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First up is the all important mic preamp. The ARC utilises the Buzz Audio BE40 True Class A high speed amplifiers developed for the MA-2.2 mic preamp. The BE40 amplifiers ensure accurate transient detail reproduction and very good noise performance. Another feature is the padless input circuit with a +15dB gain boost switch instead, providing a total mic gain range of +9 to +65dB. The mic load control adjusts the mic input impedance from 200 ohm thru to 5k ohms. This control provides another means of varying the tonal quality of the connected microphone. The 48V phantom power switch features a soft start circuit to avoid thumps and bangs. A direct output of the mic preamp stage is available on the rear panel allowing use of the mic pre section whilst using the ARC in line mode.
Next up is the line input stage which is either the rear panel balanced XLR input (with loop thru) or front panel unbalanced high impedance input. The line gain is variable from 0dB to +40dB. In addition, a -10dB pad can be switched into the balanced input to cater for those hot signals from D-A convertors. In addition to attenuating the input, the -10dB switch raises the input impedance from a nominal 20k ohms to 70k ohms which allows the driving device to freely deliver high level without undue distortion.
Output and high pass filter
Here's where you select the mic or line input to feed the main output of the ARC. The output gain control provides +10dB of additional gain as well as acting as a fader. This control can be useful for setting the correct level into -10dBv devices such as computer sound cards. Also available here is a polarity reverse switch with mute in the centre position. Another switch selects normal output or side chain monitor, which allows you to hear what is being fed into the sidechain of the compressor section and therefore any EQ being applied.
Next up is the clean/tranny switch. In clean mode, the audio path is direct. In tranny mode, a steel transformer is switched into the signal path introducing low frequency harmonics and providing yet another tonal variation to the signal. The high pass filter (part of the equaliser section) features variable filtering of low frequency signals from 25Hz up to 450Hz. The filter has a musical 12dB/oct slope and can be switched into the main signal path (IN), or into the sidechain (S/C) of the Opto Compressor, or when selected to EXT, the filter is available externally via the rear EQ in/out XLR's.
The four band parametric EQ features high and low shelving sections. The low shelf features two selectable turnover frequencies and utilises a true inductor (choke) resulting in a very tight sounding bottom end control. The high shelf offers a broad or tight shelving curve. The tight curve allows you to boost or cut the very top end without much effect to the mid band. Each section can be individually switched in to the main path (IN) or into the sidechain (S/C) of the ARC Optical Compressor. When switched to EXT, the sections are available externally via the rear panel EQ in/out XLR's.
Following that are two mid band sweepable equaliser sections with adjustable bandwidth (sometimes referred to as "Q"). The BW control features a tight notch setting when fully counterclockwise. The frequency range of mid band 1 is 30Hz to 700Hz or 300Hz to 7kHz when the x10 switch is engaged. Mid band 2 sweeps from 160Hz to 3.4kHz or 1600Hz to 34kHz when x10 is selected. Once again, each midband is selectable into the main path, the sidechain of the compressor of into the external EQ path. Very VERY handy !!
Optical compressor FET limiter
Incorporated into the ARC is a single channel version of the Buzz Audio SOC1.1 Stereo Optical Compressor and a FET Peak Limiter. The limiter/compressor combination can be set before (PRE) or after (PST) the equaliser section or out of the main path altogether (EXT). When selected to EXT, the Compressor is available for independant operation via the rear panel Comp in/out balanced XLR's.
The comp drive control varies the amount of compression, similar to a threshold control on other compressors. Comp ratio is switched 2:1, 5:1, 10:1 or 20:1 but all ratio's feature a soft knee characteristic. Compr release time is selectable from 100 milli-seconds to 1.6 seconds and also includes an auto position which is program dependant. Three attack time settings are available, with fast being very fast for an optical type compressor. Finally, a link switch allows linking to another ARC for stereo operation. Compressor gain reduction is displayed with a 12 element bargraph display.
