Bottlehead Crack

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

  1. Jeb

    Jeb Friend

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    Do you guys feel that the Crack can do sufficient justice to the Schiit multibit DACs to make them a worthwhile investment solely for that pairing?

    At what point does it become overkill for this amp?
     
    Last edited: Dec 10, 2015
  2. Hands

    Hands Overzealous Auto Flusher - Measurbator

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    A modded Crack with the right tube selection should work well with the Bifrost Multibit and Gungnir Multibit, unless you're worried about using the SE output on the latter. Yggdrasil would probably be overkill. But if you're only running a stock Crack, or maybe with speedball, I wouldn't think going beyond Bifrost Multibit would be worth it. I haven't heard just a stock or speedball Crack, since mine came with film output caps and a stepped attenuator, and now it has different caps, a choke, same stepped attenuator, and a wider selection of nice tubes to pick from.
     
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  3. velvetx

    velvetx Gear Master West/Vendor Spotlight Moderator

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    Oh look at you Mr Fancy Pants :). I have to ask @CEE TEE if his Crack was modded but to me all iterations I have heard are great paired with the HD6x0. I heard it through a Gungnir Multibit and a Audio GD (dont remember the model).
     
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  4. Hands

    Hands Overzealous Auto Flusher - Measurbator

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    LOL, I bought it used with most mods already applied. Fishski fixed it up for me, since it developed issues shortly after I got it. I made him do the other dirty work of swapping caps and adding the choke (choke is cheap, but difficult to fit).

    Seriously, though, you should see this thing. It looks pretty, eh, used? The wood case has fallen apart on me a couple times and is currently being held together with super glue and packaging tape. Fancy as can be? :)
     
  5. TMoney

    TMoney Shits on SBAF over at Head-Case to be cool

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    @CEE TEE, if you get some tubes, please bring them to the January SF meet as I'd love to play around with them. I really like the warm, pleasing sound of the crack 2 with stock tubes but I would definitely be interested in finding a pairing that sounded a bit more transparent as a change-up.
     
  6. Hands

    Hands Overzealous Auto Flusher - Measurbator

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    Try a 5998 paired with a neutral, airy, wide, layered tube for input. Also a better pot or stepped attenuator supposedly makes a big different, granted I've only heard one with the stepped attenuator.
     
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  7. Jeb

    Jeb Friend

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    Thanks Hands & Velvetx. I think a Gungnir Multibit might a good move then for future proofing since I'll also probably use it for my speakers too.

    I'd like to take the Crack as far as I can with upgrades. I have received the Speedball Kit to fit and over the last few weeks have also gathered various parts upgrades & the necessary fixings: film output caps, bypass caps, new volume-pot (and a nicer knob!) and a Triad PS choke.

    I know the stock Crack quite well now, so I'm looking forward to implementing these upgrades one at a time and hearing what each of them might bring to the table.

    Just need some free-time to make a good go of it.
     
  8. TMoney

    TMoney Shits on SBAF over at Head-Case to be cool

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    I'll have to give that a try.

    I don't use the pot at all. I just leave it open and use my pre.
     
  9. Hands

    Hands Overzealous Auto Flusher - Measurbator

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    Cool, Jeb! Let us know what you think as you go along with mods. :)

    What film caps did you end up getting?
     
  10. CEE TEE

    CEE TEE Massdrop's Golden Child (MOT)

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    Crack at mini-meet and currently: Stock Tubes, Speedball added. All parts are stock.

    Yes, I need to shop for X-mas first but would love to have a couple tubes coming that have been recommended here...can bring if I have some by the next meets.
     
  11. Jeb

    Jeb Friend

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    @Hands - Mundorf MCaps and MCap Supremes to bypass them. The 100uf 250v MCaps are not too expensive (still £30 each) and not crazy big (will still be a tight squeeze). To be honest I don't know if they are good but the advice from others seemed to be that any film cap will be likely be an improvement over the stock electrolytics.

    Then I found some cheap soviet-era teflon caps (£3 each) to use for bypass caps instead so I'll probably try both and see how they sound. There's quite a lot of love for the Russian teflons on the BH forum.

    what do you have in yours?
     
