Sunday, November 11, 2007

The Wooden Cased headphone amp

Inspired by the the headphone amp on diyaudioprojects and after purchasing a wood body Grado phono cartridge, I decided to make my headphone amp in an old Essential oils cedar box. Grado also make a wooden cased headphone amp but a friend said he tested the CMoy styled amp against the wooden boxed Grado and believed his to be better sounding. The owner of the Grado headphone amp agreed!

I never intended this headphone amp to be portable. Though the amp weighs very little it is bulky. All connections are at the back. An aluminum strip at the back of the amp holds all the connectors and the on/off switch. Large holes had to be drilled to take the body of the connectors and drilling the soft cedar was difficult without causing damage. Movable compartments inside the box allowed my to have separate battery and amp cct. brd. areas with two spots for spare 9V batteries. Aluminum and bitumen adhesive (flashing) strips line the whole inside of the box and speaker dampening vinyl also lines the lid.

Cotton coated pure silver (.4mm) wire is used in the signal path. Over size power caps (330uf low ESR) and polypropylene input caps (.47uf) were mounted on the tiny cct. brd. with all the other components. I wanted the passive parts as close as possible to the OP amp chip the OPA2134PA. The chip was socketed with a gold pin socket. The cct. brd. was mounted on plastic stand-offs encircled with rubber grommets (resonance reducing). Two 9V batteries and a voltage divider network provide the +/- 9 volts for the chip.

The test set-up was a portable CD player with a line-out, new Grado SR80 phones and my home made Cotton ConneX cables. Bass was a bit muddied and there was a nasaliness in female vocals. A NAD C542 replaced the portable player and things got a whole lot better! I'm usually a speaker freak when it comes to listening to music. But two hours latter I was still glued to the lounge in a world of my own listening "up-close-and-personal" to both live and studio recordings. How would I describe the amp - "GREAT"!

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