SPL P8

You don’t always want ‘colour’ in a mic preamp. In fact, there’s a strong argument for making them sound as transparent as possible...

The market for microphone preamps is an interesting one. Some designers aim to add character and warmth by deliberately colouring the signal with valves, audio transformers and/or other circuitry in the signal path, while others strive to produce the cleanest, most transparent signal path possible — the proverbial ‘wire with gain’ that adds nothing and takes nothing away from your precious signal. SPL’s new P8 preamp falls into the latter category, utilising a discrete transistor preamp circuit (rather than the more usual op‑amp hybrid topography) to offer a flat and wide frequency response, very low noise and minimal distortion. Its circuitry is designed to provide plenty of headroom, and there’s enough gain range here to allow the preamps to handle anything from hot active microphones to low‑output passive ribbons.

Pieces Of Eight

The P8 is a 1U rack module containing eight identical microphone preamps. SPL have a long track record of designing high‑quality microphone preamps, of course. I owned their excellent GoldMike dual‑channel mic pre and Channel One single‑channel unit many years ago, both of which included valve circuitry to add a little flavour, and I rated them highly. Since then, the company have explored a number of different approaches to mic preamp design, including the high‑voltage Crescendo 8. With the P8, SPL have taken what might be described as a more audiophile approach, with a design that, while not close to being at what I’d consider the budget end of the market, is more affordable than — yet arguably just as highly specified as — lots of single‑channel boutique mic preamps.

SPL’s fully discrete preamp circuit was designed for wide bandwidth (fast slew rates) and low distortion. Importantly, it maintains a musical character when it’s pushed close to clipping, but essentially the circuit’s function is simply to make the mic signal bigger, rather than to change it. SPL’s designers explained that the preamp consists of a total of eight transistors for signal processing, and five transistors in the current mirror circuit. An FMB2222A dual bipolar NPN transistor package handles the differential input stage, and the thermal coupling helps optimise common mode rejection. BCP56 and BCP53 transistors are employed in the output stage to deliver the wide frequency response necessary to handle fast transients.

The rear panel hosts eight Neutrik XLR connectors for the mic inputs, along with two DB25 D‑Sub connectors (wired to the AES59/Tascam spec) for the line outputs. There’s also an optional ADAT interface that allows you to use the P8 as an audio interface expander, and this has dual ADAT ports for S/MUX support of higher sample rates. As standard, the DB25 output is linked to a second DB25 connector allowing the signal to be split without the need for an external...