The Best Pro-Ject Tube Box S2 Review

by Bruno Brozovic

This is the very first review of one of the key components – the phono preamplifier. So I decided to write a Pro-Ject Tube Box S2 Review article.


If you’re an avid vinyl lover, you know that a good phono preamp is essential to getting the best sound out of your turntable. Pro-Ject Audio Systems, a company known for producing budget-friendly high-performance analog components, offers Tube Box S2 MM/MC phono preamp. This phono preamp boasts a fully discrete circuit design without using any operational amplifiers and comes with replaceable tubes for tube rolling and sound-shaping.

The Tube Box S2 is compatible with most MM and MC cartridges on the market, with a wide range of gain, loading, and capacitance settings. Its sonic presentation is described as full and relaxed, with a blossoming midrange more typical of much more expensive designs.

In this review, we’ll take an in-depth look at the Pro-Ject Tube Box S2, examining its features and performance to help you determine if it’s the right phono preamp for your vinyl setup.

Pro-Ject Tube Box S2 Review

Pro-Ject Tube Box S2 Specifications

  • Tubes: 2 x ECC83 (12AX 7A)
  • Input impedance: 10 ohms, 100 ohms, 1 kΩ, 2 kΩ
  • Input capacitance/impedance: 47pF, 147pF, 267pF, 367 pF, 487 pF and 587 pF* / 47 kΩ, together with other input impedance settings without any influence!
  • Input gain: 40 dB, 43 dB / 50 dB, 60 dB and 63 dB
  • Noise floor: 80 dB (A weighted) at 40 dB input gain, 75dB (A weighted) at 50 dB and 63 dB input gain
  • THD: <0.02% at 40 dB input gain <0.05% at 50 dB and 63 dB input gain
  • RIAA-equalization curve accuracy: +/- 0.4 dB/20 Hz – 20 kHz
  • Subsonic filter: at 20 Hz with 18 dB/octave
  • Input: 1 pair of RCA/phono sockets
  • Line-level output: 1 pair of RCA/phono sockets
  • Outboard power supply: 18 V / 1.000 mA DC, suitable for your country’s mains supply
  • Power consumption 470 mA DC, <1W in standby
  • Dimensions: W x H x D with sockets 103 x 73 x 131 mm
  • Weight: 410 g without power supply

You can download & view the manual here->Pro-Ject Tube Box S2 Manual

What Vinyl Setup You Should Have For Pro-Ject Tube Box S2?

The Pro-Ject Tube Box S2 phono preamplifier is a tube-based preamplifier designed to enhance the sound quality of vinyl records. Here’s what I can tell you about what vinyl setup should be used with the Tube Box S2 and what can be gained from it:

In terms of technical specifications, the Pro-Ject Tube Box S2 has an input gain of 40dB, 43dB, 50dB, 53dB, and 60dB, with a noise floor of 80dB (A-weighted) at 40dB input gain and 75dB (A-weighted) at 50dB and 63dB input gain. It is compatible with both moving magnet and moving coil cartridges, and it features replaceable tubes for sound shaping and tube rolling.

Pro Ject Tube Box S2 Back Side View

When it comes to the vinyl setup needed to use the Pro-Ject Tube Box S2, the phono preamplifier can be connected to a turntable with a phono output via RCA cables. Additionally, the total capacitance of the cabling from the cartridge to the preamp can contribute to the sound quality, and the Pro-Ject Tube Box S2 features switches to adjust the capacitance value.

Using the Pro-Ject Tube Box S2 phono preamplifier with the right vinyl setup can result in enhanced sound quality, particularly when it comes to the warmth and richness of the sound produced by the tubes. The “true” tube design of the Pro-Ject Tube Box S2 preamplifier is said to provide a more authentic and natural sound, without relying on solid-state amplification.

Pro-Ject Tube Box S2 Phono Preamplifier (Silver)
  • Suitable for MM and MC cartridges
  • Precise RIAA equalization in two parts, passive/active
  • Fully discreet circuit design without OpAmps
  • 2x ECC83 tubes (replaceable)
  • Front-sided Subsonic filter button

Sound Test

This is a great phono preamp. It’s deceptively small, but it packs enough power to make it sound much louder than playing a record. The sound quality is also great. I like that the gain can be set to several different levels to get the ideal balance between phono preamp gain and main system amp gain.

