Classic Audio by Michael Fidler


Phonostage Mono Switching

Mono LP

The mono switch seems to have evaporated from phono stages at the end of the 20th century, with most units on the market today leaving it out regardless of price. Although mono discs can be played through a stereo pre-amplifier without any gross ill effects, there are substantial and audible benefits to be had from summing the two channels together; summarised and demonstrated with sound samples.

Practical Line Input Circuits

Line Connectors

Line level inputs are an essential part of most audio equipment, and although nothing could seem simpler than connecting a line level voltage to internal circuitry, there is almost always a need for some interfacing circuitry. A discussion of line level in the real world, the requirements of the interfacing circuitry, RF filtering, versatile unbalanced line inputs, and several balanced input circuits for all occasions.

Practical VU Meter Circuits

VU Meter

VU meters are certainly very aesthetically pleasing devices, and are still quite useful in a domestic setting, but unfortunately the contemporary circuitry that feeds them falls seriously short in many ways. A brief discussion of the VU meter standard followed by a revised list of objectives and an improved driver circuit.

Connecting Active Speakers to Power Amplifiers

Monitor Converter

Active studio monitors are a very attractive option for high quality home listening. However, many HiFi amplifiers lack even an unbalanced line level output, making their mating to a typical system seemingly impossible. A brief discussion of why active is better, followed by a simple, low cost passive circuit to allow a balanced line level connection to standard amplifier speaker level outputs.