Sealed Lead Acid Power Unit

KingRex SLAP Battery

After the T20U audio amplifier was released, KingRex continued to work at ways to explore its potential. Two high specification power solutions are now therefore available as alternatives to the standard switching transformer supplied with T20 series amplifiers – a linear power supply unit (KingRex PSU) and this new Sealed Lead-Acid Power unit (affectionately known as SLAP) for truly uncompromised power delivery.

Why switching, linear and battery power?   

The power source is particularly crucial to Tripath amplifiers. Switching power adaptors are inexpensive and commonly available, but a poor choice for audiophiles seeking to avoid background noise and distortion created by the high-frequency switching and unwanted harmonics inherent in its design.

Linear power supplies, like the KingRex PSU, are far superior in this regard, but the AC to DC conversion and rectification process passes alternating current through an array of transformers, diodes, voltage regulators, and other potentially compromising components before neat DC is output to the amplifier or DAC.

The SLAP (Sealed Lead-Acid Power battery) unit is able to supply appropriately rated pure direct current without such conversion and therefore extends sonic performance to a level beyond even the PSU in terms of mid-range transparency and treble smoothness.

Design Considerations

It is difficult to provide pure DC for high wattage power amplifiers because of the large capacitors (or large capacity batteries) required. The output stage of a power amplifier during peak power operation will draw on instantaneous high current from the DC voltage rails. As the DC voltage is supplied by the rectifier triodes, which convert AC to DC, and the filtering capacitors, which smoothen out the rippling voltage and also act as the reservoir, the performance of the power supply largely depends on the capacity of these components. When the output power of the amp is relatively low, the demand on the current is small and steady – the supply will be stable and will not deteriorate. But when the output power is relatively high, more DC current will be drawn from the capacitors, putting a strain on the rectifier triodes and causing AC ripple voltage. When a ripple voltage exists, it will cut short the recharging time of the capacitors and develop a 120Hz pulse noise that in turn interfere the output stage transistors, inducing distortion within the audible frequencies.

The best solution is to use an over-rated power supply capable of extremely large current (probably 5 to 10 times that required under normal demand) and very large capacitor(s) to sustain the supply. A suitable specified battery power supply can thereby fulfill the dual role of large current and large capacitor.

The KingRex SLAP uses a YUASA NP7-12 (12V/7AH) sealed lead-acid battery whose maximum output is 105A w/o pulse noise. For a sub-20Watt output Class T or Class D amplifier, this is way in excess of its mean DC requirement, creating ample headroom for peak demand.

In many locations, mains filtering and condition is essential for optimal performance. The meandering journey made by AC power from its source via substations, transfer lines, current boosting and suppresion facilites – not to mention sources of interferences within buildings (radio and EM waves, HT noise produced by fluorescent lighting, refrigerators and an array of motor) – make it desirable to isolate audio equipment from mains power as much as possible. When charged, the SLAP battery power supply provides total independence from the AC environment. Internal AC power is only used for the charging stage and this can be totally isolated from the main power control board.

The KingRex SLAP has interior auto charging/ discharging power managing design. It auto-detects battery voltage and auto-adjusts the charging current to protect the battery from over-charge or over-heat and increaes battery life. For discharging protection, a low voltage detective circuit cuts output automatically when the voltage falls below 10.5V. Charging is a simple one-click operation with smart monitoring. A dual color LED indicator on the front panel shows power and charging status.

All internal wiring use AWG18 copper wires. The DC output terminal is a specialised three pin XLR connector made by Contech in the USA. The maximum current capability is 6 amps. The rigidly constructed measures 185 x 146 x 156mm with a 6mm thick aluminum face plate. All the components used in SLAP are of the highest quality and have been selected through intensive listing sessions.

RRP: £275 (inc VAT)


Input voltage:
AC90-260V, 47-67Hz

Battery type:
12V nominal SLA

Battery size: 12V / Ah

Charging current:

Battery type: Lead acid chemistry

Charging current:
Constant current / constant voltage / float.
Stage 1: 750mA
Stage 2: 400mA
Stage 3: float charge current: 200-400mA

AC and DC input fuses

Mean Time Between Failure (typical battery lifespan): 30,000 hours by MIL-STD calculation

185 x 146 x 156mm


To place an order in the UK or EU, send us an email or visit Item Audio >