The fast attack peak limiter utilises a FET (field effect transistor) for the gain reduction element and the release time can be selected fast, medium or slow. The Limiter can be independantly switched into the ARC main signal path (Post EQ) or accessed via the rear Comp In/Out XLR's. It is always Post the compressor when used in combination. Although primarily designed to catch peak levels that would otherwise cause "overs" on digital recorders, the peak limiter can be used for some very heavy compression effects. Limiter action is displayed with a single LED.
The combination of the Opto Compressor with EQ-able sidechain and the output Peak Limiter give the ARC a very powerful dynamics package indeed. The peak limiter (always post the Opto compressor) has the ability to catch transients missed by the slower opto action thereby providing a near zero attack time compressor system.
Last but not least is the meter select switch which displays on the 12 segment bargraph the input level (ie post the mic/line gain stages), or output level (what is leaving the ARC main output). The meter can also be switched off. The over led is driven by a circuit that monitors audio level at critical points within the ARC-1.1 signal path and will light when levels exceed +20dBu. Finally a power on/off switch completes the picture.
• Main Path Frequency Response (measured without EQ, Comp/Limiter or Tranny switched IN)
• Mic Input to Mic Direct Out - 3Hz to 400kHz (-3dB)
• Mic Input to Main Out - 4Hz to 400kHz (-3dB)
Bal Line Input to Main Out - 3Hz to 250Khz (-3dB)
Bal Line In with Tranny selected - 12Hz to 100kHz (+/-1dB),+5 @ 250Khz, -3dB @ 400Khz
Instrument Input to Main Out - 9Hz to 300kHz (-3dB)
• External Path Frequency Response
Compressor External Path (no Limiter) - 5Hz to 250kHz (-3dB)
Compressor External Path (with Limiter) - 5Hz to 80kHz (-3dB)
Equaliser External Path (with all EQ zeroed and no HPF) - 5Hz to 200kHz (-3dB)
• Total Harmonic Distortion
Mic Input to Mic Direct Out - 100Hz=0.005% 1kHz=0.005% 10kHz=0.015%
Compressor External Path (no Limit, no GR) - 100Hz=0.01% 1kHz=0.004% 10kHz=0.006%
Compressor External Path (with Limit, no GR) - 100Hz=0.01% 1kHz=0.01% 10kHz=0.02%
Compressor External Path (10dB of GR @ 20:1, Rel at 16, +10dB Make Up Gain) - 100Hz=0.15% 1kHz=0.15 10kHz=0.18%
Limiter in External Path (10dB GR, Release Slow) - 100Hz=0.2% 1kHz=0.08% 10kHz=0.18%
Bal Line Input to Main Out - 100Hz=0.0015% 1kHz=0.001% 10kHz=0.001%
Bal Line Input to Main Out with Tranny - 100Hz=0.3% 1kHz=0.05% 10kHz=0.015
Instrument Input to Main Out - 100Hz=0.08% 1kHz=0.025% 10kHz=0.025%
• Noise (all measured A weighted ref to 0dBu = 775mV RMS)
Mic Input (65dB gain, 150 ohm source impedance) -71dBu (EIN 132.5dB)
Bal Line In (10dB gain, 150 ohm source impedance) -95dBu
Unbal Line In (10dB gain, 0 ohm source impedance) -100dBu
Compressor External Path (no Limiter) -90dBu
Compressor External Path (with Limiter) -80dBu
Equaliser External Path (no cut/boost) -90dBu Levels (0dBu = 775mV RMS)
Maximum Mic input level = +14dBu
Maximum Bal Line input level = +23dBu (+33dBu with -10dB Pad engaged)
Maximum Unbal Line input level = +10dBu
Maximum Output level (all outputs) = +23.5dBu
• Power requirements 115V/230V selectable on rear panel
• Dimensions 2U rack mount, 300mm deep
Specifications are typical of a production unit and are subject to change without notice. 0dBu reference = 0.775 volts RMS.