Bottlehead Crack Headphone Amplifier Kit Review

[MadMan]

What's this test illustrating again, I think I remembered from an earlier post.....it's showing that the 2nd Harmonics introduced in the amplifier are destructive when it comes to real music rather than synergistic....something along those lines?

Standardized 'normal' Intermodulation Distortion tests only use two frequencies to see IMD. There are a number of standard frequency pairs for this to test capabilities at different frequency ranges. The purpose of a multitone test is that it's meant to be reflect 'real music' (you know, that excuse which subjectivists always bring up because they don't understand that their music is made up of a sum of sine waves anyway) by using more than two tones. It's also more convenient than having to run numerous different frequency pairs.

 

[PeteL]

I hate tubey gear because of said hum and noise. Like, why would you insist on noisier sound! Anyway, with high impedance phones it's less audible so less of an issue.
Schiit's Saga has very little noise which I respect, but it's likely so hybrid it barely qualifies heh

A more diplomatic way to say that would be that it is arguably easier to deal with this with the smaller signal of a line stage.

 

[ElNino]

Here is the multitone with unity gain:

View attachment 80983

Thanks for posting this! I think it illustrates pretty well how high levels of IMD tend to create an artificial "distortion floor" when listening to real music that can be a lot higher than a device's actual noise floor. It comes across as an audible "greyness" behind the music that's not immediately objectionable but fairly easy to pick out by ear once you've heard it a few times. Some R2R DACs have the same issue.

 

[Feanor]

When people say this, they are only making a comment about the variability in the sound of amplifiers in comparison to the variability in the sound of speakers. In other words, compared to the difference in the sound of different speakers, all amplifiers sound the same. When put into this correct context it is difficult to disagree with it. Moreover, the inescapable implication is that for the great majority of people in the great majority of home settings, spending more than a few hundred dollars on an amplifier could only be justified on some other basis than the quality of sound. Or to say this in a way that most audiophiles would likely find more tenable, if you spent more on an amp than half of what you spent on your stereo speakers, you did not spend your money wisely. But of course there is more to it than just sound quality. Very many of us like to pretend that all we really care about is the sound quality when we all know perfectly well that this is not true. It is the aesthetics and intangibles that make us feel like we have been transported into some different realm, or so far into the future that we have lived beyond our mortal years. With the right aesthetics and intangibles, we are left salivating and more than willing to pay whatever price has to be paid for nirvana. Also, a pair of backlit dancing galvanometers helps a whole lot. (One thing that doesn't matter is the quality of the AC/DC conversion, i.e., the power supply. You don't have to be concerned with noise on the DC rails, because all you need to take care of that is one of those little LED doohickeys that Paul at PS Audio sells. )

Laying it on a bit thick, eh Kais? (... Speaking of subjectivity )

Whereas it's almost certainly true that for "great majority of people in the great majority of home settings", the difference in sound of amplifiers is effectively immaterial. Let's understand that no single individual conforms entirely to the "average person" stereotype.

I don't necessarily agree that the price you pay for an amp shouldn't be more than 1/2 what you pay for your speakers: it's good advice for the "average person", no doubt. (That said, I have paid far more than I ought to have for amplifiers ... and I am talking strictly SQ in present contest.)

I do believe in the usefulness of objective measurement. Furthermore I do believe that measurement can shed like on the perceived SQ of components, though the correspondence of measurement to perceived quality is imperfect at the current SOTA. If that weren't so, why would we worry about the difference between the typical AVR and Purifi amp or best measuring DAC? Why would we so assiduously read Amir's reviews?

Finally I do believe that amplifiers can and do sound different, (although competently designed & build amps will sound very similar). Whether you are satisfied with great similarity or a fussier probably depends on whether you are the "average person" or not.

 

[SIY]

Belief is far inferior to evidence.

 

[Balle Clorin]

I have built some Bottlehead kits, very satisfying to build your own amp, and Extremely good building manuals with fantastic support forum.
I know it does not measure perfectly but it is a joy use. Forget about sub -100db differences no one can hear, with tubes you actually listen past the problems if you match the equipment properly..
I recommend to build a kit just for the experience and fun, It is very rewarding to see how the glowing tubes actually can play music..

 

[KaiserSoze]

Laying it on a bit thick, eh Kais? (... Speaking of subjectivity )

Whereas it's almost certainly true that for "great majority of people in the great majority of home settings", the difference in sound of amplifiers is effectively immaterial. Let's understand that no single individual conforms entirely to the "average person" stereotype.

I don't necessarily agree that the price you pay for an amp shouldn't be more than 1/2 what you pay for your speakers: it's good advice for the "average person", no doubt. (That said, I have paid far more than I ought to have for amplifiers ... and I am talking strictly SQ in present contest.)

I do believe in the usefulness of objective measurement. Furthermore I do believe that measurement can shed like on the perceived SQ of components, though the correspondence of measurement to perceived quality is imperfect at the current SOTA. If that weren't so, why would we worry about the difference between the typical AVR and Purifi amp or best measuring DAC? Why would we so assiduously read Amir's reviews?

