Stereo Power Amplifier


The Peasant is building a new set of power amplifiers for his home stereo. This project is based on an old PS Audio design, with some updates and improvements. The goals for this project are to provide a higher power and cleaner sounding amplifier that runs cooler than the original PS Audio amplifiers when driving inefficient electrostatic speakers. Some help and guidance for this project was received from various members of the DIY Audio Forum.

The Peasant was fortunate enough to have an empty pair of Bryston 4B chassis', obtained from a former Bryston dealer who had originally purchased them as display units. These came equipped with heat sinks, power inlet/fuses, and output binding posts. All we need to do is add the innards!

Here are the current schematics for the amplifiers, each unit will be a stereo amplifier that can be bridged into mono. The basic design is from the PS Audio Model Two C Plus series of amplifiers, with various upgrades including matched parallel output devices, power supply improvements, and component upgrades. The circuitry will continue to change slightly as tweaks and further refinements are added.

Main Amplifier Schematic

Power Supplies Schematic

Note that there is very little in the way of protection circuitry and fuses in this amplifier. There is a short turn-on delay for the output power supply to minimise thumps, and a couple of line fuses, but no other protection. This is not recommended for most applications, since any problems caused by accident or parts failure can potentially cause a huge amount of damage, up to and including complete destruction of the amplifier and any speakers that may be connected. However, the speakers that will be used with these particular amplifiers are almost indestructable, and the risk of catastrophic amplifier failure is more than compensated for with the better sound achieved by not including the extra circuitry in this case.

Below is a picture of the bare printed circuit boards for the amplifer sections, as well as the bridging adapter, fully populated. These are home-made double sided pc boards created with the toner transfer method.

Each preamp/driver section has it's own dedicated regulated power supply circuit board as shown.

Next is a picture of one amplifier channel being tested and adjusted. The power supplies are already constructed and installed in the chassis.

And finally, pictures of the finished amplifier. The project has been a great success so far, with the first amplifier achieving or surpassing the original design goals. The sound is much more dynamic than the original, with sounds seeming to leap right out at you. Detailing is far superior, with a wider, deeper, very stable soundstage. And the amplifier runs much cooler, only getting a bit warm when run hard, as opposed to the original PS Audio amplifiers which required fan cooling at higher volumes. Power output is measured at 150 RMS Watts per channel into 8 ohm loads and 225 Watts into 4 ohms.

This first amplifier will now be auditioned at length, with further refinements and improvements made. Eventually, the second amplifier will be constructed to match the first one, including any modifications. Updates, as always, will be added as they become available!