Technical Requirements of Phono Preamplifiers by Tomlinson Holman
The two articles below were written in the 1970’s, nearly a decade before the arrival of the CD and the ‘perfect sound forever’ claim made by Philips. There was a lot of focus on phono amplifier performance at the time which it could be argued was triggered by the arrival of very high performance turntables – the Linn Sondek and Japanese Direct Drive systems from Technics for example – but there were others like Micro Seki, Thorens and so forth as well. These turntables were for the most part, quiet with low motor noise and decent quality pickup arms.
The arrival of Quadraphonic systems required much greater bandwidths and this had to be matched with improved cartridges that offered better tracking performance and a newer, greater understanding of the electro-mechanics of the pickup itself, and in particular the stylus, emerged as a result.
Holmans first article investigated the dynamic requirements of phono amplifiers and represented the best effort at the time – and probably still so – to understand the absolute outer limits of phono amp overload requirements. The general consensus that was cemented from this work, and that of other investigators and cartridge manufacturers at the time (Shure being chief amongst them) was that a typical phono amp should deal with peak outputs of at least 25cm/sec (5cm/sec being the nominal output). This of course does not include factors like ‘hot cartidges’ providing 6-10mV re the nominal 3mV output levels and ‘hot recordings’ where the general levels on the disc, and associated peaks, were higher than average. On top of this, overhead for the inevitable crackles and pops was also required.
The second article presents a practical MM design which should be read in the context of the available semiconductor devices at the time.