  12. Hands

    Hands Overzealous Auto Flusher - Measurbator

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    Only caps I really know about are the fat output ones. It came with 100uf Solens, but I changed those to 68uf Jantzen Crosscaps based on some personal feedback I received and some online research. The bass roll-off on the 68uf really doesn't seem that noticeably over 100uf.

    @fishski13 would know more about everything else in my Crack, ha.
     
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  13. dubiousmike

    dubiousmike Friend

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    The use of film output caps makes a lot of sense to me given that this is a component the amplified signal has to pass through right before the output, but that is serving the essential purpose of blocking dc from reaching the drivers. Back when I first joined head-fi, there were quite a few users advocating Woo audio's pricey upgrades to all blackgate caps (back when they were still available), because they were supposedly so much better sounding than ordinary electrolytics.

    To put this in perspective, here are some comparative measurements (posted on diyhifisupply) of the dissipation factors of a couple of different types of electrolytics, vs. blackgates vs. the lower capacitance version of the cheap obbligato film output caps that I'm running in my crack (at 100hz):

    * Rubycon Electrolytic 47uf/450v: 0.061
    * Panasonic 47uf/450v: 0.035
    * Blackgate 22uf/350v: 0.026
    * Obbligato [Film] Power Cap 47uf/500v: 0.00015

    Kind of makes you wonder why anyone would build a high priced amp in a chassis that isn't large enough to house film caps, at least to the extent the signal is passing through them.

    Regarding the amount of capacitance, I did perceive an increase in deep bass going from 91uf axons to 100uf obbligatos, but from the graphs posted on bh, 9uf should be de minimus in terms of bass rolloff (at least with 300 ohm Senns). Maybe it is just how these particular caps handle particular frequencies.

    On a related note, I still can't quite wrap my brain around the concept bypass caps that are wired in parallel to the output caps. Do some frequencies pass more readily through the one than the other? If so, doesn't that create timing disparities in the signal? As an experiment, I tried some of the little Russian teflon's in mine for a while. They look cool, and I thought it was an improvement at first but later convinced myself that the ultimate sound was slightly less clear and pulled 'em.
     
    Last edited: Dec 10, 2015
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  14. Hands

    Hands Overzealous Auto Flusher - Measurbator

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    Some input tube comparisons on the Crack, paired with a rebranded Tung Sol 5998.

    Sylvania 12BH7A (Large yellow font, small-to-medium sized grey plates, D-getter): Good extension on both ends. Lively and dynamic. Good resolution and air. Good texture. Decently neutral. My main problem is that is has a noticeable dry, grainy sound. Paired with the more neutral, lively nature, the grain makes it a bit unpleasant.

    RCA 12BH7A (Long dark grey/black plates, double wings on top of mica, dimpled D or Square getter): Good dynamics. Fairly smooth sounding. Probably the least fast and detailed of the bunch, yet details somehow have this pure and smooth nature to them as if they're not tainted by false grain. Thick and lush, though bass can be a bit tubby. Does well with male vocals. Might lack some treble extension. Slight mid scoop out that leads up to a slight upper-mid/lower-treble emphasis. Enjoyable, but not for everyone.

    Philips Miniwatt 12AU7 (Holland made, I think. Crooked and tilts to the left, which is funny.): Similar tone to the RCA above, but more even throughout. Nothing missing or standing out. Not quite as tubby, but still on the lush, warmer, thicker side of things. The least in-your-face of the bunch, in that it takes a step back and presents a wider stage. Extension sits somewhere between Sylvania and RCA above. Very smooth and balanced sounding. Not at all offensive sounding, but not boring either. Could use a bit more dynamics, but not bad. Honestly, it helps balance out the Crack's inherent bassy, thick nature by being less in-your-face, more neutral sounding. This is the type of tube that doesn't impress immediately, but you appreciate it the more you listen.

