DIY Audio Home
Wheatfield Audio HA-4 Headphone Amp
PLEASE READ - Commercial usage of information on this site:
I consider all the information that I post here to be in the public domain. So, you can use it however you want, for commercial or non-commercial use.
That said, I would appreciate it if you at least let me know if you are going to use any of the circuits or especially PCB Gerber files to make commercial products, or to sell bare PCB's.
There are some cases where products are being sold not only with my permission, but active involvement. The "Millett Hybrid" effort and others at HeadFi are examples (and excellent models of how the DIY community should work, in my opinion). There are other cases where I have asked vendors to sell PCB's as a service to hobbyists. And there are other cases where companies are manufacturing and selling PCB's, chassis, etc. without contacting me at all.
In ALL of these cases, I make no profit from any of the sales. Zero, zip, nada. I have a normal "day job" that pays the bills, this is strictly a hobby with me. So please do not expect me to provide the level of technical support that you might expect when buying a product. I try and help, but it sometimes takes me days - even weeks if I'm traveling for work - to respond.
Thanks for your indulgence in reading this!
This is a solid-state headphone amp that has crossfeed circuitry and some pinna-related EQ circuitry. It's shaped kinda like a head. The idea was that you could use it as a stand for your headphones when they weren't on your head.
I designed this as a commercial product, but it turned out to be just a little too much for the average audiophile, so it never went into production. A total of 5 of these were built.
Here's the Datasheet (BIG 526k PDF file) and User's Manual (BIG 469k PDF file) for your reading pleasure. They give some details about the EQ and crossfeed functions.
The amp has two PCB's inside - one is the headphone amplifier and power supply, and the second has the EQ and crossfeed circuits on it. The amp is a conventional solid-state amp, using Burr-Brown OPA134-type op-amps and BUF634 buffers.
Schematic for PCB1 (48kB PDF file) and PCB2 (33k PDF file).
PADS-PCB source and Gerber files for PCB1 (91kB ZIP archive) and PCB2 (72kB ZIP archive) (see my CAD page to get freeware PADS-PCB). If you make any changes to the PCB please REMOVE the Wheatfield Audio name and copyright (you have my permission to do so!)
The PCB's could fit inside a normal chassis without too much trouble.