SPL Phonitor x

Mastering Grade Listening

Headphone Amplifier and Preamplifier

Welcome

Thank you for choosing the Phonitor x. The Phonitor x is the ultimate headphone amplifier, offering connections for headphones operated both balanced and unbalanced. With up to 3.7 W output power, it delivers impressive performance. It also functions as an excellent preamplifier capable of driving power amplifiers or active speakers.

VOLTAIR technology, also known as SPL 120V Rail Technology, is featured within the Professional Fidelity series. This technology makes the Phonitor x an outstanding device in terms of dynamic range, signal-to-noise ratio, and headroom, delivering an exceptional sound experience with serenity, transparency, and realness.

Getting Started

Read thoroughly and follow the instructions and security advice in the enclosed Quickstart. The Quickstart can also be downloaded online.

Press the [Table of Contents] button to access the table of contents.
Press the [Front View] button to view the front of the unit.
Press the [Rear View] button to view the rear of the unit.
Press the [Bottom View] button to view the bottom of the unit.
Press the [Previous] button to return to the previous content.

Front View

The front panel features the following controls and indicators:

1 Standby: Power standby button.
2 VU Meters: Displays input levels.
3 Phonitor Matrix On/Off: Activates or deactivates the Phonitor Matrix.
4 Crossfeed: Rotary control for adjusting the interaural level difference.
5 Angle: Rotary control for adjusting the interaural time difference, related to speaker placement.
6 Laterality: Control for adjusting sound perception differences between ears.
7 Volume: Main volume control.
8 Analog Source: Selects between analog inputs (RCA or XLR).
9 Digital Source: Selects between digital inputs (USB, coaxial, optical).
10 Mode Switch: Selects audio signal mode (Stereo, Stereo with Laterality, Mono).
11 Output/Mute Switch: Selects output (Loudspeakers or Headphones) or mutes the signal.
12 Balanced Headphone: Balanced headphone output jack.
13 Standard Headphone: Standard headphone output jack.

Rear View

The rear panel includes connections and controls:

13 Mains Switch: Power switch.
14 Mains Voltage: Selector for mains voltage (115V/230V) and fuse holder.
15 Analog Audio Inputs: XLR and RCA input connectors.
16 Digital Audio Inputs: Optional USB, Coaxial, and Optical input connectors.
17 IR PGM Volume: Button for IR remote control programming.
18 AMP CTL: Amplifier control output for remote power on/off.
19 Audio Outputs: XLR and RCA line outputs.

The rear panel also features wiring instructions for XLR and RCA inputs, DIP switches (located on the bottom), and safety warnings regarding electric shock.

Bottom View

The bottom of the unit contains DIP switches for configuration.

A close-up view shows DIP switches labeled 1 through 6. The factory setting is indicated.

VOLTAIR – 120V Rail Technology

VOLTAIR is the synonym for SPL's 120V Rail Technology within the Professional Fidelity series. Audio signals are processed with an unequalled +/-60V DC, which is twice the voltage of discrete operational amplifiers and four times that of semiconductor operational amplifiers. This technology achieves outstanding technical and sonic performances, particularly in dynamic range and headroom, and sonically in reproducing fine details for a relaxed audio experience. Music sounds natural.

SPL's 120V Rail Technology refers to the internal audio processing voltage (+/- 60V DC) and should not be confused with the external mains voltage (e.g., 115V or 230V AC).

Comparisons

Diagrams illustrate how VOLTAIR Technology compares to other circuits. The relationship between operating level and maximum level is crucial for classification; higher operating voltage positively impacts dynamic range, distortion limit, and signal-to-noise ratio.

A bar chart comparing Operating Voltage shows SPL's 120V Rail Technology at 120V achieving a higher operating level than +/-15 Volt circuits. Another bar chart shows Dynamic Range, with SPL's 120V Rail Technology at 120V achieving 141.4 dB compared to 124.2 dB for OPA 134@30V.

Decibel (dB) scales represent exponential increases. A 3 dB increase doubles acoustic power, +6 dB doubles sound pressure level, and +10 dB doubles perceived loudness. The VOLTAIR Technology offers superior performance in maximum level and dynamic range, approximately 12 dB higher than common components. THD measurements show an improvement of over 8 dB compared to the TL071 at 30V, corresponding to over 130% improvement in sound pressure level.

Further charts compare Max. Audio Level and THD&N, showing SPL-OP@120V outperforming OPA 134@30V and TL071@30V.

Phonitor Matrix

The Phonitor Matrix creates a speaker-like listening experience on headphones by calculating time and level differences with specific frequency responses to emulate real loudspeaker placement. This allows the brain to correctly identify sound direction, minimizing hearing fatigue.

