Extron ASA 204 (part number 60-552-30) — an active audio summing amplifier that folds four stereo unbalanced sources down to four mono outputs without the level loss and channel interaction of a passive Y-cable.

Summing stereo to mono is one of those jobs that looks trivial until someone does it with a splitter and the result is quiet, phase-smeared and loaded down. The ASA 204 does it actively: four pairs of RCA inputs, each summed to a mono signal on a balanced or unbalanced output, with DIP switches that set the gain relationship so the output level matches what the downstream amplifier expects. Frequency response holds to 20 Hz through 20 kHz within 0.05 dB, THD+N sits at 0.03 percent at 1 kHz, and common mode rejection exceeds 75 dB across the audio band. The whole unit occupies a quarter-rack 1U footprint.

Key Capabilities

• Four stereo unbalanced inputs on four pairs of female RCA connectors
• Four mono balanced or unbalanced outputs on double-stacked 5-pole 3.5 mm captive screw connectors
• Frequency response of 20 Hz to 20 kHz, plus or minus 0.05 dB
• THD plus noise of 0.03 percent at 1 kHz; signal to noise better than 90 dB balanced
• DIP-switch gain selection covering +9 dB down to -9 dB depending on wiring and signal presence
• Quarter-rack 1U metal enclosure, 0.5 lb, with rack, furniture and pole mounting options

Where It Is Used

Classrooms, lecture halls, courtrooms and paging systems where several stereo program sources feed a mono distributed loudspeaker system. It is also common in conference rooms and medical education spaces where a laptop, a codec and a media player all need to arrive at one mono zone amplifier at a consistent level.

Specifications at a Glance

• Inputs: 4 stereo unbalanced, RCA, greater than 10k ohms, -10 dBV nominal
• Outputs: 4 mono balanced/unbalanced, less than 50 ohms unbalanced, -10 dBV nominal
• Audio performance: 20 Hz-20 kHz +/-0.05 dB, 0.03% THD+N, CMRR above 75 dB
• Enclosure: 1.7 in. H x 4.3 in. W x 3.0 in. D metal, 0.5 lb (0.3 kg)
• Power: external 12 VDC supply; 3 year product warranty, 7 year Everlast power supply warranty

Also referenced as Extron ASA204, ASA-204, part number 6055230.