This PDA-sized two-channel mic preamp and A/D converter provides convenient location sound recording via S/PDIF input.
by Mike Rivers, 10.15.2007
Mike Rivers has a long list of credits with Rounder, Folkways Legacy and the Smithsonian. He has a degree in Electronic Engineering and is the author of the last Mackie Hard Disk Recorder manual.
Location recording media has changed over the years, but front-end preferences for portable recording are still as follows: compact size, battery operation and very good built-in microphones and/or a respectable mic preamp. Most modern flash memory recorders make excellent recordings when fed high quality source signal, but their built-in mics or mic inputs often leave much to be desired. To make a good microphone recording, it’s often necessary to carry along an outboard preamp.
Before flash memory recorders were commonplace, Core Sound — a company dedicated to the needs of the location recording enthusiast — developed the PDAudio card, which turned a PDA (Personal Digital Assistant) into an audio recorder. The Mic2496, developed shortly thereafter, provided an analog front end to the PDAudio system.
Features
The Mic2496 is a two-channel mic preamp and A/D converter. Output is S/PDIF TOSLink optical and coaxial (the “coaxial” output is actually an 1/8-inch phone jack). There’s no analog output, limiting its utility to recorders with a digital input. Inputs are via a single 5-pin Mini-XLR type connector (Switchcraft TA5 Series). For this review, Core Sound provided a mic input breakout cable to a pair of XLRs and a digital output cable with a conventional male RCA plug. Power is either from a 9-volt battery or 7 - 14 V DC external supply.
The A/D converter is 24 bit, providing sample rates of 44.1, 48, 88.2 and 96 kHz, selectable by two toggle switches on the outside of the case (one selecting between 44.1 and 48 kHz, the other doubling the rate). Alternate sample rates of 32/64 kHz and 176.4/192 kHz can be selected by internal jumpers. Other internal jumpers change the microphone power to 9 V for use with Core Sound’s binaural microphone system, employing DPA 4060 or 4061 mics, and to raise the coaxial S/PDIF output level for compatibility with Sony Walkman-style TC-D3/7/8 recorders.
At maximum gain, 43 dBu (6 mV) at the input produces 0 dBFS at the digital output. At this gain setting and with the input terminated with a 150 ohm resistor, quiescent noise is around -73 dBFS: a respectably low level. At minimum gain, -2 dBu in yields full-scale output. Input impedance is a practical 1.6 kilohms. A toggle switch controls the phantom power.
Fast Facts
Applications Location recording when you can use a digital output
Key Features Compact size; wide choice of sample rates; clean sound; battery power
Price $549; mic breakout cable, $35; coax adapter cable, $35; TOSLink cables, $15-30 depending on length and configuration; AC adapter, $12
Experienced occasional crackles when recording from the “coax” S/PDIF output
Score The Mic2496 — while pricey compared to modern portable preamps — sounds good and takes up little space, but gets bristly when connected in a useful manner. It needs a facelift and it’s getting one.
Level control is by dual concentric pots. With no clutch tying them together, tweaking the record level can be a bit fiddly. Signal level indication is by a pair of LEDs, -12 dBFS “activity” (green) and –1.5 dBFS “clip” (red). Other LEDs indicate phantom power and low battery. The preamp is packaged in a solid 3- x 5- x 1 3/8-inch black anodized aluminum case, and it weighs a mere 10 ounces sans battery.
Core Sound estimates five hours operation on a standard 9-volt alkaline battery with phantom power off, and four or more hours when using phantom power (depending on the microphone’s current requirement). The review unit had no power switch, but current models do include a recessed power switch.
In Use
I used the Mic2496 with a variety of new and old dynamic and condenser mics, and concluded that it sounds much like other non-exotic contemporary transformerless preamps. It doesn’t add any particular character, but it’s clean and reasonably quiet. If you’re familiar with Mackie XDR preamps, you know what the Mic2496 sounds like.
With only two level indicators displaying essentially a 12 dB working dynamic range, it’s best to use the Mic2496 with a recorder that has decent meter resolution. The on-screen meters of the companion Core Sound PDA are fine, but a Nomad Jukebox 3’s meters leave a lot to the imagination. I’d prefer the lower level LED indicating between -16 and -20 dBFS: typical “analog 0 VU” level on a digital recorder.
I didn’t really hear the effect of truncation on casual recordings when feeding the Mic2496’s 24-bit optical output to the 16-bit input of the Jukebox 3. More serious recordists will likely use it with a 24-bit recorder. While comparing the Mic2496 with various preamps using assorted mics in the studio, the Mic2496 was a little crisper than a Soundcraft 600 console, not as warm and full as a Great River MP2, but very similar sounding to a Mackie 1402 VLZ-Pro mixer.
The digital output is IEC-958 Type II (consumer format) with no copy protection. The sample rate flag embedded in the data stream is fixed at 48 kHz regardless of the actual operating sample rate. Most modern digital recorders don’t care about this flag, synchronizing Word Clock to the incoming S/PDIF data. While happy at 48 kHz, an aging Sony PCM-2300 DAT didn’t like the Mic2496’s 44.1 kHz output, refusing to record until I forced the sample rate flag to 44.1 kHz using a Digital Domain FCN 1 format converter. If you plan to use this preamp with older equipment, be aware of this issue.
I greatly dislike mini phone jacks, and this one was no exception. I experienced occasional crackles when recording from the “coax” S/PDIF output. An NTI Digilizer confirmed that, indeed, it was not a very robust connection. The TOSLink optical output, however, was completely solid.
My principal requirement for a portable recording system (beyond basic sound quality, of course) is robustness — ideally a straightforward recorder requiring only microphone cables and possibly AC power. The Mic2496 is sized to fit back-to-back with an HP iPAQ PDA, making a neat handful, but cables emerging from three sides of the preamp made combining it with the Jukebox 3 a bit awkward. Careful cable dress is important to avoid a messy spaghetti pile. I would have preferred the preamp outputs on the rear, leaving the front free of cables, but seeing how crowded things are inside, I doubt this was possible. (The manufacturer responds: In part thanks to these comments, a $599 Mic2496 V2 is debuting at AES, and on it we’ve moved all cabling to the rear and all controls to the front; also, it adds zero-latency monitoring, raises the 48-volt phantom power current available to a true 10 mA per channel, and now has six level-monitoring LEDs per channel that indicate -40, -30, -20, -10, -3 and clip. — Ed.)
Summary
The Mic2496 is a clean and quiet full-featured preamp that covers the bases for portable recording. Use it with a recorder that takes an S/PDIF input, either coax or optical, and watch those record level meters!
Review setup
Mic24/96, Creative Labs Nomad Jukebox 3, Sony PCM-2300 DAT recorder, TASCAM CDRW-5000 CD recorder, Computer with Cool Edit Pro and Lynx L22 sound card, Great River MP2H preamp, Mackie 1402 VLZ Pro mixer, Soundcraft 600 console, NTI Digilizer, Minilizer, and Minirator. Microphones used for test were AKG C-451 and C-414, Neumann U-87 and KM-84, Studio Projects LSD2, Beyer M88, M260 and M160. Monitoring with Sony MDR-7506 headphones and KEF 103.2 speakers.
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