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Apheared’s Project Scrapbook

Apheared’s Project Scrapbook

I live in Manhattan on the Lower East Side. Manhattanites are the perfect headphone canidates. It’s all you get to listen to. We don’t HAVE cars. We walk or subway or cab ($$) everywhere. I listen to headphones 4-10 hours everyday.
I built the Jasmin Levallois’ version of the pocket amp using the OPA4134 (the quad version of the Burr Brown OPA134), but it got distorted very quickly and had no stomp, even for Grado SR-80s. It just didn’t have enough juice. I fixed that by rebuilding the amp and paralleling the opamps suggested by Skippy and the circuit found in Burr-Brown’s AB-051 application note: Double The Output Current To A Load With The OPA2604 Audio Opamp.

If you use Grados, build this. It is, by far, the best sounding OPA variant I’ve built (I’ve built many, many times many). It is so much better than just a single output stage. It has full, deep, effortless sound and worth that extra chip, believe me. It’s not just for blasting; it changes the sound dramatically for the better at all volume levels. If you want a crossfeed section, add it yourself – after exaustive testing I do not like any of them, at all. It only has a gain of 3. What? Apheared building something with only x3 gain? Yes. It’s intended only for Grados with a line-level source. MAYBE low ohm earbuds, and MAYBE up to 60 ohm, efficient cans. That’s it.

NOTE: This thing can probably fry your $200 cans easily. It can also seriously hurt you. I’ve measured 2.5V coming outta each side. If I lay the Grados on the couch, and GO OUTSIDE, I can hear them playing through a steel door with ambient outside noise and 20-25′ distance, enough that you can clearly hear the lyrics. With the dual 12V and the parallel opamps, it quintupled the output. At least.

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