Processing and Control for Professional AV Installations
Legacy Hardware

304 Headphone Amplifier

The Symetrix 304 Headphone Amplifier is a 1-in / 4-out amplifier designed to drive multiple headphones of any impedance. Symetrix proprietary high voltage drive technology gives the 304 the ability to drive high impedance headphones with the equivalent output voltage of a much larger power amplifier, yet provides more than ample current for low impedance phones. The four stereo outputs automatically adjust output power to match the load impedance.


There are two separate AC supplies coming out of the PS-3: 8.5 VAC @ 1A and 34.5 VAC CT @ 250mA. Pinout is as follows: 8.5 VAC on pins 6 and 1, 17 VAC on pins 7 and 3, center tap @ pins 4 and 5 are connected to earth ground. This is when viewed at the end of the PS-3 7-pin DIN plug.

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Simply use the “thru” jacks to feed to the additional 304(s). This connecter is also convenient to patch headphones into an existing audio chain, for example: the signal going to a power amplifier could be routed to the input of the 304, the 304’s “thru” output signal would go to the amplifier, thus the audio feeds both the amplifier and the headphones.

Approximately 200mW at 60 ohms or 21dBm at 600 ohms.

Check input signal. Is it too hot, or is it already distorted? Check for output loading. Are you running too many headphones per channel or possibly one of them is shorted? Are all the channels distorted or dead or just one?

No, the only option would be to use a 12VDC to 117VAC inverter with the supplied PS-3 inline power supply.