Bottlehead Crack

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

  1. zfeldma

    zfeldma Rando

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    @Jeb's and others' tube reviews were super helpful, but thought I could add some updates since prices for some of those tubes have gotten nuts.

    I have found myself with A BUNCH of tubes. I bought a Crack with Speedball that came with some tubes, including Telefunken ECC82, for what I thought was a decent price, then managed to pick up another Crack with Speedball for about the same price that came with Mullard CV4003, Tungsol 5998, and a goldpoint stepped attenuator [so can sell the first one whenever I have time to replace a diode that came loose :(].

    Before the I got the second one I had picked up what I hoped was a lightly used Chatham 5998. Also a pair of Svetlana, and a few of the cheaper options that are recommended around the web.

    Power Tubes:

    Tungsol/Chatham 5998: is damn expensive. $125-175
    ---It's a set it and forget it tube. I've had not desire to switch to one of the others.
    ---Maybe worth the high price to not have to worry. The space and air is impressive. Adds a subtle playfulness to the music. Very low noise floor.

    Svetlana: Cheap
    ---There is a bit of harshness. If that were gone would be very close to Tungsol 5998.
    ---If you've got a mellow signal could work well.
    ---Has the air and separation that makes the 5998 special. Low noise floor.

    RCA 6as7g: Medium price
    ---Sound very nice. Mine has high noise floor and some microphonics issue otherwise would be great. I could totally live with this over the 5998 if the noise/microphonics were lower.

    RCA JAN 6080: low/med price
    ---Like RCA 6as7g, mellow but satisfying tone, but again mine has high noise floor. Not the 'best', but totally fine other than noise floor.

    Cheap Option:
    Svetlana is a little harsh, so find a good copy of RCA 6as7g or even RCA JAN 6080 and I think you'll be sitting pretty good.



    Signal Tubes:
    Here's where the fun is...and the fun is cheap.
    I should preface that a lot of the tubes don't have enough bite for classical music for me. I like to hear the sharp edge of trumpet and violin. I'm pretty sensitive to sibilance, but still like my violin to capture the abrasiveness when appropriate bordering on caustic.

    Expensive ones...
    Mullard CV4003:
    The Good: Little Black Dress tube. Perfect for all occasions. Non-fatiguing.

    The Bad: Expensive. Too mellow for some music. Missing bite.
    Telefunken ECC82 Ribbed Plate:
    The Good: Fun level of extreme detail that is nice for classical music. Non-fatiguing even with level of detail.
    The Bad: Expensive. Weird echo that is super annoying for anything like blues that already had a lot of echo/reverb in it.​


    The Cheap ones....
    Amperex ECC82:
    The Good: Low/Med priced. Non-fatiguing. Could match well with harsher drive tube. Bit more lively than Mullard. 'Pleasant'.
    The Bad: Too mellow at times. Too middle of the road (like Mullard). ​
    Siemens ECC82:
    The Good: Med priced. Middle Ground. More detail than Amperex.
    The Bad: Less articulare bass than CBS 5814A.​
    GE USAF 6189:
    The Good: CHEAP. Just a fun fun fun tube. I can't listen to classical without this tube. Has most of the detail of the Telefunken without the echo and with more mid and low end.
    The Bad: A little fatiguing for rock or harsher music.​
    CBS 5814A:
    The Good: CHEAP. Really nice everyday tube. More lively than Mullard, but less detailed/echo than Telefunken.
    The Bad: Not much. I like more bite and sharp edges for classical.

    My daily drivers have become a tag team of GE USAF 6189 and CBS 5814A. 5814A is general purpose and the 6189 is if I know it'll be a longer classical music session. Sometimes I'll be listening to classical and feel like something is off and realize the 5814A is in.
    Super cheap. I like them so much I bought a spare of each. Probably <$20 for 2 of each.


     
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  2. Steakface

    Steakface Acquaintance

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    Like @zfeldma, I think both the 6189 and 5814A tubes are excellent for the money and can satisfy if you don't want to spend big or hunt rare. Both go well with my preference for a warmer, laid back yet detailed sound when paired with the right power tube and the HD6XX.

    I've been using the GE USAF 6189 for a bit now and it seems to be a great compliment to the somewhat veiled and bassy nature of the RCA JAN 6AS7G, I actually quite like the combo. The 6189 adds some much needed air and widens the stage a bit, all while keeping the bass from getting too bloaty like other tubes tend to do with the RCA. It also pairs well with the Tungsol 6080, soundstage has clearer definition and bass firms up a bit more but it's not as laid back as the RCA JAN pairing. Overall I found little to complain about with the 6189, at least for me, but if I were to nitpick I'd say it sounds less "exciting" than other 12AU7 tubes.

