Things have been quiet here lately as real life once again intrudes on my build time 😉 I did however manage to finish one small project over the last couple of weeks, a clone of the Grado RA-1 headphone amplifier. Well, “clone” is maybe stretching it a bit – maybe it should be “inspired by” instead 🙂 In any case, the design is nearly identical to the “cMoy” amplifier design by Chu Moy, the founder of one of the first internet forums on headphones and headphones listening, headwize. The site is not active any more, but fortunately the excellent collection of headphone-related articles that was published there has been preserved – check it out!.

The recipe for this amp is my often-used “buy cheap ebay-kit and replace parts”, but this time I’ve probably gone a little more overboard than usual with my replacements (always nice to have lots of leftover parts in your collection ;)). The resistors are Vishay-Dale RN55 mil-spec, the electrolytics are Elna Cerafine and the input caps are Blackgate N bypassed with Mundorf M-Cap Supremes. The whole thing is powered by two 9V batteries in a Bulgin holder.

And the sound: Well, with the stock JRC4558 op-amp there’s only one word for it really – disappointing! Sharp, closed-in with very little sound stage and absolutely no way to ignore that you are wearing headphones. However, the beauty of the RA-1/cMoy design is that there is only one active part, so changing the sound by changing the op-amp is very easy. I had another look in the parts boxes and found a TI OPA2107 to try instead.

The glare and the edginess is now gone, the soundstage is wider (though there’s still no doubt you are wearing headphones) and the listening is much more enjoyable all round. I might try a few other replacement opamps as well (the AD8620 and the LM4562 would be good candidates I think) to see if it is possible to squeeze out a bit more performance. This isn’t a world-beating amplifier by any means, but with the right op-amp it is isn’t bad sounding at all.


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