Ok, so as some of you may know, around my birthday this year I bought myself some AKG K 701 headphones. These are regarded as the best headphones in the world by many, and amongst the best by pretty much everyone.

Trying to play music with the K701 plugged into the headphone socket of my Technics SU-V620 New Class A amplifier resulted in slightly disappointing results, with a feint, but noticeable warbling distortion when listening at moderately loud levels and especially when the bass was turned up at all.

Turns out the K701 is very inefficient and consequently very hard to drive without the signal being distorted. Now, let's be clear here, this isn't clipped or overdriven distortion, this type of distortion is the result of inadequate amplification, like trying to drive a 200W speaker with a 10W amp.

So, hmm, the headphone output just wasn't going to cut it, and taking a look at a the various headphone amplifiers available, I quickly found out that most of them are devoid of any tone controls, and the price of high-end headphone amplifiers is quite astonishing!

I started looking at a few DIY amplifier designs and found the M³ (M cubed) amplifier at AMB.org, which is a Class A graded solid-state design that incorporates a bass boost control. This was exactly what I was looking for, solid-state for minimal colouration of the sound (compared to valve amplification) and a variable bass gain control integrated into the amp circuit. This is all I wanted to do with the K701, as I feel it just needs the bass levels a bit higher for the perfect sound (found out by experimentation with EQ on iAudio X5L, X-Fi Creative Mixer, Audigy2ZS kX DSP 10-channel EQ, Technics SU-V620 bass/treble).

Sizing up the amp's PCB available from AMB Labs, I looked around for a case to house the amp that would be big enough for all the internals, but small enough to be a reasonable size to sit on my desk.

I found the Galaxy Maggiorato GX283 made by Italian case manufacturer, Hifi2000.

The GX283 is a 230 x 230 x 80mm case. Here are some pictures of other cases in the series to show the construction:






The standard case is anodised black with a plain aluminium front panel. The black front panels are optional. So I decided to get the 10mm thick front panel in anodised black, as it looks chunkier and also allows some of my ideas for mounting the switches/knobs etc. Here is what the plain version looks like to give you an idea of the thickness difference:




Hifi2000 also do some rather fancy solid aluminium knobs, so while I was ordering away, I picked up a large one for the volume and a smaller one for the bass control.




I wanted a headphone jack that was black and solid looking to match the front panel, and Neutrik do a locking version.




The switch had to be black too, and I found one made by Lamptron that looks extremely similar to a Bulgin vandal-resistant switch:




I made some drafts for the front panel layout with Front Panel Designer, a free program provided by Front Panel Express, a company that mills panels based on your designs, and you can send them your own materials to be cut. Schaeffer in Germany is essentially the same company that serves the European market.




There were several things wrong with this draft, but you can see some of the ideas I have with insets (cavities) for the knobs and headphone jack. I wanted the headphone jack to be mostly flush with the panel and the flanged part of the knobs to be just below the panel's surface. Also an LED for the overload protection indicator was to be mounted flush.

The problems were corrected and the layout revised to be much more aesthetically pleasing. This isn't the final version, but it's essentially identical.




Internally, the amp circuit is near the front, with the amp's separate PSU circuit at the back, and the toroidal transformer as far away from the audio inputs as possible. The mini PCBs allow the momentary switch to activate a relay to turn the amp's PSU on, these PCBs are also available from AMB Labs.

Pretty neat NRG!



I saw a mod the other day where someone built a headphone amp into an old chunky SCSI tabletop cd-drive, they used the existing headphone out jack and kept the front bezel.

It looked pretty cool...

This project didn't really have an exciting progress. It was a case of buying a load of components from all over the world and soldering them to the pre-made PCBs, and them wiring them all up in the case.

Also, I just didn't have the time nor the patience to piss about with a camera during the build, so here are the final photos of the completed amp.

Here's how it looks from the front:








Part of the options in the Front Panel Designer program is the ability to plot out text to be engraved and then filled with paint. I really like black and red together, my main computer has a black/red theme (YES, I *am* going to finish it this year lol). So, I went with red filled-engraved text. Turned out nicer than I expected.






