Crack 1.1 OTL Headphone Amplifier Kit Specs


Crack 1.1 OTL Headphone Amplifier Kit Specs

“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!”

Tyll Hertsens, innerfidelity

Here is a marvelous video from Tyll of how to solder your Crack kit. Anyone can build this kit!

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“as much as I love great budget stuff, the best-sounding products are always a lot more expensive. Not this time; the Bottlehead Crack amplifier I’m reporting on today goes for just $219 (now $299), and it sounds like it’s five times that price.”

Steve Guttenberg, The Audiophiliac, Cnet News

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“With both the HD650 and the HD800, the Crack delivers one of the cleanest sound, the blackest background, the widest and deepest soundstage I’ve heard on any amp below the $1K mark.”

Headfonia Mike

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For enthusiasts who know their way around hand tools and soldering irons, there is an awful lot to like about Bottlehead’s very reasonably priced headphone amplifier kits. There’s real value in each of these creative designs, though a personal favorite is the entry-level Crack, which sounds much better than it has any right to for just $219 (now $299). My friend Steve Guttenberg of Audiophiliac/CNET fame tells me that the Crack works spectacularly well with potentially tricky headphones such as Sennheiser’s HD-800, giving them a desirable touch of warmth, harmonic richness, and all-around “life.”

Chris Martens, Playback

From Wikipedia: “Crack affects the brain chemistry of the user causing euphoria, supreme confidence, alertness, increased energy – and a craving for more crack.”

That was pretty much Doc’s experience when we built and listened to this new bang for the buck headphone amp. Our initial goal was to come up with another really easy to build, great sounding design that would harken back to Bottlehead’s early days. Crack is our version of classic OTL headphone amp designs of several years ago that were hailed as some of the best sounding of their day. Comparison of our prototype with the $10K Bottlehead reference headphone amp was a bit disturbing. It showed us why the OTL headphone amps from a few years back were so highly praised. The new kit wasn’t quite as good (whew!) but it was way closer than we expected it to be.

This is what we call a Skill Level 1 kit, perfect for first time builders. The circuit is so simple you can build it in an evening or two. A simple circuit also means a low parts count, which keeps the price low, too. Crack is an output transformerless amp designed specifically for running higher impedance (200 ohms or higher) headphones like the many Sennheiser, AKG and Beyer designs.


We employ some old circuit friends in the Crack design:

A Bottlehead PT-10 power transformer feeds a power supply configuration similar to the one made famous in our original Foreplay – ultrafast rectifiers supplying a simple C-R-C-R-C supply – with plenty of capacitance for a quiet background.

A 12AU7 configured just like the “front half” of the Foreplay III is direct coupled to a 6080 tube configured as a cathode follower. To keep the kit price manageable (the kit is about 1/4 of the price of some past OTL amps) we use surprisingly nice sounding electrolytic capacitors as the output coupling capacitors, but of course our kits often induce tweaking – in fact we imagine Crack may become the biggest cause of tweaking yet. You could spend more on different large 100uF film capacitors than you than you did on the kit and spend hours putting in different caps and comparing them. And of course you can tweak to your hearts content tube rolling different 12AU7 and 6080/6AS7 variants.


A single pair of gold RCA jacks, a stereo potentiometer volume control and a Neutrik 1/4″ TRS headphone jack complete the signal path, and the kit comes with an IEC power entry socket so you can use one of those fancy $2500 power cords on your $299 kit if you so desire. Or you can order a really great sounding cord from us for a whole lot less.

It comes in a standard Bottlehead “gravity mount” cabinet configuration where all components mount on a 10″ x 6″ laser cut aluminum chassis plate that sits on a lovely Northwest alder wood base that you assemble and finish yourself. The manual is in PDF format and you can blow up the high res photos to see each assembly step in detail. Here are a few sample pages from the manual

And before you ask, oh yes, like a lot of Bottlehead kits there are circuit upgrades to feed your craving. Consider trying something with an even more intense experience, the Speedball constant current source upgrade.

Yikes! We could end up being responsible for people spending whole paychecks on their Crack habit!

The approximate specs are input impedance 100K ohms, output impedance 120 ohms, gain about 15dB into a 300 ohm load like a Sennheiser HD600, max output about 10V into a 300 ohm load.

