Bottlehead Crack

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

  1. Mithrandir41

    Mithrandir41 Friend

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    For God's sake use helping hands to hold the wires... I did mine without them and it was a serious task.
     
  2. Mithrandir41

    Mithrandir41 Friend

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    This is mine: built in 2012 and still going strong. FB_IMG_1574308974433.jpg
     
  3. Elnrik

    Elnrik Super Friendly

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    The first thing you should do is build a custom base for it.

    IMG_20190924_122128.jpg

    https://photos.app.goo.gl/GBEfFBksFm5NQVNN9

    Just kidding. Grab a beer and stop worrying. Make sure you have a good soldering iron and multimeter. That's it.

    You got this.
     
  4. m17xr2b

    m17xr2b Friend

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    Before packing up the spare crack for shipping I gave it a good listen and a reality check for my sanity and for future projects.
    [​IMG]
    My crack has a custom Sowter transformer 150V 150mA, 6.3V CT 4.5A, CLCLC with 3x50uF oil caps at the end, resistor loading and oil output caps, TKD pot, rechargable battery -6V bias and suitable plate loading. Unrollable input tube, BL63.
    The other one is a more standard CLCRC with typical electrolytic caps, 100uF mundorf film at the end, film output, speedball, alps pot, using 2xL63.
    My softspot for British tubes is easily seen.

    Bass:
    Custom has an even low end response with far deeper low end when called for. Drums have real impact that can be felt. Standard is mid bass tilted and may sound to have more quantity but less control especially in the <60hz region.
    Top end:
    Fairly grainy on standard and lacking fine refinement, can be too incisive at times, fairly forgiving with a silibance, smearing tendency depending on headphone mods. So so micro detail, plankton will not be heard.
    Custom reaches TOTL finesse and detail if a bit relaxed and dark-ish. I won't be ashamed to put it against the Teton for detail even if it can't match the Teton's speed.
    Soundstage:
    Standard is average, lacks depth with most things on the same plane. The custom amp has exemplary soundstage and depth especially with HD580. This enabled superb imaging, almost matching a stock tubed Stellaris without the ultra refinement but not far behind. On larger scale orchestral music it presents a superb 3D image, among the best I've heard. The input tube is partially responsible for this and the reason why I wanted to build an amp around it. I'm surprised how close it's to the DNA amp but never quite reaching the same potential.
    Mids/tone
    OTL amps have good tone with high impedance HPs, that's why I enjoy them. Standard has a warm-ish, again grainy mids with a plastic underlay I blame on the output tubes.
    Custom has the third best tone I've experienced after Stellaris with PX4 and Woo WA5 with Elrog 300B/ECC32 on high impedance secondary. This might be sacrilege but I'd take it over a 2A3 Stellaris. Grain free full bodied mids with lots and lots of details, natural with a hint of warmth as it should be.
    Tone is the reason I find it so engaging and inviting.
    Presentation:
    Standard is quite up front, this in turn makes it really fun, the mid bass emphasis with the fairly neutral if one note treble is a joy for short term listening, rock is a treat.
    Custom is fairly relaxed and a few rows back with a tad darker treble overall sweet sounding while maintaining every bit of detail as the best of them. Ideal for long session, that tone coupled with an ideal soundstage and balanced frequency response makes it engaging and non fatiguing.

    This is the end of the road for the crack experiment, it's so good I won't mess with it any further and disturb the mojo. I had no idea what to expect as just high quality parts doesn't make a good amp, luck and some tuning.
    Where it's lacking compared to the Stellaris is speed, low end grunt, a bit on soundstage and imaging and the uber detail.

    As a daily amp with 35W of power consumption and 10,000+ hours of tube lifetime it's pure perfection. Why am I keeping the Stellaris? Because of PX4 and AVVT 2A3, stock wouldn't have cut the mustard even if technically superior though the DNA experience was invaluable to finding out the type of sound I want.
     
