Edited by: Mike Santora • Contributing Editor
Whether it’s Zeppelin, Sam Cooke or The Smiths, most audiophiles agree that music sounds better on vinyl. But most also agree that motor noise, speed control and tone arm tracking can have a huge impact on turntable audio performance. These were the concerns of Expressimo Audio when they began the design process of their latest audio turntables.
The turntable incorporates two motors designed by maxon precision motors. One motor is used to spin the turntable, while the other is used inside the remote control unit to raise and lower the tone arm up and down.
“It’s all in the motor,” said Brian C., chief engineer and owner of Expressimo Audio.
“When I decided to create this turntable, I had to find the very best motor on the market, something that was quiet and wouldn’t cog at very low speeds—the tone arm must move smoothly and accurately or it distorts the sound terribly.”
An ironless dc motor is an excellent choice for applications like this. These motors make the most sense when you need light weight, good acceleration, quick reaction time, quiet performance and acceptable thermal dissipation, as with a turntable.
“I perform computerized fine adjustments to vary the speed of the turntable using the ESCON Studio Program,” Brian said. The application also benefited from the small size of the motor and encoder for this particular application.
For the tone arm motion, a spur gearhead was attached to the motor, offering a 76:1 ratio for precision positioning throughout the operation of the tone arm. The turntable application requires two precision speeds—33.3300 and 45.0000. The turntable uses a touch switch circuit mounted to the front of the motor housing for operation. The motor pulley is only 0.400-in. in diameter and spins at 940.5 rpm, spinning the 12-in. diameter platter that weighs about 30 lb at a speed of 33.3300 rpm. When the motor spins at 1260.4 rpm it spins the platter at 45.0000 rpm. The motor, while in operation, draws about 0.03 amps, and the speed is accurate to ±0.001 rpm, when tested with a strobe turntable speed tester.
The DCX motor uses rare earth magnets to maximize the torque available in the 25-mm package. Maximum efficiency is 86% depending on the winding. All in all, the motor gave the design team a component that weighed less than 4 oz., had zero cogging and an ambient temperature range from – 20 to 100° C (-4 to 212° F).
Matching gearheads are also available with ratios ranging from 3.7:1 up to 4060:1 capable of delivering up to 7.5 Nm (5.53 ft-lb) of intermittent torque. Integrated encoders are also available for the motor.
The second motor, an A-max 16 is used inside the remote control movement system for the variable tune arm operation. The VTA moves at 0.001 in. at a time, with full indication through a precision indicator. Different versions of the motor use metal or graphite brushes and single or double shafts, while power ranges from 4 to 11 W. Maximum continuous torque is up to 19.8 mNm (2.8 oz-in.), and the motors weigh about 100 g (less than 4 oz).
While not a likely concern in turntable design, take note that ironless motors tend to overheat if the max load is exceeded for an extended period of time. With no metal core to handle the heat, the adhesives holding the rotor windings together can become damaged. Cored motors are still the better choice if overload concerns are a part of your design. But again, if your motor only needs to handle the heat of the guitar licks on your favorite vinyl, ironless almost always sounds good.
maxon precision motor
Filed Under: Motors • dc