I love headphones. It’s the only way I can listen to music much of the time; without them I wouldn’t be able to. At work I listen on Grado SR-80’s, which allow external sound to come through so I can still hear my phone ring and be aware of what’s happening around me. At home, I wear closed phones like my Ultrasone HFI-580’s so I don’t have to hear what’s happening around me, allowing me to enjoy my music and movies in peace. With all of this headphone listening, it was inevitable that I would eventually take an interest in headphone amplifiers, and I did. Recently, I built the Objective2 headphone amplifier (actually, I built two – for home and work) and in this article I’ll cover what led me to the Objective2 amp and my experience building it.
I built my first cMoy earlier this year, and it came out really great for my first attempt at building a headphone amp. The only problem was that it’s a poor match for the headphones I use. My headphones are all efficient low-impedance models (Grado, Ultrasone) that don’t require a lot of voltage. What they need is more current. The basic cMoy design doesn’t provide this, at least not with the OPA2132A OpAmp. I soon learned though that several DIYers have built similar “cMoy-esque” amps based on the circuit used in Grado’s RA1 headphone amplifier, which uses an NJM4556 (aka JRC4556) OpAmp, good for 70ma of current per channel. I decided to try building one, and I wanted it to be a little different. So I built it in a cigar box.
There was quite a bit of drilling and cutting involved, and I destroyed a couple boxes in the process. The volume knob is installed where the cigar maker’s medallion was previously located, which had their logo. For the circuit, I took some ideas from both the cMoy and the RA1 clones. I used some pretty high-end hardware, such as the Neutrik locking 1/4″ jack. It wasn’t because I thought it was necessary, but because it was easy to mount to the cigar box.
The result? Not very good. It’s unique, and looks interesting, but it doesn’t work very well. I ended up building two of them, and both are very noisy. Copper shielding on the second build helped, but not a lot. It might be all of the wiring needed to connect everything, or just the result of a poorly engineered DIY project based around a potentially “cranky” OpAmp, but it just isn’t a great amp. So I’ve kept the second one as a “show piece” while the first gets picked away at for spare parts. Even though it was ultimately a failed project, I’m glad I attempted it. For my next headphone amp, I’ll be using a professionally-engineered and designed circuit based around a PCB which should help ensure success.
The cMoy Headphone Amplifier is a popular, well-documented DIY project, which makes it great for beginners to take on. That’s exactly the reason I chose to do it. I followed the instructions and suggestions from the TangentSoft cMoy Tutorial written by Warren Young, and it came out great, especially for my first attempt at building a headphone amplifier.
I won’t get into how I built mine (the tutorial at TagentSoft is where you should go for that) but read on if you’re interested in seeing what parts I used and some of the problems I ran into.
I was looking for an electronics project I could build after teaching myself to solder (by building alot of Velleman 3D Christmas trees) when I came across Ross Hershberger’s Monobox amplifier project. Right away, I knew I had to build this. I tried to find a cigar box that would work, but didn’t have much luck. But then I remembered that I had some old ammunition cans laying around, and inspiration struck. It was a fun project that came out great, and I continue to enjoy it as it makes a great companion for my iPod.
This project was featured on the Make Blog: MonoBox Mods: Same Circuit, Two Builds. Read on to learn what parts I used, some of the difficulties I ran into, and to see a video of the finished ammo can amp.