    GE 5814 (Double mica, dark grey plates, square getting with a crook in it): Surprisingly lively from top to bottom. Hits harder and is more dynamic than the Philips, but maybe not as much as others. Bass isn't as taut as Sylvania's, but not as tubby as RCA...sits somewhere between Philips and Sylvania, maybe. Honestly, it sounds like the Philips and Sylvania had a baby. Clear, incisive, more in-your-face, and dynamic like the Sylvania, but with a more even tone and less grain like the Philips. "Rich" sound, but not in a "rich harmonics," or "rich texture" sort of way. Hard to explain. Surprisingly good to my ears.

    RCA 6SN7/VT-231 (Almost entirely opaque, grey glass - 40s, I think): Might be thicker than the RCA 12BH7. Sounds grainier and more U-shaped than the other RCA, but, yes, still thicker, lusher, and warmer like it. Might be faster and more detailed than the RCA 12BH7, but isn't as easy to listen to due to the tonal balance and extra grain.

    I just got the Philips Miniwatt in yesterday, and it's really growing on me. The extra slam and dynamics from some other tubes captures my attention more at first, but there's just something very pleasant about the Philips that the others don't capture. The neutrality, less in-your-face staging, great tone, smooth nature, and overall agreeable sound doesn't grab you by the nuts right away, but eventually having your nuts grabbed gets old. It draws attention to itself by not drawing attention to itself, and not because it's bland either. Just nice and balanced. Though I do find myself wanting to rotate in the GE and RCA 12BH7 from time to time too.

    And, you know what, I think this particular Philips was meant for my Crack. Why? Well, my 5998 rebrand tilts to the right, and this Philips tilts to the left. Couple that with the fact the wood enclosure is taped together right now, it makes my Crack looks extra "special" and unassuming.
     
  15. dubiousmike

    dubiousmike Friend

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    Finally installed a triad choke in my crack last night (now CRCLC) and also padded the pot with some 75k ohm shinkoh's in series with the inputs and a pair of 33k ohm resisters shunting from the pot inputs to pot ground terminals.

    Sounds better than ever - thanks to OJ, Fishki and Hands for inspiring me to finally suck it up and do the choke mod.
     
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  16. Jeb

    Jeb Friend

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    Nicely done @dubiousmike - I definitely need to do the same with the resistors - I have very little usable range on the volume control currently. Although the GEC 6AS7G seems to give a little more range for some reason. That one brand couldn't have different specs could it?

    Can I ask about mounting the choke? Did you squeeze one of the standoffs between the safety ground screw and the transformer ? I was looking earlier and there doesn't seem much room.
     
  17. Hands

    Hands Overzealous Auto Flusher - Measurbator

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    Fiskski mount my choke at the far back end of the Crack. Right behind the main transformer.

    I too could use a bit more volume range with the stepped attenuator. It's basically Really quiet -> Moderately Quiet -> Almost Loud -> Way too damn loud

    With high DR music, I can take it up 2-4 more notches, depending. Lots of unused steps at the top end! Haha
     
  18. dubiousmike

    dubiousmike Friend

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    Yeah, that's about where mine is as well. I'll post a couple of photos later on Jeb. It is a pretty tight fit. I originally thought I would be clever and use the chassis/safety ground screw for one of my choke standoffs. I went ahead and drilled hole number two - only to find that the choke is a fraction of an inch too deep (in that orientation) and the top plate could no longer fit back in the wooden base. Doh! This is all behind the transformer bell so not really visible, but I have a stupid extra screw in my plate now that is just there to cover the hole to nowhere lol.

    Padding the pot a bit definitely helps, although I am now wishing I had gone for even more attenuation for when I am using higher gain tubes. The tables on goldpoint's site lay out R1 and R2 values depending on how much you want: http://www.goldpt.com/mods.html I will probably try again and lower my R2 value at some point.
     
    Last edited: Dec 14, 2015
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  19. Jeb

    Jeb Friend

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    Pics would be great. Actually pleased I asked since I had pondered the same idea as you using the ground screw for one of the standoffs.

    Nevermind - clearly you just have an extra optional ventilation hole now :cool:
     
    Last edited: Dec 14, 2015
  20. The Alchemist

    The Alchemist MOT: Schiit - Here to help!

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    So you got your Crack @Hands ?
     

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