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Bottlehead Amplifier Discussion / Comparison Thread: Crack, SEX & Mainline

Discussion in 'Headphone Amps (full-size)' started by loquah, Sep 24, 2013.
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  1. FunyunBreath
    Thanks! They're the 30mm aluminum knobs that Parts Connexion sells: https://www.partsconnexion.com/CONNEX-80685.html

    Just had to drill out the mounting hole to 1/4" for the Mainline pots.
  2. Tom-s
    For my to-be-build S.E.X. 3.0 I’m trying a write-up / product review. Started on this because both my ordered S3X and Mainline took 6 weeks to arrive. And now have been at some anodizing company for almost a month with no clear window on when I get them back.

    This preview will be the start of my product review once the kit’s been build / tested / compared. Feel free to comment with tips and tricks! It’s my first try, but here it goes!


    The Single Ended eXpermimenters kit 3.0 (S.E.X.) or S3X is a DIY kit from the Seattle based Bottlehead Corporation. With two single ended watts to power both headphones and speakers it’s meant to drive even the most power-hungry headphones or most efficient speakers. The 6FJ7 tubes are put to work in such a way that even the most sensitive IEM are supposed to work with this kit. Being a DIY kit, although it’s not the cheapest option with 539$, it probably has a very good price/performance ratio compared to a lot of amps you can buy build at this price (even second hand). There’s a C4S upgrade (see upgrades) for a modest 45$ when included with the kit. If you’re a student like me, definitely look into DIY kits to save some money, listen to “the best” sound you can afford and still be able to breathe financially.

    My reason for buying this kit weren’t headphones; instead it will be used with speakers most of the time. As an almost full time headphone user this amp seemed the best way to venture into the world of single ended triode with high efficiency speakers (and as a first tube amp for living room duty). Powering a pair of Klipsch Heresy III speakers with 99dB/w sensitivity to modest 102dB peaks will be fine for both easy listening and movies.

    S3X is the second Bottlehead kit I put my hands on. Having build Crack about five years ago and making it FrankenCrack before convincing myself i needed to step up. Next to S3X I’m building a Bottlehead Mainline kit at the same time. Bought both of them to save the environment a bit and save my wallet from extra shipping costs.

    The order:

    When ordering a Bottlehead kit you have to be kind of patient. It took my kits about 6 weeks to get across the Atlantic. So this time was spent reading the manual, debating what components would be worth upgrading and ordering parts to implement them (and re-reading / memorizing the manual..).

    The kits arrive neatly and thoroughly packed, with a good amount of bubble wrap and Styrofoam to protect the hefty precious parts inside. As an European buyer, I got the full monty at customs for both kits. So it is a lot cheaper to have multiple kits shipped in one go.

    The manual and support forum:

    This is the most important thing with these Bottlehead kits and this is what makes them “easy” DIY kits for me. Their manuals are among the best manuals I’ve ever found with a DIY kit (at this moment working on 4 in total). It makes the kit accessible to be built by everyone. The PDF format manual is very thorough and I would recommend these kits to almost all ages (that can safely handle a soldering iron) and especially for those wanting to build their first DIY quality audio kit. The manual takes you trough the whole process step by step. Being 67 pages long, it contains everything you need from start to finish. Aside from the actual build it will guide a complete novice kit builder with everything you need to know about safety when building such a kit and clear soldering lessons for both point-to-point and PC-board wiring/soldering.

    There’s also enough advice on the best way to complete the woodwork and how to get a good-looking finish on the chokes, transformer bell and top plate.

    When you’ve completed your kit there’s another five pages on the most common mistakes and how to troubleshoot your kit. I’ve found these tips also come in very handy for troubleshooting non-Bottlehead gear.

    The Bottlehead forum is the place to be when you’re not confident about a part of your build, when you get freaky voltages, or other troubleshooting errors with your build. Apart from that it’s also the place to be if you’re thinking of eXperimenting a bit with upgrades like I did (more on this later). On this forum every question, whatever it is, is taken seriously and answered so that you’ll be able to continue your kit building journey and enjoy your product the most. This support forum is the part that got me confident enough to buy Crack (now 5-6 years ago). Be sure to have a look on it! Older topics are full of tips and tricks that might spare you some headaches with your future kit.
  3. CAPT Deadpool

    I'm assembling my mainline now and heavily modifying my crack. I would like to point out that page 38 of the Mainline manual has some parts where AC and DC are mixed up and at least one sentence is repeated. I don't think it detracts from the Mainline but should be corrected and the manual reissued. You should set your DMM to DC Volts when measuring the power supply. Also the heater 6.3V circuit should be DC not AC (at least that is what is marked on the Power Supply Board and what showed up on my meter).

