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Bottlehead Crack Headphone Amplifier Kit Review

Mad_Economist

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I'm proposing a test model that is common/routine/normal and has been used every day for close to 100 years in university and corporate research settings. Perception, learning, memory. This is in fact old-hat textbook science. Take it or leave it. Deny it or learn it. Ignore it or embrace it. Science is notoriously inefficient and costly. The EU spent billions of euros and decades building the Large Hardron Collier (CERN), and wasn't sure that it would work. Billions spent on a risky project.

Human Factors is mainstream science:

https://journals.sagepub.com/home/hfs
https://www.hfes.org/about-hfes/what-is-human-factorsergonomics
https://www.verywellmind.com/what-is-human-factors-psychology-2794905

My view is that the endless bickering in audio between the objective and subjective crowds likely follows from the lack of resources to appropriately test relevant phenomena (e.g., documented and predictable human illusions/internal cognitive constructs). Those experiencing illusions sense what they sense and this likely can never be tested with the objective measurement devices now used. The closet thing that comes to mind are functional Magnetic Resonance Imaging tools (fMRI) that scan the brain as people engage in a task, but the magnets would interfere with audio and render it useless. Useful answers might indeed require a shift to another more structured setting. But audio is just a hobby.

Genuine audio science is something very different than reporting standardized measurement summaries. I encourage people to avoid freezing on the technology and tools of a given era when newer computational resources might finally answer some of the weird, ephemeral, and dare I say "euphonic" things with audio. As always I'm not much of a believer in euphonic factors, I just seek scientific explanations that build on 100 years of data from 1,000 universities and corporations.

I worked with a professor once who was testing words that change meaning when the accent changes. The project ran into issues because the team couldn't tell the difference between RECORDED words that were supposed to mean different things. They often mixed up their RECORDINGS and therefore could not apply the correct test conditions. As everyone used and heard these words in normal conversations, no one outside the team believed the findings. ASR and others risk a similar outcome if/when they deny similar and frequently reported subjective experiences. The underlying question for this and all things in human experience is: "What part of the sensory experience is external to the person, and what part does that person construct in their own head? How was it transformed?" This is the essence of research psychology. Your smartphones were developed and refined with research psychology (e.g., Siri, Alexa, and much more).

Sample words that change as the accent changes:

https://jakubmarian.com/english-words-that-change-meaning-depending-on-the-stress-position/
In the spirit of charity, let me attempt to clarify where you are running into resistance here.

You've pretty chronically failed to differentiate between testing for the audible elements within a signal and testing factors which influence perception, including those not present in the signal. I don't think anyone here is arguing that there is no qualitative experience on the part of people who report hearing these "euphonic" phenomena - the argument is about whether that perception is actually related to the signal characteristics, and that's what @SIY is proposing to allow testing. If you cannot discern the difference between two products on the basis of their signal impacts, then what difference you discern must be from other causes - this isn't, nearest I can tell, a point of disagreement between you, me, or SIY. Heck, I don't even think we'd disagree that if the sighted impact of a component on perception of an audio system's sound was positive, this would be a design merit - if a lightbulb on top of the amp makes people, on average, enjoy the music more, that's value to the customer in my books, regardless of the transfer functions. Edit: Although note, this claim isn't being accepted out of hand - I'd actually like to specifically see it tested, in fact.

FWIW I would agree that measurement blocks from an APX aren't particularly science, particularly using expressions of relative nonlinearity that were derived in an era where twin T filters were novel, and I'm a pretty vociferous antagonist to people claiming that a low-quality-by-the-standards-of-amplifiers-or-DACs measurement implies poor quality sound necessarily (admittedly, mostly because I just keep shouting about how the weakest link in the chain is the transducers almost regardless). If folks are taking a hierarchy of SINAD performance as a hierarchy of subjective perception then...well, that, too, can really only be attributed to psychological factors :p I would expect an ABX between something from the low quintile of Amir's SINAD hierarchy and something from its top to produce a similarly null result, because the signal differences aren't dominating the differences of perception there.
 

solderdude

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In the spirit of charity, let me attempt to clarify where you are running into resistance here.

As the issues here are complex perhaps this should be:
In the spirit of charity, let me attempt to clarify where you are running into impedance here. :D
 

Mad_Economist

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As the issues here are complex perhaps this should be:
In the spirit of charity, let me attempt to clarify where you are running into impedance here. :D
:rolleyes:
 

solderdude

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O.K. so wildly varying impedance ?
 