Finally I do believe that amplifiers can and do sound different, (although competently designed & build amps will sound very similar). Whether you are satisfied with great similarity or a fussier probably depends on whether you are the "average person" or not.

I was just trying to say that it is a bit disingenuous to make sarcasm of the popular notion that "all amps sound the same", because in the correct perspective where this claim is routinely made, it is a perfectly good claim. You may very well be able to hear differences between two different amps of decent quality when one or both of them is turned up past the onset of clipping. It is not so apparent to me that this is possible if both amps are operated below the threshold of clipping. Of course an oddball amp like the one being discussed in this thread would be excluded, because all it would demonstrate is that it is possible to design an amp or amp-like device that makes different headphones sound different. The remaining question is whether you or anyone else can actually hear the difference between a good class A and a well-executed class AB, or between class A and one of the other classes when none of them are clipping the signal. The answer to this question is not entirely apparent to me, but if there is a difference, it will pale in comparison to the difference in sound of most any two different speakers. And this of course is what people mean when they say that all amplifiers sound the same, i.e., that compared to the overt differences in the sound of different speakers, all amps sound the same.

 

[ElNino]

I recommend to build a kit just for the experience and fun, It is very rewarding to see how the glowing tubes actually can play music..

For sure, tube circuits are an absolute blast to build.

Even though I don't have a use case for it right now, I've always wanted to build one of SIY's Red Light District amps: https://syclotron.com/the-red-light-district/

 

[Killingbeans]

If that weren't so, why would we worry about the difference between the typical AVR and Purifi amp or best measuring DAC?

Irrational search for perfection. I use that particular rabbit hole as a personal joy-ride quite often. Focusing on the point of diminishing returns would be a far more rational approach, but that's no fun

 

[SIY]

For sure, tube circuits are an absolute blast to build.

Even though I don't have a use case for it right now, I've always wanted to build one of SIY's Red Light District amps: https://syclotron.com/the-red-light-district/

Much as I hate to say it, I haven’t turned mine on since we moved to Arizona. 110 degree heat discourages me from running my tube gear.

 

[Feanor]

I was just trying to say that it is a bit disingenuous to make sarcasm of the popular notion that "all amps sound the same", because in the correct perspective where this claim is routinely made, it is a perfectly good claim. You may very well be able to hear differences between two different amps of decent quality when one or both of them is turned up past the onset of clipping. It is not so apparent to me that this is possible if both amps are operated below the threshold of clipping. Of course an oddball amp like the one being discussed in this thread would be excluded, because all it would demonstrate is that it is possible to design an amp or amp-like device that makes different headphones sound different. The remaining question is whether you or anyone else can actually hear the difference between a good class A and a well-executed class AB, or between class A and one of the other classes when none of them are clipping the signal. The answer to this question is not entirely apparent to me, but if there is a difference, it will pale in comparison to the difference in sound of most any two different speakers. And this of course is what people mean when they say that all amplifiers sound the same, i.e., that compared to the overt differences in the sound of different speakers, all amps sound the same.

Yes, all fair. Operating within their parameter pertaining to power, speaker impedance, etc., well designed amps all sound pretty much the same -- some much so that most people won't notice or care.

Personally I bought an amp, (Hypex-base), whose cost is about 1/10 of the amp I've been using for several years. I may sell the latter because the sound differences are immaterial and most. (Ok so the old amp is maybe just a touch "warmer" in sound but not enough to matter to me.)

 

[Robbo99999]

Standardized 'normal' Intermodulation Distortion tests only use two frequencies to see IMD. There are a number of standard frequency pairs for this to test capabilities at different frequency ranges. The purpose of a multitone test is that it's meant to be reflect 'real music' (you know, that excuse which subjectivists always bring up because they don't understand that their music is made up of a sum of sine waves anyway) by using more than two tones. It's also more convenient than having to run numerous different frequency pairs.

The nonlinearity shouldn't be conflated with its symptoms, basically. 2nd harmonic distortion of a sine wave is a manifestation of 2nd order nonlinearity in the playback system...but that isn't necessarily going to just produce innocuous and easily ignored harmonics when fed a different signal.

More broadly, you could easily argue against single sine testing on this basis, in fact, unless the desire is to know the nonlinear behavior of the system at a specific level and frequency alone.

Cool, so what actual conclusions are we gonna draw from that specific graph that Amir posted re this particular amplifier?

I'll copy & paste it up here again for reference as it was a few pages back now:

 

[solderdude]

The conclusions we can draw are:
A: The output stage adds about 10dB more garbage under 300 Ohm load conditions.
B: There is a huge amount of harmonics and IM distortion that is potentially audible which you cannot tell apart.
C: The frequency response is 'flat' with a resistive load.
D: Technical fidelity is poor compared to any decent SS amplifier such as the cheaper amp below.