    I skipped the S.E.X. and went straight to Mainline. But in the future I may want to build a speaker amp for high efficiency speakers and would like to hear your opinion of the kit.
  4. Tom-s
    Thanks for that!

    I only got my top plates in past Friday night. So last weekend i spent both days on the kits. Saturday i build the S3X and on Sunday it was Mainlining all the way (while listening to S3X)! :D.
    Finally had time to complete resistance and voltage checks of the Mainline only last night due to some long days at work.

    Here's some pictures to start with. Will do a write up later on.

    Both are bone stock for now. Will start "upgrades" later on! Can you spot some upgraditis hints? :wink:
    [​IMG] [​IMG]
    Last edited: Oct 25, 2018
  5. JamieMcC
    Tom the kits are looking good, great to see your up and running :beerchug:
    Tom-s and CAPT Deadpool like this.
  6. KcMsterpce
    I like the work put in to give them your own personal touch! That green is S.E.Xy! :wink:
    How does the final build look on your Mainline? I have seen very few photos of finished Mainline internals after the builds were completed. Have any pics? :D
    CAPT Deadpool likes this.
  7. Tom-s
    I will make some pictures of the Mainline before next weekend.
    Last weekend build the C4S into S3X. Major improvement in sound.
    Tonight i had the chance to put a new volume control in S3X. More details :)!
    It is a shunt / series stepped attenuator like the Mainline's with Shinkoh/Vishay resistors.

  8. itsikhefez
    I read every post in this thread about capacitors for Mainline but still can't seem to find a conclusive answer....
    I am highly considering tackling the Mainline later this month and wanted to swap in upgraded 10uf caps.
    Assuming those RTI Teflons are obsolete at this point, these are some reasonable options:
    Mundorf Supreme,
    Mundorf Supreme Silver/Oil,
    Auricap XO,
    Jantzen Audio Superior Z-Cap

    I will be using HD650's and either LCD2C or HD800s (need to make a decision on this as well)
    CAPT Deadpool likes this.
  9. JamieMcC

    I was thinking about selling my Mainline a little while back (temporary insanity) and decided I wanted to hang on to my RTI 10uf Teflons so swapped them out and put the original stock capacitors back in. By that time I had been using the Teflons in my Mainline with the HD800 for over three years going back to the stock ones the result was err interesting shall we say and leave it at that. However it confirmed for me that if your spending the sort of money the Mainline costs then it makes sense to seriously consider the cap upgrade options, good caps in the Mainline can have a very positive effect on the Mainline listening experience.

    Knowing the difference a higher end cap can make and wanting the new owner to have a great experience with the Mainline I picked up some used 10uf Audyn Cap Plus capacitors up on ebay and fitted them to the Mainline and was very impressed with their performance over the stock ones.

    If your not in a hurry just keep a watch on ebay keep checking the new listings for capacitors and you can find some really good deals the two Audyn plus 10uf cost me £15 for the pair!

    fwiw the Mainline and HD800 have superb synergy.
    Last edited: Oct 31, 2018
    itsikhefez, CAPT Deadpool and Tom-s like this.
  10. JamieMcC
    Hi Tom nice work on the Sex volume control did you run into any issues at all with the mod or did it all go smoothly?
  11. Tom-s
    All went smoothly. But it's a small space to work in. So you really have to take your time.
    Only mistake i made was switch the course attenuator channels left an right. As in, my wire from fine to course was to short for both to cross channels. So i crossed the resistors going from coarse to ground to make everything right again. In the end, all is ok.

    After the volume pot upgrade i set out to put in some Ruskies in my S3X.
    The most influential capacitors in S3X are the 1.5uF output coupling/parafeed capacitors. Of smaller effect are changes to the 0.1uF interstage coupling capacitors. For my S3X I chose for a budget capacitor upgrade with FT-3 NOS Russian Teflon interstage coupling capacitors and MBGO-2 output coupling capacitors.

