Bottlehead Crack Headphone Amplifier Kit Review

[Strumbringer]

I've done extensive measurement on coupling caps, which is why I'm confident that the notion of cap-rolling is utter bullshit. Ditto double blind listening tests. The data is all on my website, and I've linked to it quite a few times. If there's a measurement you think I've missed, please let me know.

edit: Also, as usual, if anyone wants to bring by a unit to test with different caps, tubes, lockwashers, wire colors, or whatever, my lab is open to any ASR member. I recognize that I'm in a bit of an isolated area, but we're close to Southern Tier Brewery and about a thousand wineries.

Got it! I did a quick search and found the article about why people are obsessed with coupling caps. Will definitely read up and thank you!

 

[SaberCat]

I've done extensive measurement on coupling caps, which is why I'm confident that the notion of cap-rolling is utter bullshit. Ditto double blind listening tests. The data is all on my website, and I've linked to it quite a few times. If there's a measurement you think I've missed, please let me know.

edit: Also, as usual, if anyone wants to bring by a unit to test with different caps, tubes, lockwashers, wire colors, or whatever, my lab is open to any ASR member. I recognize that I'm in a bit of an isolated area, but we're close to Southern Tier Brewery and about a thousand wineries.

Friend, as another engineer I hear your frustration and empathise. I agree a Capacitor is very simple; two conducting plates, separated by insulating dielectric material to store space charge; AC passes according to the capacitive impedance law, DC is blocked. ESR and other simple parameters are fully understood and characterised to be considered in designs. Shouldn't matter how its made if viewed as an ideal component.......except that in the real physical world there have to be other differences which will be and are measurable between capacitor classes, or there would not be so many types available and recommended for different applications. That is not to say there are audible differences in many or most audio applications between these various types - probably if designed correctly into an application there will be none, at least when new.

Electrolytic caps are electrochemical components however. They can suffer reverse polarisation effects causing damage which may or may not be self healing. They also suffer from chemical electrolyte changes due to time, temperature and humidity (if case sealing is compromised particularly), leading to variance in tolerance and leakage of DC possibly while in operation. Probably not audible of course unless the device actually fails....but that is more likely to be a risk in tube equipment than SS. Film caps are closer to the theoretical ideal cap - or at least less likely to exhibit parameter variances due to environmental and age related changes.

Am I saying electrolytic caps are bad for audio path use.....no I am not and they are of course used everywhere.....but old, hot or tired ones may misperform and especially in any application where reverse polarisation of the cap is possible then its not going to function as designed over time. Smaller value electrolytics don't seem to last well in particular - I've measured brand name electrolytic caps with ESR value >5 X the already high "acceptable" value in 10 year old amps, hardly vintage....the 10uF - 47uF ones, and bipolars, are often worst for some reason. Their main advantage of course is much much higher capacitance per unit volume vs film caps, and they are cheap too. As ever there are compromises to be made when selecting caps for any design application.

Film caps are almost always more stable and highly reliable over long periods of time. For those reasons I'd design them into any audio gear where cost is a somewhat lower consideration than performance, or physical size is not a limitation - otherwise, as Bottlehead obviously did, then go for it and use electrolytics - but I'd keep an open mind about swapping them out as there just might be reasons for other types to work -or sound- better.

Of course YMMV, you are quite free to be "reverse polarized" to my viewpoint !

Cheers, SC

 

[SIY]

Friend, as another engineer I hear your frustration and empathise. I agree a Capacitor is very simple; two conducting plates, separated by insulating dielectric material to store space charge; AC passes according to the capacitive impedance law, DC is blocked. ESR and other simple parameters are fully understood and characterised to be considered in designs. Shouldn't matter how its made if viewed as an ideal component.......except that in the real physical world there have to be other differences which will be and are measurable between capacitor classes, or there would not be so many types available and recommended for different applications. That is not to say there are audible differences in many or most audio applications between these various types - probably if designed correctly into an application there will be none, at least when new.

Electrolytic caps are electrochemical components however. They can suffer reverse polarisation effects causing damage which may or may not be self healing. They also suffer from chemical electrolyte changes due to time, temperature and humidity (if case sealing is compromised particularly), leading to variance in tolerance and leakage of DC possibly while in operation. Probably not audible of course unless the device actually fails....but that is more likely to be a risk in tube equipment than SS. Film caps are closer to the theoretical ideal cap - or at least less likely to exhibit parameter variances due to environmental and age related changes.

