As I’ve mentioned in the M³ post, there are a few headphone amplifiers that I was always fond of. They weren’t always expensive or exotic amplifiers, but they simply sounded right to my ears. One of these is the Pimeta from Tangent. I first came across the Pimeta quite a few years ago when one of my friends had a portable unit powered from a battery. A few years later, one of the amplifiers I’ve built was a Pimeta, that ran from a 24V regulated PS. Over the years that amplifier has been modified a few times to suit the needs of the time, including a reduction of gain and PS voltage to fit more sensitive headphones and a smaller case. Recently, after a few years of not using it, I’ve had a renewed need for, and decided it was as good of a reason as any to give it a little “upgrade”. This post is meant to share those modifications, as well as give the Pimeta some more attention, as I think its a great little amp that isn’t getting enough love on the forums.
One tool I use quite often when testing amplifier is a dummy load. Because of that I have a large box of high power (50W) resistors, and a large heat-sink that is tapped for easy attachment of the resistors to it. I typically have 8 resistors of 2ohm each, connected according to the requirement of the measurement i’m doing at the moment. More often than not, they are wired as 2 independent 8ohm resistors to measure speaker amplifiers (see Fig. 1). However, when I need to measure headphone amplifiers, I typically only need lower power loads, and therefore use a couple of resistors from the spare parts box. This got frustrating over time, soldering the resistors to a TRS plug, then soldering/clipping on a couple of wires to the scope/other test instrument. Therefore I’ve decided to do a small side-project of building a simple dummy load box for headphone amplifiers testing.