New AKGs are in…

It’s been a while since I last added to my already sizeable (and frankly unnecessary) collection of headphones, but now was the time.

Although new models come on the market regularly, the one “top of the line” model that I really wanted to get was the AKG K812. Up until a few months ago they have been very expensive and were only sold at RRP, but as they have started appearing at discounted prices I’ve renewed my interest. Although I’ve been eyeing them for a while now, it wasn’t until last week the stars finally aligned (or at least the combination of bank balance and foreign exchange rates 🙂 ) and I could finally press the “buy” button.

When it came on the market some of the first reviews of the K812 mentioned harsh treble, but on the few occasions I’ve demoed them it didn’t sound particularly harsh to me. To be on the safe side I’ve bought one of the later-model “Made in Slovakia” ones, mainly on an assumption that any treble issues might have been teething problems in the first production runs of the original “Made in Austria” series.

I’m quite a big fan of the AKG house sound – and I have been since I first bought the K501 model when it was “flavour of the month” on head-fi a little over 15 years ago (yes, time flies…). I also own the K701, K550, K495NC and a few others and just as I expected my initial impressions of the K812 are that they are “more of the same” but better. As is the case with most other large AKG models (at least for me) the K812s are very, very comfortable once properly adjusted and I think I can wear them for a long time before they start being uncomfotable. For someone who wears glasses, this is definitely not a given when you buy a high-end headphone.

Obviously this purchase impacts the audio-related budget for my next big trip (in a couple of weeks) a little bit, but that’s ok – I’m sure it’ll be worth it once I get to spend a bit more time with these new AKGs 😀


The Zen of Headphones…

Oh no, sorry – it’s the Zen for headphones 😀

This is another project from the early days of my DIY-career that I have “resurrected” by remaking the PCB. It’s an adapted version of the Zen amplifier by Nelson Pass and optimised for driving (primarily low-impedance) headphones.

The design was developed by an Italian diy’er called Marcello Pellerano back in 2002 and you can still find the original discussion thread here. In addition to the diyaudio-thread, the project was also later published as a project article on Headwize, the precursor to Head-Fi. Sadly the Headwize project repository is no longer available, but it seems the full text of that article is available here as well.

Fun fact I: Marcello’s project was the first time I ever saw the enclosures from Hifi2000/Modushop and therefore what originally led me to start using these cases.

Fun fact II: Although I haven’t copied the EQ PCB that is described in the build article, I actually own a pair of the original Grado SR-325 headphones that the amp and EQ were originally designed for. Even without the EQ, I can’t really think of a better excuse for getting the Grados out of storage and listening to them once again 🙂

My main changes compared to the original design is to use onboard heatsinks and some different footprints for the various capacitors. Especially on the output side I’ve scaled up a bit, because 32 ohm Grados aren’t as low-impedance as they were 13 years ago. Many modern headphones are lower impedance than that and so making space for bigger output capacitors seemed worthwhile.

I haven’t copied the PSU either, partly because I already have a few designs that can be used instead and partly because there are just so many other options out there now – more on that later!

Sound quality: We’ll get to that later on as well since I’ve only done bench testing so far, but it definitely works and first impressions are quite positive.

Back from Japan…

I am now back again (physically at least) from two weeks in Japan. As the trip was a holiday and I could set the pace myself there was plenty of time to explore audio-related stuff 🙂

My credit card statement tells me I have managed to take full advantage of the fact that there is a good selection of DIY parts shops in both Tokyo and Osaka – and while domestic prices in Japan tend to be lower than where I am that’s easily fixed by simply buying more stuff 😀

Special thanks to Pete Millett for providing a useful page of links for where to go shopping. Although I found most of these places on my last trip to Tokyo, Pete’s page has been very useful to me both in Tokyo and Taipei so definitely worth a mention here.

As was the case last year, this year’s expensive souvenir was also a pair of expensive Japanese-made headphones, namely these:


Another upgrade…

When I bought the Beyerdynamic T1 headphones around Christmas (see this post) I posted that my next unnecessary headphone upgrade would have to be a set of electrostatic “earspeakers” from Stax. That was mostly a joke since I didn’t really expect that I would buy another set of headphones and certainly not a pair of electrostatics. However, things change and so a birthday, a bonus and a trip to Japan later and – lo and behold – here they are 😀

Currently I am powering them from a second-hand Woo Audio WEE that I picked up from head-fi, but of course the hunt for a more permanent (DIY) amplifier solution has now started 🙂


Headphones ahoy!

I first started listening to headphones around 20 years ago. I was living with my parents and I did not have room for big speakers, I couldn’t afford to buy really good ones and I couldn’t play music on speakers when I wanted to anyway. Headphones wasn’t really a choice but a necessity at that point if I wanted to listen to music. I got a good pair of Sennheiser headphones for my birthday when I turned 15 and quickly noticed that they sounded much better than the speakers I could afford at the time (I actually still use them for my computer).