    Last edited: Nov 23, 2019
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  5. m17xr2b

    m17xr2b Friend

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    For those who asked on PM about the top plate and details, I'm not sure how this is works but from my point of view the intellectual rights belong to SBAF. Most laser companies will accept .dwg files.
    Password is: tubesforthemasses

    Rough cost in GBP:
    Laser cut plate - 50
    Chrome plate and transformer bell - 100
    Custom sowter transformer - 210 (double and triple check mounting and holes on plate, adjust as needed)
    Jensen oil caps - 130
    Jensen electrolitics 75
    Mundorf outputs - 80
    Black sockets from japan - 15
    Dual spirit chokes - 40
    Duelund wiring - 30
    Nuts, bolts and things - around 20
    Custom frame - free, had the parts from a different project but worth around 50
    Wood chassis - free, made by my father
    Resistors - 40 (tried different values for tuning)
    TKD Volume pot with remote control - free, took it from the stellaris but worth 80
    Audio Note RCA - 20
    Aluminium volume knob - 15
    GEC 6AS7G and BL63 - 500
     

    Attached Files:

    Last edited: Nov 24, 2019
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  6. Alchemy

    Alchemy Rando

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    I feel like everyone should know what the crackatwoa does. I made this awful drawing myself so it should be fine to stay up. This is really for educational purposes only. I have been asked for the c2a schematic privately by people who just want to know what the hell it's doing and I feel that a lot more people do so that is why I made this. If you are coming here from somewhere else looking to make a clone be warned you are not going to get any help with it so you better know what you're doing. Also you are more likely better off just buying the kit if you don't own most of the parts already. They put real effort into the quality of parts and chassis so it is good value, and if you ever want to get help with mods or your amp explodes you would have a support team. You also get the comprehensive step by step guide to build their kit. tl;dr Do not bother Bottlehead if you are going to be a leech.

    [​IMG]

    Any oddities with this schematic are either because the version of the c2a schematic I have is weird, or because I couldn't be fucked to do a good job drawing this. I preserved some as much of the original schematic as I felt like.

    If you wanna be super cool and upgrade your existing crack to a crackatwoa I can say right now you'll need an extra transformer for the 6aq5 heaters. Again I wouldn't bother Doc or Paul with any of this because you probably aren't going to get helped.

    IME the improvement made by the shunt regulator is massive. Depth does through the roof and bass hits HARD. For me this is what I noticed and still notice every time I fire my amp up. Also the speedball by itself was a little muddled to my ears. c2a completely remedies this.


    Known mods / part upgrades -Included BASIC impressions/reasoning behind each
    use CSD01060A diodes for the rectifier
    -No switching noise, better response. Slight sonic improvement and blacker background
    replace first (or all) 270R psu resistors with chokes (triad C7-X popular here)
    -Smoother DC. Lowers noise and helps with "richer more dynamic sound". IME amp is a little dry without it.
    replace output capacitors with film type
    -
    Better response. Smoother sound, more detail.
    replace last psu cap with film type (or all caps)
    -
    same benefits as replacing output capacitor. Paul Joppa says the last psu cap is about as important as output cap. As for replacing the other caps, I have noticed significantly smoother sound from doing so.
    replace MJE350 with MJE5731AG
    -No sonic benefit. Is stronger than MJE350, eliminates need for a heatsink in most cases (when doing current related modding etc) (note: pinout is different, so "turn it around" when you install it)
    use NiMH battery to bias 12au7 in place of LED
    -
    "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." -m17xr2b
    start bypassing capacitors (psu caps, output caps) with 1/100th value film caps
    -
    Improves passage of different frequencies. Many Van Waarde amps (same topology as crack!) have bypassed
    output caps.
    get a nicer potentiometer (blue velvet, audio note, TKD etc)
    -
    Improved channel balance especially at low volume, improved detail.
    shielded wire for signal
    -
    Lowers noise
    shield everything everywhere
    -
    Lowers noise
    grid stoppers
    -
    Can lower noise and prevent parasitic oscillation. especially if you run a 6336, still working on the crack that will have these so I haven't tried stuff yet. Paul says 200-800R iirc however I've also seen the Wheatfield HA-2 use 100R. will revise this mod when I learn more about it.
    Play with reservoir capacitance
    -
    Messes around with the low-end IME. For a while I put a 20 or 30uf bump and that made a noticeable difference.