Basics of Stereo Listening

When listening to speakers, sound from the right is perceived by both the right (red line) and left (green line) ears. The signal reaching the left ear is time-delayed, lower in level, and has a reduced frequency range due to the head's absorption and reflection. This applies similarly to the left speaker.

A diagram illustrates sound waves from right and left speakers reaching a listener's head, showing the paths to each ear.

Stereo Listening with a "Traditional" Headphone Preamplifier

Traditional headphone amplifiers often present the right signal only to the right ear and the left signal only to the left ear. This unnatural sound, missing the delayed and quieter opposite-side signals, can be stressful for the brain as it tries to locate sound direction. It can also lead to an exaggerated stereo width, placing instruments unnaturally far outside the perceived space.

A diagram shows a person wearing headphones, with colored lines representing signals to each ear, highlighting the unnatural separation.

The Phonitor Matrix corrects these unnatural effects.

How Does the Phonitor Matrix Work?

The Phonitor Matrix calculates time and level differences, along with specific frequency responses, to deliver a true rendition of speaker playback. This emulates loudspeaker placement, enabling correct sound direction identification and providing optimal conditions for listening, minimizing hearing fatigue.

A diagram shows a person wearing headphones, with colored lines representing signals to each ear, illustrating the corrected, speaker-like experience.

In Detail

An analog filter design creates interaural time and level differences for four different speaker placements. This design is controlled by the crossfeed and angle parameters.

Angle

The ANGLE switch adjusts the interaural time difference, which is related to speaker placement. Settings correspond to different speaker angles.

A diagram shows a head with lines radiating outwards, indicating various angles (22°, 30°, 40°, 55°) representing speaker positions.

Crossfeed

Crossfeed defines the interaural level difference. The six crossfeed values approximate the influences of room size, reflection, and absorption characteristics.

Two graphs are presented. The first shows frequency-corrected level difference at maximum crossfeed and 30° angle. The second shows frequency-corrected time difference under the same conditions. Both graphs illustrate how the signal is adjusted for the left and right channels.

Interaural level and time differences are frequency-corrected because sound is reflected and absorbed by the head in a non-linear fashion.

Setting of Crossfeed and Angle

Both Crossfeed and Angle parameters define the interaural level and time differences. To reproduce exact loudspeaker placement, first select the Angle parameter closest to your real speaker setup. Then, choose the recommended Crossfeed parameter from the table (e.g., Angle: 30°, Crossfeed: 3).

Various factors, including loudspeaker type, room acoustics, and individual perception, influence stereo listening. The Phonitor x offers six switch positions to finely adjust Crossfeed and match your speaker playback.

Diagrams show the Crossfeed and Angle rotary controls on the Phonitor x unit.

Table: Settings of Crossfeed and Angle

Angle parameter	Crossfeed parameter	Interaural level difference	Interaural time difference (µs)	Speaker angle
22°	MAX	0.24	133	15°
	5	0.35	165	20°
	4	0.40	210	20°
	3	0.47	220	25°
	2	0.50	230	25°
	MIN	0.60	250	30°
30°	MAX	0.40	205	20°
	5	0.49	235	25°
	4	0.56	260	30°
	3	0.64	280	30°
	2	0.70	300	30°
	MIN	0.76	335	40°
40°	MAX	0.26	290	30°
	5	0.34	355	40°
	4	0.40	400	45°
	3	0.49	455	45°
	2	0.50	480	55°
	MIN	0.60	535	70°
55°	MAX	0.34	350	40°
	5	0.44	405	45°
	4	0.50	450	50°
	3	0.58	490	55°
	2	0.52	525	65°
	MIN	0.70	555	70°

Adjustment of the Phonitor Matrix

Use the CROSSFEED switch (4) and ANGLE switch (5) to adjust headphone playback to your room and loudspeaker setup.

Play familiar audio material and listen in your usual speaker listening position.
Toggle between headphones and loudspeakers using the OUTPUT switch (11).
Set the ANGLE switch according to your loudspeaker placement (see page 14).
Set the CROSSFEED switch to match your familiar loudspeaker listening sound.
Listen to instruments panned in the stereo field to ensure they are positioned correctly.

Diagrams show the Mute, Output, Angle, and Crossfeed controls.

Matrix On/Off

The MATRIX switch (3) activates or deactivates the Phonitor Matrix. The Matrix is available only for headphone outputs; the Speaker Outputs (19) are not affected.

An icon indicates the Matrix On/Off function.

Source Selection

The Phonitor x functions as a preamplifier with up to five audio sources. It features two analog stereo inputs (XLR and RCA) and can be equipped with a DA converter for expanded digital inputs (USB, coaxial, optical).

