Symetrix 304 4 Channel Headphone Amplifier, 1 february 2000, made in USA

Link: symetrix [Owner's manual] | Owner's Manual [PDF, Ru]

Specifications

INPUT/OUTPUT
Input Type: Bridging, Balanced or Unbalanced
Maximum Input Level: +18 dBu Balanced Maximum
Output Level: 21 dBm, 600 Ohm load, >6 VRMS, 200 Ohm load
Input Impedance:  20k Ohms Balanced, 10k Ohms Unbalanced
Output Impedance: 100 Ohms

Performance Data
Frequency Response: 20 Hz to 20 kHz, +0, -1 dB
THD+Noise: 01% (1kHz, 0 dBm, 600 Ohms) .02% (1kHz, +20 dBm, 600 Ohms)
Signal-to-Noise Ratio: 95 dB
Maximum Gain: 25 dB

CONNECTIONS
Input: 1/4" TRS
Output: 1/4" TRS
Power In: 7-pin DIN

PHYSICAL
Size (hwd): 1⁄2 rack unit 1.75 x 8.5 x 6.5 in., 4.445 x 21.59 x 15.875 cm.
Shipping Weight: 4.5 lbs

ELECTRICAL
Power Requirements115 VAC nominal, 95 to 130 VAC, 50 to 60 Hz 230 VAC nominal, 207 to 253 VAC, 50 Hz