Inevitable questions:

“Why three different headphone amps? How do I choose which one I need?

Try looking here, and here’s what users are saying about various headphones used with Crack –

“For the HD650, this amp rivals pretty much anything else I’ve heard”

“I auditioned the crack for a day with HD650s and was blown away.”

“All parameters checked out right off and it’s making the sweetest music I have ever heard and that’s just with a pair of ATH A700 phones.”

“I just got the 600 Ohm DT880 yesterday and can’t tell you enough what a perfect match these headphones are with the crack.”

“Although the headphones I’ve been using with the Crack (Sony MDR-SA5000, 70 ohm) are not an ideal match, they still show off the incredible sound quality of this little amp!”

“None of my other amps has done justice to the AKG K501s like the little Crack. It’s provided a richness of sound which nicely expands on the AKG’s strengths of soundstage and midrange performance.”

“With “Nowhere Boy,” a new John Lennon biopic, the Bottlehead Crack amplifier and my old Sennheiser HD-580 headphones kept me totally absorbed in the film.”

“For those of you wondering about the new Crack amplifier, this is also very sweet and enticing set up. I think I heard the version with the extra add-on circuit. That was lovely with a variety of headphones, including the HD-800s. Ahhh.”

“the amp really sings now with the Etys, and with AKG K701s”

“This is now my favorite amp for my Sennheiser HD800s.”

“As for the sound, with my Beyer dynamic DT880’s (600_ohm)….Super sweet!! highs are smooth airy & detailed, ….midrange is very organic, detailed and transparent,…… bass extends deep and detailed (no wanting for any additional bass with the DT880’s….BTW)… and the soundstage extends well outside my head….”

“What an amazing amp! Dead quiet, the bass has incredible slam and definition. Brushes against a drumhead are stunning. It does a better job with my HD-650’s than my K-702’s but not by much”

It stands to reason that some folks will prefer S.E.X., some want Smack and some will prefer Crack. Any of them can lead to a euphoric experience.

“But can’t I turn the Quickie into a headphone amp for less?”

Yeah, but it was really designed as a preamp. And in fact it makes a better sounding preamp than Crack, and Crack makes a better sounding headphone amp than Quickie. Of course there are folks who like to have Crack and a Quickie. Both are inexpensive and readily available.

“What tubes should I use?”

For the introductory run we resurrected another old Bottlehead favorite for this kit – the “tube lottery”. Doc happened to have a large stash of old stock 6080 tubes of various brands as well as a couple hundred of the random old stock 12AU7s we used to pack with the original Foreplay kit. We decided to use these until the supply ran out, so we could get the introductory price down another $30 from what we initially worked out. The demand for Crack has been quite high and those tubes have indeed run out, but we are continuing to hunt down NOS 6080 tubes to include in your kit. That said, you could use not only 6AS7s and 6080s, but also 5998s, 421As, 7236s, and maybe some others for the output stage, and the input tube could be changed to some other dual triodes like 6922 or 6CG7 with a little care taken to do the proper tube socket wiring for the heater pins. This kit is so new that we haven’t yet explored all the possibilities.

“Can I put an output transformer on it and use it with speakers?”

Hey, once you buy it, you can do anything you want to it! However we will suggest that we have kits that are much better suited to the purpose, like the S.E.X. kit.

“Can you make me a custom version with multiple inputs, a selector switch and a stepped attenuator?”

Check out the Crackatwoa




Here is a nice review on Head-Fi, from Bill Way

and another nice Head-Fi review, by Loquah

OK…I’m gonna gush a little. I have been in the audio hobby for over 40 years and seriously into headphones for about a year and a half. I’ve tried ortho’s and have come to the conclusion I prefer dynamics. I also tend to prefer tubes to solid state. If you are a detail freak, ymmv, but for me it’s tone, tone, tone.

I have heard the buzz for some time about the Bottlehead amps and how good the Crack is with a high impedance phone. I have to say…I am NOT disappointed! I have other highly regarded, far more expensive tube headphone amps, but there is something about the bottlehead and the HD600’s or 650’s that is so far better than it ought to be at the price point. I don’t listen to metal or much rap, but pretty much everything else. Diana Krall singing “Little Girl Blue” is the best I’ve heard it…and “Santiago” by Acoustic Alchemy pulls you into the soundstage.