Wombat

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The opinion could be that the moon is made out of cheese. It does not matter if its a valid opinion.
My english is not good enough but if a opinion is conclusively verified dont we talk than about knowledge?

Exactly.:)
 

mhardy6647

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Remember -- it is useless to be a resistor.
(or, if one prefers, resistance is futile)

Just chant with me -- Ohm...
 

solderdude

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resistance-is-futile.jpg
 

L0rdGwyn

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This kit was my introduction to DIY audio a few years ago, I now spend a large part of my free time designing and building my own tube gear. Whether tube or solid state, I tend to think it sounds better when you build it yourself :) it won't win many measurement contests, the BHC kit is a fun project that could open a door to a very enjoyable area of the hifi hobby. The pursuit of knowledge, its implementation, and the reward as you grin ear-to-ear in your listening room, having completed your latest monstrosity, there's nothing like it! Thanks, Bottlehead.
 

pma

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DualTriode

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Controversially, I would argue that a blocked canal equivalent measurement - the sort you'll get with an omni capsule at the canal entrance location - can be pretty suitable for headphone purposes. Some of my peers would advocate acquiring one of these cheap Chinese IEC60318-4/IEC711 couplers that're everywhere these days, which together with a 10mm or so canal extension from your pinna would match the load of a real ear.

However, the geometry of your pinna is extremely significant to the transfer function, and it's very unlikely that neoprene has the right mechanical characteristics even if you could match the ITU-T P57 spec for the pinna's geometry. This would likely pose the single largest issue for your DIY coupler relative to a proper system.

Why the AECM206, out of curiosity? You could get a 43AG for less money and get the latest and greatest pinna.


The utility of spectral decay plots for headphones is pretty dubious - at low frequencies, this would be exponentially more true...

Hello All,

Artificial ear for testing fun:

For grins I just ordered a cheep ($130) IEC711 artificial ear on ebay plus a couple of molded silicone ears at about $9 each. It is several weeks shipping time. This should work well with the APx555 and APx1701 now on my bench.

I bought the cheep stuff prior to the GRAS 45CA $13,000.00. The GRAS is 5 weeks lead time. now on hold.

https://www.ebay.com/itm/283874335377

I am interested in testing the impedance interaction between high output impedance amplifiers and headphones like the HD6xx’s That have high resonance peaks in the mid-bass frequencies.

Thanks DT
Cast Rubber Ear.jpg
 

Jimbob54

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Hello All,

Artificial ear for testing fun:

For grins I just ordered a cheep ($130) IEC711 artificial ear on ebay plus a couple of molded silicone ears at about $9 each. It is several weeks shipping time. This should work well with the APx555 and APx1701 now on my bench.

I bought the cheep stuff prior to the GRAS 45CA $13,000.00. The GRAS is 5 weeks lead time. now on hold.

https://www.ebay.com/itm/283874335377

I am interested in testing the impedance interaction between high output impedance amplifiers and headphones like the HD6xx’s That have high resonance peaks in the mid-bass frequencies.

Thanks DTView attachment 82675
At that point I'd suggest a new thread for your exploits.
 

DualTriode

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Okay when I assemble my BlockHead Headphone test stand I will start a new thread to post the results.

Meanwhile, how does the Bottlehead Crack Headphone Amplifier sound and test different than say a Geshelli Archel2 amplifier when driving a pair of HD650’s?



Thanks DT
 

solderdude

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The reason is voltage division, nothing more.
The harmonics won't show up in any FR test they are too small.

You can calculate the difference, simulate the difference and even measure the difference even on the cheapest DIY rig you can make.

You can measure the impedance of a headphone with 1 resistor, a soundcard and a simple signal splitter cable.
 

Paperdragons

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I'm happy to see tubes being reviewed as I've wondered for a long time what they actually do to FR. For now I'm happy with tuning myself via Peace EQ.
 

Paperdragons

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The monotonically decreasing harmonic distortion (ie. HD2 > HD3 > HD 4 > HD5) and total lack of high order harmonics is, as they say, reassuringly “audiophile approved”

For over a decade (or two) the Bottlehead Crack was the de-facto partner of the HD600/HD650.

Now I better understand why.

Now if someone can design a VST/AU plugin to emulate this amp, that would be quite.. something.

A couple of SMSL dacs have a mild version. The su-8 in particular has a hilarious 'brickwall' option.
 
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