The accuracy of using a digital caliper and having the panel CNC milled really paid off and the knobs and headphone jack were exactly how I wanted them, inset into the panel.






With the amp turned on, the red ring of the switch lights up and completes the black/red theme magnificently. I sanded down the 3mm blue LED with fine grit silicone carbide paper so that it was flat and also frosted instead of clear. This gives it diffusion whereas it was clear and narrow beam to begin with.






I even had the back panel CNC milled because I didn't fancy taking handheld power tools to the anodised surface. It would be highly likely that the surface around the holes would be scratched if I attempted this with a drill and jigsaw or something! The phono/RCA holes are like an athletic track shape, and the IEC socket is a rounded rectangle with a tight radius, there's no way I could do this with the tools I have.




Right, so enough about the case, here's the inside!

As with the earlier internal layout design, the locations of the PCBs of the PSU and amp haven't changed. The main toroidal transformer is also roughly in the same place, but what has changed is that I needed a smaller transformer to provide standby power for the switch circuit, and then I moved the switch circuit and power relay to the side panel when I realised I could attach standoffs to the extrusion.




At the front you can see the inset volume pot, and also you can see where I had the headphone jack holes milled in the wrong positions! I was going on the reverse-side cutout drawings on Neutrik's site, but luckily it's quite easily to cut straight through holes even on 10mm aluminium. So I made my own.




Near the front, up on the side panel is another relay, mounted on a simple circuit that delays when the headphone output is connected to the amp, which eliminates turn-on thumps and the strange turn-off squeal I was getting with the headphone output connected to the amp directly.




That's it really, I wish I had time to take more pics but I haven't. Also this is my first amp build, so I got quite stressed a lot of the time trying to make things work, so I probably would have thrown my camera at the wall or on the floor in frustration a lot of the time, especially with the heat of 2x500W halogen lights beaming down on me!

Gotta get my thread in quick because I know Greg (Fueler) is gonna bust out his crazy media case real soon and make this effort look a bit lame in comparison

Hey, if it's good enough for companies that actually build amps..

The red filled text gives it a bit of a retro Hi-Fi feel for me. Nice.

Do I even want to ask how much it cost to get everything bought and shipped to and from various locations?

That machining really does "make" the case, it looks prfessional with them being inset like that...



Awesome job!

What was the total build cost if you don't mind me asking?

Damn steve! Looks awesome, very clean work!

I'm not sure if *I* want to really know

Nah, I probably could work out the total cost... let me tot it up...

Case, 10mm panel, knobs: €77.40 = £61.83
Custom milling @ Schaeffer: €82.10 = £65.62
Black countersunk hex screws: £4.25
Components from Digikey: £106.27
Components from Mouser: $86.45 = £43.46
Components from Farnell: £142.50
Miscellaneous components bought locally: ~£10

£433.93 (~$868) so far then...

I ordered some OPAMPs and SOIC-DIP adapters from Newark and Mouser so that I can try out different OPAMP combinations.

2x OPA637 + 5x SOIC-DIP: $77.58 = £39.00
3x AD8610: $28.56 = £14.36

So about £480 (~$960) altogether including experimentation with different parts... about double what my speaker amp cost, but meh, I really didn't have a strict budget on this and just want it to be awesome, which it is, even if I do say so myself

(the AKG K 701 headphones cost me £190 / $380, so I guess it's a £625 / $1250 headphone rig... it does of course provide endless aural pleasure )

Thats a sexy looking amp. What I would give for that setup! That looks clean and professional. For a first anything that is nothing but awesome.

Thanks

Here are some old quick photos I took that give a better sense of the size of the amp.

Nice Though for £500~ what could you have purchased that would have driven the AKG cans properly? I'm guessing that whatever it is, isn't likely to sound half as good as what you have built (I wish I had the time, patience, money and skill to build my own amps!)