I’m not a believer in $50 giant killers…but at the price point, the Crack and the Senns are good enough that I’m thinking about selling my high priced stuff and getting lost in the music.



hibuckhobby on Audiocircle

Crack teaches another audiophile important troubleshooting skills

I discovered the noise problems I was having with my Crack.

Firstly, I was getting a little interference from my system-solved by moving the Crack forward.

Secondly, all my testing and resoldering eliminated any faulty solder joints and now the Crack is dead quiet.

Thirdly, the consistent screeching sound that I heard for three nights in the left channel disappeared when my snoring wife turned over in her sleep. My left ear is very sensitive and she is facing that way in bed behind me. Her snoring is very high-pitched and very rhythmic and my HD650 added it to the music I was listening to. Of course when I lowered the volume I still heard it at the same level. And with the magic of a strip of electrical tape I ….

In case you are wondering. She always goes to bed at the same time every night. I don’t hear her go to bed when I am wearing my cans. She falls asleep in the same position while reading, her IPad is backlit so she does not use a lamp and begins her snoring around midnight when I begin hearing the “tube” noise for at least thirty minutes. I did not realize what was happening because the noise was soooo consistent. Talk about having a “DUH” moment.

Seriously, the Crack is awesome and so is the feedback on this forum. If I had not removed my headphones on that third night I would continue guessing a noisy tube. Fortunately the tubes are burning in well and are really sounding smooth and balanced.

Mike B. on the Bottlehead Forum

Holy SH*T does this thing sound good.

I was shocked that I put the thing together correctly, let alone that it makes such amazing music. It’s enough to make you into one of those motivational If-I-Can-Do-It-Anybody-Can people.

irishsammy on

Even in stock form, the crack is surprisingly detailed, punchy and dynamic for an OTL tube amp, and it only gets better with tweaks. You have to love those rare moments in life when the reality of a product actually surpasses high expectations.

skeptic on

Man this thing sounds like a dream. Thanks for all the input guys, this community truly lives up to its reputation.

brando666 on the Bottlehead Forum

I just swapped out my Asgard for the Crack/Speedball and it really brings these headphones (HD650) alive, its unbelievable and somewhat surreal. The depth, clarity and soundstage is outstanding. These should come bundled with this amp! Great combo…Kudos to Doc and his crew!! I can’t wait to experiment with tube rolling. I hear its fun.

SpaceUnicorn9, on Head-Fi

Just finished a few 3 hour long listening sessions. Are you guys seriously planning to tell me it gets better than THIS when I upgrade to Speedball? Now I know what everyone means when they sing praises of Tube amplifiers and particularly the Crack. I cant stop playing every song in my library and I have thousands which I am listening and rediscovering. Just WOW. Kudos to you Doc B for one hell of a kit.

PS: I told my dad(a big audiophile while I was growin up) to come and test out this amp with his classical music CDs and now he wont get off the recliner I had set up beside the amp!

sanadsaad on the Bottlehead Forum

First amp build, though I’m not quite fresh to soldering and electronics. I spent a few years in the Army working on Avionics for the UH-60 Blackhawk and CH-47 Chinook. Received my much anticipated package from Bottlehead yesterday 6/6 at around 1:00pm. After working on it from around 4-10pm, I had all of the soldering done on the chassis. I went downstairs and glued the based together and went to bed. When I woke up this morning I ran through all the resistance and voltage checks without issue. I’m really amazed at how easily the whole kit went together.

At about 10:00 I hooked up my new Schiit Bifrost DAC to my PC, hooked up the Bifrost to my baby Crack, and my brand new Beyer DT880/600s to the Crack. Now I know there is supposed to be some burn-in time associated with all the new equipment, but WOWOWOW does it sound amazing already!! I was seriously curious if the overall investment would pay off, and I’m happy to say that it was worth EVERY penny to get setup with some proper hi-fi. I can’t thank Bottlehead enough for providing such an awesome amp at this price. Something about assembling your own kit is just SO satisfying as well.