Select an analog audio source using the SOURCE switch (8) for RCA or XLR.
Select a digital audio source (USB, coaxial, optical) using the DIGITAL switch (9). Set the SOURCE switch to Digital.

Signals at the analog RCA input are amplified from HiFi to studio level. Sources are equalized in level when switching between XLR and RCA, provided a studio signal is present at the XLR input.

Icons illustrate the different source selections: XLR, RCA, Digital (USB, Optical, Coaxial).

Output Selection

The OUTPUT switch (11) directs the input signal to selected outputs: Loudspeakers or headphones. In the Mute position, no signal is sent to the outputs, and the VU meters illuminate red.

When set to the loudspeaker setting, the selected input signal passes through to both analog audio outputs (RCA and XLR).

The standard headphone output (13) has priority over the balanced headphone output (12). No signal is present at the balanced output if headphones are plugged into the standard output.

To protect the headphone amplifier stage and ensure consistent performance:

Turn down VOLUME before swapping headphones.
Never insert a mono jack plug into the front panel stereo jack.
Ensure the headphone stereo jack is fully inserted.
If using a 3.5 mm to 1/4" adapter, ensure it is fully screwed in or plugged in.

An icon shows the Output selection with Mute and headphone symbols.

MODE Switch

The MODE switch (10) allows selection between Stereo, Stereo with Laterality control, and Mono modes. In Mono mode, stereo channels are summed, and the mono signal maintains loudness by reducing each stereo channel by 6 dB.

An icon shows the MODE switch with options for Stereo and Mono.

Laterality

Laterality refers to the deviation of sound perception between ears. The Laterality control (6) compensates for perceived volume differences that may arise from hearing impairments. Unlike conventional balance controls, when one channel is attenuated, the other is increased (e.g., +2.25 dB for left, -2.25 dB for right). This control offers finer adjustment than typical balance controls.

Set the MODE switch to LATERALITY to control the laterality.

A diagram shows the Laterality control knob with Left, Center, and Right positions.

VU Meters

The VU meters (2) display input levels for the selected source, ranging from -20 dB to +5 dB (0 dB corresponds to +4 dBu). Sensitivity can be lowered by 10 dB via DIP switches, allowing meters to read up to +15 dB input level.

The ballistics of the VU meters are designed for optimal visual perception, with time calibration meeting BBC requirements. The rise time to 0 dB is approximately 300 ms.

If VU meters remain permanently red, even when unmuted, the protection circuit has activated, disconnecting outputs to protect headphones. Contact your local dealer for service.

Two VU meters are depicted, showing typical needle positions.

AMP CTL (Amplifier Control)

Connect the Phonitor x's AMP CTL (18) to an SPL Performer s800 using a mono mini-jack cable to synchronize standby modes. The Phonitor x offers two outputs (A and B) for use with two Performer s800 units in bridge mode or bi-wiring.

Setting DIP switch 6 to ON enables standby for connected Performer s800 units when the output selection is set to Headphone.

An icon shows the AMP CTL connection for remote power on/off.

IR Remote Control

The volume potentiometer can be controlled via any infrared (IR) remote. The Phonitor x learns your remote, eliminating the need for a universal remote. You can assign Volume up/down functions to unused buttons on your existing remote (e.g., CD player remote).

During learning, set the OUTPUT switch (11) to Mute; VU meters will light up red.
Press the PGM IR VOLUME button (17) on the rear until the Power LED brightens.
Point your remote at the VU meters (2) and press the desired button for volume control. The Power LED flashes once per push. Repeat until the LED flashes three times to confirm programming.
Repeat for the other volume function (increase/decrease). Learn mode ends automatically after the second button is learned.

Note: Strong light sources (sunlight, neon lamps, large screens) may interfere with remote control functions.

Icons show the Mute, Output, Volume, IR, and PGM controls.

DIP Switches

The DIP switches (20) on the bottom of the unit allow for various settings:

Level Increase of the Headphone Output

DIP switch 1 ON: Headphone output boosted by +22 dB.
DIP switch 2 ON: Headphone output boosted by +12 dB.
DIP switches 1 and 2 ON: Headphone output boosted by +24 dB.

Attenuate the Sensitivity of the VU Meters

DIP switch 3 ON: Attenuates VU meter sensitivity by 10 dB. 0 dB on the meter then represents +10 dBu (displayable up to +15 dB input level).

Slave Thru

DIP switch 4 ON: Input passes directly to XLR output, unaffected by volume control.
DIP switch 5 ON: Input passes directly to RCA output, unaffected by volume control.

Standby of Connected Performer s800 Power Amp when set to Headphone

DIP switch 6 ON: Units connected to AMP CTL (Performer s800) enter standby to save power when the output selection is set to Headphone.

