Son of Zen

When I first got into DIY in 1997, I started off reading The Audio Amateur, Speaker Builder and Glass Audio. They eventually combined into AudioXpress. One article that intrigued me was Son of Zen by Nelson Pass. I ordered some parts and started to build. I must admit that I had no idea what I was doing but I decided to try. When the box of parts arrived from Digikey, I had to look at the description on the individual packets to distinguish the resistors from the capacitors. However, I took a soldering course at the local community college which was a great help.

I managed to put the parts together in an Ikea box and connected it up to a pair of cheap speakers. Before I turned it on, I sent my young daughter and her friend out of the house and had my wife standing by with the fire extinguisher. She didn't know whether to laugh or cry. Lo and behold, it actually worked for a couple of minutes but then stopped and some smoke started to come out. We DIYers have all been there, done that. I worked out that heat was my enemy. Unfortunately I seem to have lost my photo of version 1.

This was my second attempt still using an Ikea box for the power supply and some of the amplifier. An umbilical cord led to a heatsink tower that housed the power resistors. It too worked briefly but I knew more heatsinking was inevitable.

I divided the amp up into three parts. The power supply is underneath on three layers of aluminium. The power resistor tower is on top.

Inside the power resistor tower. I had managed to buy a lot of 50 watt 25 ohm non inductive Dale wirewound resistors quite cheaply. I wired three in parallel to get close to the recommended 8 ohms. The heat absolutely poured out of this tower. You could have roasted a chicken in there if it would have fitted.

The actual amplifier. This didn't get hot at all and I realized later that this should have used this for the resistor tower. 

I used the amp for about a couple of years or so and I really enjoyed listening to the amp. With efficient speakers it sounded great but it only put out 10 watts. The biggest problem was the heat. In winter it was fine but it was not the amp to have in your house on a hot summer's day. By this time I was hooked on building amps and had started to try tube amps so I disassembled the SOZ and used the parts elsewhere.

It was a great learning experience.