The stand-alone mic preamp has survived all of the different evolutions the recording industry has undergone. With the DAW-entrenched studio, engineers require an array of preamps for remote recordings, smaller production spaces and permanent installs in rooms that don't have traditional consoles. Not everyone can afford the space or price tag associated with a big desk, but a variety of outboard preamps can save the day — and your wallet.
In the January 2008 issue, Mix featured tube mic preamps; this month, we're concentrating on solid-state models. While tube preamps bring their own aural excitement and old-school patina to the table, solid-state pre's provide an alternative feature set — and their own brand of coloration, if desired.
A LITTLE TECH
Transformer-coupled designs from such companies as Neve and API are common favorites among engineers. When hit with enough signal, transformer-core saturation may color the signal and even enhance harmonics. This isn't necessarily a bad thing and can be used as a creative tool, much like saturating a tube preamp. Another feature to consider is impedance (“Z”).
Audient Mico features Variphase control.
Matching a mic's output impedance to a preamp's input impedance results in a maximum voltage transfer. A properly selected mic/preamp combination can yield improved frequency response, with increased headroom and transient response. More manufacturers incorporate switchable input impedance into their designs as another creative tone-bending and/or impedance-matching option.
Operational amplifiers (op amps) are also a consideration when comparing different topologies. There are basically two types: monolithic (IC) and discrete. An op amp is the sum of its parts, including an array of transistors, resistors, capacitors and diodes. Monolithic op amps are inexpensive and are created onto a silicone chip. This design (typically found on DAW interfaces) doesn't allow the manufacturer to use individual components in fabrication. A discrete op amp (for example, John Hardy 990 or API 2520) design uses select, individual premium components for optimal performance. Designers can choose and match these individual components with superior results. Granted, there are substantial cost differences between the two, which can range from $0.10 to $100.
As most tube preamps are Class-A, there's a slew of solid-state preamps that are also considered Class-A (such as the Neve 1073 or Crane Song's Flamingo). Class-A amplifiers operate at more than 100 percent of the input cycle, with the active output devices working all the time and always carrying a significant current level. Because of this, Class-A amps run hot and are considered inefficient, but are linear and highly sought after.
Your mic collection might have a say in which solid-state preamp you choose. For example, traditional ribbon mics require a preamp with high levels of clean gain. A unit like AEA's TRP provides a generous 84 dB of gain and a minimal-path circuit design for ribbon, moving-coil and tube mics. And certain DPA mics require 130-volt power for operation; preamps such as Millennia Media's HV Series can accommodate those mics.
Some of the more standard “bread-and-butter” features to consider when choosing a preamp include switches for polarity (“phase”) inversion, input pads, and highpass and lowpass filters. A ¼-inch input matched for connecting high-impedance instrument pickups. For visual stats in reference to gain, I/O metering can vary between VU, segment LEDs or a simple clip LED. Accurate, trustworthy metering is essential when your I/O boxes are in a quiet room and not easily visible.
For those seeking an all-in-one conversion solution, mic preamps with onboard A/D converters provide a major advantage. Manufacturers like Audient, Focusrite and PreSonus offer multichannel preamps with stock/optional A/D converters featuring AES/EBU, S/PDIF, ADAT optical and even word clock I/O.
Some preamps offer unique features setting them apart from the crowd. Rupert Neve Designs' Portico 5016 offers a Vari-Phase feature that allows the user to rotate the phase of the DI in reference to the mic input. This is ideally suited for tracking guitars through a mic/DI combination and experimenting with or correcting their phase relationship. Solid State Logic's VHD preamp has a variable harmonic-distortion circuit that blends second or third harmonic distortion into the signal for different overdrive characteristics. The Grace Design m802 takes control functions to the next level, with a full LCD remote control and added control via Pro Tools HD.
Regardless of topology, a well-designed solid-state circuit can yield extended dynamic range, low-noise, high headroom and excellent transient response. If you have access to a variety of solid-state pre's currently on the market, listen and compare for yourself. For this roundup, we're featuring stand-alone solid-state preamps. What you won't find here are preamp DAW interfaces or channel strips; that's a topic for another feature. For a list of these preamps, see the charts on the following two pages.
Tony Nunes is an engineer, educator, and daddy to Brooklyn and Luc.