Am I saying electrolytic caps are bad for audio path use.....no I am not and they are of course used everywhere.....but old, hot or tired ones may misperform and especially in any application where reverse polarisation of the cap is possible then its not going to function as designed over time. Smaller value electrolytics don't seem to last well in particular - I've measured brand name electrolytic caps with ESR value >5 X the already high "acceptable" value in 10 year old amps, hardly vintage....the 10uF - 47uF ones, and bipolars, are often worst for some reason. Their main advantage of course is much much higher capacitance per unit volume vs film caps, and they are cheap too. As ever there are compromises to be made when selecting caps for any design application.

Film caps are almost always more stable and highly reliable over long periods of time. For those reasons I'd design them into any audio gear where cost is a somewhat lower consideration than performance, or physical size is not a limitation - otherwise, as Bottlehead obviously did, then go for it and use electrolytics - but I'd keep an open mind about swapping them out as there just might be reasons for other types to work -or sound- better.

Of course YMMV, you are quite free to be "reverse polarized" to my viewpoint !

Cheers, SC

I'm not an engineer. But... having done the measurements (pretty extensive ones at that) AND double blind listening tests, I'm working from experimental results. And those results show that going to a physically bigger cap (inevitable here) actually degrades the performance. No "possibly," no "might" - actual data, and presented with all experimental details, something that the cap peddlers and tweakers don't do.

Even if your ESR went up by a factor of five, it is irrelevant for a coupling cap, not to mention easily avoided by used name brand parts rated at 105 degrees (the coupling caps in my nearly 40 year old Adcom amp are still working perfectly). And I'm failing to see how a coupling cap used to take signal from the cathode of a CF could possibly be "reverse polarized."

 

[charleski]

I've done extensive measurement on coupling caps, which is why I'm confident that the notion of cap-rolling is utter bullshit. Ditto double blind listening tests. The data is all on my website, and I've linked to it quite a few times. If there's a measurement you think I've missed, please let me know.

edit: Also, as usual, if anyone wants to bring by a unit to test with different caps, tubes, lockwashers, wire colors, or whatever, my lab is open to any ASR member. I recognize that I'm in a bit of an isolated area, but we're close to Southern Tier Brewery and about a thousand wineries.

I tried the link in your signature, but could only find pictures of fancy coffee . It's in the profile if anyone's wondering.

I think a lot of the misconceptions about capacitors are quite deep-seated. I was certainly convinced about the whole electrolytics=bad idea after seeing some graphs a couple of decades ago, but subsequent evidence doesn't match what was shown back then. We still have generally reliable texts like Bob Cordell's book which dedicates an entire section (13.8) to why electrolytics are the spawn of the devil (I have the first edition, not sure if this is changed in the 2nd). According to him "capacitors change their capacitance as a function of voltage" - while this is a recognised problem with ceramic capacitors, I couldn't find any support for his contention that it also applies to electrolytics.

 

[SaberCat]

I'm not an engineer. But... having done the measurements (pretty extensive ones at that) AND double blind listening tests, I'm working from experimental results. And those results show that going to a physically bigger cap (inevitable here) actually degrades the performance. No "possibly," no "might" - actual data, and presented with all experimental details, something that the cap peddlers and tweakers don't do.

Even if your ESR went up by a factor of five, it is irrelevant for a coupling cap, not to mention easily avoided by used name brand parts rated at 105 degrees (the coupling caps in my nearly 40 year old Adcom amp are still working perfectly). And I'm failing to see how a coupling cap used to take signal from the cathode of a CF could possibly be "reverse polarized."

That's cool SIY. I have formed my perspective on audio use cases for different capacitor types based on my own experiences and research over 40 years; everyone is free to do as they see fit in a design or repair scenario as long as it's safe. High ESR or electrically leaky caps can cause lots of issues, including when used as DC blocking caps on a single ended power ouput stage for headphones or speakers (as with the BHC and many older SS amps). In reality with good branded and high quality caps ESR won't likely be an issue for years as you say. I still know that they do fail, because I've pulled out literally thousands of bad ones in old gear I've restored which measured way out of tolerance on both ESR and capacitance. DC leakage is also a known problem for old electros in HT tube circuits at least...but not likely to happen in most SS scenarios.

