Bottlehead Crack

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

  1. m17xr2b

    m17xr2b Friend

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    I'm going chrome plating in the end for both plate and bell, saw a couple of builds this way and I like the look. Nickel seems to have a yelowish tint. 120£ in cost.
     
  2. fp627

    fp627 Friend

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    Installed bypass caps on the last cap in the power supply. Volume suddenly goes really low. First instinct is to get different caps but want to run this by others before I pay $8 shipping on <$2 worth of parts.

    Before listening level was at about 9' on the pot for me. Now at 3' it's way quieter than it used to be at 9'. Tubes and everything else are the same, if I remove the bypass cap the volume comes back.

    Caps are old Russian caps shipped in from Russia (along with tubes). 2 caps are PIO (2uf and 4uf), 1 is a PIO and electrolytic hybrid (2.2uf). Issue occurs with all 3 caps, but the "amount" of volume loss varies - I don't lose as much volume with the 2uf PIO as I do with the other 2 although overall it's still way quieter with the pot at 3' vs when no bypass caps are installed. All C readings on multimeter are within spec printed on cap (caps were discharged before and after measurement).

    Also I did install a choke - not sure if that matters in regards to the issue. Input is currently CRCLC (instead of CRCRC) before going into rectifier and transformer. I doubt this would contribute to the issue but figure I should check anyways.

    On a different note, contrary to what I normally do, I have been rolling/testing tubes on this. 5 different 12AU7, 5 different 6080/6AS7G, basically plan on trying all 25 combos just to see what happens. Try about 1 hour with each combo during quick listening (unless I just don't like the combo, then it's <1 min). Will write a little on this later but before I even get there, confirmed that for me tube rolling is not the most productive use of time and is probably not something I'll do a huge amount of in the future.
     
    Last edited: Jul 12, 2019
  3. Baten

    Baten Friend

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    Lovely amp and set-up man. Enjoy!! :D
     
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  4. JeffYoung

    JeffYoung Friend

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    @fp627, measure the resistance of the caps. It sounds like they're leaking. (That would cause a higher current across the R in your CRCLC, which will cause it to drop more voltage. You could also see if that R runs hotter with the bypass caps.)
     
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  5. Cspirou

    Cspirou They call me Sparky

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    Reminds me of an Eddie Current amp
     
  6. JeffYoung

    JeffYoung Friend

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    The inspiration was actually this Moth: moth audio hero.jpg
     
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  7. fp627

    fp627 Friend

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    BH Crack in final state as of July 4th. I have no more desire to work on it and based on what I can see, I've squeezed most of the juice out of the lemon at this point anyways. Originally got it with BH Crack + SB last year. Ran for 1 week w/o SB, then installed SB and ran it stock for a while. Listen pretty much with only HD6xx as it's my only high Z headphone right now.

    I mention my perceived effect of mods in my post on the last page (22). Last bypass cap (2.2uf WIMA film cap) in the circuit reduced noise as expected after 9' on the pot. The amp is now quiet to about 1030' and noise between 1030 and ~2 is less than before. So far no/barely and possibly placebo level noticeable difference in sonic characteristics - Maybe slightly less clear/more mushy?? - Possible difference is so small I'm not even fully sure how to describe it.

    Also thank you @JeffYoung for confirming what I suspected in question above - bad bypass caps. I bought extra caps knowing they were old and expected maybe 1 to be bad, but I didn't expect all 3 to be bad.

    [​IMG]
    Caps are oriented a little weird due to space constraints.

    Choke off to the back to get it as far from the transformer as possible + make the magnetic fields perpendicular (assuming BH transformer is wound the way I expected).

    Nylon spacers not visible, but used to keep caps off of wires, frame, etc. Standoffs used to elevate choke above 6.5mm jack. Extra electrical tape also used at certain points to help give extra insulation to wires making contact with other components as noise levels increased slightly after wires got moved around (the tape worked).

    Edit: forgot to mention my case is very simple - sanded, 1 coat tung oil and dry followed by 0000 steel wool, repeat once
     
    Last edited: Jul 13, 2019
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  8. fp627

    fp627 Friend

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    As mentioned above, here are all of the tubes that I have/used. Disclaimer - I don't normally tube roll, but since this was a "project", I decided to do so here. 5x 6080/6AS7G, 5x 12AU7, made a 5x5 grid, randomly selected combos until all comparisons were done over the course of several weeks. Went back to previously tested combos at random points to see if my notes would match previous notes (they mostly did) and no "mental burn-in" was occurring. Serious listening time varied from <1 min after warmup (if dislike) to 1-2 hours after warmup.

