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

I don’t know much about wiring circuits, looks good to me. You didn’t electrocute yourself yet, so you have that going for you.


It lives!

I will begin procrastinating the speedball upgrade immediately.


First impression, was a bit of a let down with rock compared to what I’v gotten used to with a Bryston BHA-1. The bottom end is just kinda missing in comparison. I don’t know how you can make Husker Du not urgent, but the crack managed. It’s just too relaxed for me on the stuff I listen to in the middle of the day.

Then I put on Sonny Rollins “The Bridge”. Okeedokee. That sounds real nice. Gillian Welch. Holy moly.

So. it’ll be fun to try a different flavor, and learn about these glowy bottle things. I think they are called toobs. Maybe valves? Anyway, how much can there be to learn? Should be easy.

The build was easy enough for a beginner solderer with hands the size of canned hams. Would recommend. Fun building, and fun listening.

That’ll wrap this terrible build log. Now I just need to listen to it.


Famous last words. Lol.


Glad you got it going.

Just a reminder to give 100 hours for the tubes to break in. There can be surprisingly big changes along the way.

Some might disagree but I connect some old headphones and let the amp run for 5 days straight. You probably want to be close enough to notice any issues and be able to shut it down quickly though.


if it helps any i much prefer solid state to tubes for genres that are loud and ascerbic like husker du. like, i don’t want gang of four or husker du or public image ltd or nirvana - in utero to sound pretty


Yeah, punk and metal are often produced to have more edge. A lot of 1970s and 1980s content also came from independent studios with limited equipment or was mixed with energetic, outside-the-mainstream decisions.

SS amps tend to preserve the edge, while a noisy one will magnify the edge. The bite is carried in the treble, and can be easily boosted or controlled by EQ or amp. Listening tube amps smooth and roll off the treble.

I’ve not obtained a Crack in large part due to its narrow use cases.


Congrats on finishing it. This was an amazing log.

Is this something that can be solved with tube rolling or is the Crack on the softer side of tube amps? For instance, the Pendant is on the “close to solid state but better” end of the spectrum, and plays visceral music viscerally, at least with the tubes that I have.


A really good question. I have just started to look into what tube swaps can do for this little guy, but it sounds like the speedball upgrade might help a bit as well.

@ProfFalkin or @TylersEclectic would have more insight as they have owned theirs for quite a while.


@monochromios seems to have inadvertently answered this question because he referenced an older post in the Pendant thread, and when I scrolled up to take a look, I found this conversation about the Crack.


My fault I must have did a mess replying to an older post. My sincere apologies


Absolutely no need to apologize. It looks like you posted at the same time I asked that question about the Crack, and with your telepathic superpowers, you found the answer I was looking for.

And you also found a new recruit for our tube rolling thread, because he just ordered a Pendant (a year later) and can give us his impressions of all his 12ax/t/u7 rolling.

So I don’t know how you did it, but you managed to cover a lot in one post. :+1:


Also finished my Crack recently and I share similar sentiments to @mfadio above, first impressions are a little lack luster. That said I haven’t installed the speedball yet and the tubes have not had time to burn in.

Compared to my usual setup, a Liquid Platinum with 6xx and LCD-x, I find the base Crack to have much less presence in the highs (less clean and clear and more rolled off) Also the bass is there but not commanding any real attention.

Really curious what the Speedball is going to bring to the table. I also have a 6AS7G Triple Mica and 5814A NOS RCA I’m going to swap in today.


So my BHC has just got an injection if you will of some speed…

Wow, it’s a step up for sure IMO, the sound tightens up, the dynamics sound a bit punchier, the sound presentation is quicker to my ears. I am digging it, on first listen since the upgrade. I am wondering what are everyone’s favorite tubes for the BHC as well as if anyone has extras laying around that they aren’t using that they would be interested in sending my way for my review?


Give it some speed :wink:


Bought Psvane cv181 but went to headfi 6sn7 thread and that tube might fry my transformer? So I purchased two KEN RAD 6sn7 gt clear glass. I’m going to send other ones back if anyone can confirm the Cracks transformer can’t handle the draw.

People that are new to soldering or lack confidence should use an iron - which is a clip that fits on a lead and has a coil connecting the other ends. Eats heat, so you can get a good join w/o the anxiety of burning an expensive after market piece.

Using other tubes than stock. Driver: Euro (I use Amperex) E80CC tall - before 1965, need to adjust a resistor in the Speedball mod for it to work properly. Quite a few folks swear by this. See BHC home pages for details.

Power tube: GEC 6080 - better yet: Tung Sol 6A57G

For sure replace the rinky dink vol pot. Use metal legs to sit amp on not mini me feet. Don’t leave on all the time, biases in about 20 minutes.

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