Bottlehead Crack Headphone Amplifier Kit Review

[Veri]

Nice. I've had the Dayton's in my Crack/SB for years. Love the amp. I just completed building an S3X with 4 pin XLR jack and AudioNote pot. Awesome.

Any pictures to do it justice?

 

[SIY]

I did a blind A/B/X of Panasonic polarized electrolytics vs Dayton film caps as output coupling / DC blocking caps in my Crack/Speedball and all the listeners showed a statistically greater than chance ability to hear the difference. And the "preference" was 100% for the film caps. Just throwin' this out there.

Could you please describe procedures and controls in some detail? This is an extraordinary claim.

 

[SaberCat]

I did a blind A/B/X of Panasonic polarized electrolytics vs Dayton film caps as output coupling / DC blocking caps in my Crack/Speedball and all the listeners showed a statistically greater than chance ability to hear the difference. And the "preference" was 100% for the film caps. Just throwin' this out there.

I run a BHC/Speedball - after getting. a bit fed up with the standard sound I upgraded the output caps to Mundorf 100uF film caps (they are big but they do fit under the panel). I also now run a vintage Tungsol 7236 as the output tube, -along with a box of different 12AU7's (which I cannot for the life of me work out why they all sound different, yet they do !). I think the 7236 does have somewhat better output impedance characteristics than the standard 6080 but its been a while since I did that research so I may be wrong there. I also bypassed the PSU filter caps with film caps just in case it made any difference - in a standard BHC those caps are kind of in the audio path but less so in Speedball versions I think. I could not perceive any change there but they look good !

Anyway my perceived outcome of all those changes when running the BHC into Senn HD650's was a significantly improved top end (less roll off to my ears) and tighter faster bass....though not any more "full" than before. The bass is I think limited ultimately by the high op impedance of the tube output stage. There's not much that can be done about that - thats the reason for op transformers in higher end amps !

At the end of the day the BHC is a very interesting little amp which is great fun to tinker with, easy to do and undo mods on, and bulletproof due to being tube based. It will never outperform technically any half decent SS amp but if you approach it as a combo of gain and retro effect box to enjoy your music with, then why not ?

SC

 

[Strumbringer]

I run a BHC/Speedball - after getting. a bit fed up with the standard sound I upgraded the output caps to Mundorf 100uF film caps (they are big but they do fit under the panel). I also now run a vintage Tungsol 7236 as the output tube, -along with a box of different 12AU7's (which I cannot for the life of me work out why they all sound different, yet they do !). I think the 7236 does have somewhat better output impedance characteristics than the standard 6080 but its been a while since I did that research so I may be wrong there. I also bypassed the PSU filter caps with film caps just in case it made any difference - in a standard BHC those caps are kind of in the audio path but less so in Speedball versions I think. I could not perceive any change there but they look good !

Anyway my perceived outcome of all those changes when running the BHC into Senn HD650's was a significantly improved top end (less roll off to my ears) and tighter faster bass....though not any more "full" than before. The bass is I think limited ultimately by the high op impedance of the tube output stage. There's not much that can be done about that - thats the reason for op transformers in higher end amps !

At the end of the day the BHC is a very interesting little amp which is great fun to tinker with, easy to do and undo mods on, and bulletproof due to being tube based. It will never outperform technically any half decent SS amp but if you approach it as a combo of gain and retro effect box to enjoy your music with, then why not ?

SC

Interesting! So the stock blue 100 uf caps were replaced by Mundorf 100uf caps? Just looked those up and they’re pricey. Could these be a possibility:

Home

Dayton Audio DMPC-100 100uF 250V Polypropylene CapacitorMake the Dayton Audio line of metallized polypropylene capacitors your standard choice for all of your loudspeaker projects! The same high quality as the competing brands ... but at a much lower price. They are suitable for a wide range of...

www.parts-express.com

Regarding tube rolling the 12au7 and power tube, curious if that is a minor change and improvement in top end/less roll off would be a possible outcome of film caps?