Specifications

Inputs

XLR inputs

Neutrik XLR, balanced, Pin 2 = (+)
Impedance: ca. 20 kohms
CMR: -82 dBu (at 1 kHz)
Max. Input level: +32.5 dBu

RCA inputs

Unbalanced
Impedance: ca. 10 kohms
Max. Input level: +32.5 dBu

Digital inputs (optional DAC192 - 1670, until 2019) / sample rates

Coaxial SPDIF (RCA) - sample rates PCM (kHz): 44.1, 48, 88.2, 96, 176.4, 192
Optical TOSLINK (F06) – sample rates PCM (kHz): 44.1, 48, 88.2, 96
USB (B) – sample rates PCM (kHz): 44.1, 48, 88.2, 96, 176.4, 192

Digital inputs (optional DAC 768xs - 1850, from 2019) / sample rates

Coaxial SPDIF (RCA) - sample rates PCM (kHz): 44.1, 48, 88.2, 96, 176.4, 192
Optical TOSLINK (F06) – sample rates PCM (kHz): 44.1, 48, 88.2, 96
USB (B) – Encoded PCM (kHz): 44.1, 48, 88.2, 96, 176.4, 192, 352.8, 384, 705.6, 768
DSD: DSD1 (DSD64), DSD2 (DSD128), DSD4 (DSD256)

Outputs

Balanced headphone output

Neutrik 4-pin XLR connector
Pin wiring: 1 = L (+), 2 = L (-), 3 = R (+), 4 = R (-)
Impedance: 0.36 ohms
Damping factor: 180 @ 40 ohms
Frequency range: 10 Hz to 300 kHz (-3 dB)
Crosstalk at 1 kHz: -90 dB
THD & N: 0.00091 % (at 0 dBu, 1 kHz, 100 kohms load)
Noise (A-weighted): -98 dBu
Dynamic range: 130.5 dB

Standard headphone output

Warning: Never connect a mono jack cable to the standard headphone output (front panel stereo jack). Ensure the stereo jack is fully inserted, otherwise a short circuit might damage the headphone amplifier!

6.35 mm TRS connector
Pin wiring: Tip = Left, ring = right, sleeve = GND
Impedance: 0.18 ohm
Attenuation factor: 180 @ 40 ohms
Frequency range: 10 Hz to 300 kHz (-3 dB)
Crosstalk at 1 kHz: -90 dB
THD & N: 0.00091% (at 0 dBu, 1 kHz, 100 kohms load)
Noise (A-weighted): -103 dB
Dynamic range: 135.5 dB

Max. Output power (at +30 dBu @ 1 kHz)

2 x 1 W at 600 Ohm impedance
2 x 2 W at 300 Ohm impedance
2x 3.7 W at 120 Ohm impedance
2x 2.9 W at 47 Ohm impedance
2x 2.7 W at 32 Ohm impedance

Line outputs

Neutrik XLR, balanced, Pin 2 = (+)
RCA, unbalanced
Frequency range: 4 Hz to 300 kHz (-3 dB)
Crosstalk at 1 kHz: -106 dB
THD & N: 0.00085 % (at 0 dBu, 1 kHz, 100 kohms load)
Noise (A-weighted): -103.8 dB
Dynamic range: 136.3 dB

Internal operating voltages

Analog: +/- 60 V
Digital: + 5 V and + 3.3 V (optional)

Power supply

Mains voltage (switchable): 230 V AC / 50 Hz or 115 V AC / 60 Hz
Fuses: 230 V: T 500 mA; 115 V: T 1 A
Power consumption: max 40 VA
Stand-by power consumption: 0.7 W

Dimensions (incl. feet)

(WxHxD) 10.94 x 3.94 x 12.99 in (278 x 100 x 330 mm)

Weight

9.48 lbs (4.3 kg), unit only
11.90 lbs (5.4 kg), shipping

Important Notes

Version 1.6 – 03/2020

Developer: Bastian Neu

This manual describes the product but offers no guarantee for specific characteristics or successful results. Unless stated otherwise, contents correspond to the technical status at the time of delivery by SPL electronics GmbH. Design and circuitry are under continuous development and improvement; technical specifications are subject to change.

© 2019 SPL electronics GmbH. This document is the property of SPL and may not be copied or reproduced without prior authorization. Sound Performance Lab (SPL) continuously strives to improve its products and reserves the right to modify the product described herein at any time without prior notice. SPL and the SPL Logo are registered trademarks of SPL electronics GmbH. All company and product names are trademarks or registered trademarks of their respective companies.

Declaration of CE Conformity

The construction of this unit is in compliance with the standards and regulations of the European Community.

The CE conformity mark is displayed.

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