I just can’t believe how QUIET the amp is. No static, no hums, buzzing, just crystal clear music. Now I can truly listen to everything that was recorded. I won’t rabble on as I’m sure you guys know all of this already, but I wanted to take the time to post that my build came out better than I could have imagined I have yet to order the speedball kit, but I’m anxious to see what it adds to the equation some time in the future.

From the package to my ears in less than 24 hours!

Thanks Bottlehead!

audioclass, on the Bottlehead Forum

The instructions the came with the kit were easy to follow. The sound is incredible, just as everyone else has said.

pshinn, on the Bottlehead Forum

I got my Crack/Speedball recently expecting some cheap fun with good amount of coloration, but I’m seriously surprised by how good this amp sounds. Much more neutral than I had anticipated, with excellent control and detail. This is a great amp period. Crack and HD800 are making some sweet sweet music right now…thanks and kudos to the folks at Bottlehead.

peanuthead, on Headfi-org

After frying one of my LEDs, the Queen/Bottlehead was nice enough to send me a replacement.

Everything checked out so I fired it her up and plugged in my new (to me) cans.

It’s after midnight and I’m still listening. The sound is so engaging I can’t stop.
Ottmar Liebert, Ray Charles, U2, Willie Nelson, and now some Yo Yo Ma.

I now know what people mean when they say “black background”. There have been a couple of occasions tonight when small sounds were staged such that I turned my head to see if it was a live sound in my room.

This is my first piece of tube gear – I can’t believe I have been missing out on this all these years.

And to think I built/wired this thing up myself.

I’m astounded by the sound I am hearing. Thank you Bottlehead folks for a fun and fantastic sounding amp.

I’ll follow up with pictures of the completed Crack tomorrow. Too busy listening right now… :-)

sladef34 on the Bottlehead Forum

well, almost a year later and over the holidays, I finally built my crack w/ speedball kit. having built a couple of bottlehead foreplay preamps before, I knew exactly what I was in for – straight forward instructions, quality components, and something to marvel at in the completed build. true to form, the crack was much fun to put together and I was very happy that there were no problems at all with the build. I auditioned the crack for a day with HD650s and was blown away. in stock form, this amp rivals most other amps that I have had the pleasure of listening to. after what couldn’t even be called a break-in period, I went to work on the speedball upgrade which went flawlessly as well. the upgrade is well worth the minimal cost IMHO and while i’m no audiophile, the upgrade really does tighten and give more depth to the music. the final touch was the tung-sol 5998 and clear top 12au7a – another worthwhile upgrade. thanks again to Zlobby for putting this whole thing together and to Doc, Eileen, and the entire Bottlehead team for this amazing amp!

Dynagroove, on

Oh my. Never thought a headphone could sound this good.

Hey all.

Got my kit in Thurs. Started soldering last night and just finished it today.
All parameters checked out right off and it’s making the sweetest music I have ever heard and that’s just with a pair of ATH A700 phones. Just ordered a pair of HD600 this morning so I’m sure they will be a second wow factor.
This is the 1st time I’ve built anything like this and it went off without a hitch.
I’ll post pics a little later tonight…

TonyMc, on the Bottlehead Forum

I just got the 600 Ohm DT880 yesterday and can’t tell you enough what a perfect match these headphones are with the crack. Just so much texture and detail.

Now I just need to do the speedball upgrade and roll a few tubes…

TonyMc, on the Bottlehead Forum

I’m delighted to report that my crack + speedball are up and running! All voltages read exactly as they should, and it sounds absolutely fantastic. I’ve never heard Billy Holiday’s “Songs for Dintingue Lovers” sound so good.

When properly paired with high impedance phones, the crack has a serious “wow factor” that does not require golden ears to appreciate. It is a night and day improvement over any portable amp I’ve ever heard and bests many/most well regarded commercial desktop options as well, irrespective of cost, per my experience at CanJam. My prior Woo 3, for example, even with pricey nos tubes, is thoroughly outclassed by the crack.

hopeful, on the bottlehead Forum

First, let me say thanks to the forum and the excellent instructions that come with the kit. Much to my amazement the Crack actually worked after I finished building it. I am not good with building things but I was careful and slow and triple-checked everything. It sounds wonderful-black quiet background, wonderful bass and midrange and highs that are sweet and delicate without being at all harsh. All for $200.

