This review page is supported in part by the sponsors whose ad banners are displayed below

Reviewer: David Kan
Financial Interests: click here
Digital Source: Deltec PDM Two DAC, Marantz SA6820
Power Amp/integrated Amp: KingRex T20/T20U, Dared VP-20
Speakers: Loth-X BS-1, Klipsch Synergy F2, Mark & Daniel Maximus-Mini
Cables: Clearaudio Silver Line interconnect, Deltec Black Slink interconnect, Luscombe LBR-35 interconnect, OCOS speaker cables by Dynaudio, Aural Symphonic Digital Standard digital cable
Power Cords: Aural Symphonic Missing Link, Ensemble Powerflux
Power Line Conditioning: Monster Power HTS-1000 Mk II
Room Size: 15' x 13.5' x 8 diagonal setup, carpeted concrete slab floor, suspended ceiling and all walls finished with drywall (basement with small window on one side, which is concrete foundation wall with insulation).
Review component retail: $450

The higher power
Battery powered! The very words sound like abracadabra to certain audiophiles. To them, getting off the grid means getting off the hook of expensive power conditioning and power cords while embracing the handsome bonus of power purity. For obvious reasons, battery power is more difficult to achieve in power amps than preamps. Yet with all the rave reviews stirred up by Jeff Rowland's Model 2/BPS 2 in the 90s -- and more recently Red Wine Audio's Signature 30.2 and 70.2 -- users of low output power, 12VDC operated Tripath-based amps have been craving battery power for a long time. Enter SLAP, the witty acronym for sealed lead acid battery power supply from KingRex, the manufacturer of the Tripath-based T20 and T20U.

My first taste of battery-powered Tripath amp came at the hands of the Trends TA-10 and the idea has fascinated me ever since. Through further encounters with KingRex T20 and Winsome Labs Mouse, I tried to devote some time to battery-powered solution for these amps, somewhat superficially though due to my own lack of knowledge and resources. So instead of ducking the issue and just doing the usual rounds of audition, I decided to turn this review into a continuing education program. I posed myself some fundamental questions: What's wrong with other forms of power supplies? What can battery power supplies offer that other don't? Is an SLA battery the only viable solution for battery power? Consider the following TOC for this article:

1. Why battery power
2. Why SLA battery
3. The design of SLAP
4. Audition of SLAP with KingRex T20 and T20U
5. Comparison with other SLA power supply

Why battery power
Is battery power truly the cult image worthy of worship? Or is it just a golden calf in the absence of a better idol? That happens to be easy to tackle since KingRex has already done the preaching here. Of the three most common types of power supplies for audio amplification, a switched-mode power supply (SMPS) is the most convenient but susceptible to high-frequency switching noise and distortion. Linear power supplies use a more sophisticated rectification process during AC-to-DC conversion but the overall result depends on circuit design, components and the actual usable capacity on reserve. Battery power supplies offers pure DC current integrity but have to be done right. KingRex explains:

"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 diodes, which convert AC to DC, and the filtering capacitors, which smooth 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 and the demand on the current small and steady, the supply will be stable and not deteriorate. When the output power is relatively high, more DC current will be drawn from the capacitors, putting a strain on the rectifier diodes 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 interferes with the output stage transistors to induce distortion within the audible frequencies. The best solution to overcome this is by adopting a power supply capable of extremely large current (probably 5 to 10 times of what is required to meet normal demand) and very large capacitor(s) to sustain the supply. Under such circumstances, a reliable battery power supply can fulfill the dual role of large current and large capacitor."

Make no mistake, a linear power supply can also be designed to fulfill "5 to 10 times of what is required to meet normal demand". But when we're talking about a low budget Tripath amp, the major prohibitive factor is cost. Let's refresh our memory. The Tripath TA2020 chip inside the T20 operates on 8.5VDC minimum and 14.6VDC maximum. The SMPS of the T20 is rated at 12VDC/3A. The optional $170 PSU linear power supply, which outputs 13VDC, incorporates a 48V toroidal transformer coupled to a full-fledged regulatory circuit of eight audio-grade aluminium electrolytic capacitors of 5 x 2,200uF (AC input) and 3 x 4,700uF (DC output stage). The current amperage is still restricted to 3A due to the 48VA transformer (48VA = 16V x 3A, which is maintained at 13V/3A output by the regulator IC). Surely they could have gone overkill with a 96V (16V x 6A) transformer and doubled up the caps but the chassis would have been at least double or triple the size. Now the SLAP is triple the size. Let's see what it offers. It houses a YUASA NP7-12 sealed lead acid battery rated at 12V/7AH designed to yield instantaneous maximum current of 105A without pulse noise. Now that's a lot of amperage. Is that overkill? Definitely not from an audiophile standpoint. What's more: breaking free from the grid means complete isolation from voltage fluctuation, radio frequency interference and electromagnetic garbage that could be traced all the way back from your home appliances to substations and power plants. That's what every audiophile loves to hear.