In Praise of the Quadratic Audio MC-1 Step Up Transformer

We’ve been stocking, and using, the Quadratic Audio MC-1 Step Up Transformer for some time and our affection for it is undiminished; however it still seems to be pretty unremarked in audiophile circles, despite favourable reviews such as in The Ear in September 2023.

Our customers know that we prefer to use Step Up Transformers (SUTs) over phono amplifiers with active gain Moving Coil (MC) stages.  That’s not to say that active gain MC phono amps cannot be good, because plainly many are good, but such goodness tends to come at a price, and very often a modest Moving Magnet (MM) phono amp combined with a good SUT can offer cracking sonic and musical performance for not much money.  Most MM phono amps are actually very good, irrespective of price, but most MC phono amps with active gain circuitry disappoint, in our experience/opinion.  Many MC phono amplifiers do use internal SUTs, and these can be excellent (Phasemation’s EA-350 and EA-550 are good examples) but very often use off-the-shelf transformers which offer unremarkable performance.  Things get much more exciting when a good standalone MC SUT is paired with a good MM phono amplifier.

We need to talk a bit about gain and loading, when it comes to MC cartridges, which have varying output voltage (from as low as 0.01mV to 0.5mV) and wildly different generator coil impedances (typically from 1ohm to 40 ohms).  Gain is probably the most important criterion, and the aim is to lift the low cartridge output to a broadly nominal 5mV to suit the MM input of a phono amplifier.  So, if we take a typical MC cartridge with output of around 0.2mV to 0.3mV, then we need to multiply the output by around x20, which is a very common gain ratio for MC SUTs.  Some MC cartridges have higher outputs of around 0.5mV so in that case, the optimum gain ratio needs to be around x10.

While gain is the most important consideration, we also need to consider the effective impedance loading of the cartridge, and established wisdom on this subject suggests that effective loading should be around 10x the coil impedance, but actually there’s usually a great deal of acceptable wiggle room around that 10x number.  Cartridge coil loading is extremely easy to accomplish with an active gain MC phono amp, where the loading is simply resistive, achieved by placing a resistor across the input of the amplifier, but with SUTs, things are not so simple – you can read a good technical explanation of all this on Rothwell Audio’s website here.

All of which means that, while many cartridges are happy running into a SUT with 1:20 gain ratio, where the cartridge output voltage is 0.5mV or more, a SUT with a lower gain ratio is better.  This bring us to the Quadratic Audio MC-1, which has two gain options – 22dB (1:12.5) and 28dB (1:25), so it’s pretty flexible and suitable for all but the very lowest output MC cartridges.  Gain adjustments require setting jumpers inside the case, but the manual is very clear on how to do this.

Most modern Ortofon SPUs do like gain to be more than 1:20 to come on song, and the Quadratic Audio MC-1, in high gain mode, is pretty much optimal for use with SPUs, liberating the bold character, dynamics and tonal colours that these cartridges are capable of delivering, when paired with the right ancillaries.   Worth noting that the SPU Synergy has a relatively high output of 0.5mV so gain is best set at around 1:10, but happily the Quadratic MC-1 has a suitable low gain setting, so all is good there.

We mostly use our MC-1 with either  Phasemation PP-500, or Ortofon SPU#1 cartridges.  The MC-1 is blessedly hum-free (as are Phasemation SUTs) so straightforward to place on a shelf or a system rack.  As long as you use good quality fully screened cables (eg screen connected at both ends), you won’t get any hum, and anyone used to playing with SUTs will understand that this is a very positive note.  Internally, the MC-1 has jumpers to change both ground lift and Faraday Shield Lift, but we have yet to encounter any need to change from the standard settings – should anyone have a hum or interference issue, then these settings options are useful to ensure silent running.  The MC-1 doesn’t really have any particular sound character, in that it’s sound is not coloured or emphasised, but it does have a beautiful way with handling small musical details as well as portraying soundscapes and sound localisations rather magnificently.  That means it sounds natural and engaging, which after all is what most of us want in an audio component.

So, to sum up, the Quadratic Audio MC-1 is a very well made, very well conceived, flexible and extremely fine sounding MC step up transformer that’s very easy to recommend, particularly for someone who has a need for different gain options in one unit.  The MC-1 really is impossible to criticise, being a wonderfully even-handed musical performer that’s extremely easy to live with.