variable bias versus fixed bias guitar amp

The design also employs a DC servo for DC offset control. The DH-220C incorporates a full-complementary JFET input stage and a push-pull VAS. Each output pair is biased at 200mA for low crossover distortion. The amplifier employs two output pairs and is capable of delivering more than 120W/8Ω using the original Hafler power supplies. The design uses most of the original infrastructure of the DH-220, including the chassis, the power supply, heatsinks, and the original output stage power MOSFETs (Photo 3). There is also an excellent interview with Erno Borbely, designer of the DH-220 that was conducted by Jan Didden. The original DH-220 manual is available for reference. A different output board is necessary for the DH-500, P230, and P500 because they employ three pairs of output transistors and have different heatsink profiles. This design can also be used to upgrade the Hafler DH-200, DH-500, P225, P230, and P500 amplifiers. Photo 2: The new PCB set is ready for installation. The design is implemented on two PCBs, one as a drop-in replacement for the original Hafler circuit board (analog front end, AFE) and the other as a new board (OPS) that consolidates all of the output stage wiring and components within the heatsink and under the main PCB (Photo 2). Here we describe the circuit (Part 1) and the assembly (Part 2) of the DH-220C upgrade. This article describes a construction project for the Hafler DH-220 lateral MOSFET power amplifier (Photo 1). That makes them a perfect choice for a re-build project. A huge number of them were sold and a good number of used ones are still available - both in working and non-working condition. The amplifiers had good power supplies and were reasonably well-built. These output devices were well-known for their smooth sound, reliability, and ruggedness, and as a bonus they are able to survive in the Hafler power amplifiers with no protection circuit other than a fuse. They were among the first to introduce the then-new Hitachi lateral MOSFETs to the audio power amplifier arena. This amplifier was developed for David Hafler by Erno Borbely, a frequent contributor to audioXpress and its predecessor publications. The Hafler MOSFET power amplifiers are legendary for their performance and price point.

Variable bias versus fixed bias guitar amp