In tube gear I've restored the coupling caps between the stages have almost always been paper (often leaky to DC after years) or film types.....I don't think I've ever seen electrolytics used for this purpose in vintage tube amps, but if you have one that does and they are working well after 40 years then great stuff. In SS equipment yep they are everywhere - but whenever I see them in old audio gear I will replace them with new electros or -if they will physically fit in the small signal sections- polyester film types, which are closer to being ideal caps.

Cheers,
SC

 

[SIY]

We still have generally reliable texts like Bob Cordell's book which dedicates an entire section (13.8) to why electrolytics are the spawn of the devil (I have the first edition, not sure if this is changed in the 2nd). According to him "capacitors change their capacitance as a function of voltage" - while this is a recognised problem with ceramic capacitors, I couldn't find any support for his contention that it also applies to electrolytics.

As I noted in the posts on my website, it's a matter of application. For coupling, the effects Bob talks about are not relevant. Ditto the stuff from Cyril Bateman. Other than NP0, I wouldn't use a ceramic cap or an electrolytic in, say, the frequency-determining elements of a filter or in certain positions in passive crossovers. But that's not the same as a coupling cap.

 

[charleski]

As I noted in the posts on my website, it's a matter of application. For coupling, the effects Bob talks about are not relevant. Ditto the stuff from Cyril Bateman. Other than NP0, I wouldn't use a ceramic cap or an electrolytic in, say, the frequency-determining elements of a filter or in certain positions in passive crossovers. But that's not the same as a coupling cap.

Most of his antipathy is directed at electrolytics used in the return leg of a NFB loop. But he specifically addresses coupling capacitors as well: "Voltage-dependent capacitance variation will cause distortion at frequencies where the value of capacitance plays a role in setting the gain. For example, variation in the value of a coupling capacitor will change the 3-dB low-frequency cutoff frequency of the circuit, resulting in signal-dependent gain and phase at very low frequencies." (1st Ed. Pg. 266) And at various points he stresses that a coupling capacitor should be "of very high quality."

All this depends on the issue of voltage-dependent capacitance. Unfortunately I can't find any research showing this in electrolytics, except with massive super-capacitors made for electric cars. The evidence you show certainly indicates that there's no measurable change even at very low frequencies. But there's clearly a deep-seated animus against electrolytics among well-respected amp designers, so it's not surprising that DIY amateurs pick up on this.

 

[SIY]

Most of his antipathy is directed at electrolytics used in the return leg of a NFB loop. But he specifically addresses coupling capacitors as well: "Voltage-dependent capacitance variation will cause distortion at frequencies where the value of capacitance plays a role in setting the gain. For example, variation in the value of a coupling capacitor will change the 3-dB low-frequency cutoff frequency of the circuit, resulting in signal-dependent gain and phase at very low frequencies." (1st Ed. Pg. 266) And at various points he stresses that a coupling capacitor should be "of very high quality."

All this depends on the issue of voltage-dependent capacitance. Unfortunately I can't find any research showing this in electrolytics, except with massive super-capacitors made for electric cars. The evidence you show certainly indicates that there's no measurable change even at very low frequencies. But there's clearly a deep-seated animus against electrolytics among well-respected amp designers, so it's not surprising that DIY amateurs pick up on this.

Yeah, it would be nice if Bob backed up his assertions with actual data. But the data might not support the text. I’m surprised that even though this stuff is trivial, no-one seems to have bothered to acquire and publish it.

 

[Varail]

Hi.. can anyone help me please ?

Can you tell from this pic if this is 1.0 or 1.1 ? I want to buy one and need to make sure I can switch it to 220V.

Thank you

 

[Varail]

Your photo shows a 1.1.

I have both a 1.0 and 1.1

The transformer on the 1.0 is a PT 3
The transformer on the 1.1 is a PT 10

GREAT ! Thank you !

Would you by any chance know which and where the wires should be soldered to move it from 110V to 220V ?