According to Pete: Headphone Amp Project/High-Current Output Stages
I design and build a headphone amplifier, and go on a journey of self-discovery (and learn some hard lessons).
Welcome to the latest edition of ATP! This time I design and build a headphone amp specifically designed to operate at the end of a chain of guitar effects boxes, and be able to take stereo input from stereo effects like delay, chorus, etc. But oh, the best laid plans of mice and Petes...
This project tells the tale of many design iterations, bad case cutting and the importance of cool stickers, as well as the value of measurements over blind hypothesis and assumptions. And what starts out as a really simple circuit that doesn’t really work right ends up being, still, a fairly simple circuit but works a whole lot better.
You can’t get all of the components in the project from us, but here’s the list if you want to follow along:
- Aluminum Enclosure
- Barrel Jack
- Proto PCB
- ⅛” Stereo Output Jack
- (2) ¼” Input Jacks
- (2) Black Metal Knobs
- (2) 10k Log Pots
- (3) 100uF Electrolytic Caps
- For power and DC block to headphones
- (4) 0.1uF caps
- Coupling input signal from pots and decoupling reference voltages
- (6) 100k resistors (in Resistor Pack)
- Set up reference voltages and feed to op amp
- (2) 1k Resistors (also in Resistor Pack)
- LM317 Voltage Regulator
- Setup for 7.5Vout with 240 ohm and 1200 ohm resistors - you’ll have to scrounge your stash for these
- (2) 2N3904 Transistors
- (2) 2N3906 Transistors
- Analog Devices OP275
- And a sweet sticker of some kind for when you, like me, inevitably drill errant holes in your case
It’s worth a mention that the ProtoPedal pre-cut case was out of stock when I started this project, otherwise I would have gone with that. But since it was out, I basically free-handed the whole shebang. For better or worse, it’s all about the journey.