 

[Veri]

Wow those are big capacitors, haha

 

[SIY]

Interesting! So the stock blue 100 uf caps were replaced by Mundorf 100uf caps? Just looked those up and they’re pricey.

Imagination can cost a lot! In the actual DBTs I did, the film cap was a V-Cap, costing over $300 per cap.

(Non-spoiler: they were outperformed by some cheap bipolar electrolytics)

 

[Strumbringer]

Thanks for the request Veri!View attachment 181843View attachment 181845View attachment 181902

OK! @GPJ - Looking good. It looks like you used the Dayton caps that I was asking about in my above post. So, we made some new terminals for the new 100 uf caps, as well? Gotta learn how to do that. Can you tell me if these replacement caps might solve (or at least help) the issue I noted with lack of definition and "blurry" presentation?

Mine is pictured below and I'm hoping to find out if replacing the stock blue 100 uf caps like you did will help my problem:

 

[SIY]

OK! @GPJ - Looking good. It looks like you used the Dayton caps that I was asking about in my above post. So, we made some new terminals for the new 100 uf caps, as well? Gotta learn how to do that. Can you tell me if these replacement caps might solve (or at least help) the issue I noted with lack of definition and "blurry" presentation?

Your problem has zero to do with caps. Perhaps the real problem is that you're itching to spend money on something to make you feel better.

 

[Strumbringer]

Your problem has zero to do with caps. Perhaps the real problem is that you're itching to spend money on something to make you feel better.

LOL, I don't think so, actually. It's just that I have this amp and I want it to be a bit better, otherwise I'm going to sell it. That's the truth. If I can get the blurry softened high frequencies to be more defined, it's a keeper. I like the low end presentation and overall, it pairs well with my 300 Ohm headphones.

 

[SIY]

LOL, I don't think so, actually. It's just that I have this amp and I want it to be a bit better, otherwise I'm going to sell it. That's the truth. If I can get the blurry softened high frequencies to be more defined, it's a keeper. I like the low end presentation and overall, it pairs well with my 300 Ohm headphones.

The cap won’t do it, but there may be an alternative. How’s the gain? Can you play it as loudly as you like without the volume up to full?

 

[Strumbringer]

The cap won’t do it, but there may be an alternative. How’s the gain? Can you play it as loudly as you like without the volume up to full?

The volume is great, actually. I have the RME ADI-2 DAC at +7 dBu and I only have the Bottlehead volume at 9-10 AM at the most.

You know, maybe I'm introducing some distortion on the BHC with my ADI-2 output being high (this level was recommended to me by others). Perhaps if I set it at -5 dBu, there would be more clarity and obviously more range on the BHC volume potentiometer.

 

[SIY]

The volume is great, actually. I have the RME ADI-2 DAC at +7 dBu and I only have the Bottlehead volume at 9-10 AM at the most.

You know, maybe I'm introducing some distortion on the BHC with my ADI-2 output being high (this level was recommended to me by others). Perhaps if I set it at -5 dBu, there would be more clarity and obviously more range on the BHC volume potentiometer.

That would be an easy thing to try.

The possibility I had in mind was some matching transformers. If you had (say) a 4:1 stepdown, the 6080 would have a much easier load to deal with, but it will drop the gain (thus my question).

 

[Strumbringer]

The step-down transformer sounds like a logical idea, but likely not practical to rebuild the amp.

Quick adjustments on levels out of the ADI-2 DAC to see the effect on the BHC. I changed the reference level to -5 dBu (from the previous +7) and have the volume set to about -40 dBr. The output meters are peaking just shy of 50%. This allows me to have the BHC potentiometer up to Noon. It does sound more crisp in the high-end and a bit more definition. I suppose this means I was putting too much level into the BHC and was likely getting those "desirable" (to some people) tube distortion artifacts.

Previous settings I had read elsewhere, stated I should have the ADI-2 peaking just shy of the yellow/red Over reading and around 0 dBu on the volume knob. If I did that, I would be pushing the input stage of the BHC quite hard, and perhaps resulting in the effect I was complaining about.

