The Headphone Monitoring Amplifier for 500 Series.


About this item




The Headphone Monitoring Amplifier for 500 Series.

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 individual volume control.


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

Phase Inverse Ø

With the phase inversion switch, the phase 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.

Wie ist das möglich?

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 analog circuitry.

The Phonitor Matrix parameters

The two main parameters of the Phonitor Matrix are Crossfeed and Angle:

• Crossfeed determines the opening angle of the stereo image.
• Angle determines the opening angle of the stereo image.


The “Crossfeed” parameter of the HPm is continuously adjustable via the crossfeed control

Speaker Angle

The “Angle” parameter can be adjusted in three settings: 20°, 30°, and 40°. The studio standard is 30°.

Center Level

To make the listening experience even more perfect, the level of the center of the stereo image needs to be attenuated when the Phonitor Matrix is active. This ensures that not only the position of all sound sources is correct but also their volume. With HPm, this parameter, which we call “Center” in the Phonitor Matrix, can also be adjusted in three settings. You can choose between attenuation of -0.5dB, -1 dB, or -1.5 dB. The standard for an authentic representation of the stereo image is -1 dB. During conventional listening on headphones, our brain can compensate for a certain level of false playback representation – but this is very exhausting and leads to listening fatigue.

Summed up

The SPL Phonitor Matrix corrects the false representation of the stereo sound image, which makes it much easier to find the right decisions for mixing and mastering engineers. So nothing stands in the way of a successful and long mixing session on headphones.

Phonitor Matrix

With the Matrix switch, the Phonitor Matrix (Crossfeed, Speaker Angle, Center Level) can be activated or deactivated.


Input & Output; balanced

Maximum input & output gain
21 dBu
Input impedance
10 kΩ
Output impedance
150 Ω
Common mode rejection
> 82 dB
Frequency range (-3 dB)
10 Hz – 100 kHz
THD & N (0 dBu, 10 Hz – 22 kHz)
0.03 %
Noise (A-weighted)
-92.3 dB
Dynamic range
113 dB

Headphone Outputs, 1/4″ (6,35 mm) TRS Jacks

Tip = Left, Ring = Right, Sleeve = GND
Max output power (600 Ω)
+18 dBu
Max output power (300 Ω)
+15 dBu
Max output power (32 Ω)
+5 dBu

Dimensions & Weight

Double-spaced module for 500 Series
Unit weight
0.8 kg
1.76 lbs
Shipping weight (incl. packaging)
0.9 kg
1.98 lbs

Reference: 0 dBu = 0,775V. All specifications are subject to change without notice.


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