I have felt compelled to attempt my first review after recently building Bottleheads premium diy headphone amplifier offering the Bottlehead Mainline. I have built a few of their kits now and the Mainlines abilities have really stood out from other amps I have built or owned in the past.  The design is about a year old but the linage and some of the techniques Bottlehead have developed and used in its topology can be traced back much further and has trickled down from their highly regarded custom headphone and speaker amplifier designs.
 
There are only a couple of reviews about so thought it would be a good idea to add some of my own initial impression of how the amp sounds as a reference to come back to later and perhaps reappraise. I'm not going to go over the technical specs as these can be easily found on the Bottlehead website.
 
So on with my two cents worth.
 
How does it sound? Abridged version
 
The Mainline sounds to me very much like the type of amp that is easy to fall in love with!
 

 
Refined Treble experience
 
The Mainlines treble reproduction is well balanced and incredibly enjoyable. With both the Sennheiser HD800 and Beyerdynamic T1’s which are both known to be a little finicky in this area the higher registers are beautifully rendered, crisp, clean, nuanced, accurate and just oh so revealing yet still remain refined and effortlessly smooth, never impolite (unless its on the recording). Cymbals, high hats ting and shimmer tantalising, tin whistles are never shrill and a trumpet screams convincingly brassy.
 
Bottlehead masters of midrange magic.
 
The Mainline simply excels in its midrange delivery and the sense of presence achieved is glorious.
The high praise the Mainline has received in the headfi community certainly feels justly deserved to me and the mid range is certainly where a goodly dose of Mainline/Bottlehead magic can be said to be happening. Texturing, note weight, layering, density of tone, decay and the oh so delicate nuances of those finer details in vocals and acoustic instruments that headphones like the HD800 are capable of resolving from musicians/artists likes of Eva Cassidy, Ruth Moody, Melody Gardot, Gregory Porter, Cara Dillon, The Whailin  Jennys’ Alison Krauss, Alicia Keys (the list goes on and on) can be very captivating.
 
Be it light and breezy or fast and heavy the Mainline feels effortlessly capable and has handled everything I have thrown at it so far with finesse and constantly amazes with its ability. 
 
There is definitely a sense of naturalness here and music feels more alive, be it the sense of an orchestral piece building to its crescendo the mournful weep of violins the wail of a electric guitar solo or a naked and laid bare for all to see unaccompanied fragile and delicate vocal the Mainline is capable of digging deep and conveying considerable emotion.
 
Bass
 
This is harder to explain I don’t want to say the normal things like tight, punchy, fast and clean or impactful as it is all of them and I feel they alone they don't do the quality of the bass justice.  My observation of bass is that it portrays the sound and texturing of lower register piano the deep mournful weeping notes of cello/violin or the resonance of a deeply plucked double bass string, Uilleann pipes, martial drums, deep vocals all with a tangible sense of instrumental accuracy. It might not be head thumping ,earth shaking bass but it is resolving, textured, deep and very accomplished bass.
 
Thoughts on sound stage
 
As a previous hot rodded Bottlehead Sex and Crack amp owner my observations are very much in line with Loquah’s excellent Mainline review (in fact it’s a struggle to find something new to say he has done such a good job and is a hard act to follow).
 
For me the Mainline here is all about accurate separation, positioning, layering and giving individual instruments their own sense of space and individuality of tone without merging into the surrounding instruments while still being coherent and immersive. With the Mainline the sound stage feels like a banquet laid out before you and is without doubt a feast for the ears. You can sit back and take in the glory of the whole table and the feast laid out before you or zoom in and concentrate your attention on devouring your favourite morsels. The Mainlines abilities here are superb. While it is not the most spacious super wide of sound stages that can amaze but can also feel a bit unnatural at times the sound stage is portrayed in a very coherent, competent and compelling manner.
 
Take away impressions 
 
The Mainline has exceled with everything that has been thrown at it so far, rock, string quartet, symphonic, funk, bluegrass and acapella as examples.
 
The high point without doubt for me is how the Mainline portrays small ensemble acoustic music such as folk and bluegrass and both associated male and female vocal, the naturalness,  speed, finesse and delicacy this amp is capable of revealing with the HD800 can be/is truly stop you in your tracks beguiling. It has the ability to resolve and articulate the smallest of details then serve them up in the most delicious of ways.
 
The Mainline amp is a real triumph from Bottlehead, combined with the Sennhiser HD800 they make for a beguiling and highly enjoyable combination which has very much redefined my personal expectations of what is capable with headfi and without doubt sets a incredibly high benchmark with its performance at its price point.