    What I noticed with these upgrades was a positive effect on soundstage/details/tone with the parafeed capacitor change. This cap colours the sound quite a bit, so trying a few different caps in this position to match headphones/speakers can be worth it. The interstage coupling capacitor brought out more details, little extra musicality and tightened up the bass (most noticeable). In the future I plan on upgrading the parafeed capacitor to Audyn True copper max or Jupiter coppers when funds allow.

    I'll leave S3X for a while now. More upgrades (power supply, input, output) to follow. I'll focus on Mainline caps next week.

    Some pictures:
    JamieMcC likes this.
  12. JamieMcC
    Tom smart idea to insulate the metal bodies of those Russian caps, I did wonder if you planned to construct the upgraded attenuator on a small board separate from the build then drop it in place just leaving the connecting of the left and right channels and grounds to do in situ.

    I have yet to try any copper foils in my Sex but have a little experience of using them in a couple of other Bottlehead amps Mainline & Eros.

    I burnt in some 0.47uf Duelund Cast Copper foil, paper in oils (intended for my bottlehead Eros phono) in my Mainline adding them as bypasses to the RTI teflons. They probably had around 300hrs on them before they were swapped into a the Eros. I liked them in the mainline and was very tempted afterwards to try the 0.01uf Duelund silver foil bypass cap.

    The Bottlehead Eros I built in 2016 was already sounding very capable I had done a few common mods which were to use hand matched all Teflon capacitor RIAA stages, The 100uf electrolytic cathode capacitors were replaced with 98uf mkp film ones a few strategically located Kiwame resistors and the EROS builders go to output cap the Russian 0.22uf Teflon these are often recommended on the Eros thread, plus of course some NOS EF86 chrome plate Telefunkens tubes.

    The 0.47uf Duelund cast coppers replaced the Russian 0.22uf Tefons and while I thought they made a positive impact as bypasses in the Mainline in the Eros they truly shined and ratchetted up the performance the 3D spatiality and density of tone they delivered was on a whole different level than before.

    Tom-s likes this.
  13. Tom-s
    Building a separate input board to use with the Elma rotary switches would be endgame. But those would need to be custom made in higher quantities that would make it both expensive and unpractible. So that’s a no-go.

    S3X for me was a budget build extra to Mainline and my first venture into the world of high efficiency speakers.
    And I must say, an eyeopener! This sounds so alive, so real, so open.
    What I learned most from S3X and Mainline after living with my upgraded Crack for many years is that it’s better to upgrade to a higher level amp/dac versus spending money that coupe almost get me a new amp on exotic caps/tubes.

    So while Duelund caps will possibly take S3X to another level i’m holding my money for a fully packed Stereomour II and keep the upgrades for S3X more fit to it’s price range (Audyn true copper max).
  14. Doc B.
    I've been trying to make that point for 23 years. Thank you. Refined circuit design will pretty much always trump boutique parts. We came up with the Crackatwoa as an alternative to putting silly expensive caps and tubes in a Crack, and a good part of why we make so many different headphone amp designs is to allow builders to experience this idea.
  15. L0rdGwyn
    Wasn't sure where to share this since the Crackatwoa does not have its own HF thread, but man oh man, this tube...

    I have collected and compared nearly every Crackatwoa compatible, reputable 6AS7 variant power tube out there, with the exception of the GEC 6080 and 6AS7G since they are nearly impossible to find in the USA. Tubes I have in collection include several Tung Sol 5998's, a Tung Sol 421A, multiple Western Electric 421A's, Bendix 6080WB (graphite), Chatham 6080WB (graphite), Tung Sol 6080's, Tung Sol 6AS7G's, Mullard CV2984, and a handful of others.

    I recently received an Ebay notification on a saved search a created well over a year ago and had completely forgotten about: "Tung Sol 7802", I had read an instance of a Bottlehead forum user mentioning that this tube was sublime, but pretty rare. A was fortunately able to acquire five of them for around $80, what a steal! When I first got the tubes, I gave them a passing listen, assumed that they fell somewhere in the 6080 lineup in terms of performance, and went back to my default, the 421A.

    Then the other day, I decided to give them another go. WOW I have been missing out. IMO, after doing some comparisons, this tube easily rivals the 5998 and WE 421A in terms of clarity, resolution, soundstage. I would say it is a little brighter than those two tubes and more mid-forward, but an absolutely pleasing listen and a top performer in my Crackatwoa.

    Just wanted to share this PSA: if you happen across one of these tubes, don't hesitate to grab it, truly a diamond in the rough.

    Last edited: Nov 9, 2018
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