Field Test: Oram GMS Al Schmitt Pro-Channel

Jan 1, 2004 12:00 PM, By Michael Cooper

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When British pro audio manufacturer Oram set out to build the GMS (Grand Master Series) Al Schmitt Pro-Channel compressor/EQ/preamps, mass-market appeal was not at the top of its list of design criteria. Renowned analog designer John Oram was intent on following Grammy™-winner engineer Al Schmitt's exact specs for the I/O and controls for the mic/line preamps, compressor and 6-band quasi-parametric equalizer comprising the Pro-Channel. But as great minds often think alike, critical engineers should find a lot to savor in this high-end, solid-state channel tailored for recording and mixing.

LAY OF THE LAND


The six-rackspace-high Pro-Channel is currently available only in a single-channel configuration, although Oram promises a stereo version will soon follow. The unit's sculpted front panel is gorgeous, and the layout is thoughtful. The preamp and compressor sections are situated to the left and right, respectively, of the unit's VU meter, with the equalizer's controls stretching across the width of the front panel below.

The Pro-Channel's rear panel features three alternate mic/line inputs on XLRs, a single XLR audio output and a multipin connector to link to the unit's external power supply. You'll also find control-voltage I/O jacks here; these TRS connectors provide sidechain access to the compressor section and can also be used to link two (or more using parallel wiring) Pro-Channel compressors together. (The tip connection carries the analog signal for sidechain applications, and the ring connection carries the DC control voltage for linking.) A two-position switch alternately calibrates the front panel VU meter's 0VU reading to +4 or +14 dBu to better accommodate the system's +28dBu headroom. (The +14dBu setting only affects the meter's post-EQ reading and not other meter source points, which I'll discuss later.)

The rackmount unit connects to its beefy external power supply unit using the included 9-foot multipin cable. The power supply unit provides two multipin connectors for powering up to two Pro-Channels, although the supply delivers enough juice to drive at least five units. The power supply unit also features a detachable AC cord, a power switch and status LEDs for the power rails.

THE PREAMP SECTION


The Pro-Channel allows you to toggle between two preamps (you can't use both simultaneously): one, transformerless and the other, transformer-balanced. Either of these preamps can receive a single mic or line input from any one of the three rear panel XLR connectors. You can connect three different mics, for example, to the XLRs and then choose each mic input in turn via a three-position rotary switch on the front panel. This would allow quick and easy A/B/C mic comparisons or switching between alternate vocal mics on verses and choruses. Unfortunately, the XLR inputs are nonlatching, inviting a cable to be inadvertently yanked out with phantom power applied. (Clients occasionally trip over cables in the control room!)

A 23-position, stepped gain control provides up to 70 dB of gain for either preamp. Minimum gain for the transformerless pre is unity (0 dB) and 20 dB for the transformer-balanced pre. (The lowest five settings on the gain knob, which step you through the first 20 dB of gain, have no effect on the transformer-balanced preamp.) Three red buttons independently activate phantom power for their respective XLR inputs, and a temporary Mute button kills audio output while switching phantom power on/off or switching among mic inputs or preamps. Another button inverts the phase of any XLR-input signal.

The Pro-Channel doesn't offer a DI input for instruments, but I don't see this as a negative. In my experience, such add-ons rarely, if ever, sound quite as good as dedicated high-end DI boxes due to compromises in impedance matching that result from users trying to adapt a DI input to circuitry that is optimized for mic input.

COMPRESSOR AND EQ SECTIONS


The Pro-Channel's optical compressor follows the preamp section and can be switched to be either pre- or post-EQ or completely bypassed. A continuously variable threshold control joins 11-step attack, release and ratio controls. Attack times range from 1 to 50 ms, and release times from 0.05 to 4 seconds, with smaller increments of change occurring at the bottom of each range, as they should. Likewise, the ratio control's steps cover a 1.4:1 to 30:1 range with smaller jumps in value at the bottom of its range, allowing for subtle tweaks. A separate 23-position control provides 0 to 22 dB of makeup gain, in 1dB increments.

The Pro-Channel's equalizer is a 6-band, quasi-parametric affair, with each band sporting its own frequency, boost/cut and bypass controls (the latter with status LEDs). A global bypass switch is also provided for the entire EQ section. Sub (bass-frequency), Lo-Mid, Hi-Mid and Air (high-frequency) bell-response bands each offer a choice of 23 center frequencies and up to 12 dB of boost/cut by way of 23-position stepped controls. A black button for each of these bands toggles the bell-curve response between 1/3-octave and 1-octave bandwidths. Separate low- and high-shelving filters are also provided, each offering a choice of 11 corner frequencies and the same (23-position, ±12dB) boost/cut controls as the bell-curve filters.

