Pros: Satisfying project even with only moderate skills, incredible sound, detailed, smooth, readily available tubes
Cons: Quite large
I have created a thread to discuss and compare the Bottlehead range of headphone amplifiers so I'll share a small excerpt here just abouthow the amp sounds, but I'd recommend heading over to the thread for much more information and opportunities to read other people's opinions and discuss your thoughts: http://www.head-fi.org/t/683012/bottlehead-amplifier-discussion-comparison-thread-crack-sex-mainline#post_9831533
As a top of the line amplifier, I had high expectations of the Mainline. My initial impressions were just OK - it sounded good, but not amazing and I wondered if it was actually better than the lower-priced S.E.X. After spending a bit longer listening to the Mainline, I can confirm that it's a clear step ahead of the S.E.X. and also of any other amplifier I've heard so far. What's a little deceiving though is the way in which the Mainline impresses, but read on - I won't spoil the fun and tell you everything in the intro!
Clean, crisp, extended and detailed, but oh so polite.
The Mainline delivers smooth, but fully extended treble without a hint of hash or grain. There's no lack of detail or clarity, but a complete lack of harshness and fatigue. The Mainline's treble presentation is the best I've heard as yet in my headphone journey. Cymbals, percussion and high frequency textures are present and clean with good weight and presence, but are well-balanced with the rest of the sonic picture. Music can still be sibilant, but only as a result of a poor recording, not because of the amplifier. As strange as it sounds, that's a good thing because it means the amp isn't adding harshness or edge to good recordings, but while also not smoothing over poor recordings - it's presenting what's there in a really polite, but accurate way.
The mids from the Mainline are simply sublime. There's a weight and substance to the mids that is reminiscent of the Crack at its best, but significantly better.
Of all the Mainline's sonic traits, the midrange is probably the defining factor to my ears and it's the weight of notes which signifies the difference. Instruments and vocals sound and feel real. I had never really noticed before that other amps of mine create a really enjoyable facsimile of the instruments in the recording. The reason I had never noticed is because I hadn't heard it done just right. Hearing the Mainline has redefined my expectation of midrange presentation from an amplifier. There's no thickness or creaminess to the midrange sounds, just a solidity and presence that's beguiling and magical.
I wondered for a while if I'd hit a sweet spot on certain tracks, but listening to a range of tracks showed that the Mainline excels on a range of instruments, male and female vocals, transient sounds (such as drum hits) and sustained notes - everything just sounds so real.
I've stated previously that the one short-coming of the S.E.X. in my eyes was it's slightly lean bass presentation. I'm pleased to report that the Mainline strikes a perfect balance between the Crack and the S.E.X. It's tighter than the Crack, but fuller than the S.E.X.
Similar to the mids, the bass from the Mainline is weighty and realistic. There is plenty of presence at the bottom end, but no bloat or bleed from the bass. As I mentioned earlier, the impedance switch can tighten or loosen the bass presentation slightly depending on your headphones, but on either setting (given appropriate impedance headphones) the bass is excellent - full, punchy, and quick with great impact, incredibly realistic weight, and just the right speed of decay.
There's not a lot more to say about the bass of the Mainline - it just does what it should - presents the bass in a realistic way that's accurate to the recording. There no emphasis or alteration that I can hear - just clean, accurate bass that's perfectly balanced with the rest of the audio spectrum.
Staging & Imaging
If I had to choose one area that the Mainline has failed to meet my expectations, it's in the area of stage size, but this needs some explanation...
The Mainline's stage is more intimate than the S.E.X.'s and I simply adore the space and size you hear when plugged into the S.E.X. The Mainline's presentation is more intimate than the S.E.X. - once again about halfway between the presentation of the Crack and the S.E.X. If the Crack is a front row seat and the S.E.X. is a 10th row seat, then the Mainline is probably a 3rd or 4th row seat. I'll discuss the differences between the Mainline and the S.E.X. in the comparison section.
The Mainline's staging is open and defined despite the more intimate placement of the music so it's not like the staging and imaging is poor, it's just not in line with my personal preferences. That said, I'm not sure that the incredible realism and weight I discussed earlier would be possible with the more distant presentation of something like the S.E.X. and I would trade that level of realism for anything
in the world.
You might be worried that a more intimate presentation equates to a congested or crowded sound - well don't be! Sounds are clearly separated and defined and the weight of notes discussed earlier make the imaging some of the most accurate and realistic I've heard. While only moderate in forward projection of the sound, the Mainline's stage is wide and has good height.
Perhaps the strongest aspect of the Mainline's staging and imaging is its ability to separate different sounds while maintaining a single overall auditory picture. This amp manages to keep a perfectly coherent representation of the musicians while also perfectly defining each sound in its own space. You can hear every instrument, vocal, noise and texture on it's own and yet also simultaneously as a part of the overall sonic tapestry. Sounds pop out of the recording when they're meant to and blend in when they're meant to, but at any time you can single out any individual sound or instrument and hear it completely on it's own without negative influence from other sounds in the recording. This all makes for an incredibly engaging listening experience and it's got me really wanting to try the Mainline with some HD800s to see what it's really capable of when it comes to staging and imaging.
The Mainline's sound is effortless. It's controlled, polite and completely coherent. At first listen you may not be "wowed" by this amp, but on extended listening you soon realise that every track you hear sounds as solid and real as you've ever heard it. Nothing jumps out to amaze you, but everything sounds excellent.
I used to work for Bang & Olufsen and one of the key traits with their audio and video gear was an attention to lifelike reproduction. At first, lifelike reproduction sounds ordinary and everyday - it's only as you spend more and more time with it that you appreciation of it grows because it's completely believable and never fatiguing because nothing is overdone or enhanced. The Mainline reminds me a lot of this approach to audio - nothing is emphasised or highlighted so it's not an exciting sound, but it's a real sound and that continues to be enjoyable for hours on end and days, months and years of listening.
The sound of the Mainline is accurate, clean, smooth and controlled. It's incredibly balanced across all frequencies and it delivers the same auditory experience on every track I've tried across all kinds of genres. This is an amp you buy to listen to and enjoy for the long haul, not to "wow" you or amaze you in the short term. The realism of sound from this amp is still enlightening me as I continue to listen - it's a subtle kind of marvelous that has to be lived with for a while to fully understand, but it's addictive and amazing once it starts to sink in.