Bottlehead Crack

Discussion in 'Headphone Amplifiers and Combo (DAC/Amp) Units' started by OJneg, Oct 3, 2015.

  1. elmoe

    elmoe Friend

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    Interesting, I rolled all my old 6sn7s (Sylvania vt231 bad boys, Ken rads vt 231s, NOS Tung sols, NOS RCAs and a bunch of others) but still stuck with the Siemens 12au7 in mine. It always sounds better than the 6sn7s I tried to my ears.

    Really like the rail idea. What's the third RCA for in your build? And what did you add next to the power cable connector there, I can't tell, looks like a 12V input maybe?
     
  2. m17xr2b

    m17xr2b Friend

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    The third RCA input is for the remote volume control, but that will be used on the other speedball crack build and couldn't leave an empty socket in this case.

    Next to the power connector is a vintage style fuse holder.
     
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  3. elmoe

    elmoe Friend

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    Aha, gotcha!! What kind of remote volume control are you implementing? I've been looking to add one to my MPX3 but I haven't settled on anything yet. I've been looking at possibly going with a Goldpoint stepped attenuator and a remote kit from bent Audio http://www.bentaudio.com/parts/step.html but the prices are steep...
     
  4. m17xr2b

    m17xr2b Friend

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  5. m17xr2b

    m17xr2b Friend

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    I'm really surprised by this Crack. Even if it's non speedball it sounds better than the speedball version ever did.
    The Mundorf evo oil caps I disliked before have none of the darkness I heard before. I've also put a 100uf Mundorf Mcap bypassed with a 1.2uF clarity cap as the last one in the psu.

    The amount of detail this thing can extract is ridiculous. I've always thought of the crack as a slow warm amp.
    Separation is up there with the best, extension especially at the top with a Bendix and Sylvania 6F8G is kind of hard to believe. Neutral in the mids, tons and tons of detail with very little sign of grain. Love how cymbals shimmer. Soundstage isn't the largest but still feels spacious with every instrument in its distinct place. Even with fast paced music it keeps up easily.

    I wonder why(better components)?

    [​IMG]
     
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  6. elmoe

    elmoe Friend

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    First off, that amp is gorgeous. I really like how you got the wood to look.

    Components made a big difference in my build. Switching out output caps in particular really took the amp to another level. That being said, I also use a Bendix tube and to me ears that made the biggest difference, even more so than the 12AU7s I rolled, comparing it to the stock 6080. That tube in that amp is a very very good match.
     
  7. m17xr2b

    m17xr2b Friend

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    I've used the same tubes and caps before but it didn't sound as good. The OG crack wasn't built by me. I suspect the upgraded wiring and resistors might have something to do with it.

    Bendix 6080 slotted is my nr.2 tube, only surpassed by the GEC 6AS7G. It has slightly more detail than the bendix but rounder edges in a good way so it sounds more musical.
    Poping in the GEC is dangerous especially at night, it's hard to stop listening and turn it off.
     
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  8. elmoe

    elmoe Friend

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    You're killing me, now I'm gonna have to hunt one down... ;)
     
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  9. m17xr2b

    m17xr2b Friend

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    The crack is finished. I'm still shocked at how good it sounds without speedball. The Apex Teton has the same topology as the stock crack only with a much better power supply and running the tubes at higher bias I'm sure.

    The huge output caps are russian 100uf KZK white line. Performance wise they sit in between the Mundorf MCap and Evo Oil. They don't have the richness of the oils but at less than half the price it's hard to complain and are miles better than the electrolitics.
    I love the fact it's dead silent, with the headphones plugged in, switching it on I can't hear any difference in background.
    This little piggy will soon go to the market.

    [​IMG]

    [​IMG]
     
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  10. m17xr2b

    m17xr2b Friend

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    Fresh from vacation I started the second crack. Diverging from the standard build takes exponentially more time for the small bits.

