Tuesday, October 16th, 2012 | by Adam Kagan
Audio Engineering Associates, more commonly referred to as Wes Dooley’s AEA, is well known for its fabulous ribbon microphones, both museum quality reproductions of the RCA 44, as well as newer designs, including the R92, R84, and the phantom-powered A840 and A440 ribbons. In 2009, AEA released the RPQ preamp, which was tailored to complement ribbon mics by providing very high gain combined with very low noise specs. Recently AEA has produced a version of the RPQ mic preamp as a 500-series module for API style racks.
Fundamentally, the RPQ500 is identical to the original rack-mounted two-channel RPQ preamp. The amplifier provides 81 dB of gain while the CurveShaper™ circuit provides high pass and high boost equalization. The unit will accept mic and line-level signals, and provides switchable phantom power for condenser microphones. The heart of the unit is a JFET amplifier with terrific specs, including a noise floor below -130dBu (A-weighted) and a frequency response from 3hz up to 100khz. The input impedance of the RPQ is 10kΩ, which is much higher than a typical preamp’s input impedance of 1kΩ, and therefore doesn’t load the output of a ribbon mic, allowing the mic to transfer its energy to the preamp without a change in tonal character. Basically, the higher input impedance translates to a more true sound from low output impedance ribbons or dynamic mics.
These days so many companies are touting their preamps’ character or color — big, vintage, warm, tube-y, transitor-y, or just plain thick and dark. More often than not, the best preamp for the job is one where the preamp doesn’t color the sound, but the instrument, mic choice and placement define the sound. That is where the RPQ500 shines. It provides extremely clean mic gain for ribbons, dynamics and condensers (yes, even tube mics will sound their cleanest).
The front panel of the RPQ has five large, chrome plated, knurled knobs that feel very industrial and have a positive feel, especially the detented gain control. The top two knobs control the high frequency boost and frequency, then below those is the low frequency rolloff control followed by the mic pre gain and, finally, the output gain control. Each EQ band has its own on/off pushbutton switch as does phantom power, polarity and the mic/line selector. For gain setup, the stepped gain pot, which uses switched resistors, controls the first 56 dB of gain, with roughly 4 dB per step. The output gain knob can then continuously adjust the gain from full off to an additional 19 dB of gain. Where does the last 6 dB of gain come from? The output of the module is driven by a balanced line amplifier with 6 dB of fixed gain, for a total possible system gain of 81 dB.
When using the line input, the first gain stage is simply bypassed, injecting the line signal into the EQ circuit first and then into the output fader. This setup allows inputs from microphone level all the way up to line level, with the RPQ’s maximum output level reaching +28 dBu balanced, or +22 dBu when driving an unbalanced input. Three LEDs on the faceplate monitor the preamp signal, showing signal present (green), nominal levels (yellow), and peak levels (above +23 dBu, flashing red).
The String Session
In my first session with the RPQ500, I slid two units into my 6-space API lunchbox and toted it off The Village Recorders for a string session. The group consisted of 6 violins, 1 viola and a cello. The live room in Studio A accommodated that size group well, with a clean, dry studio sound.
We had a severe shortage of stereo pairs of tube and ribbon mics due to another large session at the same time, so the microphones that I brought along as extras wound up being the meat and potatoes for the recording. My normal setup for a group this size would be an XY pair for the center, usually an ORTF pair of cardioids or a Blumlein pair of ribbons, depending on the size and sound of the room. I usually supplement the center array with pair of spaced omnis, as well as spot mics on individual sections, which would only wind up being used for solos or featured moments. Being a relatively small, dry room and a group that was violin heavy, I went with an ORTF pair of Miktek C5s, about 7 feet off the ground and about 24 inches behind the conductor’s podium. This was lower and closer than I would use for a bigger sounding room, but a nice setup for this room.
I flanked the ORTF pair with a pair of C 414 EBs set to omni and spaced about four feet either side of center and about six feet off the ground.
