GWado - DIY CMoy / Grado RA1 Headphone Amp
DIY Headphone Amplifier
Want to get canned in the best possible way? Well you need a headphone amplifier to drive those expensive cans hard and clean. I used a Burr Brown OPA2134PA which is a low distortion dual opamp available for only $AU7! For about $20 to $30 in parts, you can really get canned with a DIY headphone amp! Cheap when you think I paid near $AU300 for Grado head phones.
Gio first brought the CMoy to my attention when I saw his portable CMoy mint tin headphone amp. Mine was never meant to be portable but would be the system I can turn to when the wife is home and doesn’t want to hear music.
Grado makes a fine looking headphone amp in a mahogany box, the Grado RA1. I really liked the idea and look of a wooden enclosure and I wanted a timber boxed "quality" headphone amp. I call my headphone amp the GWado.
DIY CMoy Headphone Amplifier
I generally followed the original CMoy plans. The input caps are locally available 0.47uF polypropylene caps (Mex/Tenta). The power supply caps are 330uF low ESR. 0.1 uF polyester/mylar (green) caps are used directly on the power pins of the chip.
Figure 1: CMoy Headphone Amplifier Schematic
I wanted all the parts as close as possible to the chip to stop RFI etc so a small protoboard was used. A gold plated machined socket is used, this way I can easily upgrade the opamp. A small 10K dual gang pot is used for attenuation. Wiring was completed with left over cut offs of pure silver wire and cotton insulation.
Photograph 1: Protoboard CMoy Headphone Amplifier
Photograph 2: Protoboard CMoy Headphone Amplifier - Underside
Wooden Box Enclosure - GWado - DIY Headphone Amp
I found the perfect cedar box complete with removable compartments. The box was a little knocked about so a quick sanding and a couple of coats of a spray on polyurethane spruced it up. The inside of the box was lined with bitumen back aluminum foil for shielding.
Photograph 3: Aluminum Foil Shielding
A strip of 3 mm thick aluminum connects the power switch, gold plated RCA plugs and headphone jack. The pot was also mounted on aluminum strip and double sided taped to the inside front of the box. I wanted no screws or anything visible at the front except the attenuator knob. The circuit board is mounted to the bottom of the box on plastic computer stand-offs. The stand offs have rubber grommets on them that act as dampeners. Working with the soft cedar box was very difficult particularly because I had to drill big holes in the back. It was cramped and frustrating, but well worth the effort.
Photograph 4: CMoy Headphone Amp Enclosure - Rear
Speaker dampening material was used to line the inner lid of the box over the shielding and the battery compartments are lined to hold the batteries snug. Low profile felt feet were added to the bottom and now we are ready to get canned.
Photograph 5: CMoy Headphone Amp Enclosure - Inside
Photograph 6: CMoy Headphone Amplifier - Inside
Listening Notes - GWado - DIY Headphone Amplifier
A cheap portable CD player and ear buds were used for the smoke test. A pair of my DIY silver interconnect cables coupled the player to the GWado. Use cheap ear buds to test the amp for the first time, just in case there is a problem.
I usually like my sound through speakers but I was enjoying the Grado SR80s / GWado combo. I did notice the bass was bloomy and once noted some resonances on voice. It was time to swap out the cheap player and a NAD C542 took it's place. Remember this headphone amp was never intended for portability. A true Hi-Fi sound gushed from the phones in one side of my head and out the other. I was transfixed. The phones are brand new and so is the amp, I can't wait until they are both broken in. While typing this article I have been enjoying a great and very private listening session. Yes the wife is home and we are both very happy.