    I have two variations of the 5814A tube, both RCA and CBS. Both tubes have a different personality; the RCA is laid back, the CBS is more dynamic. I always liked the RCA 5814A with the Svetlana "Winged-C", the warmer and more relaxed signature calms the harshness of the Svetlana while retaining its wider stage and air. The only downside to this pairing is that dynamics seems to take a hit and it may be a bit too relaxed for some. When pairing the RCA 5814A with the RCA JAN 6AS7G it gets too warm and relaxed for my tastes.

    I currently use the GE USAF 6189 + Tungsol 6080 for the extra soundstage and detail, but sometimes I switch to the RCA JAN 6AS7G if I am feeling it. Sadly, both my Tungsol and RCA JAN power tubes are a little noisy and microphonic. I still like the RCA 5814A and the Svetlana, I feel they make a great pair, but only if you want a relaxed and airy sound.

    -Edit 4/18/21
    I tried the CBS 5814A with the both the RCA JAN 6AS7G and Svetlana "Winged-C" and didn't like them as much as my other kits, but for some reason the Tungsol 6080 + CBS 5814A pairing is fantastic. Just an overall excellent sound - not quite laid back but not harsh or offensive - dynamic, punchy, and even quick. Great separation and soundstage too. Needs a good warm up period to reach its peak. To nitpick, it's not as airy as other pairings. It may be a new favorite, definitely worth trying out for a while.
     
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    Last edited: Apr 18, 2021
  3. Alchemy

    Alchemy Rando

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    Holy fucking hell this took a long time. I kept thinking it was broken only to find it was the output from my dac..

    Presenting my entry for "nuttiest crack"

    [​IMG]

    If this thread isn't actually dead by now I'll post internal shots later as they are quite insane. I just really don't feel like getting gloves on to take the top plate out right now.

    Points of interest:
    • Actually a Crackatwoa.
    • Chassis made from 1/4in (what I believe to be) type 630 stainless steel.
    • Dual mono power supplies with only film capacitors. No electrolytic caps are present in the signal path.
    • Triad C7x choke present on each power supply.
    • Antek transformer can handle running 6336/6528 tubes.
    • Secondary transformer on the back to handle the driver tube. Switchable from 6.3v to 12.6v DC rectified via DPDT switch.
    • TKD 2cp2511 pot with gain switch at the front. I went for this over stepped attenuator stages because I feel the ability to dial in the volume, as well as the uninterrupted experience, is more beneficial than any small improvements I would get. I also did not go for a relay based attenuator as that would not have fit in the chassis. If I decide to do this later I have thought about repurposing my gain switch as a pot bypass.
    • Driver tube biased via NiMH battery + 5822 diode. Current set resistor adjusted to hit 85v on the plate.
    • Sockets and RCA jacks are silver plated, Cardas Quad Eutectic used here because imo silver->silver->silver = good bond.
    • Output capacitors double-bypassed with 1uf film and 0.22uf teflon.
    • Shunt regulator current set resistor lowered to 9 ohms to push it to the limit.
    • This amp is electrically and magnetically shielded because of the stainless. There is more inside to shield the chokes and transformer.
    • Internal AC filter added.
    • 100R grid stopper resistors added to prevent parasitic oscillation with 6336/6528. I also feel these would be good to have if anyone out there runs a 5998..
    • And a bunch of other tweaks you would expect to see on any crack.


    As far as how it sounds right now what I can say is it has -->ZERO<-- background noise even after prolonged use. This was my main inspiration for this build. Other than that I am waiting on some parts to hopefully repair my DAC. I did run it for a bit and I found it unfathomably smooth for the most part with overall separation being immaculate as I would expect from dual mono supplies. I'll add my impressions when I get a good listening session in with my 6SN7 collection.

    There is a lot more to unpack with this amp that I can't think about right now. I've been waiting to post this for a long time, and am just happy I finally can.

    Yes I know it is a bit dirty. This metal is the most vile filth attractor in the known universe. What is more, whenever I polish it I remove the circular brush finish, and its a royal pain to etch it back in with a razor blade and a microscope.