    6080 and 6AS7G: RCA 6080 (1935 mfg, stock tube), Tungsol 6080, Svetlana NOS 6N13S, Svetlana NOS 6N5S (reads 6H5C if using English alphabet), and Thomson 6080WA.

    12AU7: Brimar CV4003 (NOS), Tungsol 12AU7W (modern prod), Tungsram 12AU7 (NOS), RFT 12au7 (NOS), stock 12AU7 (unknown tube as all print missing except for 12AU7) - my guess is I got lucky and got a Philips - of about 10-15 mfg, Philips are the only old tubes I could find pictures of online where there is no extra metal in the two little holes on each side of each plate. Or maybe it's all wishful thinking. Don't care enough about tube rolling to investigate further.

    Favorite combos, leaving out extra details since there is so much feedback on the BH Crack + these same tubes on multiple sites already:

    Stock RCA 6080 + Stock 12AU7 - Overall didn't like the RCA 6080 with any of the 12AU7, but if I had to pick one 12AU7, this would be it. Had a very easy listening and relaxing sound that I listened to for 2 hours very easily. RCA 6080 was bearable with the modern Tungsol (missing bass and bass was missing definition), Overall the music was disjointed and not cohesive with RCA 6080.

    Tungsol 6080 with Stock 12AU7 or Tungsram - Tungsol 6080 has nice tone and timber with stock 12AU7, kind of a "fun and enjoyable sound" (think flashing interior and exterior lights on cheap car fun, not my $100k+ 911 is refined and fun to drive kind of fun). Slightly unstructured and loose sound with Tungsram, but overall was enjoyable if you like the (old) Tungsram sound. Loss of resolution with either 12AU7, especially in bass.

    6N13S - DOA, no comments.

    6N5S + stock 12AU7 or RFT - Probably my favorite tube overall but probably because this combo is not in the same "spirit" as stock BH Crack + SB. Takes away some of the warm easy attitude. Bass can be slightly slappy which is overall something I really dislike (not to be mistaken for slam which I like). Missing resolution and details on the high and low ends (and this is on top of the fact that BH crack already lacks resolution comparatively speaking. Good tone, but after a long time the sound got slightly fatiguing for me (few of the other tube combos did for me). The RFT 12AU7 is not bad with 6N5S if you want the crack to have a brighter sound but various parts all over the spectrum would randomly seem too elevated.

    Thomson 6080WA + Brimar - Warm combo, plays on strength of BH Crack. Bass seemed to retain more texture than most or all combos. Slightly more punch in mid bass, a tiny bit of slappiness too though. Overall this combo seemed to have the least loss in resolution (but BH crack is still only going to have OK resolution at best). Despite warm sound signature, this also increased treble impact, kind of in the way a Ygg increases impact and seems to highlight all and any one part of the music at the same time (but this combo only increases for treble). No annoyance or sibilance though. Enjoyable with lone and higher female vocals.

    Overall, preferred combos didn't necessarily make the amp better, they just fixed or changed various aspects of the amp that are not "there" or that are "not my preference". These are my "best" combos because they matched my preferences, not because they are the best at technicalities and/or measure better-er / gooder. Conclusion is tube rolling is still not my favorite activity but they do make a difference here. I still prefer to find a few tubes/combos that I like and then buy 1 or 2 spare sets of said combos, sell the rest.
     
    Last edited: Jul 13, 2019
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  9. dasman66

    dasman66 Friend

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    @fp627 - can you provide some more details on how you mounted your choke in that location? In your FS post, you mention epoxying it so you don't need to ground it... so I assume some sort of metal standoff... and I see screw/nuts mounting the choke to the standoff (but no screw heads on the top of the plate).

    I have a choke sitting here to install on mine, but haven't because I don't really want to drill more holes in the top plate. Whatever you did may be the ticket, but admit I'm afraid of just epoxy to hold something in permanent tension...

