Amp Camp Amp

Here is another one of Nelson Pass’ brilliant designs, the “Amp Camp Amp” or ACA for short, that I managed to put together (halfway at least – as usual…).

First launched a couple of years ago, the ACA was developed by Nelson for an “amp camp”, an audio maker event and the schematic since posted as a project article on his website firstwatt.com. The ACA is a very simple and easy to build class A amplifier that produces around 5W (which goes surprisingly far in most “at-home” applications). To make the ACA more “beginner friendly” it is designed to work off a 19V switching adapter from a laptop computer. This makes it cheap to build and ensures that an inexperienced builder does not have to worry about mains wiring etc.

For this build, I have used the “official” boards from the diyaudio store. There is also a very sexy looking custom chassis for the ACA in the diyaudio store, but since they would be shipped from the US and I would be hit with well over 30% extra in VAT, import duty and brokerage fees I elected not to go that route.

Instead I found some special heat sinks from ebay to brighten up an otherwise black chassis 😀 The main argument for choosing these was otherwise that they are 80mm long as opposed to the more commonly available 75mm ones which would be just a tad small for the ACAs recommended mounting. The quality is decent although the colour washed off a bit while I was threading them (using lots of spirit for lubrication). The aluminium alloy is also a bit softer compared to the Fischer or Alutronic heat sinks I normally use, but that isn’t necessarily a problem.

As usual with the Pass designs, the components for the ACA are completely standard “off the shelf” types and the only part that could be difficult to obtain is the 2SK170 input JFET. There are a few alternatives though (the 2SK246, 2SK369 and LSK170 should all work if you just respect the pinout) so even that should not deter prospective builders.

The original ACA design used external switching supplies but I prefer to keep the PSU internally in the chassis, because the laptop supplies are a bit impractical. Instead, I have got a standard “industrial grade” 20V/100W SMPS from Mouser in a 3″x5″ open-frame format.

Looking forward to the Xmas holiday where I should be able to make some more progress on this one 🙂

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