Quadratic Audio MC-1 Moving Coil Step Up Transformer

Description

The Quadratic Audio MC-1 Moving Coil Step Up Transformer (SUT) is designed by Jam Somasundram, who previously worked for Pass Labs where he designed the HPA-1 headphone amp circuit, and before that he was director of engineering for Cary Audio.  So, there is true design pedigree behind Quadratic Audio.  Coincidentally, Jam is also a customer of Ammonite Audio and a couple of years ago he sent us details of his new Quadratic Audio SUT but we were too dim-witted to realise that this was something we should be interested in offering here!  Luckily, Quadratic Audio is now distributed in the UK by Symmetry Systems, and we are very happy indeed to be (belatedly) a dealer for the MC-1.

Our customers know that we like SUTs, which generally deliver the full benefits of moving coil cartridges – active gain MC head amps and phono stages can sometimes (but not always) sound a tad sterile, compared to a good SUT.  The qualification here is “a good SUT” and not all SUTs are created equal.  In particular, SUTs are often prone to picking up hum, and placement can be a nightmare – that’s one of the reasons why we like Phasemation SUTs so much, since they are pretty much immune to hum pickup, as well as sounding glorious.  But, the Phasemation SUTs are fixed gain, which is great for any MC cartridge needing around 26dB (1:20) gain, but not so good for cartridges requiring lower gain settings, or indeed higher gain than 1:20 such as Ortofon SPUs.  Here the Quadratic Audio MC-1 steps in, with 1:25 and 1:12 gain settings which covers almost all cartridge needs, bar extremely low output cartridges like Audio Note Io etc.  The high gain setting is very well suited for mainstream Ortofon SPUs, which really appreciate rather more than 1:20 gain.

The Quadratic Audio MC-1 is very solidly built, unusually with the well screened transformers mounted onto a printed circuit board.  This board is where gain can be set; also ground lift and Faraday Shield settings (see below).  As shipped, the MC-1 is set to high gain (28dB) and with ground and shield configured for best results in most systems, but the user has the option to explore these settings in the rare event of noise/hum problems.

 

 

 

 

 

 

 

 

Hum and Noise Rejection

MC cartridges put out very low voltages. The MC-1 step-up transformers are specifically designed to operate optimally in that environment. Stray magnetic fields can cause problems, as most
experienced audiophiles working with phono cartridges know. The MC-1 transformers are encased in mu-metal cans which block out a lot of stray magnetic interference (greater than -30dB isolation). Additionally, they are manufactured using a hum-bucking technique which greatly increases the ability of the transformers to reject induced magnetic field pickup typically coming from nearby power transformers and motors.
The ability of the transformer to reject hum induced into the transformer itself is only part of the hum rejection equation because hum can be induced in the cables and wiring of the overall system leading up to the transformer primary. Hum bucking transformers inherently have superior common mode rejection ratios (CMRR) which helps mitigate this problem.

The MC-1 transformers include internal “floating” (not internally connected to either the primary or secondary) Faraday shielding which ultra-isolates the primary side of the transformer from the secondary.
Jumpers are available on the circuit board that allow you to bond the Faraday shields to the system or even float them completely. Detailed instructions are printed on the circuit board. The MC-1 is delivered in the configuration that typically gives best results. Finally, there is a Ground Lift option. Engage or disengage if needed for best hum rejection.

Instruction Manual

The MC-1 manual can be seen and downloaded from the manufacturer’s website here https://www.quadraticaudio.com/quadratic-manual.pdf 

Specifications

Gain Setting High: +28 dB
Gain Setting Low: +22 dB
Frequency Response: 10Hz – 100Khz
Recommended Load: 47k
Dimensions: W 6.5” (165mm)
D 8.0”(203mm) H3.0”(76mm)
Weight: 4.2 lbs. (1.9 kg)

Reviews

The Ear (UK) September 2023  https://the-ear.net/review-hardware/quadratic-mc-1-a-positive-step-up/