The equalizer's four bell-curve bands each provide a plethora of frequency choices but only minimal overlap between adjacent bands. Center frequencies range from 5 to 160 Hz for the Sub band, from 150 to 2k Hz for the Lo-Mid, from 1 to 12 kHz for the Hi-Mid, and from 10 to 32 kHz for the Air band. The low-shelving filter offers corner frequencies from 40 to 300 Hz, and the high-shelving filter from 6 to 18 kHz. I wish the shelving filters offered slightly greater extremes in their frequency choices, but they should serve most applications exceedingly well.

Each of the six equalizer bands features a blue LED that glows brighter as in-band energy increases, or not at all if the energy falls short of the LED's fixed threshold. Together, these LEDs serve as a simple spectrum analyzer that provides a visual aid in making EQ decisions. The LEDs light even when their associated bands and the entire equalizer section are taken out of circuit. Apparently, the LEDs are also influenced by each band's filter controls, as they vary in brightness as you change gain and frequency settings. Nice!

The only major omission for the equalizer section is a master output level control. Lacking this feature, A/B (i.e., EQ In/Out) comparisons are difficult to make and final gain-stage adjustments (when the compressor is placed pre-EQ) are problematic. I also occasionally missed having lowpass and highpass filters to work with in the EQ section while recording vocals and bass guitar.

The Pro-Channel's VU meter can be alternately switched to show the audio signal's level at the preamp output, compressor input, compressor output or main (post-EQ) output. Alternatively, the meter can be switched to show the compressor's gain reduction. An Inset Trim control, located just below the meter, provides ±2 dB of meter adjustment to recalibrate the gain-reduction readout to 0 dB when no signal is present.

IN USE


The Pro-Channel's knurled control knobs have a great feel and their detents oblige repeatable settings, but their hash marks are difficult to see when viewed at an angle or in low light. Titling for incremental frequency and gain settings (the latter for both the EQ and mic pre) are spaced close together, making it difficult to ascertain what position the associated control knobs are set to. I often found myself counting the number of detent clicks when setting these controls to repeat former settings. That said, the controls' wide range and plentiful adjustments are precisely what make them so useful for exacting tracking and mixing applications.

In an A/B test recording acoustic guitar with a spaced pair of DPA 4011 mics and Apogee Rosetta A/Ds, the Pro-Channel's transformerless preamp sounded virtually identical to my Millennia HV-3D/8. The sound was open and detailed, and the track exhibited an ultrasmooth spectral balance and outstanding depth. In comparison, the Pro-Channel's transformer-balanced preamp brought upper mids and low highs more forward. I loved the added presence and subtle saturation that the Pro-Channel's transformer-balanced preamp lent to vocals and drums. For recording delicate acoustic instruments, I preferred using the transformerless pre.

The Pro-Channel's optical compressor sounded warm, completely transparent and fluid on vocals and bass guitar. With moderate attack and release times employed, it even handled steel- and nylon-string guitars without pumping. Considering its optical design, I was also surprised by how much the Pro-Channel's compressor could make a snare drum track pop. Another plus: The unit's VU meter shows would-be gain reduction even with the compressor bypassed, allowing you to dial in reasonable settings in front of clients before activating the compressor.

The Pro-Channel's EQ allows only broad tonal shaping and not the surgical notching that a true parametric design affords. That said, I always found it to be very responsive, musical and sweet-sounding.

CONCLUSIONS


Besides the omission of a master output-level control for the EQ section, my main complaint about the Pro-Channel's feature set is that there are no direct inputs or outputs for the compressor and equalizer. As it is, if you want to use an alternative preamp with the Pro-Channel's compressor or EQ, then you'll have to suffer the additional amplifier at the Pro-Channel's input. At a list price of $8,525 ($16,430 for the stereo unit), I'd like to see more flexibility. Of far less concern is the cursory nature of the owner's manual, which is vague on some points of operation.

On the plus side, the Pro-Channel sounds truly excellent. And service-oriented Oram goes the extra mile for its customers, keeping its office open throughout both European and U.S. business hours. The Pro-Channel's price tag puts it out of reach of most small studios, but the unit's impressive sound and superior build quality make it very worthy of consideration by those who can afford it.

Oram, 011-44-1474-815300, www.oram.co.uk.


Mix contributing editor Michael Cooper is the owner of Michael Cooper Recording, located in beautiful Sisters, Ore.






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