Headphones

While I have a dedicated listening room, I often must work at home in the evenings. I have a nice tube rig in my office, but I also have two other people in the house. I can't often listen to music via speakers while I work. I discovered the Headwize site and got interested in headphones. I've built several versions of Chu Moy's pocket headphone amp and his simulator. They're really great and easy to build. I enjoyed it so much that I built a tube headphone amp as well, see below.

Here's a picture of my latest CMoy amp. I built it on a PCB that I made using the photoetch process. I laid out the PCB traces using a CAD program and then printed the circuit onto overhead transparency film which was used to expose the board. This circuit board measures only 1.7 x 1.8 inches.

On the left are some finished PCB's for the CMOY amp and crossfeed adapter. On the right is the CMOY AMP mounted in a small case from PacTec that I got from Mouser Electronics.

Here's the PCB I designed for my CMOY. You can download this image into Microsoft Word and then resize the image to print your own transparency.

Morgan Jones Headphone Amp This little gem came from the Headwize site as well. It uses three 6922 tubes. It's the first tubed device that I ever built from scratch. I built it into a Hammond 10X6 steel chassis. The sound is wonderfully tube-like without being rolled off. I very much like it. I've used it to drive Sennheiser HD600's and HD280's as well as a pair of AKG 301's. It drives them all!

The power supply is different from the one shown in the article and uses a Hammond 269EX transformer (190-0-190V, 65mA) and 155H choke (5H@ 70mA). I used the DuncanAmps power supply designer to design it, what fun! Click on the image to the right, above, to see the Duncan Amps PSU Designer Screen for the power supply. It's shown both with 26.6mA of idle current and then at 48mA full load at 4 seconds.

Soft Start Circuit (Click to Enlarge)

Soft Start Circuit

Since the solid state power supply comes up to full voltage almost instantly, I built a soft-start circuit to apply the HVDC after the tubes had warmed up. The cicuit shown here closes the relay about 20 seconds after the power is turned on. Since relays can switch much higher AC voltages than DC, I used the relay contacts to break the center tap connection between the power transformer and rest of the power supply. I had a double pole relay and paralleled its contacts, increasing its current carrying capacity. The relay I used had a 5V coil and contacts that were rated for 5 Amps at 250 volts. A 3V relay would probably be better, since the circuit only provides about 4 Volts to the relay coil. Adding an LED to the ciruit as shown would provide an indicator to show when the amp has come out of the "standby" mode. Since the soft start ciruit was an afterthought, I had to build it as small as possible in order for it to fit into the case.

Inside My Morgan Jones

I've paired my Headphone amp with the very capable Toshiba SD 3950 DVD player on the nightstand by my bed. I could listen to this rig all night!