Nice to see your room hasn't got any tidier yet ... !

edit: maybe a Graham Slee Solo? Though of course, lacking the bass control.

Really nice setup. Makes me wish I had more money for things like that. I barely have enough for a set of AKG headphones let alone what you paid to make that amp. So this Technics amp I have here at home with its headphone jack and 100W/channel can't power them properly? How many W/ch do they require?

haha... yeah... same old mess... it's not much better now

The Graham Slee Solo and Woo Audio 6 SE are about the same price and have been recommended to work well with the K701...

It really would be a gamble me buying any pre-made amp though, unless I went over to Manchester or somewhere to audition some (Liverpool has nowhere near the city centre, I think there's one HiFi shop in the whole city, Richer Sounds doesn't count lol)

I guess in a way it's like building a kit car, buy all the parts, tweak the design a bit, put it all together and add a few bits... if anything goes wrong I can fix it which is a bonus

the problem with the headphone output on my speaker amp is not the volume as such... I think maybe the headphone output has it's own amplifier... it's not like I have 150W coming out of the headphone socket lol... anyway, for all my other headphones the headphone output is fine, but the K701 I have to turn the volume to about 50% instead of 20-25% for normal listening, and it's already sounding slightly distorted...

Basically, the headphone output on almost every speaker amp is an afterthought, so it can't drive all headphones with a clean signal...

Fantastic job. I'm impressed!

Me being of an electronics background I really appreciate the work you have put into that.

Ten out of ten.

I was a bit worried that I'd assemble the circuits and then it wouldn't work, but the amp and PSU went without a hitch, worked first time, and then continued to work while I messed around changing a few components here and there...

I actually had the most trouble getting the momentary switch to relay working right and the flourescent lights in my bathroom turning off somehow causes enough of a power spike to deactivate the latch!!! I got a suggestion to wire up a 10uF polyprop motor-run cap across the L & N of a mains plug, along with a ~200K 1/2W resistor, and plug it into the same multi-way extension as the amp... I haven't tested it yet as it is a bit random with the light-off turning the amp off, most of the time the amp stays on, but somewhere between 1 in 3 and 1 in 20 times, the power spike turned the amp off... hopefully not anymore...

Flourescents have massive current inrush and are about 50% efficient or something aren't they? Pain in the arse for me though, I spent a few days thinking the amp or a component was overheating and switching off...

Awsome project! I really like the thick, milled aluminium and the internals are pretty tidy gj.

So how is the relay wired up? Voltage? Reading over your earlier post, it appears you have a separate circuit for the switch with a transformer. I think I see a regulator and a small filter cap. Surely that regulated AND filtered power source take care of any sort of small voltage drop off the main line?

That's a very impressive job for sure, I wish I had the patience to tackle something similar I have to settle for retail products, but am quite pleased with my Sennheiser HD 650's powered by a Musical Fidelity X-CAN (v2).

I've never tried the AKG K 701's but would love to give that rig a spin - I may have missed it, but I didn't see anywhere about how it sounds?

Fantastic job nrg and it was a very interesting read - thanks.

(thats not a bad price on the 701's too - where did you get them?)

Amazon does them for £182

yeah lol, you'd think so... using a voltage regulator for the 12v relay control circuit, you have a capacitor before and after the regulator to smooth out voltage fluctuations... I actually increase these from 470uF and 10uF to 3200uF and 470uF (made little or no difference)... also I put Class X capacitors across the Live and Neutral, and across the Neutral and Earth, along with a suppressor (VDR) across Live and Neutral (this reduced how often the amp turned off because of lights, but the problem remained)


Well, I don't really have much to compare it to, I have used plenty headphones, even now I use three headphones for different purposes (Westone UM2 with Shure Tri-Flange modded to Bi-Flange - for portable use / travelling, Sennheiser HD25-1 II for DJing, and K701 for music/movies/games)...

These other headphones are right at the top of their league too, but they are closed in design, so the K701 has a much wider stereo image just for having an open-back design.