Now, I did discover some little things that may help other newbies. First, take your time and only work for an hour or two at a time. Plan ahead and read the directions several times and run through your mind where things go. Next, give your solder iron plenty of time to get hot. It took mine about 15 minutes because it was cheap. Also, the small tube in front barely glows so I was freaked out when I couldn’t see the glow. But i turned out the lights and could see it but it is faint. Get yourself a good digital readout meter. It has many uses and is worth the money so you can be accurate. The specs on resistance and voltage readouts are quite variable, as it says in the manual. If your readings are in the ballpark , don’t worry about it. I melted one of the terminals on the switch even though I was warned in the manual. It is easy to do even with a 40 Watt solder iron. I used a magnifer with a ring flourescent lamp and it was invaluable. I didn’t need alligator clips on the meter since the negative probe fit right into #11 tab. Radio Shack has 2% Silver solder and it was cheap and easy to use. I also used a “third hand” base with alligator clips and a magnifier-nice but not essential.

I would encourage anyone with an interest to try this kit. Believe me, if I can build it, you can build it. You will be rewarded with an excellent headphone amp- on par with my $700 ASL tubed amp. Enjoy!

musiciseverything, on the Bottlehead Forum

Preliminary Listening Impressions:

Although the headphones I’ve been using with the Crack (Sony MDR-SA5000, 70 ohm) are not an ideal match, they still show off the incredible sound quality of this little amp! First and foremost, the amp is as quiet as a tomb….a very pleasant surprise considering the AC heaters. The music that leaps out from that pitch black background is very dynamic, with excellent balance from one frequency extreme to the other. The bass is taught and deep, very well defined and powerful. The mids are revealing, but not harsh. The highs are detailed, but not in a way that is
shrill or fatiguing….I can listen to this amp for hours without interruption.

Most importantly, this amp is incredibly ‘musical’! I don’t have to crank the volume to be able to hear deep into the recording, and sonic cues normally lost with other amps flow right through this simple circuit….now I understand why Doc B. named this thing ‘Crack’, it is intoxicating! ;-)

I’ve got a few upgrades planned for later, but I’m really not in much of a hurry to get ’em done, as the amp sounds fantastic as is. When they do get done, I’ll keep this thread updated.

Stay tuned….


Mikey, on the Bottlehead Forum

The Crack is the amplifier of choice while exploring my budding interest in high resolution audio downloads. it’s being fed from Audirvana running on my MacBook Pro via a late model HRT Music Streamer II cabled with Audioquest Jade interconnects. None of my other amps has done justice to the AKG K501s like the little Crack. It’s provided a richness of sound which nicely expands on the AKG’s strengths of soundstage and midrange performance.

My thanks to everyone at Bottlehead for this lovely little kit and the happiness it’s bringing.

SPaulMac, on the Bottlehead Forum

“With “Nowhere Boy,” a new John Lennon biopic, the Bottlehead Crack amplifier and my old Sennheiser HD-580 headphones kept me totally absorbed in the film. The scenes with a teenage Lennon (Aaron Johnson) and Paul McCartney (Thomas Sangster) learning to play guitar together in John’s living room sounded so realistic I felt like I was eavesdropping on history. When they start playing in clubs the soundstage expanded, and the Sennheisers put me in the best seat in the house.

“King Kong” was a treat, especially the jungle scenes with the giant insects and bird noises coming from all around my head. True, you’re not going to get bona fide surround sound over headphones, but the Sennheiser HD 580 and Crack amp produced a remarkably open soundscape. Closed-back headphones, like Monster Beats Pro, confined the sound to the space between my two ears, but the Beats did a better job when Kong and the dinosaurs got physical in the jungle. I could feel the weight being thrown around with their body slams.”

