Phoenix Engineering Eagle PSU and RoadRunner Tachometer

Peace of Mind and a Touch of Convenience

Equipment report
Phoenix Engineering Eagle PSU and RoadRunner Tachometer

The Eagle is a two-piece unit with the smaller controller housing the frequency generator, user interface, and logic circuits. On the front panel of the control unit, there are three control buttons (–, +, and STBY) and a display. In normal operation, the “STBY” button cycles between 33.3rpm, 45.0rpm, and standby (motor off) mode when pressed and held. The larger remote amplifier boosts the small signal from the controller to create the 115VAC (or 230VAC) output. One benefit to the two-piece configuration is the ability to place the signal-boosting amplifier away from the cartridge, tonearm wires, and phonostage input to keep AC-generated 60/50Hz noise away from the low-voltage audio signal chain.

Like the RoadRunner, the Eagle is also microprocessor-controlled with modes for standby, sleep, normal operation, voltage calibration, and factory default programming. Carlin mentions that the Eagle is the only commercial PSU to use Direct Digital Synthesis (DDS) technology to create the sinewave for AC regeneration. He also feels other PSUs that are based on Phase Locked Loops (PLL) can have issues with frequency wobble and poor resolution while those using Pulse Width Modulation (PWM) can suffer from poor resolution as well. The DDS function generator is a 28-bit device that feeds the digital signal to a 10-bit voltage output DAC. Technically, the spurious content is reported to be below -60dBC, since the highest frequency output is around 81Hz. The DDS is claimed to generate a clean sinewave with less than 0.04% total harmonic distortion (THD). The minimum step size of the frequency generation is 35µHz—small enough to make adjustments during playback without the changes being audible (more on this later), which is where PLL and PWM can have poorer performance due to the issues Carlin mentions above.

The Eagle PSU and RoadRunner are designed to form a closed-loop system when connected together. There is a single cable interface between the units that allows the RoadRunner to transmit the platter-speed calculation to the Eagle. The Eagle monitors the turntable speed, and if (and only if) long-term drift is outside of a specified error window (unique to each speed setting), the correction is calculated and applied by the PSU within the rotation using the small frequency steps mentioned above. When this correction is being applied, the Eagle’s display will “blink” the decimal point to indicate the function is being implemented. Carlin told me that the corrections will be fewer as the system warms up and stabilizes, and that is what I observed on the six ’tables that could be tested with the complete Eagle/RoadRunner system.

Six of the thirteen turntables mentioned above were subjected to a second round of testing (using the same test procedure mentioned above) with the complete Eagle/RoadRunner closed-loop system. All six ’tables showed improved measured results yielding stability within the specified window of +/-0.005rpm under all conditions. The improvement in measured performance due to negating speed-stability variances of turntable tolerances, warm-up, and drag forces was remarkable. Every one of the turntables showed measured speed results that were between 33.330 and 33.338rpm worst case, with the majority of the readings between 33.333rpm and 33.336rpm.

The RoadRunner, by itself, gets a high recommendation for its real-time speed-calculation and display. Whether the Eagle can be used with the ’table or not, the RoadRunner serves a useful function of reporting speed during actual playback under all conditions. It has earned the right to be a tool for my usage during normal turntable playback, reviewing, or setup. Coupled with the Eagle PSU, the combination produces near rock-solid speed control of the turntables that work with this complete system. In listening tests, there were no audible downsides; the Eagle/RoadRunner system’s speed-control implementation only brought peace of mind and a touch of convenience. This combination is also highly recommended if the turntable can use both.


Type: Digital tachometer
Case: One-piece extruded aluminum
Operating modes: Standby, sleep, normal
Power requirements: DC Supply 9VDC 100mA nominal, normal; 5mA, sleep
Display: Six-digit LED direct readout of platter speed in rpm
Resolution: 0.001rpm
Frequency stability: Crystal-controlled +/-2.5ppm (+/-0.00025%)
Option: Direct connection to Eagle PSU provides digital synchronization of platter speed to +/-0.005rpm
Dimensions: 2.50" x 1.1875" x 3.565"
Weight: 4 oz.
Price: $235

Type: Turntable power supply/speed controller
Case: One-piece extruded aluminum
Operating modes: Standby, sleep, normal, voltage calibration, frequency calibration
Power requirements: DC supply 24VDC 800mA nominal, normal mode; 20mA, standby; 5mA, sleep
Output voltage: 115/230V RMS nominal, adjustable from 85 to 115VAC and 170 to 230VAC
Distortion: Less than 0.04% (DDS output)
Speed adjust: +/-1.0rpm in 0.1rpm steps in normal mode; +/-1.0rpm in 0.01rpm steps in calibration mode
Min freq step: 35µHz
Freq stability: Crystal-controlled ±100ppm
Freq accuracy: +/-0.01%
Controller dimensions: 2.50" x 1.1875" x 3.565"
Amp dimensions: 4" x 2" x 6"
Weight: Controller, 4 oz.; amp, 2 lbs.
Price: $525

449 Terrace Lake Ct.
Green Bay, WI 54311
(920) 468-3296