This realisation meant that when I first started building DIY audio stuff, headphone amp designs were an obvious choice because of their simplicity and ease of building and the first DIY audio forums that I started frequenting on the internet were also headphone-related, mainly (which is now defunct as a discussion forum) and (which is still very active and has thousands of members worldwide).

Fast forward to the present and although I don’t really need headphones anymore at home, they are still an indispensable part of my audio and DIY hobby. In fact I have already got a sizable collection of headphones for virtually all imaginable occasions and uses, so I need another pair about as much as a goldfish needs a new bicycle 🙂 However, just because I don’t need more headphones doesn’t mean that I can’t trick myself into buying another pair occasionally and that’s exactly what I did now 😀

As with most of my audio-related spending the cost per purchase seems to be going steadily up and this time is no exception – it’s a pair of Beyerdynamic T1s. This is Beyer’s range topping model and although I found a good offer from Amazon to ease the pain a little they are still priced at an absolutely eyewatering sum considering it is a pair of headphones… 🙂 The T1 is a semi-open, high impedance (600 ohm) design. The high impedance means that an amplifier is mandatory, but that’s obviously just an excuse to build a couple of more of those so that’s fine 😉

Sound quality out of the box is very good, comfort is quite good although these are (as noted in several reviews) pretty heavy. Build quality is excellent but more in a “solid engineering” way than the “pure luxury” way of some of the competition though: The cable is a standard Sommer cable and the plug is a standard Neutrik – very good, but not especially luxurious. More impressions coming in due course, but right now I imagine I’ll be listening to these quite happily for a long time (while browsing the Stax range of electrostatic headphones obviously 😉 )


Project files: Szekeres VE headphone buffer

What is it?
This is a board for my version of Richard Murdey’s Szekeres VE (for “virtual engine”) buffer. This design is based on the original buffer concept by Greg Szekeres published at headwize a long time ago (c. 2002). The Szekeres buffer was one of the original headwize designs that I was very interested in when I started building amps due to its simplicity, but I never really got round to it. When I stumbled upon Richard’s revised version I had to try it – just to see if it was as good as I had imagined all those years ago (well, almost 🙂 ) Oh, and be sure to check out Richard’s site for some other very interesting DIY designs as well.

How big is the board?
The board measures 3.925″x1.95″ (just under 10×5 cm.), so just small enough for a 5×10 cm board service at itead.

What is the status of the board?
The board is in version 1.1. I have tested v1.0 and made a couple of alterations to the board as there were some minor space-issues here and there, but nothing serious.

Does it use any special/expensive/hard-to-find parts?
Yes. The power resistors are TO-220 types, Caddock MP-915 or MP-930 or equivalent and they are quite expensive. The FETs are cheap but need to be matched, so buy 10 pcs. or so. The heat sinks are Fischer SK129 types (or any one of many equivalents)

Anything else I need to know?

  • The layout is pretty tight so the mounting sequence is quite important, especially if using heat sinks taller than 25mm. Start with mounting the small resistors on the board. Then loosely assemble FETs, power resistors and heatsinks before mounting them one by one on the PCB. The mounting sequence should be to first to solder the heat sink pins and then the FET/resistor pins in place before tightening the FET mounting screws. Then move on to the next heat sink.
  • There is only room for small capacitors on the board so a regulated PSU is recommended (several options available from this site 😉 )
  • The FETs are the IRF510 types recommended in the article. The FETs need to be matched as described in the article as there is no way to null DC offset.

Download design files here

Related information:
Note: Always read the “intro post” for additional important information about my designs.
Refer to the RJM audio site for BoM and information of component selection.


A well-balanced sound…

Inspired by a recent thread on a Danish headphone forum, I finally summoned up the courage to do something I have been planning for a while, namely to convert my AKG K701 headphones to balanced drive. Balanced drive in theory provides double the voltage swing and four times the output power of normal single-ended drive. In the case of fairly power-hungry headphones like the AKGs that should translate into better sound, especially in the bass. Obviously, the real benefit is that it provides a perfect excuse to build another headphone amp or two 😀

Normally converting headphones to balanced drive means replacing the stock cable, but converting the AKGs is quite easy since the stock cable is four-conductor and so already provides for split return signals. The only effort is therefore to chop off the old TRS plug and solder on a 4-pole XLR instead. I used a Neutrik NC4-MXX and I managed to find a grey boot for it to make it look a bit closer to the original look.

Reusing the stock cable also meant that I could reuse the original plug to build a balanced to single ended adapter to ensure the headphones can still be driven by unbalanced amps. Visually I admit it isn’t the most elegant solution in use, but it works without issues 🙂

If you have a pair of K701s and want to try the mod, here is the head-fi thread that describes the connections in the stock cable.

Headphones with a couple of extra connectors on :D

Headphones with a couple of extra connectors on 😀