e.g., GE) are often bright while others (e.g., RCA) may be thick, warm, and fuzzy. I generally prefer “long plate” 12AU7s because they fill out the lower end.

Beyond the overall tone, some tubes exhibit flaws and quirks that you may love or hate. This ranges from painful whines and whistles to a distorted frequency response that overemphasizes highs, mids, or lows, and they also vary by level of harmonics.

EDIT: For giggles try a very worn tube. This can be educational about how tube performance changes over time. For me, worn tubes generally lack treble extension and detail. They go burp…burp…burp…


Thanks for the suggestions!


If you’re looking for new tubes for your Crack, this Crack tube rolling thread in the Bottlehead forum might be useful. One of the main posters in that thread also posts tube reviews at Tube Maze.

And finally, this chart might be helpful. I downloaded it from a random site, so can’t vouch that everything is 100% accurate, but for the most part, it appears to align with my experience:


That table does not list my favorite, thank goodness.

:face_with_hand_over_mouth: :no_mouth: :sweat_smile:

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Nice, thanks! Funny, last night when I wrote this I was all like “Crack’s a gimmick” and today I’ve been listening to it all morning and I’m like “Crack’s amazing” again. We’ll see how I feel in a couple more hours, but maybe I just need to get more used to the sound.

Glad the Clear Tops I ordered are in the “Clear/Detailed” part of the chart since that’s what I think I want more of. Definitely looking forward to seeing how they sound and will save this chart for future reference.

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Listen for yourself. I’ve been sorely disappointed by some high-profile vintage tubes. Mine were either seriously worn or I heard them differently than others. Vintage involves a lot of unknowns and variability, and the supply has been picked over for a long time. You are in competition with the electric guitar amplifier and speaker markets – both of which tend to use a lot more tubes per amp than headphone amps. The nice thing about the Crack is that you only need singles rather than matched pairs. Singles are much easier to find and often cheaper too, while matched pairs may not actually ‘match.’


Thanks for the link. I don’t own the Bottlehead Crack but I do run one of the listed under “sort-of-drop-in” which is the 12BH7A. Mine is an RCA 12BH7A variant that sounds quiet syrupy. I did not enjoy it at all at first when I only owned cheaper headphones. However, after acquiring better headphones (my ZMF Aeolus) I finally appreciate what this tube can do. It has risen to the top as one of my favorites along with a few other 12AU7 tubes. So, perhaps one might look into what upgrades are necessary to allow 12BH7A to play in their Bottlehead Crack in order to open up possibilities of other families of tubes.


Clear Top tube arrived about an hour ago. Oh, yeah this is much better!


Nice to hear! The RCA clear top is hard to beat for the value. The crack responds very well to tube rolling as you’re noticing and can transform from super warm / gooey sound to fairly tight and detailed (tho not to the level of SS) with the right tubes. I definitely would not make a final determination on how the amp sounds based on stock tubes and encourage at least a few different quality power / driver tubes to get a sense of how each tube influences the sound. Synergy between power and driver tubes is a big thing. Sometimes a driver tube will sound fantastic with one power tube, but meh with another (and vice versa).

Some good lower cost power tubes that would probably be an upgrade over stock are the Chatham/Tung-Sol 6AS7G or Chatham/Tung-Sol 6080(WA) - don’t pay more than $50 for either. Tung-Sol 5998 have some of the best clarity but are also skyrocketing in price/scarcity, but worth trying if you can find a single for ~$100. GEC 6080 is another great tube and while expensive NOS, you can get some great prices on used tubes that still sound great if you’re patient.

If you’re open to more adapters, I’m a huge fan of the 6J5/6C5/L63 single triode families running as pairs for driver replacements. A pair of 6J5 is electrically equivalent to a single 6SN7 so I do believe you need speedball (disclaimer)… They’ve gotten more expensive but still a fair bit cheaper for NOS than top-tier 6SN7 and 12AU7.

These GEC L63 are top notch for clarity and detail. Available NOS here: L63 CV1067 GEC KB/Z NOS VALVE TUBE - Langrex

The Brimar 6J5G (also NOS available through Langrex) are a great alternative with a little more warmth but still great detail.

Have fun!


I seriously don’t understand how the 6XX has soundstage now.

The Clear Top tube basically solved all my problems with the Crack. Combined with the Custom Cans mod (with the “m” foam), this now sounds better (to my tastes at least) than cans and rigs I’ve heard that cost thousands of dollars. Holy shit.


Welcome to synergy and harmonic distortion. I always have trouble justifying my later purchases after revisiting the HD600.

Sound is not a very complex physical or biological process (e.g., versus vision). We’ve been able to record and reproduce high quality sound since ~1930 to ~1960 so it’s quite mature technology.