Pro-Ject Phono Box S3 B Phono Preamplifier - Black

Balanced Phono Gain, at an Entry-Level Price

The Pro-Ject Phono Box S3 B is an MM/MC phono preamplifier built around a fully balanced signal path. The "B" stands for balanced, Pro-Ject's term for a symmetrical gain stage carried all the way from input to output.

It accepts a balanced input through a 5-pin mini XLR connector. That matches the balanced tonearm output on turntables like Pro-Ject's own X2 B. A standard RCA input is included as well, for turntables without a balanced cable.

On the way out, it offers both a balanced XLR pair and a standard RCA pair. That means it connects to almost any amplifier. This is Pro-Ject's entry point into balanced phono preamps, sitting below the pricier Phono Box DS3 B.

Tuned for Both MM and MC Cartridges

Gain switches between 40dB and 45dB for moving magnet cartridges, or 60dB and 65dB for moving coil. Input impedance covers 10, 50, 100, and 1,000 ohms, plus the standard 47 kOhm setting for MM cartridges.

Input capacitance switches between 50, 150, 300, and 400pF. A subsonic filter cuts rumble below 20Hz at 18dB per octave, useful on a warped record or a turntable prone to footfall.

Signal-to-noise ratio reaches up to 110dBV on the moving magnet setting. On moving coil, it reaches up to 90dBV. RIAA accuracy is rated within 0.3dB across the full 20Hz to 20kHz audible range.

It measures 206 by 55 by 153mm, or 164mm deep including its rear sockets. Weight comes in at 930 grams without the included 18V power supply. Silver and black finishes are both available.

What Reviewers Are Saying

Philip Beaudette reviewed the S3 B for SoundStage! Hi-Fi in June 2023. Listening to a classical piano recording, he wrote, "I didn't just hear Buniatishvili's playing; I felt it."

He also praised its neutrality, noting "the S3 B has no real character to speak of," and its low noise floor, which he said "provided a quiet backdrop" on a Beethoven symphony recording.

Andrew Dewhirst reviewed it for Future Audiophile in April 2025. He wrote that music played through it "felt like it had some new life," adding that the S3 B "does a great job of not adding any color to the sounds."

Who Is This Preamp Best For?

• Anyone whose turntable has a balanced tonearm output. Its 5-pin mini XLR input takes full advantage of that connection.
• Listeners who want proven, independently reviewed sound quality. Multiple named reviewers praised its neutral, low-noise performance.
• Owners of both MM and MC cartridges. Switchable gain and loading cover either type.
• Anyone who wants balanced connectivity without paying flagship prices. It's Pro-Ject's most affordable step into balanced phono design.
• Not the right fit for anyone who wants the extra features of the DS3 B. The step-up DS3 B adds capabilities this entry-level balanced model doesn't include.

How Does It Connect to Your System?

Connect a balanced turntable cable to the 5-pin mini XLR input, or use the standard RCA input if your turntable doesn't have a balanced output.

Run its balanced XLR output to an amplifier with balanced inputs, or use its RCA output for a standard single-ended connection. Set the rear dip switches for gain, loading, and capacitance to match your cartridge before you start listening.

Pairs Well With

Building your system? Here are some great companions for the Pro-Ject Phono Box S3 B:

• Turntables with a balanced tonearm output to match
• Phono cartridges, MM or MC, matched to its switchable gain
• Integrated amplifiers with balanced XLR inputs
• Interconnect cables, balanced or unbalanced, to connect its outputs

Frequently Asked Questions

What does the "B" in the name mean?

Balanced. It refers to the fully symmetrical, balanced signal path running from its input to its output.

Do I need a turntable with a balanced output to use it?

No. A standard RCA input is included alongside the balanced mini XLR input, so it works with most turntables.

How is this different from the Phono Box DS3 B?

The DS3 B is Pro-Ject's step-up balanced phono preamp, with added features beyond this entry-level balanced model.

Can I use this with a moving coil cartridge?

Yes. Its 60dB and 65dB gain settings, along with lower loading options, are built with moving coil cartridges in mind.

What's the warranty?

Pro-Ject covers the Phono Box S3 B with a two-year warranty, extendable to three years with product registration.

See It in Action

Kronos AV Review Diaries takes a close look at the S3 B:

Audio Center Poland unboxes the S3 B:

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Learn More

Want to learn more about balanced connections, matching a phono preamp to your cartridge, or getting the most from your vinyl collection? Visit our Learning Center for guides, tips, and expert advice.