Bottlehead Crackatwoa OTL tube headphone amplifier build

[Simas87]

Hi there! IMO, the Espressivo was pretty disappointing from a sound standpoint. Very nice build, but it was outshined sonically by the Bottlehead Crack + SB as well as the Crackatwoa. I am a proponent of DIY, so I would say build a Bottlehead kit

Good evening, thank you advice! I do like DIY projects! Have you ever had your hands on Bryer A2 and Icon Audio HP8? They are on flea Bay for very similar price...

 

[L0rdGwyn]

Good evening, thank you advice! I do like DIY projects! Have you ever had your hands on Bryer A2 and Icon Audio HP8? They are on flea Bay for very similar price...

I have not, sorry! These days all of my gear is DIY more or less.

 

[Rigel]

I have not, sorry! These days all of my gear is DIY more or less.

Congratulations on the job, very nice. Enjoy it.

 

[L0rdGwyn]

Congratulations on the job, very nice. Enjoy it.

Thank you, believe it or not, it has a new owner already! But I think he is enjoying it

This is my current main amplifier, a 6A5G SET of my own design and build from scratch. I haven't shared it here in a DIY thread, I have other amplifiers in various states of completion, I took a very deep dive down the tube DIY rabbit hole this past year.

 

[Rigel]

Very good finishing too. Congratulations.
Maybe one day I will also cheer up with the tubes.

 

[L0rdGwyn]

I enjoy them, obviously the measurements of a no NFB single-ended triode amplifier aren't going to blow anyone away, but I find the sound delightful and tube gear is fun to design.

Here is a recording I made of my system using a Zoom H6 digital recorder, XY mic configuration recording 120 degree stereo. Obviously not the same as in real life, and further compressed by YouTube, but I think it gives a flavor of the sound. This is all analog, system below:

Turntable: Thorens TD 125 MKII (restored and rewired for 2x 3-pin XLR balanced output)
Cartridge: Hana EL MC
Phono: DIY balanced input MC phono featuring Lundahl LL9226XL MC input transformers, triode-strapped D3a / EF86 gain stages, all-in-one passive RIAA
Amplifier: DIY MH4 input / 6A5G output 3.75W single-ended triode featuring Lundahl LL1620 output transformers
Speakers: Snell J/II (restored, re-crossovered, drivers / tweeters replaced)

Maybe I should post this somewhere on a dedicated thread, just don't know if what I like to work on is of much interest to ASR readers.

The song is Moanin' by Art Blakey & the Jazz Messengers.

 

[axtran]

As a former owner then, @L0rdGwyn, what would you recommend to someone looking to purchase a Crackatwoa? What upgrades (outside of tubes) should I get that you found actually high value?

 

[L0rdGwyn]

As a former owner then, @L0rdGwyn, what would you recommend to someone looking to purchase a Crackatwoa? What upgrades (outside of tubes) should I get that you found actually high value?

You might try changing the output capacitors to metallized polypropylene films over the stock electrolytics. BH even includes zip tie mounts to fit larger capacitors. Given the amp comes with the "Speedball" active loads at stock and the power supply is shunt regulated, I would most everything else as is.

 

[SIY]

You might try changing the output capacitors to metallized polypropylene films over the stock electrolytics. BH even includes zip tie mounts to fit larger capacitors. Given the amp comes with the "Speedball" active loads at stock and the power supply is shunt regulated, I would most everything else as is.

Unfortunately, that will do exactly zero for the performance. Well, it might degrade it slightly, but likely not to an audible extent.

 

[L0rdGwyn]

How unfortunate indeed! I wouldn't call cap swapping high value, but it is something @axtran can try and judge for him/herself. Short of major circuit changes (e.g., changing the power supply circuitry and using a Si-based power supply regulator in place of the tube shunt reg, Maida reg or otherwise), swapping out components will not significantly change the objective performance. If you are a believer in making changes based on your own subjective impressions, then try the cap swap, but this is not the forum for that type of discussion.

