Arsenal Audio R20 Mic Preamp

Arsenal Audio has been launched by API to supply audio tools that can reach a lower budget while still maintaining the no-compromise aesthetic of the mother make.

The R20 is a 2U rackmount unit that carries the Arsenal Audio military green fascia with two sturdy handles and a pair of VU meters. There’s one gain knob, four switches and a 1/4-inch TS instrument input socket per channel at the front, with an XLR mic input and parallel XLR/TRS line outputs at the rear.

There is nothing but the battle-ready essentials here and, as with the R24 EQ, you wonder whether something more refined lies under the hood.

In detail

The R20 is a solid state amplifier based around the latest THAT Corp op amps. Most API units use the famed 2520 discrete op amp, which is where the Arsenal Audio range differs.

The THAT Corp 1512 used in the input section is stated as having near discrete performance – ie, similar to what is achievable with a circuit using individual transistors and passive components. Though many standard op amps (ICs) possess adequate performance, the high demands of microphone signal amplification can push them to their limits with regard to frequency bandwidth, linear gain ranges and signal to noise ratios.

Using a specialist op amp such as the 1512 can pay dividends for the fragile and precise needs of the mic preamp. The output of the R20 plus utilises a THAT Corp IC (the 1646) to balance the amplified signal for line level connection.

The controls for each channel are simple. First off, there is a continuously variable gain

pot which sweeps through 46dB of gain for the mic input and 21dB for the instrument.

Above that is a peak LED which lights as the amplification level reaches into the realms of distortion. The intensity of the LED relates to how far into distortion the signal has gone, which is a lot more useful than simply lighting up as the signal clips.

The row of four switches to the right of the gain knob control +48v phantom capability, the -20dB pad (-10dB for instrument input), phase inversion and input source (mic or instrument).

The LED above each switch indicates their ‘on’ or ‘up’ state – simple. Next to the switches is a 1/4-inch TS instrument input. In the centre above the military dog-tag name plate are the two tank cockpit style VU meters. The components and controls used could be condensed into a 1U rack unit with smaller VUs, but the martial aesthetic would be lost, and there’s nothing like knobs and switches with a good bit of finger space around them.

Sound

Considering the look of the Arsenal Audio range you would expect a heavy, gritty Rock ‘n’ Roll sound to match, but here the sound deviates from the image.

Behind a bomb-resistant 5mm thick front plate the clutter-free circuit delivers a clean and tonally transparent signal path. Despite the conservative 55dB of mic gain there is noticeably high headroom coupled with a distinctly unnoticeable noise floor. Even when the peak LED flashed ‘alert, distortion imminent’, we could not detect any audible signal clipping.

(2 pages; go to page: 2)

[Source] Robbie Stamp