Bottlehead Mainline high-end headphone amp build

Hi everyone

I'm new to headphones and recently bought a set of Sennheiser HD650 cans.
They are great but which headphone amp to get the best from them?
I'm a bit of a hifi nut and decided to go for broke and get something killer
So earlier this year I bought the Bottlehead Mainline headphone amp kit after a lot of umming and ahhing.
Headphone regulars in the High End Audiophile Thread pointed me toward Bottlehead so thanks guys.
(Edit, I'm sorta feeling I'll want to try some high end cans. Cant wait to see what it does first tho.)
I was asked if I could post a build log, so here goes ...

The kit as it will hopefully look.
https://bottlehead.com/?product=mainline-headphone-amplifier-kit
They had an offer running at the time with a $250 discount, lucky me



Onto the build!
The primer/paint/lacquer is old cellulose left over from a car respray about 10 years ago.
It worked fine apart from running out of black. Ebay rescued me. (cellulose paint isnt so easy to find these days)
Unfortunately it is a finger print magnet, I'll clean and wax it later.
I forget to take pictures sometimes, please excuse.

The kit, nothing seems to be missing, nice.
(edit. I have about 7 resistors I cant find in the build notes, I've no clue where they are used. Bit worried!)


Wooden base before/during gluing.
I used the very glue from my loudspeaker build in 2011, amazing it was still ok.
The wood is really nice, I plan on keeping its character with a clear varnish.
Perhaps a light stain would help, plenty of time to decide.
The base plate was used to be sure the base was properly square.




The first coat of black paint.


Sorted the screws before starting, too easy to get wrong otherwise.
(with an ice cube tray)


Assembling the major components for soldering. (soz for the dust, I deleted the wrong photo)



More to come ...

 

Great use of the ice cube tray

 

Volume switches mounted on the stand off plate
These switch in different banks of resistors for a very high fidelity volume control.


Volume controls fitted, underside, solder points labelled to avoid screw ups


The C4S boards. (dual shunt regulators)
C4S boards before soldering



To be sure I hit the right spot this helps a lot
soldering assistant


C4S boards soldered


Bias-RegulatorBoard before solder



C4S and Bias-Regulator Board progress



Bias-Regulator and Power supply before soldering



Bias-Regulator and Power supply rear soldered



power wiring


PSU board fitted


signal wiring


potentiometers finished


Progress so far


It looks to be close to 1/2 way complete.

 

Edit: Jump ahead to post #10
The following posts are about problems getting images to load.


Looks like using tinypic was a bad idea, lots of the pictures wont load. (-edit: turned out to be a browser crash not a tinypic problem)
The site reports "the image xxx cannot be displayed because it contains errors" yet they already have loaded ok.
Can anyone recommend another host that doesnt require a login?

 

Mufflore I always use postimage.org(or postimage.io). Simple and easy.

And congrats on the amp build!

 

Cheers.
I'm using Imgur, it seems to be working well on my 1st post.

edit
All done.
Some images are still not loading here but they load ok going straight to imgur.
What can you do.

Now they have all stopped loading here, what?
Dammit, imgur says they dont exist now, yet they were loading earlier.
I'll try postimage.org ...

 

All 24 photos on imgur from your 2 posts load fine for me.

 

Thanks for checking, I just did the same on another browser and that works fine.
Firefox makes the site report the images dont exist.
I need a beer.

Was a browser crash.
Restarting firefox works now.
Odd it made the image hosts report the images didnt exist, it must have screwed with the URLs.

 

The pictures are working fine on my end Mufflore. I am using Google Chrome.

The build is moving along nicely....great pictures

 

Thanks gw

I forgot to mention, 9.5% silver solder is used throughout the build.
It needs a fair bit higher temperature and as short a solder time as possible.
This is using a cheapy Maplin solder station which has done admirably. I'll replace it with something more sturdy when it dies.
My brother had one which didnt last long but he kept it on for long periods of time.
I leave it off until there is a lot to solder and get it done rapido. Seems to work, I've got at least 4 years more life out of it

The PSU tests (performed much earlier) passed with flying colours.
I havent tested anything else yet, fingers crossed all the solder joints are good.

Last nights progress:
Painting the wood with Rosewood Sadolin.
Its a nice colour and good protection that lets the wood quality show through.
I wondered if the colour of one coat would be enough and quite like it. I may do another coat, not sure yet.
When it has fully cured it will be sprayed with the cellulose lacquer used on the black paint surface. They go together well, tested to confirm.



Signal output wiring.
This was a bit of pita.
The instructions arent quite correct. I cut one leads length too short to fully tie down yet all cuts were exact.
Its not a problem as it pushes against a metal pole instead of the volume control shaft and is rigid.