 

[SIY]

How unfortunate indeed! I wouldn't call cap swapping high value, but it is something @axtran can try and judge for him/herself. Short of major circuit changes (e.g., changing the power supply circuitry and using a Si-based power supply regulator in place of the tube shunt reg, Maida reg or otherwise), swapping out components will not significantly change the objective performance. If you are a believer in making changes based on your own subjective impressions, then try the cap swap, but this is not the forum for that type of discussion.

Spending time and money on something that best case won’t make performance worse is not something that should be recommended.

 

[L0rdGwyn]

...best case won’t make performance worse...

According to the ethos of this forum, that is indisputable fact, other places it is not and it doesn't align with my personal experience. I'm well aware that counts for nothing here. This is not an amplifier for objectivists, if measured performance is the goal, there are well-measuring amplifiers reviewed here at a fraction of the cost of the Crackatwoa.

I do tube DIY for personal enjoyment, I'm not in search of ultimate audio truths, I thought my projects might still be of some interest here. I don't adhere to strict objectivist beliefs, so I won't share my projects on ASR going forward since it will surely be a point of controversy.

 

[SIY]

According to the ethos of this forum, that is indisputable fact, other places it is not and it doesn't align with my personal experience. I'm well aware that counts for nothing here. This is not an amplifier for objectivists, if measured performance is the goal, there are well-measuring amplifiers reviewed here at a fraction of the cost of the Crackatwoa.

I do tube DIY for personal enjoyment, I'm not in search of ultimate audio truths, I thought my projects might still be of some interest here. I don't adhere to strict objectivist beliefs, so I won't share my projects on ASR going forward since it will surely be a point of controversy.

Please understand that I’ve done both extensive measurements and rigorous listening tests of coupling caps. So I’m talking from a position of some experience.

I also have cynically noted that Bottlehead seems to use a lot of design features that I’ve published and discussed on line over the years. Like LED biasing (even using the devices I’ve recommended), CCS loading, cascode current sources… so I’m reasonably familiar with the circuit operations.

The coupling cap stuff is utter bullshit.

 

[raindance]

@SIY - I must say, I tend to agree with you here. I rebuilt a tube preamp and replaced all the coupling caps with recommended "audio grade" polyprops and all I really got out of it was a ton of crosstalk and added noise because the new caps were so large (or should I say HUGE) that they spanned a much larger portion of the PCB. As a result though, it sounds "different"

 

[L0rdGwyn]

Please understand that I’ve done both extensive measurements and rigorous listening tests of coupling caps. So I’m talking from a position of some experience.

I also have cynically noted that Bottlehead seems to use a lot of design features that I’ve published and discussed on line over the years. Like LED biasing (even using the devices I’ve recommended), CCS loading, cascode current sources… so I’m reasonably familiar with the circuit operations.

The coupling cap stuff is utter bullshit.

I have not seen changing from e-lytic to film capacitors reflected in the measurements I've taken, but in certain circumstances I have thought it to be an audible improvement. I won't say that is a fact, only the conclusion I came to personally. If one were to purchase this kit, the opportunity is there to try it and the buyer can develop their own conclusions, or not.

 

[SIY]

I have not seen changing from e-lytic to film capacitors reflected in the measurements I've taken, but in certain circumstances I have thought it to be an audible improvement. I won't say that is a fact, only the conclusion I came to personally. If one were to purchase this kit, the opportunity is there to try it and the buyer can develop their own conclusions, or not.

So because you wasted money, others should.

 

[SIY]

@SIY - I must say, I tend to agree with you here. I rebuilt a tube preamp and replaced all the coupling caps with recommended "audio grade" polyprops and all I really got out of it was a ton of crosstalk and added noise because the new caps were so large (or should I say HUGE) that they spanned a much larger portion of the PCB. As a result though, it sounds "different"

Yeah, in my measurements, big caps (super expensive) picked up significantly more noise than cheap electrolytics. The coupling cap stuff is remarkably silly.

 

[L0rdGwyn]

So because you wasted money, others should.

And we'll end it there, take care.

 

[axtran]

Thanks for the feedback, everyone.

 

[smodtactical]

@lordGwyn really appreciate your work and great amps. TBH I am confused why you would post this stuff here though where most people will never appreciate it because they base their entire lives off SINAD. Pretty sure many people here believe tube amp is outdated and obsolete technology of no value in audio.