- Harp Delay
- Harp V2 Delay
- Harp Tone+
- Harp Octave
- Harp Attack
- Harp Break
- Harp Shield
- Flat Cat
- Harp Reverb
HARP AMP PROJECTS
OTL TUBE HEADPHONE AMP
The driving force behind this project was the desire to listen to my mp3 player in comfort with a set of headphones instead of earbuds. Besides the benefit of a good set of headphones is the addition of a crossover network which blends both channels and allows a more realistic and enjoyable listening experience. The inspiration and basic design for this project came from HeadWize, an excellent site with many good projects.
The amplifier schematic is from "A Top-Level Headphone Amplifier" and was designed by Andrea Ciuffoli. I made a couple minor changes to suit my needs such as a 6SL7 at the input with 220k plate resistors, cathode bypass caps for the additional gain required by my mp3 player, and a 220 ohm cathode resistor for the E182CC to reduce current draw and allow the use of a smaller 60mA power transformer. The 60mA power transformer does reduce overall gain some, but I needed the smaller transformer to fit in a 4" x 8" chassis.
The power supply is adopted from "An OTL Tube Headphone Amplifier" by Kurt Strain. But I am using a CLC filter instead of a CRC filter and the 2 channels are not isolated.
The crossover network is borrowed from "An Enhanced-Bass Natural Crossfeed Filter" by Jan Meier and is an excellent addition.
I find the amp a pleasure to listen to and a worthwhile project. This was a tight build and you have to prepare your layout very carefully to fit everything in a 4" x 8" chassis. What would I do differently? Well I would do a couple things: I would eliminate the volume control, use a 12AX7 in the preamp for a little more gain, and I would use a 100mA power transformer to allow the use of a 68 ohm cathode resistor for the E182CC as the original designer intended.
For questions or comments, email me at email@example.com