Aphex Systems 1100MkII Mic Preamp
By Barry Rudolph
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Since introduced in 1999, Aphex's 1100MkI, with its great sound and super-low noise, quickly reached a unique orbit in the vast universe of high-quality microphone preamplifiers. The single-rackspace, 2-channel tube MkII adds several new features, but is otherwise unchanged from the original--good news, as the 1100's elegant and remarkably prescient design looks to become a modern classic.
There are also buttons for -20dB pad, polarity, phantom power on/off that slowly ramps up and down to avoid pops, MicLim on/off, noiseless mute on/off with rear panel jack and the A/D controls (sync clock source and internal sample rate). The new AKM AK5394A A/D converter chip supports 44.1 through 192kHz sample rates and will transmit and accept external clock via rear panel BNC jacks. There are also rear panel AES/EBU, S/PDIF and Toslink optical digital audio output connectors.
The 1100 is a transformerless hybrid design comprising a Class-A variable gain (-3dB to 41dB) PNP transistor differential input amplifier followed by a dual-triode (12AT7) differential tube stage (21 dB) that uses Aphex's Reflected Plate Amplifier circuit. This two-stage front end is followed, after the dual-optocoupler noiseless muting circuit and unbalanced insert loop path, by another RPA output amp (3dB gain) for a total system gain range of 21 to 65 dB.
MicLim uses a specially designed, optically coupled attenuator as a dynamic load resistor across the 1100's input. A very fast peak limiter looking at the output of the first RPA stage controls this attenuator. As the input stage is about to clip, MicLim instantly lowers the input impedance and, therefore, the microphone's output level, avoiding preamp overload. To make MicLim more effective when using low-impedance mics (50 ohms or less), the MkII now comes with Z-Comp--impedance compensation switches on the rear panel. Z-Comp adds 150-ohms resistance in series with the mic's impedance. The 1100 has a 2k-ohm input impedance.
LoCaf is a very effective highpass filtering system with 11 corner frequency choices from 30 to 195 Hz. LoCaf is actually a servo-cancellation circuit with a second-order Butterworth response characteristic that applies an out-of-phase signal component to cancel out all frequencies below the selected frequency.
Using MicLim and LoCaf is like a dream come true for a compulsive, full-level maximizer like myself. On top of LoCaf, with MicLim, you can add up to 16 dB more level before preamp clipping. (The whole idea is to prevent ugly preamp clip by accidental overload from unpredictable sound sources.) If you are willing to accept an occasional MicLim "clamp", then you can record much hotter and still never clip the 1100 or your DAW's input.
IN THE STUDIO
I tried out MicLim and the digital output on a vocal recording and used one more 'click' (4 dB) of gain when accepting a few unnoticeable MicLim clamps. I never once clipped my Pro Tools|HD3 rig running at 24/96 kHz. On close-miked acoustic guitars or big and loud guitar cabs, LoCaf was the most precise filter I've ever used to carve out boomy low frequencies for hotter levels into the compressor.
IS IT A STAR?
Aphex Systems Inc., 818/767-2929, www.aphex.com.
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