Pro-Ject Phono Box RS2 phono preamplifier The Decca Curve

The Decca Curve

The Phono Box RS2 has a rather rare playback option: the mono-era Decca LP EQ curve.

Prior to the mid-1950s, different record companies used different recording EQ curves (emphasis) and expected consumers to use corresponding (de-emphasis) curves when they played back the LPs. Many mono-era "hi-fi" preamps—for instance, the McIntosh C8 "Audio Compensator"—offered a variety of EQ options. Around 1954, the Recording Industry Association of America (RIAA) stepped in and convinced the various US labels to standardize on RCA's "New Orthophonic" curve, which became the RIAA curve still used today. Companies "soft-converted" to the new curve, selling through their pre-RIAA inventory and running existing metal parts in the pressing plants until worn out. In Europe, standardization was slower, according to some accounts. Stereo records worldwide have always been cut with the RIAA curve, interwebs chatter and rumors aside (footnote 1).

The Decca curve, used for early-era mono LPs, has less high-frequency preemphasis: It boosts the signal 3dB less at 10kHz during disc-cutting, and the playback curve attenuates 3dB less at playback. This was visible in JA's published test results.

According to a Pro-Ject staffer, Pro-Ject CEO Heinz Lichtenegger is "a collector and lover of classical music, especially the works of the Vienna Philharmonic" on Decca, including early 1950s LP records. McIntosh Group PR manager Julia Lescarbeau claims that some European classical records were made with that curve up to 1962, when the German DIN adopted the standard RIAA curve.

If you have an annoyingly bright-sounding record, regardless of when it was made, dulling the top octave by switching in the Decca curve may make it less strident. Of course, you could also use, with more control, a properly designed treble tone control on a preamp or integrated amp.—Tom Fine

Footnote 1: Michael Fremer has some very strong views on this topic, which I agree with. See

Pro-Ject Audio Systems
US distributor: Sumiko Audio
6655 Wedgwood Road N., Suite 115
Maple Grove, MN 5531
(510) 843-4500

Anton's picture

Thank you for reviewing it!

Julie Mullins's picture

Thanks for reading, Anton. It was my pleasure (as you might have guessed). Wish I still had it here. ;-)

Ortofan's picture

Are there any plans for reviewing it?

Jack L's picture


It is a real bargain:$1,999 for an Austrian built MM/MC fully in/output balanced dual-mono phono-preamp.

What impressed me most is the use of discrete active devices only & PASSIVE RIAA EQ !!!!. This shows the Austrian designer(s) knows music as much as the preamp design. Austria (ie: Vienna, classical music capital for the world for centuries, no wonder!".

Yes, passive RIAA EQ sounds so much better than the conventional NFB loop EQ used in most most commercial photostages available in the marketplace irrespective of selling price. Ny experience.

Only 'booboo' this preamp designer made, IMO, is the use of switching power supply BUILT-IN on the same circuit board ! To save manufacature cost, I guess.

IMO, NO repeat NO switching electronics should ideally ever be used in any phono-linestages. It will simply impair the sonic musicality.

Glad Pro-jet knows making it up with an outboard linear (non-switching) power supply with additional cost of $800.

Yes, power supply of a preamp is so so crucial for its sonic performance particularly when MC is involved.

FYI, my factory-matched headamp for my moving coil cartridge (both made in Japan) is a single-ended Classs-A fully symmmetric OTL push-pulll topology using discrete solidstate devices, powered by +/- D-size batteries. Only batttery power supply can assure no PS rippling noise & ground induced noise. Period. The sonic reward is: to say the least - very dark quiet music background.

Likewise, I've used a huge battery 'reservoir' to power the 6.3V heaters of the triodes used in my design/built phonostage+linestage.
Passive no-NFB-loop RIAA EQ for best sound, absolutely.

Listening is believing

Jack L

nidaje's picture

Doing a review of a truly balanced phono preamplifier like the Pro-Ject Phono Box RS2 I would expect that the reviewer at least is capable of meeting the criteria for that specific product and being able to supply the needed balanced phono signal, not just a single wired RCA signal path whatever that path might cost. The reviewer says: "My tonearms have RCA cables, so, although I did try the balanced XLR inputs with adapters, I wasn't able to explore the Pro-Ject's "ideal" fully balanced operation (footnote 1)."
Reviews are some times deepened by a "follow-up". Can You supply a "follow-up" with "fully balanced" contributions and with the Power Supply UNI 4.
Comprehensive is comprehensive.

nidaje's picture

Thank You Tom Fine for unveiling some of the methods You as a producer use in order to assess the end result of Your efforts. I own CD Box RS2 T and Power Box Uni 4-way and am going to acquire a phono preamp. No doubt this will be it.