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This is the sixth in a series of reviews dedicated to the concept of 32Ohm Audio as embodied by the store of that name in downtown Portland/Oregon and described here - Ed.

Reviewer: Srajan Ebaen
Financial Interests: click here
Source: iPod Classic 160GB, Wadia 170iTransport [on review]
Headphone amplifier: KingRex Headquarters, Trafomatic Audio Experience Head One [on review], Red Wine Audio Isabellina HPA w. Wadia battery power socket [on review], Yamamoto HA-02, Woo Audio Model 5, Luxman SQ-N100 [on review]
Headphones: audioTechnica ATH-W1000 & ATH-W5000 'Raffinato', Sennheiser HD800 with ALO Audio custom cable, Grado PS1000, AKG K702 with ALO Audio custom cable
Headphone stands: Sieveking Sound Omega
Cables: ALO Audio links, mini-to-1/4" converter pig tails, ASI LiveLine
Review Component Retail: $345

Rx prescribed by ALO Audio. It's not a new legalized drug but miniature headphone amplifier cleverly named. You'll still swallow hard once you inspect it and actually hear what it'll do.


As I wrote in our feature piece on Ken Ball's 32Ohm Audio store in Portland which became the inspiration for this review series, "...I hooked up with Matt MacBeth of GR9 Technologies*, a brilliant EE industry veteran who most recently worked on Klipsch's iPod accessories and the Image X5 headphone. We designed the amp to be the sonic frontrunner of all portable amplifiers while maintaining an affordable price.


"Our next product will pair up with it using an identical enclosure. Also running off a Li-Ion battery, this new device will take the digital signal off the iPod into its own high-performance DAC and output analog into the Rx. This is poised to redefine the landscape of portable audio as we know it. My partner is very bright and has been working with Apple on this for quite some time; this product will feature 'Works with iPhone' approval. We are also working on a balanced version of the Rx using a 4-pole mini plug as well as a 24-bit/96kHz USB DAC."

The Rx is the size of a very slim cigarette pack, i.e. all of 2.5 x 0.5 x 4.2 inches wide by thick by long to hold a single row of probably about 12 ciggies if it were empty. The enclosure is an extruded alu shell left clear or anodized red or black that's closed off with 1/16th Hex-bolted covers. Power is generated by two 3.7V rechargeable Li-On batteries to give an estimated "17 - 30 hours of playtime at typical listening levels".


Charging is supervised by a dedicated chip** and connection with a wall socket is by supplied Chinese 9V/1.2A SMPS wall wart. That sports a clever hot-swappable power plug insert to accommodate all global prong scenarios (you're sent the appropriate one for your country). Output current for the Rx is above 200mA and peak swing voltage a studly +/- 7.45V to deliver the goods into even full-size serious cans like top Grados and Sennheisers. The power supply is described as not "a rail splitter but real bipolar" affair.

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* Matt's CV also includes having been senior electrical engineer at medical devices firm Nuvo Inc, owner/engineer at Purified Audio and design engineer at Audio Authority and Clarion Corp USA. As program manager for Klipsch and their Apple business liaison for several personal audio products, he oversaw the Image X5 headphones and iGroove and RoomGroove line of iPod/iPhone accessories and managed advanced development technology platforms such as networked A/V, HTIB and BluRay products.
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** "Most portable audio products only provide a constant current source to charge their batteries. At best this limits battery life. Inadequate charging circuitry can actually be hazardous however. The Rx's circuit is much more complex. It constantly monitors the voltage and current capabilities of the batteries. This intelligent charging determines the optimal current and voltage feeds that will best charge the batteries and preserve their life expectancy.