SPL HPm - Dual Headphone Amplifier 500 Series Module

HPm is a 500 Series double-slot module headphone monitoring amplifier with Phonitor Matrix for two headphones.

The headphone output stage
The HPm delivers full headphone sound - twice! The output stage of the headphone amplifiers is designed as a push-pull amplifier in Class AB mode. The bipolar transistors share the amplification of the positive and negative half-waves, which produces a higher gain and a higher output voltage than in Class A operation, where only one transistor amplifies both half-waves.

The output stage transistors are thermally coupled and thus run particularly coherently, which contributes to a consistent and stable sound image. The power supply has a buffer circuit with low source resistance, ensuring generous current reserves even when operating low-impedance headphones. Both headphone amplifiers provide an individual volume control.

Stereo/Mono/Mute
The audio signal can be switched between stereo and mono. In the Mute position, the headphone outputs are muted.

Phase Inverse
With the phase inversion switch the phase the of the left or right channel can be inverted (180°).

Tip: M/S - Mid or Side?
By using the MONO and the phase invert switch in combination, it is possible to only monitor the M or S signal. When "Mono mode" and phase inversion is active, only the S signal is played back.

If the phase inversion is switched off, the Mono signal corresponding to the M signal is played back. Separate monitoring of the M and S signals has become a standard for many mixing and mastering engineers.

The revolution in the headphone amplifier: Phonitor Matrix
The Phonitor Matrix enables mixing and mastering engineers to create perfect mixes on headphones, which will translate perfectly to all types of stereo speaker systems.

Music is normally produced and mixed for playback on stereo speakers. Listening on headphones is different from listening on loudspeakers. The biggest difference is the lack of crossing signals of the sound signal from the left speaker to the right ear and from the right speaker to the left ear. These crossing signals are missing in conventional headphone listening, because there are no signals crossing from one side of the headphones to the other. This results in an unnaturally wide stereo stage and sound sources are not played back at their correct position in the stereo field.

The SPL Phonitor Matrix can correct this false stereo image with an analog circuitry.