Ortofon ST-7 MC Step-Up Transformer (Dual Mono)

The Ortofon ST-7 is a dual-mono step-up transformer that passively raises the tiny voltage of a moving-coil cartridge to MM level — with no power, tubes, or transistors involved.

Why the ST-7?

For many MC fans, a good step-up transformer is the tonally most honest way to get the needed gain: instead of active electronics with their own noise, two carefully wound transformers do the job. In the ST-7, each channel sits in its own Permalloy-shielded housing, which minimizes crosstalk and interference. 24 dB of gain suits a wide range of MC cartridges with 2 to 60 ohms internal resistance.

What you get

A calm, unobtrusive gain stage between MC cartridge and MM phono input: wideband (15 Hz–45 kHz), cleanly channel-separated, and without the noise floor that budget active MC stages bring along. You simply place it ahead of your existing MM input.

Who is the ST-7 suited for — and who isn't it for?

Ideal for owners of an MC cartridge with an MM phono input who want the tonally purest path to matching. Straight talk: a step-up transformer needs to match your cartridge's impedance — if your MC lies well outside 2–60 ohms, it isn't the right choice. And if you already own a very good active MC phono stage, you don't strictly need it.

Our verdict

The ST-7 is a high-quality, universally usable MC step-up transformer that turns an MM input into a full-fledged MC access point — passive, low-noise, and long-lasting. At HD Zürisee in Wädenswil, we'll check with you whether the turns ratio and impedance suit your cartridge.

Technical data

• Type: passive MC step-up transformer, dual-mono design
• Gain: 24 dB (at 47 kOhm, 1 kHz)
• Suitable cartridge internal resistance: 2–60 ohms
• Load impedance (output): > 47 kOhm
• Frequency response: 15 Hz–45 kHz (+0/−2.5 dB)
• Channel balance: < 0.5 dB
• Channel separation: 70 dB (1 kHz)
• Construction: separate sandwich winding, Permalloy shielding per channel
• Connections: RCA input/output L/R, ground terminal
• Dimensions (W×H×D): 122 × 43.5 × 102 mm
• Weight: 0.79 kg

Frequently asked questions

Why do I need a step-up transformer like the ST-7?

A moving-coil cartridge delivers far too little voltage for an MM phono input. The ST-7 passively raises this signal by 24 dB so the MM input can process it cleanly. You connect it between tonearm and phono stage — with no power supply at all.

Which cartridges suit the ST-7?

Moving-coil cartridges with an internal resistance of roughly 2 to 60 ohms. What matters is matching the turns ratio and impedance to your cartridge — if it doesn't match, the sound suffers. Tell us your cartridge and we'll say whether the ST-7 is the right choice.

Why buy the Ortofon ST-7 at HD Zürisee?

Because the right impedance matching decides the sound. We advise you on which transformer suits your MC, and integrate it cleanly into your system. HD Zürisee in Wädenswil is an authorized Ortofon dealer — call or write to us.

Goes well with

Goes well with: a matching cartridge, a phono preamp, and a high-quality turntable.