    Took 12 hours to reach this point:
    [​IMG]

    Custom support for the PSU
    [​IMG]

    20 hours later I was ready for the first switch on.
    [​IMG]

    Worked from the first go. 5 hours later the PSU was ready:
    Jensen 2x220uF screw terminal electrolitics, 3x50uF Jensen oil, two UK made chokes and cree diodes.
    [​IMG]

    The SQ jump from the standard electrolitic to the oils was significant. Next up speedball:
    [​IMG]
    [​IMG]

    Increased depth and size of soundstage, more dynamics but overall the jump wasn't as significant as the psu upgrades.

    Output cap upgrade with more oil.
    [​IMG]

    The biggest sonic benefit and completes the amp. Makes sense as the output caps were an obvious bottleneck and this lets all the components shine.

    I have four other mods in mind but I'll want to enjoy and familiarise myself with the sound.
    I used star grounding instead of daisy-chaining because I didn't want to use the top plate as signal ground.
    The build was carefully planed over the past months to make sure I use as much of the space as possible.

    The power transformer is a custom ordered Sowter 50VA and I want to let it and the other new components burn in for a while.
     
  11. JeffYoung

    JeffYoung Friend

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    Yeah, that's my one beef with the Bottlehead designs. But at least it's easily corrected.
     
  12. m17xr2b

    m17xr2b Friend

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    First of the mods, battery bias:
    [​IMG]

    NiMH solar batteries to replace the red leds, something I learned from Morgan Jones. In theory lower resistance than LED. The current acts like a trickle charge and the batteries should last years.
    Only one battery is needed normally but I'm playing with other input tubes and needed 4AA per side for 5.2V.

    The difference is subtle but there. The first half of the frequency seems clearer, smother and because of it bass is more defined. Mids are a touch lighter. Can't hear any downsides. Not bad for a 7£ mod.
     
    Last edited: Sep 19, 2019
  13. m17xr2b

    m17xr2b Friend

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    Second mod, bypassed caps. Go big or go home is my mantra...sometimes.

    [​IMG]
    Duelund CAST 0.47uF for PSU bypass and Vcap TFTF 0.15uF for output caps bypass.

    Duelund adds overall refinement, it's not obvious but taking it out after a while you get the sense something is missing. Not worth it by any stretch but I do like the overall effect.
    Vcaps are are not so subtle, midrange is more muscular, not overdone with increased high end presence almost to harshness but not quite. The verdict is still out on these, while the PSU bypass is an overall improvement this is more situational, the Crack becomes picky of tracks, on most it plays to their strength, very Teton like with more umph and without the ultimate resolution. On others it's harsh and can be piercing.

    The PSU is the place to bypass and with only one cap it can be of higher quality.
     
  14. m17xr2b

    m17xr2b Friend

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    Now that my amps are finished, the question remains: To speedball or not to speedball?

    [​IMG]

    The one on the left is my pet project, cost no object crack build, custom high end everything, no speedball,NiCa battery bias. I wanted the Apex Teton in smaller form factor without sacrificing quality. I have achieved that goal.

    The other one is a typical upgraded crack, choke, 100uF film for output and last psu, SiC diodes.
    Both fed from the Pavane, speedball crack from a jensen xlr to rca box. The VR102 tube can't be used in any way with the stock crack transformer so the ECC32 is the closest sound wise.

    [​IMG]

    Bass: non speedball punches harder, faster and lower. 20% difference between the two but the softness of low end with speedball really takes away from immersion. Could very well be other components at play such as caps, I'll never know.
    Tone: grain free on non speedball, might as well listen to the Stratus, as smooth as can be. Grain is easily identified A-Bing on SB, tone is not as pure with a hint of plastic.
    Soundstage: average size on speedball, absolutely huge on non speedball(30% ish).
    Imaging and detail: speedball appears more balanced with the top end having more focus and making non speedball a touch dark. Even so non speedball has vastly more microdetail because in the other case there's smearing. Imaging is about the same.

    Something's telling me the oil capacitors for output and PSU are outpacing speedball. The lower amp has plastic film caps.

    In my view speedball is optional, it makes more sense in a stock amp but if planing to upgrade I would skip it and get better caps and components. It somehow shields the signal path from the potentially crappy stock psu, the theoretical advantages for a high impendance supply isn't as impressive when actually listening side by side and I think it does more harm than good.

