The Mini-amp
This was my fist real attempt at building a headphone amplifier. After reading a lot about the subject on the head-fi and headwize forums, I decided to try my hand at building something. The design uses an OPA134 opamp and a BUF634 buffer per channel. The design is shown in TI's datasheet for the BUF634 buffer IC but modified to have a lower gain. The design worked like a charm and I was very impressed with the improvement it offered over the headphone socket in the Harman/Kardon intergrated amplifier I had at the time.
Because I wanted a stand-alone unit I build another version of the same design with an integrated power supply (a simple dual design based on two 78L09 voltage regulators). This worked very well and was the first headamp I managed to finished and case. Here is is on my workbench. The mains wiring looks a bit worrying...
Because I already had the enclosure on hand I had to do some creative mounting of the volume pot. It was a bit fiddly but it worked just fine.
This was how the amp initially looked. The front panel is laser-cut from 2mm aluminium. It was wet-sanded with 1000-grit paper but I wasn't really happy with the finish. The perforated top cover was the original one that came with the enclosure.
On the shelf next to my H/K receiver. The amp measures just 10x10 cm and is literally dwarfed by the receiver.
After a while, the friend who had helped me laser-cut the front panel suggested that he could bead blast it for me as well (no doubt hoping to end my complaining about the way the front panel looked). This turned out extremely well and I decided to take the opportunity to show off the internals of the amp as well. I managed to get hold of a sheet of 1.5 mm. transparent PU which I used to make a new top cover.
I think the bead-blasted front panel really improved the looks of the amplifier.
This amp was in use for quite a long time, first by me and then by my brother. As mentioned earlier it is a vast improvement over the headphone socket of most integrated amps but it wasn't quite as good as my next project, the META42.
©Uffe Nisbeth 2002-2004 Last update: Sept. 28, 2004