The New Balanced S3 Phonostage

The Phono Box S3 B comes in a new, larger enclosure. Due to the bigger case, we were able to bring new features to our S3 phono preamplifier. The new steel & aluminum chassis with aluminum buttons brings very high rigidity and effective isolation from interference. The Phono Box S3 B is available in silver and black and is ready for use in any hifi setup.

‘B’ for Balanced

In addition to settings for MM (Moving Magnet) cartridges, the Phono Box S3 B allows you to upgrade to True Balanced operation with a MC (moving coil) cartridge on most Pro-Ject turntables. Balanced transmissions consist of a hot and a cold (also called + and -) signal. Both signal chains effectively carry the same musical information. A True Balanced gain stage can now extract the final musical information out of the +/- signals and subtract the hum and noise picked up during the transmission. This is the same concept used with every microphone in every professional recording studio worldwide.

Not Just Balanced, Also Discrete

The gain stage of the new Phono Box S3 B uses a fully discrete layout. A discrete circuit is composed of electronic components that are separate, individual devices. The amplifier section here is comprised of discrete componentry (no integrated circuits) which results in a more costly and time-consuming process but delivers the best sound quality.

Semi-Passive EQ

After treating the balanced +/- signals independently they are added back together and processed by the semi-passive RIAA equalization stage. By keeping the gain stage fully symmetrical we can optimize signal-to-noise and keep interference to a minimum, sending the EQ section an optimal signal with which it can it can do its job. For the balanced XLR outputs, a balancing stage generates a symmetrical signal so you benefit from balanced signal transmission again. The RCA outputs are by nature single-ended and their signals are served directly by the RIAA EQ.

Cartridge Loading Options

New to the S3 line, all settings can be easily adjusted on the faceplate. You can connect two turntables at the same time. Each input setting is stored in the memory. A large gain range from 40dB up to 65dB is possible. You can match it with a wide variety of cartridges and seamlessly integrate it into the rest of your hifi system, matching the volume levels accurately to other sources like CD players or streaming devices. The loading options for MM and MC are designed for compatibility with a wide array of cartridges. Ultra low values like 50pF or 10 ohms allow you to account for special situations, for example less-than-ideal higher capacitance cables. The Phono Box S3 B has always got you covered!

Phono Box S3 B Reviews & Accolades

Pro-Ject Phono Box S3 B Wins Outstanding Product Award from Hi-Fi NewsPro-Ject Phono Box S3 B Balanced Phono Preamp Wins Outstanding Achievements Award from SoundStage! NetworkPro-Ject Phono Box S3 B Balanced Phono Preamp Wins Secrets Thumbs-Up Award

Additional information
Weight 0.93 kg
Dimensions 16.4 × 20.6 × 5.5 cm



  • 5-pin mini XLR balanced input
  • Balanced XLR outputs
  • Fully symmetrical & discrete gain stage
  • Setting easily adjustable on faceplate
  • MM & MC capable
  • Dual-mono design
  • Semi-passive RIAA equalization
  • Low noise / low distortion
  • Aluminum enclosure protects against interference
  • Available in silver or black


  • Input impedance: 10, 50, 100, 1k, 47k ohms
  • Input capacitance: 50, 150, 300, 400pF
  • Gain (+6dB using XLR Out): 40, 45, 60, 65dB
  • SNR MM (40dB): 103dBV, 110dBV (‘A’ weighted)
  • SNR MC (60dB): 85dBV, 90dBV (‘A’ weighted)
  • THD at 1kHz: <0.001% MM, <0.005% MC
  • THD (20Hz-20kHz): <0.008% MM, <0.01% MC
  • RIAA equalization curve accuracy: <0.3dB / 20Hz-20kHz
  • Subsonic filter: at 20Hz with 18dB/octave
  • Input: 1x 5-pin mini XLR / 1x pair RCA phono sockets
  • Line-level output: 1x pair RCA, 1x pair XLR
  • Power supply DC: 18V/500mA
  • Power consumption: 18V/170mA DC, <0.5W in standby
  • Dimensions: 206 x 55 x 153mm (164mm with sockets)
  • Weight: 930g without power supply


“This is where the S3 B is without peers. There simply aren’t any European-made balanced phono stages at this price that can be so easily matched to one’s cartridge and amplifier. The term “benchmark” or “reference” is often thrown about carelessly in product reviews. However, the S3 B is a benchmark product. It’s unlikely that a company without Pro-Ject’s manufacturing expertise and scale could build something similar for the same price. Its exceptional functionality establishes a new bar for what a customer can expect in a $500 phono stage. My hope is that other companies will follow suit, but for now, the S3 B sits alone as an incredibly special product.” – Philip Beaudette, SoundStage Hi-Fi 2023 Product of the Year

“…the X2 B/S3 B pairing is truly revolutionary. I hope the rest of the industry copies it as there are no excuses for not facilitating a simple balanced output from an MC cartridge if Pro-Ject can deliver it for under £2000. To paraphrase Jon Landau when he first saw Bruce Springsteen: ‘I have heard the future of vinyl playback’. You simply won’t believe this combination.” – Ken Kessler, Hi-Fi News ‘Outstanding Product’

“The Pro-Ject Phono Box S3 B phono preamplifier and Pro-Ject X2 B turntable combination is an excellent platform to build an analog playback system with. They produce an engaging and lively sound quality from vinyl records and are built to last. And to make them even better, there is a solid upgrade path to get even better sound quality out of both of them.” – Gene Hopstetter, Secrets of Home Theater & Hi-Fi

“How does the in-house S3 B phono stage hold up? The basic character is analytical but comfortably warm, a great vinyl amp. One click and we can rasterize from MM to MC. A new connector on the back – and we switch from Cinch to XLR. As already mentioned, there are no competitors.” – Andreas Gunther, LowBeats (Germany)

“…we also want to know whether the true balanced connection makes a difference compared to the unbalanced connection. First of all: That’s true. A more nuanced resolution and a much more lively dynamic impact can be achieved with the XLR connection of the Pro-Ject X1 B to the Phono Box S3 B phono preamplifier.” – Fritz Schwertfeger, Fairaudio (Germany)