Vinyl turntables require an RIAA preamp, not only to EQ the signal appropriately, but also to present the right impedance to the cartridge and apply a suitable level boost — few audio interfaces can do this properly.Photo: Wikimedia/Creative Commons
I want to record some vinyl into my DAW, and I know that I need not just a turntable but also an RIAA preamp because this applies a de‑emphasis EQ curve. But does this preamp serve any special purpose other than that — as in, is it also performing any level boost or impedance matching functions? Or, given that I’m recording rather than playing back vinyl records, could a turntable simply be plugged into any audio interface and the EQ applied after amplification?
Cam Levy
SOS Technical Editor Hugh Robjohns replies: Yes, as well as the slightly complicated de‑emphasis filtering, there’s impedance matching and lots of gain involved. The impedance matching is critical to the resulting frequency response as well as the dynamics, and there are very different requirements for MM (moving magnet) and MC (moving coil) cartridges. The resistive element is generally fairly consistent for a particular cartridge type, but the capacitive element can vary a lot for MM pickups, depending on the cartridge and the tone‑arm cable wiring. MC pickups typically need around 70dB of gain while MM pickups more usually need 40dB or so. Most RIAA preamps use conventional voltage gain configurations, like conventional mic preamps, but moving‑coil pickups are really (balanced) current generators and so there are some specialist RIAA preamps that use a current mode for MC pickups that is said to offer better performance.
As well as slightly complicated de‑emphasis filtering, there’s impedance‑matching involved and lots of gain.
It’s possible to connect a turntable directly to some audio interfaces, but not many. RME’s ADI‑2/4 Pro SE, for example, can accept, amplify and equalise direct MM cartridge inputs but the impedance‑matching options are limited. The tricky thing is optimising the gain structure while applying such enormous EQ correction — leaving enough headroom to accommodate clicks while maintaining a suitably low noise floor. The latest A‑D converters are just about there, but it’s a bit borderline. For now, I think a good analogue RIAA preamp remains the best quality option.