Bottlehead Crack

This is the question I’m most interested in. I suspect the answer is “no”. I’ve always been curious, so I recently built one to exclusively use with my vinyl setup and HD6XX.
I have everything stock and only added 1 uf bypass film caps to the stock output caps which added some air to the top end. I like the stock tubes just fine. I have some low level tube noise and I hope that gets better as the tubes break in.

I guess I just need to finish the case and move onto a S.E.X. build for my Low impedance headphones.

 

Is it tube noise or hum? If the latter then the choke mod will remedy that annoyance. If the noise is random tube noise it may be the tube itself. Another tube may be in order.

 

Paul over at Bottlehead says anywhere between 75 - 90v is totally acceptable here. Also, there is a vast ocean of 12au7 equivalent tubes. Tube rolling would be more in the vain of rolling different vintages and manufactures of the same tube. Although I will say with a 6SN7 at stock CCS settings I get 84v.

In my amp I've rolled about 20 different makes of 6SN7. The differences between each are colossal.

You can also run 7193's and 6J5G's if you wanted.

 

Thanks to @tommytakis I got a Speedball into my Crack and I love it! I’m interested in trying out different tubes since one of the stock ones is microphonic. I read through the thread and all of the tube recommendations don’t seem to be available. I’m debating to try any more mods or just stop at different tubes once I find some. Maybe I should put up a WTB or PM me if you have any spare tubes to sell.

 

I'll send you a PM... I've got boatloads of Crack tubes

 

Kind of want to revisit the crack but with a bigger case so I can fit caps and other upgrades / parts more easily and an upgraded transformer.

Is the above literally a crackatwoa?

 

With crackatwoa you shouldn't need to fiddle with the power supply. BH added a shunt regulated PSU which isolates well so film cap upgrades, chokes and such wouldn't have the same impact as in the Crack. Can't stop you from trying. Crackatwoa can take 5A tube outputs e.g. 6528...big boy,

My own experience with a super crack, even after adding a tube rectifier, quad chokes in two psu rails, all psu film caps, fancy resistors, custom power transformer and others, upgrading the output caps to VCap ODAM made a substantial difference compared to the rest.

It's fun playing with it but you really need the real-estate.


Not a lytic in sight.


The crack will hit a scaling wall eventually just because of the operating point, running the output tubes hotter is a must to get the best out of a 6080 based OTL. That requires a full redesign and you end up with the Apex Teton basically.

P.S. I do love my OTL amp, it's just so smooth and effortless, the perfect slow day background listen.

 

I know we PM'd about it before when you first started and said that it was basically an Apex Teton in terms of both topology and sound, but now that you've had it for a while, I guess are there any fundamental differences between this and the Teton in terms of sound?

 

Yes, the Teton is overall the better amp.

The proof is in the pudding, Teton draws over 100W and the crack is at just 30W.
Fancy components can only do so much, having multiple diy amps at the same time it's not unusual to find the same component be it chokes, caps or tubes to range from horrible to excellent in various circuits. Having a silver, dolphin tear impregnated component doesn't guarantee much after the initial dopamine shot.

This amp does concludes my research into how far the crack can be modded and I find myself agreeing with Bottlehead. It's better to get a stock Mainline and do simple upgrades e.g. parafeed cap than a Crack and upgrade the nuts of out it. Mind you this build will trade blows with a Stratus but it's the farthest anyone has taken a Crack. At some point you find you're too deep and can't think objectively. For an enthusiast audio nut and diy'er exploring how and why the sound changes with different settings is valuable information for future purchases. The whole process brought me a lot of enjoyment that's for sure.

The Teton has an immediacy and speed few amps can match, when I hosted a small meet a while ago people commented the Teton and Stellaris were in a class of their own with the Teton slightly behind with HD650s and the Cavali LG, a top tier amp was a notch or two below. Others such as WA5 sounded mid-fi next to these.

My opinion is the crack suffers from low transconductance due to the low operating point. Tubes will last forever so hoarders will never use their plunder but time is short and I'll be happy to burn them faster. The Teton can get too hot to touch the top plate, part of the business but the increased transconductance loweres THD by a fair margin, better damping factor, lower output impedance and is much more linear. The input tube, the 6SN7 sounds far better IMO running hotter in the Teton. In theory the Crack is LED bias with no caps and should be purer, in practice the auto bias of the Teton in the more linear region of the curves sounds miles better to me even with a lytic cathode cap.

I'll be decommissioning the crack experiment and stripping it for parts, it's been a great journey but all good things must come to an end. Next is to start on a Teton clone-wannabe journey, I already have all the parts but had to postpone multiple times. Jumping from 150V to 300V on the high voltage side triples the bom cost, requires respect for life ending mistakes and clever design for heat and EMI management.

