Bill Carlin of Phoenix Engineering, LLC, has created two very useful accessories for turntables. The first is the RoadRunner digital tachometer ($235) which can be used on any ’table to precisely measure the speed in real-time of each rotation of the platter. The second product is the Eagle PSU ($525), a high-power, digital turntable power supply that controls the turntable speed, if the turntable uses an AC motor that derives its rotational speed from the wall plug’s 60Hz (or 50Hz) frequency. When the RoadRunner and Eagle PSU are combined in a system that can use both, the accessories form a fully automatic closed-loop speed controller that creates long-term speed stability and compensates for drive-system irregularities.
With the RoadRunner, the speed setting of any turntable can be observed in real-time all of the time. Installation is fairly straightforward. A small rare-earth magnet is attached via its adhesive side to the edge of the platter. The magnet weighs approximately 0.10–0.12 grams, which is less than 3%–10% of the tracking force of most cartridges; so there should be no concerns about the weight of the magnet disturbing the platter balance. The RoadRunner tachometer is attached to its sensor board via a supplied cable. The sensor board is placed on the plinth so the magnet passes within ¼" (or closer without touching) of the on-board Hall Effect sensor to trigger detection. Once the RoadRunner is powered up, the display will show five dashes and the sensor detection can then be verified by rotating the platter until the magnet is directly over the sensor. When this occurs, a sixth dash will appear on the display verifying proper installation. All that’s left is to start the platter and view the RoadRunner display once the ’table is up to speed.
At the heart of the RoadRunner is a microprocessor that is driven by a temperature-compensated crystal oscillator (TCXO) with +/-2.5ppm (+/-0.00025%) frequency stability. The displayed speed of the platter rotation is measured to 0.001rpm resolution. The ability to see a real-time digital speed indication of platter rotation under any condition (unlike most strobe-like devices) is a key advantage of the RoadRunner. With this ability, the effect of the entire drive-system tolerances (belt thickness, tension, slippage, creep, pulley-step ratios), warm-up times (bearing, belts, motors), and drag forces (from different mats, clamps, outer rings, and the stylus) are all revealed by the changes in speed displayed by the RoadRunner.
After several hours of in-house observations, I created a test procedure that allowed me to record the performance of several turntables at remote locations. The procedure entailed measurements during 15 minutes of turntable warm-up and an additional 5 minutes of rotation after the LP was placed on the record, complete measurements of beginnings and endings of songs on an entire LP side, and a few minutes of measurements of the LP runout groove. These steps were followed by an additional set of 2-minute measurements with the stylus removed from the record and then with the LP removed from the platter.
Using this test procedure, I tested 13 different turntables (Acoustic Signature, Basis Audio (3), Grand Prix Audio, Kronos Audio, Nottingham Analogue, SME, TW Acustic (2), VPI, Walker Audio, and Wave Kinetics) with the RoadRunner tachometer alone. All but two direct-drive units and one closed-loop (speed read and adjust) belt-drive unit were subject to system tolerances, warm-up times, and drag forces to one degree or another. Of all the variances, stylus drag had the biggest and most consistent effect; it also had some variance at the beginning vs. the end of the record. (Tip: In most cases, when setting turntable speed, it is best to set the speed with the stylus in the grove playing a record if possible.) With the RoadRunner monitoring the speed, ’tables with the ability to adjust speed could be set for optimal conditions with the stylus playing a record.
The Eagle PSU is a 25-watt AC-voltage-regenerator motor-controller/power supply with speed adjustment of +/-1.0rpm in 0.01rpm steps. The Eagle features automatic voltage reduction (level selectable during calibration) for each speed, a soft start to lessen the stress on drive belts, ability to startup in 33.3 or 45.0rpm mode, speed calibration modes, jumper selectable 115VAC or 230VAC output voltage, 100–260VAC/50Hz/60Hz input voltage, operating-pulley selection mode, and a third speed range selection (untested during the review) for 78rpm records, if the turntable has the correct pulley, with a wider range of +/-6.0rpm in 0.1rpm steps.