I don't have the required audiophile vocabulary to waffle on and describe the sound, but the first thing that struck me and my housemates when first testing the amp was how incredibly clear the M³/K701 set up is. With the bass boost at zero gain, you can hear all the bass, but it's like it's taking a back-seat to the rest of the performance... increasing the bass gain to somewhere between 50 and 80% really integrates the bass in with the rest of the frequency range and is much more enjoyable than listening to the K701s with a flat gain...

The K701 has a somewhat sparkly mid-treb range that sounds very shrill at first, with vocals becoming piercing and cutting through a mix more than they ought to... over time (500-1000 hours) this shrillness mellows to make vocals incredible enjoyable to listen to, the sparkliness remains so percussion sounds very crisp and detailed, but it's not piercing any more...

After listening to this rig, it made me yearn for some really good female vocals and I ended up buying a couple albums from Kate Price and one of Loreena McKennitt... I rip to FLAC and then listen from my computer as it actually has a better sound than my Technics CD player (probably because of my mods to the soundcard) these albums are a delight to listen to with the M³/K701, like angels singing to me

I also bought all the albums I could find for Ulrich Schnauss, who makes the most beautiful electronic music in my opinion... reminds me a bit of Jean-Michel Jarre and Isao Tomita... certainly all masters of synths... but Schnauss is more modern and has a more finally polished sound... I'm listening to his first album right now and also listened to it last night... the twinkling sounds in "Nothing Happens In June" sound like they are bouncing around the room, while the staccato electronic beats cut through a lush rhythm and melody of analogue sounding synths... it's nearing aural ecstasy right now lol

The K701 goes so damn low too, and it's all clear all the way down to subsonic haha... so for heavier stuff like the tougher forms of dance music, the K701s still sound incredible... my HD25s have more bass power but it isn't quite as refined... the UM2s have an incredible warm, full bass, but the mid-treb doesn't have the sparkling clarity of the K701s, nor the wide stereo image...

I love all my headphones, they all bring a smile to my face

How does your X-CAN v2 compare to other amps or un-amped? Does the valve design change the sound noticeably?

yeah Amazon do them from PlanetGizmo (£182 + shipping I think)... you can buy them from PlanetGizmo's site too... there's a different in price/shipping

I ended up getting mine from Thomann in Germany for slightly cheaper... €233.00 so about £186 with free delivery

they are also available from US eBay sellers... but you might get surprise import duty and magic Parcelforce completely made-up tax like I did on my UM2s (£40 charge on top of $270 headphones)

Well I'm not sure I agree with that, you certainly described it well and I get where you are coming from, which is more than can be said of some 'expert' reviewers!


That's something I can also relate too - they do bring a smile to your face.

The X-CAN is an extremely good amp - the HD 650's are pretty lame when plugged straight to an ordinary amplifier, I have a Musical Fidelity A3 Amp and A3 CD player, but they don't have a headphone output, so you have no option than to use an amp for cans. The 650's can be hard to drive satisfactorily, probably like the 701's? They just sound lifeless without an amp and you have to turn the volume up, which brings all the associated problems of hiss and distortion.

I have tried them through a Cambridge Audio 340 amp which gave a reasonably good result, but when routed through the X-CAN direct from the A3 CD player with Chord Cobra 3 interconnects, the difference is startling! The first thing I noticed was the sound stage, very open and extremely lifelike and transparent. Like the 701's, the open back design just brings music to life. I go to a lot of live performances, everything from rock to classical and have a very wide range of tastes. But I was always disappointed with the sound at home from headphones and could only get what I wanted from my loudspeakers (which really p*#*%s of the neighbours!). With these I feel like I am at a live show. Classical music is especially good with this setup, the 650s have a particularly rich sounding bass which I think is enhanced by the valve design on the X-CAN. Vocals are very good and piano as well, which can often be disappointing through headphones. I think the Cobra 3 interconnect helps too. The final movement of Mahler's 9th Symphony is just spine tingling through them and Pink Floyd just sounds amazing, especially the SACD of Dark Side of the Moon. I'm into a female vocalist called Perla Batalla at the moment and she has a CD of all Leonard Cohen songs - her voice through headphones is like you say "angels singing to me"! I have not tried them through any other headphone amps though, so don't have anything to compare with. I want to give the X-CAN v3 a go, as it's reviewed as a significant upgrade to the v2.

