Installation amplifier
SD125.4
Four channels of 125 W, 500 W shared across channel pairs, low-impedance or 70/100 V output, and set-up over the unit’s own wireless access point — in a half-rack 1U chassis.
- Dimensions
- 44 × 220 × 319 mm
- Weight
- 2.8 kg
- Standby
- Under 0.6 W
At a glance
Automatic, across each channel pair
Channels 1 and 2 share the supply, and so do channels 3 and 4. When one channel briefly asks for more than its continuous rating while its partner asks for less, the spare power is made available automatically. Nothing to set.
Lo-Z and 70/100 V from one chassis
Four low-impedance channels driving 4 Ω to 16 Ω, or two constant-voltage outputs at 250 W — with no external transformer between them.
Configured in a browser
The amplifier hosts its own access point and its own web app. Join its Wi-Fi, open a browser, and configure inputs, zones, outputs and settings. Nothing to install on anything.
UMAC™1 Class D
A full-bandwidth PWM modulator with ultra-low distortion, fed by a UREC™2 universal switch-mode supply with power-factor correction.
Five circuits
Short circuit, DC, undervoltage, temperature and overload.
Per-zone and per-output
EQ, crossover and gain, delay and driver alignment, polarity, compression and limiting, with speaker presets that can be customised, exported and imported.
Fan-cooled, and quiet when idle
Fan speed follows temperature, and the fan switches off entirely when the amplifier drops into standby. Keep the ventilation apertures clear.
Under 0.6 W
The unit draws 150 W in use and under 0.6 W asleep. It wakes on signal, on a network command, or on a 12 V trigger.
Power Share
The published output figures are not two different amplifiers. They are one 500 W supply, divided two ways.
Each pair of channels draws on a 250 W budget. Run evenly, that is 4 × 125 W across four zones. Collapse each pair onto a single channel and it is 2 × 250 W. The total is the same either way, and so is the amplifier.
None of it is a setting. The amplifier does this by itself: when one channel briefly demands more than its continuous rating and its partner is demanding less, the spare power is handed across automatically. It is there to hold up under music, which is the load that actually asks for it.
Front panel
The panel prints its own legend: five indicators in a column, each labelled, framed by two hairlines that break around them. It reports at a glance what the unit is doing, without a screen to read or a menu to walk.
Indicator behaviour as published in the SD125.4 user manual, firmware V1.8.0.
| Status | Off — mains power disconnected. Green — amplifier operational. Pulsing green — standby. Amber — standby triggered over GPIO. |
|---|---|
| Input | Off — no input signal. Green — signal present on one or more inputs. Amber — limiting or clipping on one or more inputs. |
| Output | Off — no output signal. Green — signal present on one or more outputs. Amber — limiting or clipping on one or more outputs. Red — a channel pair is in overload or protection. |
| Network | Off — no Ethernet network detected. Green — Ethernet network detected. |
| WiFi | Off — Wi-Fi disabled. Green — Wi-Fi enabled. |
Connections
Signal connections are made on RCA phono and Euroblock connectors, with a stereo S/PDIF digital input and a stereo S/PDIF output for daisy-chaining. A GPIO Euroblock connector exposes some amplifier functions to external control, and the unit connects to a network over RJ45 Ethernet or Wi-Fi. Mains arrives on an IEC 60320 socket; there is no power switch, and the amplifier is operational as soon as it is connected.
Outputs are marked CH 1 to CH 4 and carry a CLASS 2 WIRING warning: do not touch the output terminals while the amplifier is powered.
Distribution
Low impedance
Four zones, one residence · 4 Ω / 8 Ω
Living room Nakymatone invisible
2 speakers · 8 Ω
Kitchen Nakymatone invisible
2 speakers · 8 Ω
Listening room Waterfall Audio glass
2 speakers · 4 Ω
Courtyard Architettura Sonora
4 speakers · 8 Ω
70 / 100 V line
Two runs, one venue · constant voltage
Main floor Gray Sound
10 speakers · 20 W taps · 200 W of 250 W
Terrace Architettura Sonora
6 speakers · 30 W taps · 180 W of 250 W
Specification
| Channels | 4 × Lo-Z (4 Ω – 16 Ω) / 2 × Hi-Z (70V / 100V) |
|---|---|
| Output power @ 4 Ω / 8 Ω | 4 × 125 W |
| Output power @ 70V / 100V | 2 × 250 W |
| Power Share (up to) | 2 × 250 W, across each channel pair (Ch 1/2, Ch 3/4) |
| Total system power | 500 W |
| Output voltage | 70 Vp / 140 Vpp unloaded — bridged 140 Vp / 280 Vpp |
| Output circuitry | UMAC™ Class D — full-bandwidth PWM modulator, ultra-low distortion |
| Signal-to-noise ratio | > 106 dB (A-weighted, 20 Hz – 20 kHz, 8 Ω) |
|---|---|
| THD+N (typical) | < 0.05% (20 Hz – 20 kHz, 8 Ω, 3 dB below rated power) |
| Frequency response | 20 Hz – 20 kHz (+0 / −0.8 dB, 8 Ω, 3 dB below rated power) |
| Input impedance | 20 kΩ balanced / 10 kΩ unbalanced |
| Power supply | UREC™ universal switch-mode with PFC and standby converter |
|---|---|
| Operating voltage | Universal mains, 100–240 V, 50–60 Hz |
| Power consumption | 150 W |
| Standby consumption | < 0.6 W |
| Power ratings | 1% THD @ 120 Vac and 230 Vac |
| Protection | Short circuit, DC, undervoltage, temperature, overload |
| Dimensions | 44 × 220 × 319 mm (1.7 × 8.7 × 12.6 in) — half-rack 1U |
|---|---|
| Weight | 2.8 kg (6.2 lbs) |
| Operating temperature | 0 – 40 °C, indoor, below 2000 m |
| Cooling | Fan-cooled, temperature-controlled; fan off in standby |
| Ventilation | 80 mm clearance to the ventilated faces |
100V line mode operates @ −1 dB (≈ 90 V).
In the box
- Amplifier unit
- Mains power cable for the sales territory
- Input connector × 2
- GPIO socket connector × 1
- Output connector × 2
- Adhesive rubber feet × 4
- Document pack
Mounting hardware
| Rack ears | 2 |
|---|---|
| ½ rack plate extension | 1 |
| ½ rack mounting plates | 2 |
| Rear supports | 2 |
Documentation
Specification sheets and installation documentation for the SD125.4 are in production. Ask and we will send what exists today.
Terms
-
UMAC™ — the manufacturer’s name for the output stage: a full-bandwidth PWM modulator with ultra-low distortion, quoted here as the manual states it.
Full-bandwidth is the part that can be checked: signal-to-noise, distortion and frequency response are all quoted across the whole 20 Hz – 20 kHz band into a real load, rather than at one convenient frequency.
-
UREC™ — the manufacturer’s name for the power supply: a universal mains switch-mode supply with Power Factor Correction and a separate standby converter.
Universal means one unit for any territory — 100 V to 240 V, 50 or 60 Hz. The standby converter is what holds standby draw under 0.6 W.
Specifying the SD125.4?
Selective Amplifiers are sold through custom-installation dealers and specifiers. Tell us the zones, the speaker types, and whether the runs are low impedance or 100 V, and we will confirm the configuration.