    Mods possible if transformer can handle it
    parallel 30.6R resistor with 75-80R resistor (not tried yet!)

    -Should increase current
    DC rectify 12au7 - check valvewizard for proper procedure (killed all the hum I had) (use low noise diodes)
    -
    Gets rid of hum to driver tube if there are problems

    Things that have crossed my mind that I believe are unneccessary
    Elevated heaters (check valvewizard for how to do this right)

    -Lowers heater hum in theory, IME does nothing on the crack.
    Humdinger
    -
    Resolves issues with unbalanced heaters. use in place of center-tap resistors
    Soft start (can use a 5v phone charger and NC relays for small, no noise operation, manually switched)
    -Only "necessary" when running very, very high voltage. This normally helps extend tube life. If you switch off after the psu (reservoir cap) you'll get inrush current which will actually be worse.

    If you have any mods in your crack please share them! I will gladly add them to the list.


    I would also like to go into exotic tubes that seem to work very well in the crack but I don't want to go off the rails because there are in fact quite a few tubes for this thing. I will therefore just mention here that there are tubes beyond the 12au7 and its million variants and save the bulk for another post..

    Driver tube:
    Drop in:

    12au7/ecc82/5814a/7316/cv4003 etc...
    6sn7/vt-231
    6f8g/vt-99
    -if you want to get into the 6sn7 rolling hellscape there is a thread on head-fi called the reference 6sn7 thread.

    Mod required:
    12bh7a
    e80cc/6085
    VR102 (m17xr2b is only one known to run this tube because hes super cool)
     
    Last edited: Dec 11, 2019
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  7. m17xr2b

    m17xr2b Friend

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    I'd consider trying to increase the bias as a mod after you build it. The 6080 is coasting and could do with more current, that's I think one of the biggest differences between the crack and the Teton besides parts quality. This may need a resistance on the grid of the output or worst case a coupling cap.
    If you're using the crackatwoa transformer I believe it's much beefier than stock crack. That thing could run a 6528A, a tube I'd high recommend trying, the end game of any 6AS7G, don't tell the 422A and gec fanatics.

    I don't think you need soft start, I research this when I was building mine. Some say it will avoid cathode stripping but that happens at 700V+. Stick with AC heating, simple is best, if you have noise get better tubes, it's amazing how fast you fill out space with small things and I can't see any benefit for the effort for IDHT.

    Just a thought, great, great write-up. I'd wish we could compare amps.

    It's not a mod per say and won't have any sonic benefits. If running tubes such as VR102 the MJE350 will dissipate more heat and needs heatsinks or MJE5731AG without(keep in mind the orientation is reversed)
     
    Last edited: Dec 11, 2019
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  8. Alchemy

    Alchemy Rando

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    Yea I was (EDIT: am going to, very soon) going to include what each mod did and explain what replacing the mje350 does and why I am not implementing soft start or any of the other things in the "I am not gonna do this" section. I came to the exact same conclusions about soft start too and actually unless you switch it before the psu altogether you'll get inrush current which could be bad. The dc heater wasn't an issue for me as I had the parts + space. It ends up being a rectifier and a 10mf cap for the 600ma driver current which isn't bad imo.

    I built a c2a clone specifically to run a 6336/6528 and I have to say we should keep this tube to ourselves. The clarity and overall refinement on this tube is spectacular in every range of sound, granted I have only run jan 6as7g's and a couple basic 6080's otherwise. I am using an AS-1t150 same as mban which can handle the ~7.1 amps I need to run the whole thing (website claims 20% over spec on 60hz power is fine).