    Thanks
     
  10. fp627

    fp627 Friend

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    @dasman66

    I bought JB Weld (not the quick set stuff) but other metal based epoxy will work too. For reference, IIRC it's rated at 5000+ PSI once cured - more than enough to hold a <1lb choke upside down.

    Attach standoff to choke as shown in pictures (get standoffs with threaded ends, use nuts to attach). The choke will look like it's on 2 feet at this point and the amp frame will have electrical contact with the choke frame. Then I mark where the standoffs will make contact, I scratch the surface of the amp frame a tiny bit to give epoxy something easier to bond to, put choke down, then apply epoxy generously around the area, but don't make a mess. Used rubber bands running in multiple directions to hold everything still for 24 hours - epoxy was cured by then. Because the metal standoffs touch both metal frames, the choke remains grounded as well (do not use so much epoxy that there is no contact).
     
  11. dasman66

    dasman66 Friend

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    Thanks.

    I think I got it, but any chance you could post a photo from the side that shows the choke installation? It is only visible from the top in your many photos (I'm most interested in seeing the actual standoff - I've never found anything other than nylon and want to make sure I have a visual of it before I go hunting.

    ---------EDIT----------
    NVM... I'm just going to buy metal spacers from HD and cut the threads myself. Less hassle
     
    Last edited: Jul 21, 2019
  12. bilboda

    bilboda Friend

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    I have found that tubes could take a considerable amount off of time to burn in. A Pavane 12AU7 sounded like a waste of money, until it didn't. If you have other amps that you cycle thru, give some of those tubes an extended run and see if they don't flesh out for you.
     
  13. fp627

    fp627 Friend

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    @dasman66 - I ordered standoffs on digikey or mouser. Forget which, but they are $1-2 each and you won't have to do any extra work other.

    @bilboda - As far as I could tell, only the new production 12AU7 I had wasn't burned in (as expected). I normally burn in 50-150 hours before I make any serious judgement on most tubes (I don't tube roll, but I normally have 1-2 backup tubes for whatever amp) although I realize for some tubes they do don't take on their actual sound until past 250... On the flip side I have found that after 100 hours, the tube generally has it's sound set and it's only small bits of improvement afterwards. If I don't like a tube past 100 hours, I generally don't like the tube ever.
     
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  14. m17xr2b

    m17xr2b Friend

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    Well, screw chrome platting on aluminium. It just doesn't work, on one plate they tried three times but it still ended up flaking

    [​IMG]

    Still, the topside is good and I've started building the test crack which will be without speedball. Except for the transformer everything is new.

    This time without screws drilled into the chassis for the bigger caps and choke.

    [​IMG]

    Had some flaking near the bottom socket so I decided to top mount and painted the excess black to somewhat match the silver/black theme I'm going for

    [​IMG]
     
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  15. JeffYoung

    JeffYoung Friend

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    Did you nickel-plate under the chrome? Triple plating uses a layer of copper, then nickel, then chrome. I'm not sure though whether it's the copper or the nickel that reduces flaking (or maybe even both of them).
     
  16. m17xr2b

    m17xr2b Friend

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    Didn't do it myself, sent it to a specialist company. I believe the process is to polish, then nickel and finally chrome.

    It's weird, the other plate didn't have nearly as many issues and the aluminium is from the same company. Maybe different batches, who knows.
     
  17. JeffYoung

    JeffYoung Friend

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    That's a drag. You'd think a specialist would have done it right.
     
  18. yotacowboy

    yotacowboy McRibs Kind of Guy

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    IIRC it should be copper, nickel, then chromium. If it's flaking, it's usually bad surface prep or bad copper buff.
     
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  19. elmoe

    elmoe Friend

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    Added some RCA preamp outputs today to my Crack, wired to the pot which means I need to turn it up majorly for volume, so I might rewire to the headphone out instead, but for now it is working and sounds pretty great!

    [​IMG]
     
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  20. m17xr2b

    m17xr2b Friend

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    When I got home today the last piece of the puzzle of was delivered, 4 screws.
    Almost possessed I ignored all my other commitments and started working immediately, without food, water or rest.

    6 hours later it's alive.

    [​IMG]



    [​IMG]

    I never cared much for the 12AU7 family, 6SN7 or death, at least for the Crack.

    [​IMG]

    Everything I could is from Vishay except for some parts I already had with duelund copper wire. I'll change the caps after some burn-in.
     
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