HCC86: hybrid-capacitor-coupled-86 headphone amplifier, my first offical PCB headphone project. The design goal is "an easy to build, good sounding and powerful all-purpose hybrid headphone amp for electronics DIY beginners". I have never done an DIY project using PCB layout, might as well do it the fancy way this time.
This is still work in progress, the design itself has pretty much settled, just have to order some boards, do a test build and fine tune the component values.
Some "not so usual" features:
* Designed for DIY build and DIY build only. The boards are layout to be as "DIY beginner friendly" as possible. All parts are DIP, pads are spread out, easy to solder and hard to bridge cross by mistake.
* Two input options: nornal CD input and LOD (Imod, Sansa fuze) input. The LOD input has DC blocking caps so there is no need for an external cap box. Due to the high input impedance of tube circuit, the internal DC blocking cap value can be fairly small, allowing the builder to use fairly high-end signal caps at reasonable build cost.
* Volume control is of shunt configuration, the sound is less influenced by the potentialmenter, allowing the use of reasonablely priced parts (default is Alpes RK27, "alps blue") and still obtain good sound. Does require good quality input resistors, though.
* Tube is loaded using CCS and the cathode is biased using diode (s), the operating point will be fixed by CCS and diodes, no manual adjustment required. Just build and run.
* Output stage is biased into class-A by about 30mA using CCS ic's. This helps to open up the sound stage.
The "not so un-usual" features:
* low voltage throughtout. No worry of getting zapped by the high B+.
* gain stage tube is ECC86, which gives good performence at low voltage since it was specifically designed for that kind of operation.
* The output stage utilizes 4x BUF634 (or LME49600) in parallel, per channel, powerful enough to drive most dynamic headphones with authority (maybe not the orthos, though).
* Output is capacitor coupled. No DC offset to worry about.
This is not a cheap build by any stretch of imagination. Parts cost will be in the $300~$400 range. Some mid-level boutique parts will be on the standard BOM, there is not much need to upgrade once the build is complete. All parts will come from Mouser and Partsconnexion.
* Skill level requirement: Very low. The builder does need to know how to do basic soldering and can use a drill to drill the aluminum enclosure. A multimeter will be helpful but not necessary.
There are two boards involved, each is 4x3.1" (the max size allowed by eagle-lite). One is the HCC input/output board containing input/output section and the tube; the other is PSBU86 containing power supply and buffer section. These two boards will be linked together by short jumpers. They will fit into a Hammond 1455N1601 or 1455L1601.
Edited by AudioCats - 6/29/13 at 2:30pm