 

[SIY]

The step-down transformer sounds like a logical idea, but likely not practical to rebuild the amp.

Quick adjustments on levels out of the ADI-2 DAC to see the effect on the BHC. I changed the reference level to -5 dBu (from the previous +7) and have the volume set to about -40 dBr. The output meters are peaking just shy of 50%. This allows me to have the BHC potentiometer up to Noon. It does sound more crisp in the high-end and a bit more definition. I suppose this means I was putting too much level into the BHC and was likely getting those "desirable" (to some people) tube distortion artifacts.

Previous settings I had read elsewhere, stated I should have the ADI-2 peaking just shy of the yellow/red Over reading and around 0 dBu on the volume knob. If I did that, I would be pushing the input stage of the BHC quite hard, and perhaps resulting in the effect I was complaining about.

Yeah, you have so much headroom to spare that trying to squeeze the last dB of S/N out of it is a sucker's game. Very good thinking!

 

[Balle Clorin]

I did not read all 20 pages, but I built 2 Bottlehead kits, Seduction RIAA and preamp Foreplay where I added a balance control myself.
It was great fun and I learned alot and gave a great sense of achievement . The kits cannot measure as a Topping but I will never sell them. The manual and support and forum is just fantastic. Maybe I should get a Sennheiser and a Crack just for fun

 

[Veri]

I did not read all 20 pages, but I built 2 Bottlehead kits, Seduction RIAA and preamp Foreplay where I added a balance control myself.

You're telling me I can build myself a S.E.X, a Seduction and a Foreplay??

 

[Haider]

I have a Bottlehead Crack + Speedball. I love the way my 600 ohm Beyer DT 880's sound with this amp. I also like the way my HD-600's sound with it. I had HD-800's but had to sell them, the treble gave me headache, but when I had them, the Crack was my favorite amp to use them with.

I don't listen to it much. (I actually don't listen to headphones of any description much these days.) But it is a "FUN" headphone amp especially with my 600 ohm 'phones.

I equipped mine with a switch to allow going back and forth between the stock 100 uF electrolytic and a 100 uF mylar film capacitor for coupling the amplifier to the load. I purposely did not pay attention to which position was which on that switch when I assembled the thing. I A/B'd the sound using a number of different headphones, and the difference between the two positions was NOT subtle. There was an IMMEDIATELY audible difference between the two switch positions- one sounded kind of "raspy" in the highs - as though there was some distortion of the highs, or some ringing or noise bursts kind of thing. The other position the treble sounded quite smooth. I did not know which was the electrolytic and which was the film cap, but I knew almost instantly that I prefered one switch position over the other. After a few weeks I looked under the chassis top and saw that it was the film cap that I preferred. Make of this small sample size, not exactly double blind, no control group used, study what you will. But the conclusion I draw is that film caps sound better when they are in series with the audio signal than polarized electrolytics. Maybe a non polarized electrolytic would sound as good if you could find one with a high enough voltage rating, I don't know.View attachment 80856

That looks cool retro...

 

[SaberCat]

Interesting! So the stock blue 100 uf caps were replaced by Mundorf 100uf caps? Just looked those up and they’re pricey. Could these be a possibility:

Home

Dayton Audio DMPC-100 100uF 250V Polypropylene CapacitorMake the Dayton Audio line of metallized polypropylene capacitors your standard choice for all of your loudspeaker projects! The same high quality as the competing brands ... but at a much lower price. They are suitable for a wide range of...

www.parts-express.com

Regarding tube rolling the 12au7 and power tube, curious if that is a minor change and improvement in top end/less roll off would be a possible outcome of film caps?

Hey sorry for late reply - have been busy with work. Yes the Dayton's should fit the bill also - the Mundorf's are indeed pricey though at the time I got a good deal on the pair from a (good feedback) european seller on eBay. The power tube change to the bass performance was very noticeable - far more so than 12AU7 change-outs. I actually bought the 7236 before I added the Mundorfs so I think that aspect of it was definitely op tube related. I bought and tried several different 6080 types before I located the 7236 and have stuck with it ever since. The 12AU7 changes are more subtle. The one I like best is an RCA cleartop - I am probably well into psychological/subjective territory in the sound quality by this point however !

