The Marvelously Addictive Bottlehead Crack Page 2

Listening Impressions
Again, due to the 120 Ohm output impedance, this amp is really designed for high impedance cans. I'd recommend the Sennheiser HD 600 and HD 650 as perfect matches. The Sennheiser HD 800 is also a great phone for this amp, though it might be a little pricey to strongly recommend for this pairing. On the other hand, its amazing resolution will let you peer into every mod you make if you're thinking about the Crack as a long term tweaking platform. I'll also recommend the Beyerdynamic DT880 600 Ohm as a good match, though I don't find them as warm and comfy as the 600/650. I used the HD 800 and HD 650 for my listening tests.

I included the Woo Audio WA3 in my listening set-up for comparison during listening tests. It's also an OTL design that uses the 6080 output tube, but has two 6922 input tubes instead of the single 12AU7A tube of the Crack. My source was Amarra on a MacBook with optical digital out feeding the new Asus Xonar Essence One (which I find myself liking quite a bit). I used the unbalanced outs to splitters and then on to the two tube amps.

My initial impressions of the Crack prior to comparison testing was that it was surprisingly clean and tight...and dead silent. Yes, it did have some lushness, but mostly it just sounded good to my ears. With my 650 plugged into the Xonar (a solid-state amp), the sound was obviously tighter and more detailed, but had a harder nature. Clearly, the tubes of the Crack did a great job of delivering detail and oomph while also softening the edges of the sound somewhat.

The differences between the Crack and the Woo were far less noticeable than the jump from the solid-state Xonar. Both tube amps were significantly softer and lusher sounding. After a while of listening with both the HD 650 and HD 800 some trends began to appear. Generally, the Woo seemed a bit more relaxed and even in its upper mid-range to treble response, while the Crack seemed a bit more forward in the upper-mids to mid-treble, and then seemed to roll off the high-treble more than the Woo. I would say the Woo WA3 was a bit more refined sounding but lusher, with the Crack seeming a tad hard in comparison. On the other hand, the Woo sometimes seemed to gloss over some of the micro-dynamics of a tune, while the Crack seemed a bit more punchy and controlled.

The thing about tube amps, though, is that all the characteristics I noted could easily change with a little tube rolling. While I'd certainly play around with various tubes on the Woo, I wouldn't be nearly so apt to start hacking into the circuit with capacitor, resistor, and potentiometer changes as I would with a Crack I built with my own two hands. In fact, with the Crack, I'm certain I'll be back inside messing around with the innards.

The Bottlehead Crack is a superb introduction into the world of DIY audio. The parts quality is very good, the documentation is truly excellent, the Bottlehead forums provide fantastic peer-to-peer assistance, and construction is very easy. The Bottlehead Crack is an outstanding first project for the novice audio DIYer. The big win, however, is that once you've finished your build, you'll have a fantastic sounding amp for your high impedance headphones. I simply can't recommend the Bottlehead Crack highly enough, if you've got a yen to try a little soldering, this is the way to go. You'll love it!

Bottlehead web site and Crack product page.
Bottlehead forums are a spectacular resource, go to the Crack sub-forum for questions and assistance building this amp.
A Bottlehead forum threads on suitable tubes for rolling and output cap upgrades.
Bottlehead Crack thread on Head-Fi.
Another great resource is the diyAudio Foums.
A good place to get upgrade parts for your Crack is Parts Connexion and Michael Percy Audio.
A good place to buy tools is Stanley Supply.
Here's a really cool review of the Crack at, don't miss the pictues of his beautiful build at the end of the article.
For resistor color codes check the Wiki page here and the chart below.


9415 Coppertop Loop NE
Suite 101
Bainbridge Island, WA 98110
(206) 451- 4275

MacedonianHero's picture

Just one tiny thing...blowing on a solder joint (cooling it quickly) will not cause it to be a "cold solder" joint. What it will do is cause larger grain structures in the joint. This is not a good thing as cracks can more easily propagate through solder joints with large grain structures (over ones with smaller grain structures). Cold solder is not fully liquifying the solder during the soldering operation. Basically applying solder with both liquid and solid phases. If some readers are interested in soldering, the industry standard (if they're so inclined to look it up) is J-STD-001 by IPC. For under $300, this amp looks like it gives great value to performance. Cheers

Tyll Hertsens's picture

Thanks for the tid-bit. yes

Armaegis's picture

>>blowing on a solder joint (cooling it quickly) will not cause it to be a "cold solder" joint. What it will do is cause larger grain structures in the joint


I'm confused on your usage of the word "grain structures"... higher cooling rates almost always results in finer microstructure (smaller grains, thus more grain boundaries). Are we on the same page or am I misreading something here?

MacedonianHero's picture

For soldering, the ideal cooling profile is 1-2'C per second. Anything more will lead to larger grain structures and less reliable solder joints in the end. 

Armaegis's picture

By larger grain structures, you mean more grain boundaries correct?

drheadphone's picture

Thank you so much for the review, the video and the resourceful links. I bought this amp a few weeks ago to pair with my Sennheiser HD650/800 headphones. I have to admit I'm a little intimidated with initiating my first DIY project. At the very least, I feel inspired.

Tyll Hertsens's picture

.... if anything, I wanted to inspire people to give this a shot. Glad to have given you the nudge.