 

I just finished building the crack, so I won't give any sound impressions, but god damn the wiring instruction and layout of the circuit in the manual was giving me heart burn. So much extra wire used, nothing precisely cut and so many wires crossing over. Layout seems meh as well.

It's been a very, very long time since I've designed a circuit, so I'm probably just going in to my grumpy old man phase, but if I was still in university, this rats nest of wring would be yelled and chewed out by my professors and I'd be told to rip it apart and start over. /rant over

It really make me appreciate the other DIY kits I've assembled. IMO price is too high for the thought put in to the kit and it should probably be updated. Sound is good though so sigh.

 

Just purchased this modded BHC/Speedball.

I’ve been reluctant to fall into the tube hole, but also keep hearing how great ZMF/tube synergy is, so finally gave in. Decided I’d look for a ‘good’ amp to see if I like the tubes/ZMF combo. Liking the sound but looking to upgrade the power tube.

Hoping to find something less expensive than TS 5998 which seems to be the top recommendation. Other options?

 

the first post in the thread has links to good reviews of both 6080 and 6AS7G reviews. Personal favorites:

Tungsol/chatham 6as7g - great all arounder, my daily driver
Tungsol 7236 - maybe a little brighter, sounds a little more detailed, but probably isn't
SED - bass
RCA 6as7g black/grey - similar to the Tungsol 6as7g, but warmer

but synergy with your input tubes is going to be key...

 

I think a good condition 5998 is nothing short of magical, though.
Sorry

 

Thanks -- should have looked there first. A friend sent me a link to @m17xr2b 's post about his BHC mods since the amp I bought is heavily modded. Didn't think to look at the top of the thread -- my bad.
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< edit > Actually, based on my initial/superficial look at the posts linked from the top of this thread, I feel like an complete idiot. < /edit >
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Synergy with input tubes is going to be ... interesting. One of the mods for my amp is that he added dual octal sockets for 6j5 tubes, although it can still use the single 12AU7 socket (either/or). I've got lots of 12AU7 tubes (12AU7, 5814, CV-4003 -- used in Liquid Platinum w/ adapter) but only a couple pair of the 6j5s.

Opinions seem to be fairly evenly split between 'The 5998s are the best, no question' and 'There are other, less expensive options which are close to just as good.'

 

I'll agree with @Baten that there is something that the 5998 adds that can't be touched by other power tubes. That said, for a more economical, but performs at a high level, I'll recommend (if you are open to using adapters) using a Dual A2293(CV4079) for the power.

The Chatham 6AS7G if you can find them, are nice - I also use these as a daily driver, along with GEC 6080 (though can be pricey these days for either of these tubes).

 

Wondering if I should get a BH Crack again. OR get a used liquid platinum maybe... a crack with the speedball toggle sounds like something fun to play with though.

Any advice? I don't think something like a Shortest Way / SW51 can be found easily in EU. At least for sure not anymore.

 

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, though that’s not the best listening experience for source gear, 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 listening, I was completely transported, just getting a 3D experience of euphoric sweetness that carried me away. I made comments like “I understand how the 6XX could be endgame now” and meant it.

After a few days of listening for many hours a day, though, 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 also just ordered a Svetlana 6N13S to compare.) 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, something 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, etc. 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”.

(There's also more modding that could be done to the Crack, but again, someone else would have to do it, and I don't know anything about that.)

And it’s all 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 save 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.

 

Hey Eric, great write up, you should introduce yourself in the new members section though.

 

Nice write up. In a round about way, you have very similar gear to me; the Rebel is essentially the same as my M3, the Crack, and HD650/6XX.

It's perhaps simplistic, but you can elevate both these setups by aiming for that elusive 'synergy'. Pair the Crack/HD6XX with a sharper DAC to tame it's overly syrupy tendencies. I've got mine after an ESS9038 DAC that gives it a teeny bit more liveliness and sizzle. For the Rebel Amp, I'm running Focal Clear on that. The combo can *definitely* be a bit lively (seriously, it can make your eyeballs pop out of your skull like old school cartoons). So I've got that paired with my Soekris R2R DAC, which is a touchy less edgy, and makes it more enjoyable for longer sessions.

Last potential option for making the Crack a bit less syrupy, I use mine with a JJ ECC802S and a Cetron 5998. These both seem to be more detailed and less syrupy tube options. The JJ is a bit of a dark horse, in that nobody ever seems to recommend new production. But after trying a few different NOS and new production options over 10+ years, I keep coming back to this tube....

 

Oh, that's an interesting idea! I'm starting to wish I hadn't returned the Geshelli J2 I had, because that might actually be just what it needs. I still have the ESS Modi+ I could try, but I actually found that tuned to be less crisp and trebly than the AKM J2.