Phono Preamplifiers

The popular 2M Red from Ortofon [HFN Oct '08], one of the highest output MMs available, still only produces 6.7mV (re. 1kHz/5cm/sec). However, you might be surprised to learn that with the most vigorous LP groove excursions (typically +15dB, and rarely +18dB), it is possible for the 2M Red to deliver peak outputs up to 50mV into your chosen phono stage. If the phono input cannot handle this, it will clip and send a burst of distortion that's amplified right up the signal chain from these tens of millivolts up to the tens of watts – or more – feeding your loudspeakers.

The ability to handle these momentarily high outputs is reflected in the 'input overload margin' that I discuss in all our phono preamp lab reports. The higher the phono stage gain, the lower the input overload level – in the R35's case its maximum +76.5dB MC gain represents a boost of x6680 so even with its massive 22V (balanced) output it only requires an input of 3.3mV to clip the output stage. This is why it's important to carefully select the optimum gain for your choice of cartridge. Fortunately the R35 has more than enough headroom for every type of pick-up – the inset Graph shows the point at which it clips when set at the +42dB (red), +46dB (cyan) and +50dB (black) MM gain. PM