Passlabs Amplifier Projects
Son of Zen

While the performance of the A40 was very good, I decided to build the Son of Zen. Mainly because the obscene simplicity and absolute lack of compromise just appealed ;-)

Since this was a "just for fun" project I sourced much of the material surplus, the main exceptions being the FETs and the power resistors ..... you just don't find these things lying around !

The initial incarnation was 50W. Given this was the edge of the design I was concerned about device stress and after corresponding with NP decided to modify the circuit for dual FETs on each limb of the balanced circuit.

I didn't try to make it "look nice", I just wanted to hear it run. The transformer, while huge and rated at 20A continuous didn't like the warm weather and one hot summers day erupted into a tower of smoke.

The resulting incarnation runs at 68V rail-to-rail with a constant current draw of 15A.

The amp is incredibly transparent, effortless and a real pleasure to listen to ..... just can't get the wife to allow it in the house, and you can't just "pop it inside for a quick listen" :-(

Amplifier from the front
 The amp is sitting alongside a TV, the 19" rack-mount width tells you how tall it is ....... and it takes 2 people to lift!
With the front open the power supply can be seen. This cabinet was in fact a battery charger before it's re-birth. The design was perfect, with separate front & rear compartments. The rectifier bridge is 2 "power-blocks", seen in the top left. The rails run though high current chokes seen on the top right.
Inside the rear the 4 heatsink blocks (2 FETs each) can be seen with the biasing resistors mounted on the top heatsinks. The open-spacing for the top is very deliberate ... this gets hot!

Runs at about 260F, or 126C on the top heatsinks. The FET blocks run "comfortably warm".