ModWright PH 9.0 Phono Preamplifier Making Headroom

Making Headroom

While we are accustomed to the typical MM being spec'd at 3-5mV output, and MCs some 10x less than this, in practice all pick-ups will deliver far higher outputs when tracking the most highly modulated vinyl grooves. For example, the ever-popular 2Ms from Ortofon [HFN Oct '08, Mar '11 and Jun '21] will deliver peak outputs up to 50mV, so any phono stage with insufficient input headroom will clip and the distorted signal will remain so regardless of the 'linearity' of your amp and speakers.


With its passive RIAA soaking up a lot of gain, the ModWright PH 9.0's input headroom is not especially generous for any of its six MM/MC settings. We saw something similar with the all-tube Zesto Andros Deluxe II [HFN Sep '21]. So, instead of a typical ~100mV limit for its '40dB' MM input, the PH 9.0 offers just 14mV of 'breathing room' before distortion hits 1% – a mere +9dB headroom over the 5mV output of our hypothetical MM. However, this being a low-feedback tube circuit, overload is progressive and so its headroom increases to 23mV at 2% THD, 30mV at 3% and 51mV (or +20.1dB) if we relax the limit to 5% THD. Typically, the higher a phono stage's gain setting the lower its input headroom, but that's not the case here as, presumably, the input 6C45 defines the margin. All three MM settings offer a very similar trend of input level vs. THD [black trace, inset Graph] as do those for MCs – 1% THD for a 2.8mV input, 2% for 4.6mV up to 10.1mV [or +26dB re. 500µV; red trace] for 5%. For best performance choose low/medium output MM and MCs into the '0dB' gain setting. PM

ModWright Instruments
Amboy, WA, USA
Supplied by: Elite Audio Ltd, Fife
01334 570 666