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Recommended Component 2025 – Stereophile
Reference Class Phono Preamplifier with On-the-Fly Impedance Loading and Channel Balance Controls
The Phono Box RS2 is the ultimate phono preamplifier of the highest class. It is fully balanced from the input to the output. Electronics are fully discrete, and there are no op-amps in the circuitry. For best, most accurate sound quality, the Phono Box RS2 uses split passive RIAA and DECCA equalization.
A discrete circuit is composed of electronic components which are separate, individual devices, also called discrete components. These can be passive components, like resistors, capacitors and inductors, as well as active components, which in this case are transistors. The opposite to this would be an integrated circuit, which uses operational amplifiers (op-amps) in the signal chain.
Countless hours of listening tests and years of experience have demonstrated that even the very best op-amps do not tend to be as neutral, natural, dynamic, or vivid as circuitry using discrete components. Standard phono preamplifiers with integrated circuits have a few tens or hundreds of components, but discrete designs will employ hundreds or thousands of components by comparison. That makes for an extended and more costly design process, but it results in the best sound for your money.
"Recommended Component" Honors
Stereophile honored the Phono Box RS2 by awarding it the magazine's coveted Recommend Component status for 2025.
According to Stereophile, "Experimenting with resistive loading in MC mode, JMu [Julie Mullins] found that with the optimal loading 'the degree of detail seemed to increase, as did realism and clarity. The musicians' placement seemed to grow more spacious and specific.'"
"Tom Fine echoed JMu's recommendation and commented on how useful he found the RS2's output-balance control and the options for adjusting capacitive and resistive loading. He concluded that while this preamp is the opposite of set-it-and-forget-it, 'if you have a few cartridges in rotation and you want to spend some time dialing in a favorite sound profile, it's a great option.'"
"Options Seldom Seen Near This Price"
"The compact Pro-Ject Phono Box RS2 does a lot—or rather, it does one thing with great versatility," notes ulie Mullins, Stereophile, August 25, 2021. "The RS2 works with most MM or MC cartridges and could partner well with a setup with two tonearms and cartridges. It offers features—discrete electronics, balanced inputs, a balance control—and gain and loading options seldom seen near this price."
"A highly sophisticated phono stage, fully balanced and with all-discrete circuitry, for MM and MC cartridges, with loading options for both, the Phono Box RS2 has no equal," observes Noel Keywood, topnewreview.com. "For those interested in running a fully balanced turntable to eliminate hum and noise this is the one. Great sound quality and easy to use as well."
Extreme Cartridge Loading Options During Playback
The Phono Box RS2 is in a class by itself with it comes to options for setting the gain. Very large ranges from 40dB (voltage amplification by 100x) up to 70dB (voltage amplification by 3690x) are possible. Load impedance can be set continuously via potentiometer, a system invented by Pro-Ject Audio Systems. This allows you to seamlessly adjust the impedance during playback and immediately assess the impact of different loading options.
Cartridges, by nature, suffer from small imbalances between the left and right channels. To correct this the Phono Box RS2 introduces a new feature that is absolutely rare in this price category. A potentiometer allows you to adjust the exact center of the sound stage in ranges of 2dB to the left or right, and you can do this on-the-fly while your record plays. You will be impressed by the sonic impact that this tweak has on the realism of your music.
Fully Balanced Design
The Phono Box RS2 employs a true fully balanced design principle. Balanced transmissions consist of a positive and a negative (also called hot and cold) signal. Both the positive and negative signal chains effectively carry the same musical information. A true balanced amplifier can extract the final musical information from the positive and negative signals and removes all noise that could potentially be added along the transmission. In a true, fully balanced amplifier, like the Phono Box RS2, the positive and negative sections of both the left and right channel are treated individually, which doubles the amplifier sections by two as a result.
Split Passive EQ
The Phono Box RS2 uses split passive equalization for both of its RIAA and DECA curves. Split passive equalization allows for better impedance matching and lower deviation from the ideal RIAA or DECA curve. This is more costly to design and implement, but ensures the most accurate representation of the ideal EQ curve.
Steel and Aluminum Chassis
The Phono Box RS2 has a steel chassis which is covered by aluminum panels fastened with screws. This construction brings very good rigidity and also provides splendid isolation against airborne RF and EM interference, contributing to the extremely quiet, noise-free operation.
Power Box RS2 Phono – Linear Power Supply Upgrade
Although the Phono Box RS2 comes with a good power supply, an outboard power supply with linear construction is even better, because it can offer much cleaner power. Pro-Ject's Power Box RS2 Phono (optional, sold separately) uses a transformer with a very low core saturation and with shielding between primary and secondary windings. Such a transformer is larger than you might expect, requiring a cabinet the size of the Phono Box RS2 itself. It is also more expensive, but worth the extra cost for the performance upgrade. Pro-Ject's Power Box RS uni 1- & 4-way (optional, sold separately) provide a further step up for your Phono Box RS2 performance.
