The HPA4 from Alto is a professional-quality headphone amplifier that provides 4 independent stereo channels in a convenient 1RU rack size. Ideal for use in studio or live sound applications, the HPA4 has 4 independent input/mix sections, allowing you to create 4 different stereo mixes.
Each channel features 3 headphone outputs (1 front, 2 rear), allowing you to connect a total of 12 listeners directly to the amplifier. Each channel has its own output level control and stereo AUX in for connecting an additional signal source. Main I/O is via 3-pin XLR connectors, and headphone connections are made via stereo 1/4" connectors.
Other useful features of the HPA4 include individual treble and bass controls on each channel, as well as mono and mute L/R controls for each channel. LED meters are provided for monitoring both input and output levels.
| Number of Channels | 4 |
| Input Connections |
Rear: 2 x XLR Main Inputs 2 x 1/4" TRS Main Inputs Front: 1 x 1/4" Stereo Phone Direct In 4 x 1/4" Stereo Phone Aux Ins |
| Output Connectors |
Rear: 2 x XLR Male Main Outputs 2 x 1/4" TRS Main Outputs 8 x 1/4" Stereo Headphone Outs Front: 4 x 1/4" Stereo Headphone Outs |
| Maximum Output Level | +21 dBm |
| Function Controls |
1 x Input Gain Knob 4 x Balance per Channel Knobs 4 x Output Gain per Channel Knobs 4 x Treble Knobs 4 x Bass Knobs 4 x Left Mute Switches (with Indicators) 4 x Right Mute Switches (with Indicators) 4 x Mono Mode Switches (with Indicators) |
| Frequency Response | 10Hz - 50kHz, ±3dB |
| THD + N | 0.005% |
| Noise | > 90dB, Unweighted |
| Display |
1 x 8-Digit LED Meter Bars (Input) 4 x 8-digit LED Meter Bars (Output) |
| Dimensions | 19 x 8.5 x 1.7" (483 x 217 x 44mm) |
| Weight | 6.4 lb (2.9kg) |