Steve Guttenberg, The Audiophiliac,

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ok so the amp has been burning in for about 4hrs now and I have a moment to listen without the dogs wanting to go outside or my wife wanting something, spinning Mingus Ah Um… I can’t get over how dark the background is, no hum at all, this amp is dead quiet, channel balance is very good. I can’t get over how great this sounds, treble is excellent, crisp and well defined without being tinny or harsh. Bass, at least what there is to be had on this LP is “correct” sounding, the bass sounds deep and natural, the piano and mids are silky smooth… I’m in love. I was going to play Dark Side of the Moon next but I think I might have to bust out some Gorillaz that a buddy in the UK sent me as a gift for my birthday this year, there is definitely some bass on that one ;) meanwhile I’m going to continue to put some more hours on this amp.

As someone who has built many different kits, and a few things from scratch, this kit is the Gold Standard man let me tell you… anybody on the fence or unsure if they can assemble one of these, I can’t think of a better “first kit” for anybody. The components, the instructions, you simply can’t go wrong, take your time, don’t rush it, and you will have a seriously fantastic sounding amp, not to mention the satisfaction of having put it together yourself.

hasafraker, on the Bottlehead Forum

Impressions from the Seattle Head-Fi meet –

Dan Schmalle and Queen Eileen: The Crack is amazing. I’m sure someone would have tackled me at the door, but I really wanted to just run out the door with it and keep it for my own. I’m sure your mega tape system had a lot to do with the great sounds I was hearing. Never mind. The Crack is seriously good for not serious money. Well done!

Head-Fi member bhjazz

Particularly stunning to these ears were The Tape Project and Bottlehead Crack. There is crack in my future.

Head-Fi member curbfeeler

For those of you wondering about the new Crack amplifier, this is also very sweet and enticing set up. I think I heard the version with the extra add-on circuit. That was lovely with a variety of headphones, including the HD-800s. Ahhh.

Head-Fi member flatmap

More impressions –

I’m writing just to add my voice to the chorus: The Crack headphone amp is an excellent kit. It was my first build ever and I’m still amazed that the thing actually (1) works and (2) sounds great. The supplied RCA 6AS7 and Toshiba 5963 tubes sounded pretty good with Etymotic ER4-S IEMs, but I replaced them with a Tung-Sol 5998 and an RCA 6680 “clear top.” The result: lower noise floor and the amp really sings now with the Etys, and with AKG K701s. Many thanks to everyone at Bottlehead for a great experience. Crack was my first kit, but it won’t be my last.


fipple8, on the Bottlehead Forum

This is now my favorite amp for my Sennheiser HD800s. I have a bunch of other amps – including OTL tube jobs: Little Dot MK III, Cavalli BIJOU- and solid state: CK² III, RS Hornet, Audio_GD FUN, Audio_GD Compass, M³, and an unfinished ß22 / δ22. Oh, and one hybrid- a modded Musical Fidelity XCAN V3.

Head-fi member milosz, on the Bottlehead Forum


Dear Eileen & Doc,

My dose of CRACK with SPEEDBALL chaser arrived yesterday.

I have been using a Schiit Asgard with a Meier Audio Corda StageDAC to burn in my Beyerdynamic DT 880 600 ohm MANUFAKTUR fones.
Source is the coax digital out from a Toshiba DVD player, as I recently moved and my 14 year old NAD CD player gave up the ghost on power up :-( .
Being a nub to headphones, I thought that sounded great. Was anticipatin’ the arrival of some bottled goodness, tho’.

Last thing I listened to on this system was an MP3 world music compilation that I put together (great for burning in as it lasts 5 and a half hours).

I unpacked your product, plugged in the toobs (or valves as we say down under), hooked it up and flicked the switch.
I intended to to wait half an hour to let the toobs warm up. But impatience got the better of me, and I had a quick listen after 5 minutes.

Within a nanosecond, I heard a cymbal strike.

What struck me immediately was that I was listening to a cymbal, as opposed to a 16bit / 44khz facsimile of one.
I was instantly hooked. Your website should have a surgeon general’s warning on it.

Now, to be fair, the Asgard sounds great for the price & your assembled product costs twice as much as it, delivered to Australia.
But, to quote Dan Brown, I now see that cross-dressin’ trannies are the “dark con of man”.

Thank you, thank you, thank you so very, very much for not falling prey to such a con, and making bottled goodness affordable for working class nubs such as myself.

Yours forever in drooling thankfulness,

John Tuggey,

Morisset, NSW, Australia.