In this room, the wall behind the conductor is covered with heavy drapes, so almost no sonic information gets reflected into the backs of the microphones. I probably could have used a wide cardioid setting for the flanking mics, but the omni pattern has better sounding off-axis pickup.
For spot mics, I used a pair Cathedral Pipes Regensburg Doms (tube LDC) on first and second violins, along with a Cathedral Pipes Notre Dame (tube LDC) on cello and a Miktek CV4 on viola. The console, a Neve 8048, contained mostly 1081 modules, which were used for all the mics except the omnis, which I chose to run through the AEA RPQ500s.
I chose the AEA preamps for the omnis mainly because I am not a huge fan of 414s as room mics, since in this capacity they tend to be somewhat dull and flat sounding. I hoped the RPQ’s Curveshaper™ EQ would help with the sound of the 414s. Right off the bat, the ORTF pair sounded very good, representing the stereo spread and imaging very well, and sounding well balanced, if only slightly bright during strident sections. The 414s took about 45dB of gain from the RPQ, which is only halfway up its range and I opened up the high end of the mics with the HF gain about halfway up (maybe 8 or 10db) and the frequency set to around 12Khz. Although this looks like a drastic boost, its effect was very pleasant and musical, without sounding harsh, phasey or EQ’d. The high frequency EQ on the RPQ works as a peak EQ that seems to start very broad and narrows in Q as the center frequency goes up. This gives a nice “tone control” type effect rather than a typical peak-style EQ’s tone. The low frequency rolloff is a shelf-type circuit that seems to have a gentler slope as the frequency rises. The LF works very well as a rumble filter at low frequencies and then becomes a more musical low shelf cut as the frequency rises allowing the proximity effect of close-miked instruments to be gently tamed.
For their first recording, the RPQs nailed the gig. They sounded super-clear, with no coloration or noise, and the high frequency EQ added just the right amount of presence to the room mics. String sessions tend to be slightly stressful, with the clock ticking while the musicians, arranger, artist and engineer all get comfortable. The simplicity of the RPQ allowed me to quickly dial in a sound despite being unfamiliar with the unit. For the final mix of these pop songs (think Norah Jones’ first album with Nelson Riddle style string arrangements, courtesy of producer/arranger Carlos Rodgarman), I will most likely use the ORTF for the main string sound and very subtly add in the room mics to fill out the sound, without sacrificing clarity and imaging. I doubt the spots mics will come into play at all, save for a rare cello solo.
Outboard Signal Processing
Back at my studio, I experimented with the RPQ on vocals and instruments and also as a signal processor during mixes. As a mic pre, the RPQ sounded great on all the mics I threw at it, from SM57s to a Royer R-122 and everything in-between. The EQ sounded great as an insert on my vocal buss, as well as on drum overheads and close miked grand piano. A few of these units would certainly come in handy during any mix.
For some reason, the high frequency EQ lifts the air in a sweeter way than most plugins and many large format console equalizers would. There is no input pad, but when tracking loud sources like drums or guitar amps, the unit could be switched into line mode, EQ could be applied and the remaining 25 dB of gain would certainly be enough for dynamic mics or room mics that don’t need phantom power. I often use an LA2 this way for tube mics that only require 15–20 dB of gain, and the RPQ feels good this way, too. Because the same JFET gain element is used for both gain stages, the line input and mic inputs have the same sonic character.
The RPQ is certainly designed to make ribbon mics sound their best, which it does, and I also found it equally valuable as a mic pre for any other mic and as an equalizer both during tracking and mixing. If you use a passive summing amp, a pair of RPQs would make fantastic output gain stage with the bonus of the CurveShaper™ circuit.
At $584 (street price), the RPQ500 is a fantastic addition to your 500 series rack. If you don’t have a 500 series rack, the RPQ also comes as a standalone two-channel rack unit, or you could even pick up a three-space 500-series rack and two RPQ500s for just about $1500 total. That’s a pretty sweet deal for mic pres with this much power and flexibility. I’m a fan of this unit, for sure.