IntroductionRA03 is a high performance half-width 19" 1-unit RIAA preamplifier for discotheque and PA use.
The feedback canceling filter reduce the acoustical feedback from the loudspeakers to the gramophone and enables up to 10 dB higher SPL before feedback becomes audible. The filter adds the two channels to a mono signal at low frequencies with a special differential filter.
The idea of summing low frequencies into a mono signal to avoid feedback is not new, but all earlier implementations uses some sort of cross-over network to extract low frequency information, adds the two channels and then add this signal back into the stereo high-frequency signals. This topology gives an undesirable phase response and will in some cases make the feedback problem worse. The Feedback Canceling Filter in the RA03 uses a special differential filter that acts like a wire if it's input is a mono signal, but will add the low frequency content of the channels if they differ.
Minimum use of rack spaceRA03 is housed in a 86 mm deep, 1 unit, half width 19" (Half-Rack or HR) aluminum enclosure, and may be built into in a standard 19" system.
A single unit can be mounted be means of a rack ear extender, two units can be mounted side by side or 10 HR enclosures can be mounted vertically in a 6 unit high 19" frame.
Due to its modest depth, the RA03 can also be mounted in a flight case vertically behind a gramophone.
Rugged construction for "on the road" useThe anodized aluminum enclosure is constructed from two 6 mm side profiles, a 5 mm front panel, a 3 mm rear panel and 1.5 mm top and bottom covers. Graphics on front- and rear-panels are negatively anodized, rather than just printed, for best possible wear resistance.
Front panelThe front panel contains a balance adjustment for the pick-up and a power LED.
Rear panelThe rear panel contains two gold plated phono sockets and a laboratory binding post for the gramophone cable, an 8-way DIP switch for pick-up load capacitance selection, two gold plated phono sockets and optionally two XLR connectors for the outputs and a FCC68 connector for the low voltage cable from the external mains transformer.
ConfigurationsRA03 is available with 3 different output configurations:
Accessories available for RA03.
RA03 Technical specificationUnless otherwise noted, specifications are for 20 Hz - 20 KHz with 600 ohms load on outputs.