Sometimes, when studying, I wanted to completely isolate myself from the rest of the world. Usually, this was the evening before an important exam, or when I needed to finish an assignment. To do this, I listened to music through the Sennheiser HD580 I borrowed from my father. One day, when surfing the web, I stumbled across Headwize. On the Headwize website I read that the quality of the sound from the headphones really improves when you use a headphone amplifier. The circuit in cd players and power amplifiers that normally drive the headphones are of questionable quality. This is because most people don't use them or don't listen very carefully, so manufacturers tend to make them as cheaply as possible. And Headwize also has lots of projects to build for yourself. I chose the Szekeres design. For several reasons: This was to be my very first complete diy project. So it needed to be simple, cheap and high quality. (It needed to be better than the normal cd player output; else it was of no use). The Tube amps looked too complicated and expensive. There was also little info in the forums, because they weren't all that popular. There were also a couple of pomp amplifiers. I didn't go for them, because I didn't trust them. I really believe that the projects-projects on Headwize sound good, but I was (and still am) convinced that opamps are to be avoided when possible. And in this case it was easy to avoid them: Build the Szekeres! There's extensive in the project description itself and also lots of discussion in the forums.
In the meantime, I also gave the Sennheiser HD580 back and bought my own headphone. A BeyerDynamic DT931 from Jan Meier, using his special Headwize offer.
I followed the advice of someone else and decided to build the DC-Coupled version. It is a little more complicated than the standard" version, but the performance gain would be worth it.
The Szekeres is famous for the fact that it is very dependent on the power supply design. So I built a regulated supply, following this design:
It has a pair of lm317/lm337 voltage regulators and has very high performance. It is not my design (I'm still not capable of designing anything electronic) but by Remco Stoutjesdijk (Ultranalog). The image of the powersupply was made by David Dlugos (T-linespeakers) as a present for my new webpage; Thanks!
The schematic of the amplifier itself looks like this:
I bought almost all the components from Conrad electronics. Although I know that I can buy better components for the same or less money at other places, I did not want to do that this time. Building the amp and making it work, was my first priority. Tweaking every last bit of performance out of it, was of lesser importance. Buying it all from one supplier, was easy and quick (3 days delivery time!)
Since this was my first project, the layout part was a real pain! I had no experience in building circuits of this complexity and simply started building. So there's hardly any layout to speak of. I used prototyping pcb's, for ease of use, and connected everything with standard copper wire. Only the in and output jacks were wired with shielded cable to prevent the pickup of hum and noise.
I made a wooden enclosure from pine and mounted the heatsinks on the outside. I used small pieces of stainless steel to mount the power connector and in and output jacks on. The case looks nice on the pictures, but it is not in real life. I gave myself to little time to make it and didn't pay enough attention to details. The pine is also 18mm thick, which makes it very unwieldy.
I forgot to make a picture of the amp with it's top cover on, but it shouldn't be hard to imagine what it looks like
And then the results: How does it sound?
Well, although you can hear a lot of potential, this one does not sound good. It has enough power, it also has good bass, but the highs are very harsh and combined with my own BeyerDynamic DT-931, that is too much. It shouldn't do this, I've asked around and it probably has oscillation or some bas solder joints. Not surprising, considering the way it was built. It also has no gain and no volume control, which isn't that big a problem, because I drive from my cd player, which has a high, volume controlled output, next to the normal output. I have used the amp very little, always with the plan "I need to fix it someday" in the back of my head. Well, I didn't fix it, instead; I've taken it apart completely. I'm currently gathering the parts to build my next headphone amplifier. Which is still based on the dc-coupled Szekeres design, but with some added features. It will have a tube (5670) gain stage, a volume control and a carefully planned layout. So I expect this new one to sound way better than this one. And also look better! Still, considering this was my first project, I don't consider it a failure at all. It was a good attempt at building something myself and really gave me an appetite to do more. I'm very proud that it worked immediately (well, after I connected the output to ground to get it to make some sound at all) and to sound quite good too.