As for the sound, with my Beyer dynamic DT880’s (600_ohm)….Super sweet!! highs are smooth airy & detailed, ….midrange is very organic, detailed and transparent,…… bass extends deep and detailed (no wanting for any additional bass with the DT880’s….BTW)… and the soundstage extends well outside my head….truly amazing kit design here gentleman, & the value per dollar is fantastic. So a big congrats to the designers on this one!!….I must say, I really enjoyed building this kit, a most relaxing way to spend my evenings….it’s been 35+ years since the last time I tackled the dynaco and/or Hafler kits…and it was very enjoyable getting back into kit building again, especially when the final sonic results are this good.

ddemy on the Bottlehead Forum

Oh yeah it’s bang for buck! If you can solder and follow directions this has got to be the best tube amp deal out there right now….

I just installed the Speedball upgrade, it’s VERY good. Much more improvement than the cap upgrade that I tried first.

Head-fi member nsorens, on the Headfi Forum

Crack at Can-Jam 2010

To my ears, the best sounding thing I heard at the show was the Bottlehead Crack amplifier. That thing beat all those $5,000 amps IMHO

Head-fi member milosz, on the Head-fi Forum

The first Crack users describe their experience with Crack

What an amazing amp! Dead quiet, the bass has incredible slam and definition. Brushes against a drumhead are stunning. It does a better job with my HD-650’s than my K-702’s but not by much. Right now I’m feeding it Apple Lossless via a RWA modified iPod. Blows away my DarkVoice 336 and my Woo Wa3. In fact I just gave the DV to my son-in-law.

Dead simple to build and incredible sound. Doc, you guys rock!

roger_s on the Bottlehead Forum

“Well, I think BH has another hit on their hands with the Crack OTL amp. I finished mine on Saturday morning and have been “hooked” ever since! I’m having a hard time wrapping my mind around how such a simple circuit can sound so good. Bass is thunderous and tight….mids warm and present….and treble crisper and more detailed than any transformer coupled design I’ve heard, even my enhanced S.E.X. amp. The amp just sounds “right” – very balanced without having any solid-state coldness or glare. In fact, I’d go as far to say that this OTL amp has all the bass and speed of good solid-state with the warm mids and non-fatiguing highs of tubes. In short, the best of both worlds – and only $199! ( $299 as of 08/16/16 – ed.)

Compared to my enhanced S.E.X., the stock Crack is very close. The S.E.X. amp maybe sounds a touch warmer, with highs that aren’t quite as eye-blinkingly clear. Bass is similar, though the Crack seems to go lower and definitely sounds tighter. I’m surprised that the two amps would even be comparable, actually, as I remember there being a much bigger sonic gap between my headphone-kluged Quickie and S.E.X. amp. The Crack gets about as loud at full power as the S.E.X. amp through a pair of 250 ohm Beyerdynamic DT880’s. Even 32 ohm Grado SR-60’s work very well on the Crack, though I’m not a fan of how they sound on good gear (the bumped-up mids and treble work great for wimpy SS-amps in iPhones and the like, but are overkill, IMO, on tubes). It’s nice to have a headphone amp that stands well on its own – I can now do a lot more serious listening in my library/computer room instead of always having to juggle discs in the living room to use the S.E.X. amp. And, I don’t feel like I’m missing out on anything. I would imagine the upgrades will only make this amp better. I have the 6080’s less modest cousin, a new-production Russian 6AS7 (a great “showoff” tube, IMO) on its way as well.

Kudos to BH for getting such a great product out there so quickly! I’d be interested in hearing other people’s first reaction to Crack……”

Dr. Toobz, from the Bottlehead Forum

“I do have a couple of amps in my gear list that I don’t really use very often (ASL Mg Head OTL and Eddie Current EC-01). Having the Crack will keep me from ever using them again”

ironbut, posted on the Head-Fi forum

“I like it.

It can definitely run with the big dogs. Incredible, especially when it only costs $199! ($270 as of 2/12/12 -ed.)

I kind of expected a similar sound to the Wheatfield HA-2 that I just sold since it uses the same 6080 tube, but it’s cleaner & more detailed.”

Todd R, from the Bottlehead Forum