It was straight forward, and extremely rewarding.  yes

MacedonianHero's picture

Totally agreed on the rewarding part. When my kids are a bit older, I'll be getting back into DIYing as a hobby. 

gorboman's picture

I had an opportunity to try the Crack. You're right about matching it with a high impedance headphones. I liked it with the Beyer DT880PRO/600. It was full sounding, smooth, but only a little warm. The Crack with the DT880/250 sounded meh. There were no HD650 to try it with, but based on your review, I guess it's a match for 300 ohm headphones and above.

Other cans that I've tried with below approval results were LCD2 and T50RP Mad Dog. A friend told me that the Crack just won't work with ortho-dynamic headphones. I'll just hold on to his word since I know so little about electronics.

HammerSandwich's picture

Clearly, the tubes of the Crack did a great job of delivering detail and oomph while also softening the edges of the sound somewhat.

Are you certain that's because of the tubes & not the high output impedance?

Tyll Hertsens's picture

That could be too.

Draygonn's picture

Glad you are giving the amp some well deserved attention.  Great match for the HD650s and HD800s. 

Willakan's picture

I just want to see how high the second harmonic is :D!

13mh13's picture

Prob. the most neglected (de)soldering accessory. But I don't DIY (de)solder w/o 'em.

Several brands out there, but some leak, and can cause a mess. Kester makes the best one I've used. The felt tip is probab. the most useful:

n_maher's picture

Great article, Tyll. 

ryebread's picture


Please update this article once the speedball mod is complete!

earwaxxer's picture

I have the Quickie. Also very enamored by it. I'm trying to get Doc to get more of his gear reviewed! I think bottlehead stuff is fantastic.

GilSt's picture

Thanks for the article!

The speedball completely removed the "veil" off the HD650's for me.

uzi's picture

First off, where was that helpful video guide when I was looking to build one of these?

I hadn't soldered in years, but after hearing stuff like the Schiit Valhalla and reading up about the Bottlehead Crack, I decide that an OTL amp was worth having for my HD650... so I built a Crack with the Speedball upgrade.  An initial problem was that I was lacking most of the tooling needed, so I had to pick up a soldering iron, a dmm, etc. etc. ... which wasn't cheap, but stuff I wanted to have anyways.

So, I was pretty close to being a pure rookie at this, took a stab at it and built things up over a few nights.  Got to the initial stage of the Crack build and things seemed to be working decently.  Unfortunately, I shorted something while testing on the way to the Speedball upgrade and blew a fuse.  Bought some replacement fuses, completed the build and then... had decent volume on one ear and hardly any on the other.  Voltages were off for one channel and the works.  A botched build, somehow.

And then began the (longer than I'd like to admit) time of sitting on the project, tinkering here and there... testing all my solder points, etc.  Eventually I figured that I'd get this thing working *someday*, so I went ahead and put in an order for some extra tubes at  When those tubes arrived, I popped some in the sockets, replacing the ones that came with it, and *boom*, it worked!  It was the tubes!  (Kinda hard to know that that was the problem with only one set of tubes, you know.) And the tubes definitely have an effect on the sound of the unit.

So now I have this for some tubey goodness and a Burson Soloist for going solid state for my HD650. They both pretty much exude the qualities you'd expect.  The Crack+Speedball has a great, colored, tube sound to it while the Soloist is exact, precise, crisp and very detailed.  Which one I prefer depends on what I'm listening to.

donunus's picture

By the way Tyll, Was the WA3 barebones stock? The one currently available at the Woo site? I'm asking since there used to be a wa3, a wa3+, and of course tube rolling options.

Dudes place's picture

I being a newb, was wondering if one of these Bottleheads could be used as a preamp for a PA  between a D/A system to warm up the sound. Just mainly wondering about the impedance and output levels.

Tyll Hertsens's picture

...should work just fine. Just like a pre-amp.

Dudes place's picture

I figured it would be fine, was just wondering if impudence would be an issue with output.

thanks, great forum by the way!

neo's picture

Did you have had the Speedball upgrade yet? I'm using the crack with the 6080 stock tubes. Don't know whether to take the tube rolling route or install the speedball..Either way, I'm satisfied with the Stock, just curious about how better can it get.

Edmunds's picture

Thanks for the review.

Would you be able to describe your perceptions of how the Crackhead and WA3 compares to the WA2?

Tyll Hertsens's picture

...haven't heard the WA2.

Hariadi JW's picture

Will Crack do well with Grado PS 1000? Thanks for the advice

nunobartolomeu's picture

Hello from Portugal,

I am wondering if the Philips Fidelio X1 combines perfectly with the Bottlehead Crack OTL, because I have found on Amazon a Philips Fidelio X1 with a lower price than the Sennheiser HD600 and I cant decide wich one is the best buy.

Thanks in advance,

Nuno Bartolomeu

P.S Congratulations for the Website that help us decide the best article we can buy.

Tyll Hertsens's picture

The X1 will work fine on the Crack, but personally I'd prefer the HD600. X1 is more bass heavy, and possibly more neutral relative to the Harman target response curve.  I like them both, but do like the open airyness of the 600.

neo's picture

Isn't the X1 30 Ohms? The Crack doesn't sound very good with low impedance headphones

lenbell's picture

i have the hd650s and will use my laptop as my source for music...what is a good DAC that will work with both the bottlehead and a pair of adam x5 speakers..ideally i dont want to unplug one to listen to the other..thanks