144 Chapter 5
With modern, low conduction resistance, semiconductor diodes, low equivalent series
resistance (ESR) reservoir capacitors, and low winding resistance (e.g., toroidal)
transformers, this problem can still arise, and the inclusion of these capacitors is a
worthwhile and inexpensive precaution. The circuit layout shown in Figure 5.1(b) is the
PSU arrangement used in most contemporary valve amplifi ers. For lower voltages, a
wider range of circuit layouts are commonly used, also shown in Figure 5.1.
5.3 Music Power..........................................................................................................
In their fi rst fl ush of enthusiasm for solid-state audio amplifi ers, manufacturers and
advertising copy writers collectively made the happy discovery that most inexpensive
audio amplifi ers powered by simple supply circuits, such as that shown in Figure 5.1(b) ,
would give a higher power output for short bursts of output signal, such as might quite
reasonably be expected to arise in the reproduction of music, than they could give on a
continuous sine-wave output. This short-duration, higher output power capability was
therefore termed the music power rating, and, if based on a test in which perhaps only one
channel was driven for a period of 100 ms every second, would allow a music power rating
to be claimed that was double that of the power given on a continuous tone test in which
both channels are driven simultaneously (the so-called rms output power rating).
5.4 Infl uence of Signal Type on Power Supply Design ..............................................
Although this particular method of specifi cation enhancement is no longer widely used,
its echoes linger on in relation to modern expectations for the performance of hi-fi
equipment. The reason for this is that in the earlier years of recorded music reproduction
there were no such things as pop groups, and most of those interested in improving the
quality of recording and replay systems were people such as Peter Walker of Quad or
Gerald Briggs of Wharfedale Loudspeakers, whose spare-time musical activities were
as an orchestral fl autist and a concert pianist and whose interests, understandably, were
almost exclusively concerned with the reproduction, as accurately as possible, of classical
music. Consequently, when improvements in reproduction were attempted, they were in
ways that helped enhance the perceived fi delity in the reproduction of classical music and
the accuracy in the rendition of the tone of orchestral instruments. In general, this was
easier to achieve if the electronic circuitry was fed from one or more accurately stabilized
power supply sources, although this would nearly always mean that such power supplies