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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. slankoe
    I dont know enough about people's experiences with crackatwoa.
    Mainline ought to be an upgrade for sure.

    I was considering the Lyr2 once, but eventually went for Bottlehead SEX. I made a review recently which can be found on the product showcase page. I'll try to provide relavant info and why you should consider the SEX.

    SEX has a remarkably neutral sound and FR goes quite low, satisfyingly high, and linear as well. I actually preferred the SEX over Mjolnir 2, overall, for powering my trusty 300ohm Sennheisers (HD650). They also had particulsr synergy with the HD700, bringing out the best of it's sound. With the Focal Utopia, SEX won me over vs Mjolnir (but Mjolnir was slightly better with the Clears, because they love that extra upper treble air).

    Here is a "very low-quality graph I made," regarding the tonal balance of SEX and Mjolnir compared.
    (exaggerated and not to scale)

    Perhaps you can extrapolate this to info about how the Mjolnir compares to Lyr 2. For technicalities overall, I'd score Mjolnir a tiny bit better, but it could be due to the extra "u-shaped," tonality (which is very tastefully done, mind you).

    Nonetheless, SEX is a single ended triode design. There will be inherent differences between it (other Bottlehead amps), and hybrid designs like Lyr and Mjolnir.

    It is difficult judging how good an amp is in regard to synergy (perhaps the most important aspect of all). I hope this helps someone. Best of luck in your search.
    Rhamnetin, moriez and gab840 like this.
  2. Tom-s
    I'm still debating wether i want to build a S.E.X. first and a Mainline after.
    Maybe i'll just build both at once because next week the Mainline will be on sale 20% off.
    So for anyone figuring what end-game amp for HD6-8xx headphones to buy, this is the moment!
    timind likes this.
  3. adydula
    I have a crack and a mainline...and they both are excellent....I find the mainline pairs better with higher impedance cans like the Beyer T1's....
    The Senn 250 ohm HD 600 are magical with the Crack (w/speedball)...the T1's on the crack are good but much better IMO with the mailine.

    Mainline is on sale again $250 off...a great TOTL amp from BH!
    alphanumerix1 likes this.
  4. rated1975
    Can someone explain what steps are involved in biasing the mainline, does this take long and how often should it be done.
  5. JamieMcC
    When I got my Mainline it pretty much made my Sex redundant for headphone use as the hd800 on Mainline is seriously good. Luckily the Sex is also a really nice sounding speaker amp and I use it for 2 channel. If the Mainline is out of budget don't hesitate about the Sex its a superb amp and at its price point its seriously good.
    Loquah likes this.
  6. JamieMcC
    Its simple to do you just need a multi-meter to measure the voltage on two terminals one for the left and one for the right channel there is a variable resistor which has a small screw on the top you turn the screw one way or the other to raise or lower the bias voltage. It doesn't actually take long to do but you need to let the amp warm up a bit first. I normally do mine every four to six months I would do it more often but my amps in a bit of a awkward position to get in and out of.
  7. timind
    If the Mainline is that much better than the SEX, it must be phenomenal.
  8. adydula
    Also...anytime you change or replace a tube,,let it warm up and then check and adjust the bias.
    Easy to do but BE CAREFUL where you grab and or touch stuff...theres voltages present that can
    harm you!!

    I hook up test leads carefully with the unit turned OFF and then turn on and let it warm up, then adjust if necessary.

    Last edited: Nov 6, 2018
  9. JamieMcC
    Good advice I always use a fly lead fixed to the ground point and my multi-meter probe then you only have one probe to handle which is I find much easier.
    deserat likes this.
  10. deserat
    It is. The sex is a very good tube amp. The mainline is, well I can't even image where to go from here. One thing I would note about the mainline though... it reveals what you feed it with and what you feed it into. When I went from the Gumby the Yggy there was no question of the difference... with the SEX it was more subtle. With the Crack I'm sure there would have been no difference. The HD600 sounds better on the Mainline than the SEX, the HD800 sounds ALOT better on the mainline than the SEX. In their class they are all wonderful amps but they are ... shall we say... priced according to transparency. I do however have a special place in my heart for the Crack, my first build and my first real ecstatic euphonic ecstasy.
    Last edited: Jul 31, 2018
    pure5152 likes this.
  11. slankoe
    I had to get an Eddie Current Zana Deux S to top my SEX amp!

    To be fair I did not try the Mainline or anything else above $1000. Of the few nice amps I owned and tried at meets/friends however, none of them had the midrange resolution of the SEX or paired as well with Utopia and HD650.

    SEX (with the C4S upgrade) is a truly underrated gem. I'd love to try a Mainline someday.
    Last edited: Jul 31, 2018
    alphanumerix1 likes this.
  12. Tom-s
    Thanks all for the advise. It's great to hear all such good comments about both amps. For me the Crack is special aswel. De journey with this amplifier is great!
    Still couldn't decide and went ahead; ordered both S.E.X. and Mainline yesterday. Can't wait to fire up my soldering iron!
    I'll build S.E.X. first, use it with headphones a bit, install CCS, and then try it as my first tube speaker amp :D.

    Edit: Ohh, and all suggestions for mods are welcome.
    Noted capacitor upgrades on both. Maybe some signal pathway improvements recommended from te start. The volume pot on S.E.X (have a spare stepped laying around). The wiring?
    Last edited: Jul 31, 2018
    moriez likes this.
  13. JamieMcC
    Tom wow you sure went for it ordering both congratulations.
  14. Tom-s
    If i'd just ordered the Mainline. I'd probably never have sex :dt880smile:.

    Now i can start venturing into the world of speakers. I'll probably start with Heresy's or other "small" efficient speakers.
    Last edited: Jul 31, 2018
    deserat likes this.
  15. smallcaps
    I'm just about to start building a SEX with my father-in-law for his 70th. Was also curious about efficient speakers as I intend to wire for 4ohms.

    How will you wire your SEX? I was mulling over 4ohms vs 8 and pairing with high efficiency Klipsh's but was curious about other options. Any suggestions would be valued.
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