Hi-Fi Basics: What a phono stage actually does

Published: 21/08/2026 // Author: Jonny

The short answer: a phono stage takes the very small signal from a turntable cartridge, applies the playback side of RIAA equalisation, gives the cartridge an appropriate electrical load and raises the result to a level a normal amplifier input can use. Without those jobs, a conventional cartridge connected straight to a line input will usually sound extremely quiet and tonally wrong.

A phono stage may be built into the turntable, built into an amplifier or supplied as a separate box. The location changes, but its purpose does not.

The three jobs of a phono stage

It adds gain

A cartridge produces a much smaller signal than a typical line-level source. The phono stage amplifies it before passing it to an AUX, CD or other line input. The required gain depends on the cartridge, with low-output moving-coil designs generally needing more than moving-magnet types.

It reverses the record's equalisation

Records are not cut with a flat frequency balance. When a disc is cut, bass is reduced and treble increased according to the RIAA recording characteristic. The phono stage applies the complementary playback response: bass is restored and treble reduced.

It means a phono stage is not simply a small general-purpose amplifier. Its frequency response is deliberately shaped for records.

It presents the intended input load

The cartridge and phono input form an electrical partnership. Input resistance, and for many moving-magnet cartridges input capacitance, can affect the result. Gain must also suit the cartridge's output. Start with the cartridge maker's recommended load and the phono stage maker's available settings.

Why a normal line input is not a substitute

A line input expects a signal that has already been amplified and has a broadly flat frequency balance. A conventional cartridge output is much smaller and still needs the playback RIAA correction. Plugging it directly into AUX therefore affects both level and tonal balance.

The opposite mismatch causes trouble too. If a turntable's built-in phono stage is switched on, its output should normally go to a line input, not through a second phono input. Applying phono gain and equalisation twice can produce excessive level and a heavily altered balance.

Some turntables offer a PHONO/LINE switch. PHONO sends the cartridge-level signal to an external stage. LINE means the internal stage has already done the work. Check the labels and instructions before connecting anything.

MM and MC are not interchangeable labels

Moving-magnet, or MM, and moving-coil, or MC, describe how the cartridge generator is arranged. For system matching, output level and the expected load matter most. Many low-output MC cartridges need more gain and a lower input resistance than a typical MM cartridge, but the exact requirement belongs to the individual model.

A stage marked MM/MC provides modes or settings for those different needs. Confirm the cartridge type, recommended load and output before choosing one. High-output MC cartridges are a useful reminder that the initials alone do not tell the whole story.

Our Elekit PS-3250 phono equaliser kit supports MM and MC operation with selectable gain and MC loading. It shows how gain, loading and RIAA equalisation are separate parts of the same job. Follow its own instructions rather than treating its settings as universal values.

Where a step-up transformer fits

A step-up transformer, often shortened to SUT, can raise the voltage from a low-output MC cartridge and provide impedance transformation before an MM phono input. It is passive and can be useful, but it is not a complete phono stage.

A SUT does not apply RIAA equalisation and does not normally create a line-level output. It still feeds a suitable phono input. Its turns ratio, the cartridge's source impedance and the following input interact, so choosing one by gain alone is not enough.

Our Lundahl moving-coil input transformer range includes several ratios for different applications. Consider that route only after the cartridge and following phono input are known. A dedicated active MC input is simpler in many systems.

Work out what your system already contains

1. Identify the cartridge. Find the exact model and whether its maker calls it MM, high-output MC or low-output MC.
2. Check the turntable. Look for a PHONO/LINE switch or a built-in stage in its specifications.
3. Check the amplifier. A conventional amplifier input labelled PHONO normally feeds an internal phono stage, but check the manual because switchable inputs and labelling vary.
4. Choose one path. Cartridge to phono stage, then phono-stage output to a line input. Avoid applying the stage twice.
5. Match before experimenting. Set cartridge type, gain and load from the relevant maker's guidance.

Key takeaway

A phono stage is the specialist interface between a cartridge and a line-level system. It provides gain, reverses RIAA equalisation and loads the cartridge appropriately. MM and MC modes address different requirements, while a SUT handles only part of the MC task. Once you know which functions your turntable and amplifier already provide, the signal path is much easier to plan.

Quick questions

Can I connect a phono stage to any amplifier?

Usually, if it has a spare analogue line input. Connect the phono stage's output there, not to another phono input.

Do all MC cartridges need a SUT?

No. A suitable active MC input can provide gain and loading directly, and high-output MC models may work with some MM inputs. Follow the cartridge maker's recommendation.