This Pro-Ject Tube Box S2 is perfect. It packs more volume (which is shocking given its small size) and its volume is loud without distorting. Compared to Emotiva’s built-in phono preamplifier, there was a difference between day and night. Seriously, I’m talking about the psychoacoustic nonsense of people babbling from a wider soundstage, adding textures and other stuff that only those with great “golden ears” can hear. not. This little box can make it twice as loud as the built-in phono amplifier. Strangely enough, he can do this without increasing the gain by decibels beyond the gain rating of the inferior built-in amplifier! It gets really loud when you turn up the gain on the function. While this is done without distortion, the built-in phono preamp distorts badly only at moderately high volume levels. Also, this Pro-Ject sounds much better at lower volumes… It’s less muddy and muddy than the built-in phono preamp… The Pro-Ject sounds clear and turns the volume down. It stays clear even when raised.

Pro-Ject Tube Box S2 - DIP Switches On The Bottom

Pro-Ject Tube Box S2 – DIP Switches On The Bottom

If you want your records to play loud without distortion, or if you want a clean, clear, unattenuated sound at moderate levels, this is a great choice. It’s a bit annoying having to pay $500 for something the size of two decks of cards, but it helps.

My only criticisms are:

The instruction manual is terrible. Seriously, I almost returned this product because I didn’t know how to set the DIP switch on the bottom. The instructions are unclear, confusing, and seem intentionally confusing. They use the “Ortofon 2M Red” cartridge as an example to set the impedance and capacitance dip switches, but the numbers are at odds with the Ortofon cartridge manufacturer’s website by over an order of magnitude. Ridiculous. After trying all sorts of dip switch combinations, they all sounded awful… In desperation, I slid every dip switch to the off position, ready to repack and return …and BOOM! That was it! This was the correct position for my Ortofon 2M Blue Cartridge. ALL DIP switch is down to OFF. Who would have thought once I did that, everything was perfect and done instantly? I’m glad I desperately tried one last thing before sending back a great product with such terrible instructions.

Pro-Ject Tube Box S2 Tube Rolling

If you want to do a tube rolling please have this in mind:

Bear in mind that the Project Tube Box S is what is commonly called a “starved plate” tube design, using a pair of 12AX7A tubes with only an 18 VDC wall wart, which means there is no more than 18 VDC on the tube plates (anodes). An AC wall wart could have allowed for a voltage doubler/tripler power supply – which would have been a little closer to real operation.

The 12AX7A data sheet specifies 100 to 250 VDC, up to a maximum of 330 VDC, on the plates (anodes) for linear amplifier operation. Accordingly, the tubes in the Project Tube Box S are just window dressing at such low voltage, and hardly linear amplifiers which is the intent of triode tubes, so distortion will be audible (and possibly even pleasing to some ears, or not depending upon the listener).

Some 12AX7A tubes from different manufacturers may sound different than others, but there will be NO correlation to these tubes running following the datasheet such as in REAL tube phono stages like the EAR834, Shure M65, Quicksilver, etc. IMO starved plate designs do a disservice to tube designs in general, and are intended to mislead unknowing buyers.

Here is what it looks like inside, and do note the integrated circuits (quad Op Amps) that are doing all of the amplification since the tubes are not:

Pro-Ject Tube Box S2 Inside Look

I think if you look at the part number, those 16-pin ICs are analog switches (maybe something to do with the gain selection switching), not opamps, which would normally be in a 14-pin package. The picture also shows the DC-DC converter section between the front panel and the steel partition, you can see multiple inductors and capacitors.

Pro-ject generally uses a JFET/triode cascade as the first stage on their better preamps, similar to that used by Manley in the Chinook, and others that support MC gains in their tube preamps. They usually follow that with passive EQ, then the other triode section in the tube as the second gain stage, and then some type of low output impedance buffer. I think the buffer on the DS2 is an opamp, whereas the S2 may be another JFET, not sure.

Link to a thread on vinylengine forum: LINK

Pro-Ject Tube Box S2 Video Review

Final Verdict

Pro-Ject Tube Box S2 is a great choice for anyone looking for a high-quality and affordable preamp for their turntable. Its “true” tube design offers a warm and rich sound that is sure to please audiophiles, and its compact size makes it easy to integrate into any system. Overall, the Pro-Ject Tube Box S2 is a great value for the price and is highly recommended for anyone looking for a reliable and high-quality phono preamp.

Pro-Ject Tube Box S2 Pro & Cons


  • True tube design
  • Affordable
  • Beats built-in preamps
  • MM and MC inputs


  • Not for everyone
  • Can be noisy using MC input
A perfect choice for any vinyl lover looking to improve the overall sound.
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