 

Looks like it's coming along nicely

 

Sorry for the delay, the amp was built a few weeks ago but its been a bit tricky since.
A hard drive crash wiped out my photos. Luckily I recovered them and my data and even got the drive going again. I think it was caused by air trapped in my water cooler that stopped water flow, making the CPU overheat while copying data.
There were a few problems with the amp that needed time to look at.
I've been poorly, busy and bought some new head phones too

I'll try and get the rest of the work log, what happened and what it is like posted later tonight or tomorrow.
This post is motivation to make me start

 

Progress so far from the top.
Only posting this because I havent got many more pictures


Wiring prepared for C4S and Bias boards



C4S and BIAS boards fitted


Amp build finished!


Amplifier operating, valves lit.

 

After assembly I followed the resistance checks around the board, all passed.
Time for first power on to check voltages.
It passed all but the last one on the bias board. I noticed a pair of diagnosis LEDs on one of the C4S boards werent lit, they were related.

Next chance to look at it was a week later.
I hadnt tied the centre pin of the biasing variable resistors to anything (2 larger red circles) so they werent registering the bias voltage change. The 2 pads were soldered together.
This fixed the left channel but the right had a further issue.
On close inspection, one connection hadnt been soldered (smaller red circle).
All tests now passed, time to plug in the headphones!



First thing I noticed was a faint mains hum but it was fairly quiet.
I resolved to look at this later and see how well it functions.

First impressions were detailed with a lack of bass.
Mid range to treble is very fuzzy, almost like distortion.
So I left it playing overnight.
Next day it was a lot better, bass strength improved a lot and the fuzziness was almost gone. Detail remained good.
Doing a full frequency sweep, it responds very flat through most of the range with a small dip at higher bass freqs but lower bass is good considering these are HD650s.
It responds quite close to 20Hz!
This amp controls lower freqs much better and allows the HD650 to reach bass levels I havent heard before.
And its a very warm sound, lovely.

Over the next week there was distortion when playing low freq test tracks (ie can hear other higher freqs not just the bass freq). This wasnt apparent playing music for a while.
Until I came across tracks with more complex passages (lots of instruments/vocals). Then found bass distorted heavily + sound cut out when pushed hard on very intense tracks.
Using a temp gun, one of the valves was running about 20C hotter than the other and it dawned on me, I hadnt set the bias voltages after fixing the bias board problems.
Setting the bias correctly the distortions were gone, super.
This also reduced the level of the mains hum to so quiet I dont notice it once the music starts.

later I noticed when the amp had been on some time, a small distortion crept into the midrange on a few very complex passages.
Earlier I noted the heatsinks temps on the underside were well over 60C and wondered if cooling them would help.
It did, the distortions disappeared, it was now working as I hoped.

Bass isnt thumpy and tbh needs a couple dB boost for my taste on some music, but that aside it has exceptional clarity, it makes these headphones sound much better/nicer.
My silver RCA leads are too short to reach the amp so very high end of treble isnt at its best yet. But its pretty impressive with Emotiva RCAs.
The sound is very rich without any bass boost. With a silkiness which is lovely with high detail music.

I previously used no pre-amp, controlling the DACs output level with Foobar or HQPlayer.
With this amp there is definitely more detail with the DACs output maxed, controlling the volume on the headphone amp. This is as expected, the amps attenuator switches in banks of resistors for high fidelity.

Compared to my hifi the headphones are a nicer experience in some ways.
Both amps operational at the same time connected to the same DAC with the same apparent volume level. (my DAC outputs via XLR [speakers] and RCA [headphone] at the same time)
The soundfield was a little wider than before. Not a match for my speakers but a good improvement.
The richness of midrange and crisper detail at high end of mid range is awesome.
My speakers have the edge on high end treble detail (due to ribbon tweeters) and bass depth/strength (due to BK Monolith sub), but the midrange of these HD650s and this amp is wonderfully warm, detailed and smooth.
Bloody lovely. Seductive.

Here ends the build log, job done and then some.
It is everything I hoped.


Then it dawned on me, the amp is working perfectly and can continue looking at new headphones.
Bad idea, I'm skint. More later.


Edit
I meant to post more impressions with the HD650s but my new phones broke my hearing memory.
In retrospect I should have written it down as it happened.

 

Love the build but tell me you didn't just spend 3 grand on headphones lol

 

Might have

They arrived Tuesday.
Listening to Dire Straits SACD. A world of sound I havent encountered quite this pleasantly before.
I've not heard my HD650s or my speakers since (10" TL woofers, magnesium mid, ribbon tweeters on an Emotiva XPA-2) so cannot vouch for the differences yet, and they need some serious time to open up fully from what I have read.
These phones are ... spectacular.

I'll do a write up if there is interest.

 

Oh please do so I can live vicariously through you wow nice phones that I could never own lol.

 

I'd better improve my vocabulary to explain them lol.

 

I checked their site out as I had never heard of them I seriously would like your impressions as the technology is fascinating.

 

Great job man.
If the amp sounds as good as it looks you have a fine piece of gear.

What tubes are running in the amp ?

I for one would love to hear your impressions of the Meze headphones...please do.

Congrats again on your amp build...looks wonderful.