DVA100 power amplifier

The DVA100 is the entry level power amplifier kit and is fully described in Electronics World, August 2001, Vol 107, No 1784. It is a modernized and extended version of a classic design originated by Hitachi America in the 1970s, commercialized as the Phase Linear 700, and made famous by Pink Floyd who used Phase Linear 700s to power their gigs wordwide until 1980. Since then a large number of companies, including BK Electronics and until recently Maplin in the UK, have continued to use the Hitachi design as the basis for kits and complete amplifiers. The vast majority of DIY power amplifier projects described on the internet today use this classic design pretty much unchanged from the original.

Although the performance of the original Hitachi design is still pretty good, even by today's standards, it does have a couple of serious shortcomings. The power supply rejection is terrible, so that attempting to run a stereo pair of power amps from a single power supply is a definite nono - separate power supplies are de rigeur for hi-fi use. The collector current of the voltage amplifier transistors is nowhere near constant, which means that the bias of the output transistors varies with signal level, causing an unwanted ( but fortunately small ) increase in distortion. My development of the classic design eliminates these problems to produce a superior measured and sonic performance.

The DVA100 is an all discrete component design with long-tailed pair input and voltage amplifier stages driving a complementary pair of vertical mosfet source followers. Judicious use of constant current sources and current mirrors ensures an excellent power supply rejection ratio as well as closely balanced collector currents in each of the long-tailed pairs. The innovative circuitry ensures that the DVA100 can deliver high power output, at low distortion, from economically priced components.

The DVA100 can use a power supply ranging from ±30V to ±50V at 2A ( mono ) or 3.5A ( stereo ) to deliver up to 100W/8 . High current power supplies delivering voltages in excess of ±40V should not be used with DVA100s when driving 4 loads. Under these conditions the single pair of TO220 output mosfets would struggle to handle the heat dissipation required of them.