    My "finalized" tube complement is a USN 6336A, a (genuine) 6SN7 bad boy, and 2 telefunken 6005's.
    I have had great experience with the RCA grey glass and Raytheon 6SN7's (the tall bottle yellow lettering). Am going to try a TSRP soon and maybe when I make an adapter I'll try some mullard 12au7's I have lying around.

    Something I will post on when I'm finished with it is what happens when you run dual mono style psu's. This transformer has two hv windings and I have the parts / space so I'm gonna give it a go. Not exactly sure what is going to happen as I am far from an electrical engineering degree but the theory is very good channel separation and maybe better response as each supply will be doing half its rated work.

    If you have any specific recommendations for the bias I would love them. Grid stopper value recommendations would also be appreciated if you have any thoughts, otherwise I'll be trying 560R, 200R, and 100R stoppers.

    By the way, have you run a 6336? I read your writeups and you had a transformer built for your "insane crack". Can it handle the heater current?
     
    Last edited: Dec 11, 2019
  9. m17xr2b

    m17xr2b Friend

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    I never intended to run 6336s, the power consumption would be to high, and I couldn't possibly manage the heat in such a small chassis already quite crowded with components. What I would say, they have super technicalities but little to no romance. Made the Teton sound solid state and while exceptional not what I was looking for in my amp. I prefer to use output tubes to customise sound and use a neutral input.
     
  10. scblock

    scblock Facebook Friend

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    I received the kit before Christmas, and finished building a stock Crack last week. I have been listening to it quite a bit in my main setup since. I appreciate the good advice I got about patience, it came in handy. I built things up over a few days and checked and re-checked things as I went which seemed to help. I had one loose wire joint in the power supply that tested fine with the amp upside down but failed with it right side up, which was an easy fix. Since then everything seems to be good.

    I used a dark walnut stain which I'm liking a lot, but I did a poor job with the polyurethane finish. For now I'm leaving it as-is, but I'll go back to refinish the wood when it warms up again.

    I'll be keeping it stock for a while longer, but eventually will wire in the speedball upgrade. Other changes or upgrades will wait for now.

    Sound is quite nice, and is a good fit with my HD650s. I'm still learning to write good impressions, so I'll leave it mostly alone for now. Did feel sort of like I was climbing into Kaki King's guitar on Frame though. Generally I'm getting a really good sense of space and instrument placement.

    I've been listening to a lot of Rush through it today, given the news about Neil Peart's passing, though this pic is from a few days ago.

    [​IMG]
    [​IMG]
    [​IMG]
     
  11. Mithrandir41

    Mithrandir41 Friend

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    That's a solid listen. Do Signals next, or maybe Hemispheres
     
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  12. scblock

    scblock Facebook Friend

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    So far today it's been a mix of CDs and LPs, about half of their discography. I just finished Fly By Night, and Signals is a good suggestion I hadn't played yet. It's on now.
     
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  13. Donald North

    Donald North Friend

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    Don’t forget a spin of Permanent Waves
     
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  14. scblock

    scblock Facebook Friend

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    I assembled and installed the Speedball boards this weekend. I built the small board last week but had to order the right side cutter tool so I could clip the leads of the installed resistors before I could install it. Installed the small board on Saturday morning and listened for a while. Built the large board Saturday night, did a final inspection and installed it on Sunday morning.

    This was only my second time soldering circuit boards and I’m not very good at it. Thankfully I’m good enough that everything went fine and worked on the first try.

    My initial thoughts after listening for several hours Sunday and yesterday are of a slightly leaner, more neutral sound, better control on the bass, and more impactful percussion. I think it’s an improvement on the stock Crack, if less lush on my HD650s. The sound from 600 Ohm Beyer 990s is definitely improved.

    It’s a really satisfying feeling to have built this.
     

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