Cheers SC

 

[Strumbringer]

Hey sorry for late reply - have been busy with work. Yes the Dayton's should fit the bill also - the Mundorf's are indeed pricey though at the time I got a good deal on the pair from a (good feedback) european seller on eBay. The power tube change to the bass performance was very noticeable - far more so than 12AU7 change-outs. I actually bought the 7236 before I added the Mundorfs so I think that aspect of it was definitely op tube related. I bought and tried several different 6080 types before I located the 7236 and have stuck with it ever since. The 12AU7 changes are more subtle. The one I like best is an RCA cleartop - I am probably well into psychological/subjective territory in the sound quality by this point however !

Cheers SC

Hello, thank you! I appreciate the added perspective. You know, a lot of guys have recommended the RCA clear top and when I got my BHC several months back, I sourced one and have never bothered to try anything else (beyond the stock one it came with). The clear top is very good and I haven't felt the need to tube roll the input stage tube. Curious what the 7236 would bring to the table- I've got GEC and Bendix 6080 and Chatham 6as7g. The latter might be my favorite power tube, but I'd be hard pressed to tell the difference between those three. I may see if can source a 7236. I've actually been most curious about the 5998, but cannot seem to find one at a decent price!

Regarding the caps, it would be great if we had measurement data from one of the guys with the means to do so. I'm really curious if the frequency range benefits from the larger caps. I suppose they must be better from the tiny stock blue 100 uf caps, but it would great to know the magnitude of difference, if measurable. Again, thank you for the info!

Nice looking build! I don't remember my Crack/SB ever having a blurry presentation. I built the amp back in 2014 and the Dayton caps were cheaper back then. I don't like going overboard with these type of upgrades. I don't believe the caps were a big upgrade but they certainly didn't degrade the sound and I am very happy with the amp's performance. Always fun to see if improvements can be made especially when it's cheap to do so.

I used insulated solder turrets for mounting the caps (see attached photo). If you look at my photo from the last post, You'll see where I drilled four holes for the 4 turrets. Then countersunk the holes in the plate for a flush screw mount. The Dayton cap wire gauge is plenty stout enough to be self supporting so they just hang freely from the turrets. Found these similar ones on e bay .... look for ....

M55155/209J01 MIL Insulated Solder Turret Terminal Lug Stud 4-40 Threaded 1/4"Hx​

View attachment 182191

Been using it this way for 7+ years with no issues at all.

You may want to ask Paul at the BH forum about the issue you are experiencing. I use Beyer DT-1990 Pro and they work great with the amp. Transport DSF files to an E50 and into the amp. Crystal clean rich sound with black background. The HD-6XX sound good with it too but ever slightly more veiled for my taste. Being older I like the brighter phones tor my natural lack of high frequency hearing.

Anyway, I wouldn't bother with high priced caps. I only upgraded the output caps and the volume pot, maybe $60 total. No further upgrades will be made. Good luck!

Much appreciated- With some troubleshooting, I may have determined, quite possibly, that my blurry presentation impression may have been the result of too much input gain from the ADI-2 DAC to the BHC. I read elsewhere that I should have certain relatively high output gain level from the DAC, which only allowed me to have the BHC volume at about 8-9 O'Clock. Now, I've really reduced the output level of the DAC (quite substantially) and run the BHC volume at about Noon and it's much, much, better. Not solid state clear, but much better.

Thank you for the information on the insulated turret. This might be a very cool project to initiate! I'm assuming the Dayton caps are not directional and can be soldered facing either direction?

 

[SIY]

Regarding the caps, it would be great if we had measurement data from one of the guys with the means to do so. I'm really curious if the frequency range benefits from the larger caps. I suppose they must be better from the tiny stock blue 100 uf caps, but it would great to know the magnitude of difference, if measurable. Again, thank you for the info!

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.