I have not really used them with my PC, but might give that a go. I normally listen through speakers in the study.

Those 701's look really comfortable too - I think I may have to try some out, we have 2 pretty decent HiFi stores near me, so I think I shall see if they stock them. I really like the idea of making your own amp though and am quite envious of what you have put together there - it looks the business.

If you like female vocal and Mr Cohen, then Perla Batalla has an amazing voice, incredibly powerful. She's not known here much, I got her CD's from CD Baby in the US. 'Bird on the Wire' is I think a stunning album, especially 'So Long Marianne' and 'Suzanne'.

(her Myspace is interesting - Barack Obama is one of her top listed friends!).

Aural ecstasy - it's the way forward.....

As I said, it looks nice! Good job

Ah, yeah I thought it would be a similar case with the HD650s actually requiring amplification to sound how they should, rather than it being optional.

Being able to have the same quality and soundstage as my speakers, but through headphones, at any time of the day is one of the reasons I didn't have a strict upper limit on the budget for this project. I've actually surpassed the fidelity of my speakers now.

They are really comfortable, apart from the bumps in the leather headband... I really don't see why they are there because almost all the weight and pressure from the self-adjusting headband comes down in one point at the centre! Imagine pressing your thumb down as hard as you can on the top of your skull, that's how it feels sometimes. It's so stupid, but apparently the leather softens up over time, or I might go and get some leather conditioner to soften it up.

The album title "Bird on the Wire" sounds familiar. Probably one that I meant to check out and forgot about by the time I'd made it from the TV to my computer! Will have to investigate further methinks. I got the Price and McKennitt CDs from CD Baby haha. I found MusicFayre is quite good too, although it takes a while.

I too don't really have anything to compare my amp to. I think one day I'd like to compare the sound of a valve amp to my solid state using the same headphones, to see what the difference is...

So far, I have the M³ which sounds stellar, and everything else I have can't drive them without distortion. I tried a Numark DM1100x DJ mixer I had lying around gathering dust, which was marginally better than the Technics headphone output... I didn't try the Vestax PMC-002 DJ mixer, although I expect it would probably be about the same.

Glad you like the look of my M³, I was a bit worried I'd cock something up with the case too, but the worst seems to be that inadequate packaging on my part meant two of the corners on the front panel are slightly bashed from being thrown around by Royal Mail and the German post (I actually looked on in horror as the lady at the Post Office counter literally threw my panel package 6 feet behind her into a big mail sack with one of those metal frames holding it open, it went CLANG as it hit the frame and then the bottom! I've learnt my lesson now lol)

Perla Batalla




Source

She sings a lot in her native Spanish, which is one of the reasons I like her - a thinking mans Gloria Estefan! A little off topic, but music tends to make me do that - as you may have noticed, it's something I'm passionate about!

Just in case you want to check her out? I think Mestiza is one of her best albums, but then they are all good!

I see most of her tracks are available in full to be listened to at last.fm, so I will definitely take a listen

ah, and 2 minute previews on CDBaby too...

[quote][/Gotta get my thread in quick because I know Greg (Fueler) is gonna bust out his crazy media case real soon and make this effort look a bit lame in comparison quote]

It would be extremely difficult if not impossible to make your headphone amp look "lame" hardnrg It turned out very nice!!

Audio guys always have better wiring habits than PC guys...wouldn't you agree?

Glad to get the Fueler Seal of Approval

The only bad thing about the meticulous wiring in my amp, is that it makes me want to twist, braid or sleeve all the wires in my PC now

Nice amp. My MMM/Opus DAC/Sextets cost little over $1300US.

You should sell those 701's and get a pair of Sextets!

why do you suggest K240 over K701?