Bottlehead Crack

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

  1. Mban

    Mban Almost "Made"

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    Yup, Antek transformer. It's more of a better-use-than-crack (aka a BUTCRK ;)).

    In all seriousness though, the changes I've implemented in this amp should make it of higher performance than the Crack-a-two-a.
     
    Last edited: May 11, 2018
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  2. Alchemy

    Alchemy Rando

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    Holy heck a fellow 1t150 / 6336 brother.. I thought I was the only one! I have to ask, have you had any experience rolling with the 6336a/b/6528? I was looking at buying an original metal plate as the 6336A I currently have sounds a little bright for me. Would love to know if there's a difference.

    EDIT: Alright your amp looks amazing, could you share the mods you made to it?
     
    Last edited: Aug 10, 2018
  3. Luckbad

    Luckbad Traded in a unicorn for a Corolla

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    Mentioned by @Ardacer in a profile post, the Crack kit is heavily discounted right now for its anniversary.
     
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  4. Mban

    Mban Almost "Made"

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    I haven't tried the 6528 as I couldn't find one for a cheap price. The 6528 also has higher transconductance, so you would need grid stoppers to make sure that it doesn't oscillate during use.

    Just some of the mods on my amp:
    - Full stepped attenuation using RN60 Vishay resistors
    - Large oil filled capacitors for the high voltage lines (no electrolytic caps in the HV line)
    - High voltage regulation based on LT3080
    - Increased current through power tube (reduces output impedance if your amp can handle the additional current on the HV line)
    - Full SiC Schottky rectification on low voltage and high voltage lines
    - Heaters DC regulated using LM1084 based reg, with oil filled caps in line
    - Use of a selectable pin array for adjusting driver tube constant current source current setting to match particular tube
    - Use of Vishay Foil resistors for grid inputs on driver and power tubes
    - Use of MKP10 poly output caps replacing the normal use of electrolytic output caps
    - Various other small tweaks throughout that I'm not remembering now
     
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  5. Curado

    Curado Rando

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    Good efforts...appreciate it!
     
  6. Curado

    Curado Rando

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    Crack threads are normally too long to follow, especially the one on head-fi. :( But this one is okay so far.

    Got some questions regarding tube rolling and your help is appreciated:

    1. It seems 6SN7 will double the current and cause excess heat on the wirewound resistors on Crack (somewhere I read from the BH forum), so will it cause damages to the Crack on the long run? In my case I have replaced these 2 wirewound resistors with the Speedball installation, so does the issue still exist if I roll in a 6SN7+adaptor?

    2. Can you guys recommend some reputable tube vendors, especially the ones with their own websites outside ebay?

    Thanks.
     
    Last edited: Apr 1, 2019
  7. Cspirou

    Cspirou They call me Sparky

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    6SN7 is not a drop in replacement, you need to do some modification in order to accept that tube type. If you already have a speedball you should find out what is the right bias current for the tube and change the resistors on the speedball. I remember seeing Dan at Bottlehead making a 6SN7 Crack himself and sold it, but I don't know the details of the mod.
     
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  8. Curado

    Curado Rando

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    Thank you very much for the explanation.

    I initially thought rolling in a 6SN7 is as simple as buying a Garage1217 adapter and a 6SN7 tube. So you mean I have to measure the bias and change the resistors on SB to accommodate the bias?:eek: If so, it's too complicated for non-electricians/engineers like me. :(
     
  9. mephisto56

    mephisto56 Rando

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  10. Curado

    Curado Rando

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    The link is great.

    Much appreciate it!
     
  11. Curado

    Curado Rando

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    Looks gorgeous!

    Where did you find these beautiful racks for mounting?
     
  12. Curado

    Curado Rando

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    From what I read, the arc could be caused by some residual gas inside the tube, leave the tube on for the whole night and the gas could possibly be absorbed by the barium deposit.
     
  13. dasman66

    dasman66 Almost "Made"

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    Please realize you are replying to a post that is over a year old... one of the reasons threads here are manageable is that we try to keep the noise level down.

    Also, please introduce yourself here: https://www.superbestaudiofriends.org/index.php?threads/new-members-introduce-yourself.17/
     
  14. m17xr2b

    m17xr2b Friend

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    A few weeks back I got myself a prebuilt crack with speedball. The Crack was my first amplifier several years ago and it's nice to hear it again.
    @Jeb has everything documented as far as upgrades are concerned and agree with his findings.
    The volume pot needs to be replaced ideally with an Alps and above. The upgrade in low level channel tracking is one thing but I got extended high end, better defined low end. It's really bottlenecking the amp where I'd say this is more important than the output caps upgrade.

    Naturally I couldn't say stock for long and upgraded one by one with each I had positive results.
    A word of caution, don't go for the Mundorf Evo Oils unless you're prepared to bypass, choke etc. They're quite warm and the Crack is very mushy in the lows/mids without other mods. The cheaper MKP are better and easier to fit.

    Raided the 2.2uf quickie output caps to bypass the output ones, to my surprise a very positive change, got some detail back where just with upgraded pot and evo oil caps it was far too dark and loose.

    Installed triad choke and upgraded the last PSU film cap, this resulted in a massive improvement in smoothness, low end got tightened resulting in super nice punch and extension. Overall it's still dark-ish but very enjoyable. As many said, there's something about the crack... musicality, funness, liquidity in mids, whatever it is I'm addicted. A must hear for any HD580/600/650 enthusiast and I'm not saying this lightly.

    Interesting design even it a bit kitchen sinkesc.
    [​IMG]


    Only the cree diodes left to install once the board arrives, maybe replace the second PSU cap with a film
    [​IMG]

    As before the Sylvania 6080 gold branded is my favorite. The Bendix 6080 solid/slotted plate, 5998, GEC 6080/6AS7G are technically better for sure but there's something about the gold branded mids that makes me keep listening for hours. Might roll my 6SN7 collection but it's really not broken with E80CC/ECC40 biased correctly.
     
    Last edited: Apr 19, 2019
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  15. gandhisfist

    gandhisfist Almost "Made"

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    The DT880-600ohm is this amps best friend IMO.
     
  16. m17xr2b

    m17xr2b Friend

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    What other high impedance headphone have you tried with it?
     
  17. gandhisfist

    gandhisfist Almost "Made"

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    Tried with the Audio-Technica R70X and the sennheisers. The sennheisers are a classic pairing, but I just really enjoy the DT880 on this amp, I think that headphone and this amp just complement each other very well.
     
  18. AllanMarcus

    AllanMarcus Friend

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    If you like the DT880, you'll probably like the T1 (gen 1). I've tried all the Senns and beyers, and the HD800 and the T1 were my favorites. Good tubes are needed for both these headphones, but mods are optional. I've compared a stock crack with speedball to a fully modded one with big ass expensive caps and other stuff, and to tell you the truth, I could not hear a difference. I install a choke and cree mods on mine, when I had one, and I did it more for the fun of doing it than for the sonic improvements.

    Tubes, now that's where you can really hear differences.
     
  19. m17xr2b

    m17xr2b Friend

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    After using the Crack for a few weeks I concluded the Mundorf Evo Oils are complete shit. Way, way too warm to the point I though the amp was broken and even with my brightest tubes it was still dark and warm. Bypassing with the clarity caps helped a bit but not enough.

    Inserting Axon true caps 75uf instead I loose quite a bit of smoothness and mid detail but the sound is much more balanced and pleasing overall. Back to the drawing board.
     
  20. JeffYoung

    JeffYoung Friend

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    There's a lot of surface area on those big caps: I wonder if you're picking up RF from your transformer (or from external sources)? You might try some physically smaller caps....
     

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