Pro-Ject Phono Box MM Phono Preamplifier - Black

The Phono Box MM — Dual Mono Circuitry in a Metal Case, for $89

Pro-Ject has sold more turntables into first systems than almost anyone, and the Phono Box MM exists for the obvious next problem: the amplifier those turntables get connected to usually has nowhere to plug them in. This is the fix, and it costs $89.

What sets it apart in its price class is the layout. Left and right channels run as separate dual mono circuits rather than sharing one, which is how Pro-Ject keeps channel separation intact and gives the stereo image somewhere to sit.

Inside the Box

Gain, Loading and Cartridges

Forty decibels of gain at a fixed 47 kΩ and 120 pF, which is the standard moving magnet load and suits the overwhelming majority of cartridges sold. Moving magnet and high-output moving coil designs are both supported.

The Noise Figures

Pro-Ject rates the noise floor at 88 dB A-weighted and distortion below 0.04 percent. In an $89 component those numbers mean the phono stage will not be the thing you notice; a worn stylus or a dirty record will get there first.

Why the Metal Case Matters

Phono signals are measured in thousandths of a volt, and everything near a hi-fi rack radiates interference — power supplies, routers, dimmer switches, phone chargers. A metal enclosure keeps that out of a circuit far too sensitive to argue with it.

Who Is the Pro-Ject Phono Box MM Best For?

• Owners of a Pro-Ject, Rega, Music Hall or similar belt-drive turntable whose amplifier was built without a phono input — this puts the record player back into the system.
• First-time vinyl buyers who would rather not spend more on the phono stage than the cartridge, and still want dual mono circuitry rather than a shared chip.
• Anyone fighting hum near a crowded rack. The metal case is doing real work, and at this price it is not a given.
• Systems where space has run out. At roughly 4.2 inches wide and 280 grams it sits behind the turntable and asks nothing of the shelf.
• Not for a moving coil cartridge. The Phono Box MM is moving magnet only, with no MC setting at all. If you own a low-output cartridge, look at our MM/MC phono preamplifiers instead.

How Does It Connect?

One pair of RCA sockets in, one pair out, a ground post for the turntable's earth wire, and a socket for the outboard 18 volt supply. The output goes to any line input your amplifier has free — aux, CD, tuner, tape.

There is nothing to configure. No switches, no jumpers, no settings to look up in a cartridge specification sheet. For a first phono stage that is a feature, not an omission, and it is why this box has sold for as long as it has.

Pairs Well With

What actually improves the sound from here, in the order that matters:

• A replacement stylus — on a used or inherited turntable this is almost always the biggest single improvement available.
• A moving magnet cartridge upgrade — 40 dB at 47 kΩ is the standard this stage was designed around, so nearly all of them will fit.
• A cleaning brush and fluid — records carry more audible debris than most people expect, and it comes off.
• A turntable mat or isolation feet — vibration reaches the stylus through the plinth, which no electronics downstream can undo.

Frequently Asked Questions

Will it work with a moving coil cartridge?

This model handles moving magnet and high-output moving coil cartridges. A true low-output moving coil needs around 60 dB, and 40 dB will leave it sounding distant and quiet no matter where you set the volume.

What does dual mono actually mean here?

Left and right have their own amplification circuits instead of sharing one. The practical result is better separation between channels, which is what gives a recording width and lets instruments occupy distinct places.

Do I need to connect the ground wire?

If your turntable has one, connect it to the ground post. That thin separate wire exists specifically to stop hum, and leaving it loose is the single most common cause of buzz in a newly assembled vinyl system.

How big is it?

About 4.2 inches wide, 3 inches deep and 1.2 inches tall, weighing 280 grams before the power supply. It is designed to live behind the turntable rather than occupy a shelf position of its own.

Is the power supply included?

An outboard 18 volt DC supply comes with it. Keeping the transformer outside the case is deliberate: mains transformers radiate a field, and a phono stage is the component least able to tolerate one nearby.

Can I use it with a turntable that already has a built-in phono stage?

Switch the turntable's internal stage off first, then run it through the Phono Box MM. Running two phono stages in series applies the RIAA curve twice, which produces a thin, shrill sound that is unmistakable once you have heard it.

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