A couple of weeks ago, MAKE photographer Gregory Hayes, designer Michael Silva, O’Reilly Web Producer Tony Quartarolo, and I had the opportunity to attend Amp Camp, just up the road from the O’Reilly offices in Sebastopol California. What’s Amp Camp? Glad you asked. A few years ago, Dana Brock held Speaker Camp, where 20 or so friends hung out in his workshop for a day and built speaker enclosures. Building on the success of that, he and Nelson Pass decided to do it again and have a day, in the middle of the wine country, to build amplifiers.
Nelson speaks of the requirements for the camp here:
Building amplifiers is generally a more intimidating challenge than loudspeakers. There are more parts involved, the function of these parts seems more exotic, and they are connected in more complex ways.
In thinking about the design, I considered whether a “chip amp” might be suitable. This would be an amplifier based around a commercially-available integrated circuit in which most of the complexity is hidden inside a single component. This approach looks easier, but is a little less “fundamental” than a design using discrete transistors to form the circuit. If you think of this project positioned on a range of DIY complexity, at one extreme you take a pail of sand and start fabricating your own transistors from scratch. At the other end of the scale you go to the store and buy a Bose system. This project leans toward the former.
Besides, who says that discrete designs have to be complicated? It is possible to build a nice amplifier with only a few more connections than a chip amp, and for a little more effort you can learn even more and get more enjoyment out of the finished product.
So Amp Camp Amp #1 is a discrete design using four transistors. It can be built for about the same cost as a chip amp and in the same amount of time. It will not measure as well as chip amps in some regards, but as a single-ended Class A design with minimal feedback it will sound good and get some high end audiophile respect.
We have to seriously consider safety as a constraint with regard to the power supply circuitry for the amplifier. We assume that most of the participants in this project do not have the skills to safely connect the components which make up an amplifier power supply to the AC power line.
I addressed this by choosing a commercially available switching supply of the type you routinely see powering up your portable computer. There are literally tons of surplus supplies available for this purpose, providing regulated 19 volts DC at more than 2 amps or so on their output and having their input going safely to the wall AC power outlet through a safety approved power cord. These supplies are isolated for shock safety and are also short-protected. At 19 volts output they do not represent much of a hazard to humans.
What? An audiophile component with a switching power supply? Get over it – it works fine.
And it does work fine. I have annotated a few of the pictures below to tell a bit of the story, but the gist of the day was everyone had a blast. People came from all different backgrounds, many didn’t know how to solder when they came, but when the day was over, they had gone well beyond making an LED blink, as many first projects go, but had built a full Class-A amplifier that would turn heads anywhere for its good looks and great sound. How neat that one of the godfathers of high-end audio was there teaching people to strip wire, bend resistors, and avoid burning themselves. To the hosts, the Brock family was friendly, and amazing to let a bunch of people into their home and share a meal and great day of exploring electronics.
So Dana and Nelson: I missed Speaker Camp, so how about we get going on round 2?
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