Over the past several years I have had the opportunity to work with and ultimately review some really great no-holds-barred microphone preamplifiers. So when I first heard Dick Sequerra (of Sequerra FM Tuner fame) and Mark Conese (owner of Ambient Recording) were working on a new microphone preamp I figured, Why bother? There are plenty of good mic pre amps available already. When they showed me the final product my curiosity got the best of me and I figured, Why not? I’ll check it out.
The idea of locating the mic pre as close to the microphone as possible has always been very appealing to me, and the Sequerra Audio Labs 1070A Microphone Preamplifier is designed from the ground up to do just that.
The 1070A is housed in a cylindrical body approximately 10 inches long by 3 inches in diameter. This preamp is designed to be in-line, strapped to a microphone stand, taking the microphone input in one end and sending it out the other end. The input end has a unique rotary switch set up that controls the gain from +10 to +70 dB in 1 dB steps (hence the 1070) using three high-quality gold contact switches. Here is how it works: a 0 to +25 dB switch sets the overall gain range, while an intermediate switch goes from +12 to +45 dB in 3 dB steps. Finally the third switch goes from 0 to -2 dB in 1 dB steps. A three-position input impedance switch has a setting for transformer-coupled dynamic and ribbon microphones that like to be terminated into a Lo-Z 150-ohm load. A 1.2 kHz intermediate position happens to work nicely as an average input impedance for the vast majority of microphones. Modern condenser microphones, on the other hand, are able to put out more level before clipping if the input impedance is higher, so a 5 kHz position is also available. A miniature toggle switches 48 V phantom power and has a corresponding LED indicator. Internal jumpers can disable the phantom power switch and bypass the input coupling capacitor, resulting in low- frequency extension down to DC while the 3 dB down point on the high end is almost 800 kHz!
By the way, the input coupler is a high-quality cap – costing about $20 – with a low-frequency cutoff at 2 Hz. Another nice feature is the 13 LED peak meter, which has a range of -30 to +21 dB with 0 dBm set at +4 dBm operating level. The ballistics are such that with a quick look you can get a fairly accurate preamp gain setting while in the hall or on the studio floor.
On the output end of the 1070A is a balanced XLR, a 1/4-inch stereo headphone jack and a high-quality, four-pin power supply connector. The power supply is set up to power four 1070A pre-amp modules, each of which are supplied with a flexible 25-foot cable. A three-position rotary switch mutes the output and selects the polarity between normal and reverse. Another rotary switch is used for a two-position high-pass filter with a gentle 6 dB per octave slope set at 100 and 140 Hz. At the time of this writing, Dick and Mark were still tweaking the exact corner frequencies.
The 1070A is differential and balanced throughout, meaning an identical signal path exists for both the plus and minus polarities of the audio signal. Most balanced inputs and outputs in pro audio gear use an extra op-amp to create an inverting signal, while the circuit path itself is single-ended or unbalanced. This, of course, is much less expensive but does not have the ability to cancel noise and distortion as a fully balanced design does.
The 1070P power supply is fully regulated with + 24, -24 and +55 V, available on all four output jacks. A second internal regulation occurs inside the 1070A preamp module. Even the phantom power is double regulated. This attention to power supply detail is necessary to achieve the incredible specifications of this preamp system.
Only the highest quality parts are used throughout the system, including all of the chassis work.
Manufacturer’s specifications include frequency response from DC to 800 kHz (-3 dB), harmonic distortion 0.0001 percent, DC through 40 kHz with internal noise at 1 nanovolt/root Hz. Maximum input level is stated at greater than 5 V RMS, while the maximum output level is + 28 dBu balanced.
Because I am between album projects, a real in-the-trenches field report is not available at this time. However, I did get a chance to check out the 1070 with Warren Bernhardt playing piano using a Shure KSM-44 and a brand new KSM-series microphone I am not even at liberty to talk about yet. The KSM-44 sounded more open than with any microphone preamp I have heard to date and with the new KSM, it took the sound of the 9-foot Steinway to yet another place (I cannot wait to tell you more about this mic). The thing that struck me was the clarity of the upper harmonics and the solidity and extension of the bottom end. Warren’s piano was totally natural and uncolored and did not require any EQ whatsoever.