    Bypass caps:
    Living with duelund silver copper hybrid on the PSU and Vcap TFTF on the outputs made me realise, sometimes less is
    more. While there's a positive increase in some areas overall cohesion and involvement is better without any bypass.

    Still haven't found the right volume knob.
    [​IMG]
     
    Last edited: Oct 21, 2019
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  15. ColtMrFire

    ColtMrFire Writes better fan fics than you

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    I've been borrowing Joshvar's SB Crack until Starlett arrives and I can somewhat echo your findings compared to my T3. SB crack gets you alot of the way there but falls behind in most areas to summit fi stuff. Especially in the bass. My T3 slammed harder/faster/tighter with less bloat.

    SB still a great amp though, with some great OTL staging, one area it bested the T3, which doesn't have the best staging.
     
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  16. Alchemy

    Alchemy Rando

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    I upgraded my crack to a crackatwoa and I found that really cleared things up, especially in the low-end. I actually put in some effort to switch between the two circuits a few times (soldering wires around) and my overall impressions were that the speedball (vs the crackatwoa) is a bit muddled.

    If anyone is curious, the crackatwoa puts voltage regulators on each channel. A few speedball tweaks come as a 6v 10000uf cap parallel with a 33k resistor from the base of the tip50 to ground and bumping the 44.2k resistor to 47k.
     
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  17. scblock

    scblock Facebook Friend

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    I finally decided I wanted to try to build a Crack and placed an order for a kit last week. And so while I wait for it to be prepped and shipped I’ve been reading through the assembly manual to see how to build it, and this thread to see what others have done. I’m seeing a lot of ideas for mods and parts replacements and tube rolling and everything else. It’s fascinating.

    I assume though that I should start with the base kit as-is, and try to just build that as best I can and then listen to that a while before I consider any mods like the speedball or a shunt regulator or the big caps, etc. Is modding this amp after building it difficult, assuming I’m competent enough to build it well in the first place? Is there anything I should consider carefully in the initial build to make later changes easier?
     
  18. elmoe

    elmoe Friend

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    Not really, if you were able to build it without trouble to begin with, are patient and take your time with it, you'll have no issues modding later on. At worst you'll need to buy more wires, but the original kit comes with a fair amount of extra already so unless you're crazy like me and choose to take it apart to rebuild it again, you should be just fine.

    The thing in my opinion that took the most consideration is the wood staining/polyurethane. Take your time with that, let things dry for days before going with second coats, make sure when you're sanding you use several different grains (and sand from rough to fine). Keep in mind if you break any parts or need a new top plate, you can always order new ones fairly cheap from Bottlehead directly, so don't be too afraid to poke holes in the plate for modding purposes.

    I'd also be careful when soldering the power switch as it is fairly fragile and putting too much heat to it for too long will ruin it. Other than that it's all fairly straightforward, just take your time, don't skip anything in the guide and you'll be fine.
     
  19. fp627

    fp627 Friend

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    In addition to what elmoe said, I would say that if you roll caps or other components, make sure there is enough space inside (or make/buy a bigger enclosure, etc.). I had to get a little bit creative to fit the caps and inductor inside in such a way to minimize heat, noise, contact with other parts, etc.

    Of course if you don't care that much about optimizing layout (it isn't going to make a HUGE difference on this amp) or just don't have a choice due to other mods, then it should be fine as long as it all fits.
     
  20. Alchemy

    Alchemy Rando

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    There isn't much of anything you need to do to "prepare" your crack for later mods. That being said It is very important to take your sweet time and build it right to begin with so you don't destroy any parts or go chasing noise. So make sure all connections are very strong and be methodical about your wiring. This and everything else is covered pretty well in the manual though. Also, elmoe's point about melting the power switch is very true and I have done it myself, but still don't skimp on the solder joints!

    The most difficult part about modding this amp IMO is choosing what to do, and in what order. I also took the time to do everything I wanted to at once so I could knock it all out in one mouser order to save on shipping and time with my amp upside-down.
     

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