SPL Phonos RIAA Phono Preamplifier - Red

MM and MC

There are two primary methods a modern cartridge uses to generate current. These are moving magnet (MM) and moving coil (MC) configurations.

Moving Magnet

Moving magnet cartridges tend to produce lush, mellow sound. By moving a magnet within copper coils a small voltage is created. MM cartridges sport very high inductance and impedance. In the latter, cable capacitance can negatively affect the flatness of frequency response and linearity of phase response. Phonos offers a selection of four capacities to fine tune the flatness of the frequency response or to willingly increase high frequencies in playback. The capacities are 150pF, 220pF and 330pF. In the OFF position the capacitance is determined by the cable capacitance.

Moving Coil

The MC design is again a tiny electromagnetic generator, but (unlike an MM design) with the magnet and coils reversed. The resulting signal is only a few hundred microvolts, and thus more easily swamped by noise, induced hum, etc. Thus it is more challenging to design a preamplifier with the extremely low noise inputs needed for moving-coil cartridge. Phonos provides a 20dB higher preampfification for the MC stage compared to the MM stage.

MC cartridges offer very low inductance and impedance, which means that the effects of capacitance (in the cable that goes from the cartridge to the preamp) are negligible. The impedance of cartridge can be set in six values: 100, 220, 470, 2.2k, 4.7k, and 10kOhm. If in doubt which impedance matches the cartridge’s impedance you can empirically determine the value for the flattest frequency response.

Subsonic Filter

Rumble from the playback turntable's drive mechanism is amplified by the low frequency boost that occurs on playback. The Phonos offers a switchable Subsonic filter to eliminate the rumble.

RIAA Equalization

RIAA equalization is a specification for the recording and playback of phonograph records, established by the Recording Industry Association of America (RIAA). The RIAA equalization curve was intended to operate as a de facto global industry standard for records since 1954.

The purposes of the RIAA equalization, which is a form of pre-emphasis on recording and de-emphasis on playback, are to permit greater recording times by decreasing the mean width of each groove, to improve sound quality, and to reduce the groove damage that would otherwise arise during playback.

A recording is made with the low frequencies reduced and the high frequencies boosted, and on playback the opposite occurs. The net result is a flat frequency response, but with attenuation of high frequency noise such as hiss and clicks that arise from the recording medium.

RIAA Curves

The RIAA equalization curves for recording (blue) and playback (red) of vinyl records. The recording curves perform the inverse function, reducing low frequencies and boosting high frequencies.

RIAA equalization has transition points in three places: 75 µs, 318 µs and 3180 µs, which correspond to 2122 Hz, 500 Hz and 50 Hz (rounded values).

The construction of the RIAA equalizer follows a design made by Douglas Self. In this design larger single capacities are exchanged against smaller multiple capacities.

Gain

The preamplification is switchable and offers three values for MM and MC.

The Normal gain is +46 dB (MM) and +67 (MC).

In the -10dB position the Phonos produces enough output level for standard consumer electronics products operating on -10dBV.

In the +4dB position the output is equally loud as modern DA converters at 0dBfs = +15dBu.