 

[milosz]

Nope it couldn't. The difference between the channels would be 0.013dB with a 300 Ohm load.
The difference in series resistance between 188 and 188.7 is negligible (0.35%)

Where are you getting these numbers "188" and "188.7" ....?

I see that adding a few tenths of ohms in series with the load here would not make much difference, you're right about that. But I'm still curious where you get the "188" from.

 

[KaiserSoze]

Yes, all fair. Operating within their parameter pertaining to power, speaker impedance, etc., well designed amps all sound pretty much the same -- some much so that most people won't notice or care.

Personally I bought an amp, (Hypex-base), whose cost is about 1/10 of the amp I've been using for several years. I may sell the latter because the sound differences are immaterial and most. (Ok so the old amp is maybe just a touch "warmer" in sound but not enough to matter to me.)

I will reiterate that it is not altogether apparent to me whether people with trained hearing (or a lot of experience) can hear the difference between two well-designed amps when neither of them is driven into clipping. In the past I would not have hesitated to say "no", but nowadays I am more in tune to the possibility that the answer might be "yes", which is why I will only say, "As compared to the typical and familiar differences in the sound of different speakers ..."

I am very much impressed by that Hypex Class-D module, the NCore, and by the completed amplifiers built using the module. I am impressed by it because I very much like the very high efficiency, and I like the fact that not only does this module demonstrate that Class D can compete with A and AB in avoidance of distortion, but even up the ante in a way that makes you stand up and pay attention. For a long time the popular view of Class D was that it was okay for car subwoofers and maybe even for home subwoofers, but not for serious high fidelity. Not anymore. No one who is informed would make any general statement dismissing Class D for having excessive distortion.

When I was younger I was impressed by the big gigantic power transformers in powerful amplifiers (and by the ginormous capacitors and diodes of course) but as I've gotten older I've become more appreciative of the different approach to amplification, which avoids the need for a gigantic transformer to supply current that is mainly dissipated as heat within the amplifier. No more 40-lb behemoth sitting on a wobbly A/V stand with tempered glass shelves that you're never entirely certain will not spontaneously collapse into a pile of glass pebbles one day along with all your expensive toys.

 

[DualTriode]

A HD650 easily get -70dB distortion levels at 1kHz whereas the Crack manages -45dB with 300 Ohm load.
At lower voltage levels the distortion may be a bit better for the crack.
Frequencies between 200Hz and 8kHz is where distortion matters the most.

The exception is not the rule.

Take a look at the HD650 impedance plot. It is anything but flat there is a great big huge High Q resonance peak at 86Hz. That means lots of stored energy and ringing in a wide band around 86Hz, not very cool unless you are into flabby bass.

For tube headphone amplifiers I much prefer planar magnetic headphones, the impedance plots tend towards ruler flat and are much more tube friendly. examples LCD2 and HE400i both on my shelf

Thanks DT

 

[Thomas savage]

Bottlehead crack is the best crack a man can buy.

 

[solderdude]

Where are you getting these numbers "188" and "188.7" ....?

I see that adding a few tenths of ohms in series with the load here would not make much difference, you're right about that. But I'm still curious where you get the "188" from.

Amir measured the output resistance as 188 Ohm and since the difference in tolerances was 0.7 Ohm...
Perhaps using 187.4 and 186.7 would have been closer to the truth of the extremes mentioned knowing Amir is always reporting about 1 Ohm too high but this is inconsequential for this case.

 

[solderdude]

The exception is not the rule.

Take a look at the HD650 impedance plot. It is anything but flat there is a great big huge High Q resonance peak at 86Hz. That means lots of stored energy and ringing in a wide band around 86Hz, not very cool unless you are into flabby bass.

For tube headphone amplifiers I much prefer planar magnetic headphones, the impedance plots tend towards ruler flat and are much more tube friendly. examples LCD2 and HE400i both on my shelf

Thanks DT

We are talking Crack and HD650 is it not. Not about (tube) amps in general...

Can you show the huge high-Q resonance (means a very narrow band) peak to exist and can you show, by for instance using CSD that bass becomes very flabby ?
Is 3 octaves really a high-Q resonance peak and 4dB in resistance huge ? Is +1.something dB going to make the bass sound really poor, especially when it is really wide band and only slightly increases 'warmth/body' ?

I did not hear any comments about flabby bass from Amir nor from the hundreds if not thousands of users owning a Crack + HD650 or HD600 or HD800 or Beyerdynamics.

Do note that I prefer to listen to the HD650 with the midbass lowered and do not prefer it increased. I have seen lots of people with great hearing abilities being silly enough to remove the foam behind the HD650 driver thereby lowering damping and increasing midbass even higher than the crack does and claiming the sound has become much better.

 

[pma]

When I see this I will probably post my measurements of Glassware SRPP+ kit. The new version is https://glass-ware.stores.yahoo.net/srppnoval.html
but I have the previous one. It has much better suppresion of mains artifacts then I can see in this review.