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 splitter, but this has to be removed in order to accommodate the ADAT card. The unit sent to me for review model came with the ADAT interface already fitted.
The ADAT card is optional — when not fitted, the P8 instead carries a duplicate set of eight line outs on a DB25 connector, allowing it to function as a splitter.
Panel Games
On the front, the styling is unfussy and workmanlike, with the eight identical preamp control sets arrayed across the front panel. Each channel has a gain control, plus four illuminated push buttons and a three‑LED level meter. Located toward the right of the panel are a sample‑rate selection button with status LEDs, and another LED for word clock sync.
The gain knob covers the range +8 to +62 dB, and there’s a switchable ‑20dB pad to deal with particularly hot signals such as close‑miked drums, brass or electric guitar amps. The switchable 80Hz high‑pass filter has a gentle first‑order (6dB/octave) slope. Phantom power conforms to the standard 48V and is available separately for each channel, as is polarity inversion. Operating the switches doesn’t produce the clicks and pops that you hear from some less sophisticated designs, and in this design transistor circuits are used to turn the phantom on and off. Given the 1U format, large‑scale meters would be impractical with so many channels and controls to accommodate, but the three‑LED system used here is sufficient to let you know what’s happening, and most of us will have more accurate metering available on the receiving device or in our DAW software.
Since there are no insert points to consider, connecting the P8 up is straightforward. The design also deliberately omits DI jack inputs — ideally I would have liked to have had one or more, but it could be argued that fewer connections helps to maintain the cleanest signal path. Some users may also bemoan the fact that the XLR inputs are on the rear panel, since that might require using a patchbay or stagebox to access them in a studio, but really it’s the best way of fitting eight preamps of this quality into a 1U rack space and there are obvious advantages in keeping the cables out of the way of the controls too.
The optional ADC8 ADAT board has dual ADAT outputs plus BNC connectors for word clock in and out. It uses AKM’s AK5538 converter chip, providing a well‑specified ADAT optical output capable of up to 192kHz using S/MUX, which makes it possible to carry four channels at 96kHz or two at 192kHz over a single Toslink cable, or twice as many if using dual ADAT connections (so the maximum sample rate for running all eight channels over two cables is 96kHz). Many audio interfaces are S/MUX compatible, so a P8 fitted with the ADC8 board could be a very practical addition to a DAW‑based setup, and setting it up as an expander for my PreSonus interface was plug‑and‑play simple — other than a mains cable, I just needed two optical cables to get set up. Precision quartz oscillators provide a low‑jitter master clock but are automatically disabled when an external sync signal is present. There’s also a USB port for handling firmware updates and other maintenance functions (not for use as an audio interface).
Performance
The specified frequency response extends from 15Hz to 200kHz, and although obviously nobody needs anything like that range to be able to hear the detail in hi‑hats and acoustic guitars, having a wide, flat response ensures phase linearity is preserved across the audible spectrum. Crosstalk is specified as being below ‑90dB at 1kHz, with a ‑30dB input signal and 30dB gain. Equivalent input noise is quoted around ‑124dBu — that’s very close to the theoretical minimum. THD (total harmonic distortion) plus noise is negligible at low to medium gain settings, and distortion doesn’t increase excessively unless the preamps are pushed to the verge of clipping. The quoted figures are THD+N: 0.0025% at 1kHz with a ‑30dB input signal and 30dB gain. Common mode rejection is quoted as 78 to 80 dB at 1 kHz, which means that balanced mic cables of the lengths used in typical studio installations will be effective in rejecting unwanted interference.
Testing the preamps with a selection of my acoustic stringed and percussive instruments confirmed the sense of transparency — it’s almost like the mic preamp wasn’t there at all!
As those specifications would suggest, these preamps have an open, transparent character — or rather lack of character! — that allows transient detail to come across cleanly, with a very strong sense of focus. That bodes well not only for drum tracking but also for recording instruments such as acoustic guitar, which can generate very strong and harmonically complex transients. Extended bandwidth and phase integrity are also beneficial when handling arrays, such as Decca Trees. Testing the preamps with a selection of my acoustic stringed and percussive instruments confirmed the sense of transparency — it’s almost like the mic preamp wasn’t there at all!
If you’re longing for a preamp that sounds warm and cuddly, then the P8 probably isn’t for you. But my take on preamps is that while you can always add ‘dirt’ to a clean signal, you can’t add ‘clean’ to a dirty one. The P8 endeavours to make itself invisible so that whatever comes out of the microphone reaches its destination without being changed, and my experience is that it succeeds in that: it captures the character of the connected microphone accurately, without adding any further colour. And even a relatively quiet sound source subjected to compression didn’t bring up any significant noise; in a typical studio situation, the microphone is likely to contribute rather more noise than this preamp.
If you’re looking for preamps to use on location, this unit weighs just over four kilograms, and if using a flight case where both the front and back are removable, the rear‑facing inputs will be easily accessible and helpfully out of your way. The optional ADAT card is probably the most straightforward option for mobile recording to a computer/interface setup, so you should probably budget for that. It would have added flexibility if SPL had included audio over USB for recording, since that would allow any existing interface to be bypassed, but using the ADAT output with a compatible interface works perfectly well.
Verdict
To summarise, the P8 is not about character or warmth: this is a mic preamp built to last and to deliver optimal transparency, combined with high headroom and very low noise. Yes, it’s a little more costly than some of the eight‑channel mic preamps by companies such as Focusrite, PreSonus and Audient, but even though ADAT connectivity is a cost option it’s more keenly priced than SPL’s own Crescendo 8, which runs on 120V power rails, and I think the price is very reasonable given the quality of what’s on offer: you get eight seriously clean, capable mic preamps that can do justice to any type of microphone, including passive ribbons.
Pros
- Extremely transparent, quiet circuitry with very wide bandwidth.
- Optional ADAT card.
- Takes only 1U of rack space.
Cons
- No USB interface capability.
- No line/instrument inputs.
Summary
A superbly clean and detailed eight‑channel preamp that delivers transparency rather than adding character.
Information
Standard version £1799. With ADAT card £2099. Prices include VAT.
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