    EDIT: more ranting.
    • Resistors were chosen with care. Kiwame for AC stuff, or Dale metal film for DC. (except where there is high power or I had spares, in which case I used Dale wirewound). I bought spares and matched all the resistors with a VERY nice 4 wire DMM and IIRC there is nothing more than 0.1% out of spec. I like to think this care is represented in the plate voltages for each channel, which when I measured with the tubes in there now, had a difference of 0.7v.
    • The chokes were 240R and 242R. This was corrected with a 2R resistor.
    • All the red/plain-white wire is 20AWG silver plated teflon stranded. The banded white wire is the same but with a silver plated braided shield as extra.
    • Kester 63/37 was used where Cardas was not because its awesome.
    • The power transistors were mounted to the plate to make life way better. no heatsinks, no heat trapping, etc. The plate is dense enough that it won't go above mexican restaurant dinnerplate hot.
    • Its not very visible, but my grounding scheme was chosen very, very carefully. There is a 14AWG "backbone" running from the IEC inlet to the 1/4in out. It was mounted to the chassis with insulated standoffs. It only touches the chassis through the 1/4in out. This method made star grounding very easy. With all of this I can say with confidence there are no ground loops in this amp.
    • I coated some outer stuff with liquid electrical tape just to be sure it doesn't touch the chassis wall.
    • The copper shielding on the output caps and transformer is really just wishful thinking. But I like to think it helps.
    • The chokes and the transformer are mounted that way so the fields they all generate do not interact (as much). This is further aided by ferrous shielding, which will block magnetic fields in this range.
    • I used a drill to twist the shit out of the wire pairs for all the tube heaters. Though this does not really matter with the DC driver tube its still a clean way to run a wire pair. All AC heaters are shielded with braided shield and routed as far from stuff as possible.
    • The two bricks on the back of the amp are 30uf 800v capacitors to aid the reservoir capacitance of each channel's PSU. The rest of the giant film caps are 200uF 1410v.
    • Every metal washer nut and bolt on this amp is stainless steel.
    • The shunt regulator circuitry is on the underside of the CCS PCB's.
    • I do not know if a normal 2907 transistor can handle the current load I have on the shunt regulator. I found some vintage 2905a transistors which is what I am using (just a bigger 2907)
    • Even though the shunt regulators simulate a very very large choke, I still found that the C7x's added some richness to the amp's sound.
     
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    Last edited: Jul 24, 2021
  4. Pancakes

    Pancakes Friend

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    Christ almighty. Internal pics pls.
     
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  5. Alchemy

    Alchemy Rando

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    Alright! Heads up the sun is catching really bad right now so I had to lower the lighting. I hope it doesn't look too dark and edgy to see what's going on.

    [​IMG]
    [​IMG] [​IMG]
    [​IMG]
    [​IMG]
     
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    Last edited: Jul 24, 2021
  6. Pancakes

    Pancakes Friend

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    I feel like you just decided to see how much possible stuff you can put together in the Crack circuit. I kid of course - it's fun to see it in mega extreme form. I hope it sounds wonderful!
     
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  7. JeffYoung

    JeffYoung Friend

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    Balls out!
     
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  8. Steakface

    Steakface Acquaintance

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    That's not an amp, it's a rocket ship! We goin to the moon boys.
     
  9. Alchemy

    Alchemy Rando

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    Small update on sound tweaking:

    I'm an idiot.

    In a previous iteration of this build everything sounded really really fucking good, and in this one it was still missing that magic. So what I did was put all the current resistors back to stock, and do two very very important things I had in my old build.

    1. leave the HLMP6000 biasing LED's alone
    2. bypass the output capacitors with these 1uf 160v vintage PIO caps: https://www.amazon.com/gp/product/B0728MJ2MR?psc=1

    I don't know if its just PIO in general, or if these are special. I bought them forever ago because they were cheap. Little did I know I was getting the best bang for my buck in my life. The way they pair with the sound those LED's help produce is unbelievable. Its incredibly alive, and there's something I don't know the audiophile words for but its like someone is pulling a towel through my head and scratching the itch in my brain with sound.

    To be clear, I am not a capacitor juggler. I do not believe bull semen or genetically enhanced beeswax as a dielectric will make that much, if any difference in sound. But these little caps make a world of difference to me, and I encourage people here to try bypassing with PIO to see what kind of mileage they get. I've actually been trying to find more of these so I can stock up for the foreseeable future, if anyone knows what that company logo is on the amazon page I linked I would love to know.

    And just before anyone asks, I tested all the tweaking changes piece by piece. I did find that a slightly lower driver voltage helps with the "snap" of the amplifier but beyond that I didn't really notice anything appreciable. The LED's and the caps are what really matter.

    I also experimented with stacked schottky diodes, cap + resistor, and combinations of the aforementioned for driver bias, but I find the punchy clean sound given off by the LED's is just plain better, though I might still mess around if I get any new ideas.
     
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