Benny Audio writes: “Understanding the Critical Aspects of the BennyAudio Turntable Drive.
Power Supply
The power source must be ultra-precise and linear. For BennyAudio, this is a 12V DC ultra linear unit. Does the power supply affect rotational parameters? Yes, it does, but don’t be misled by assumptions. I tested a cheap $5 adapter and compared it with a more expensive model I currently use. The results were slightly worse with the cheaper one. Would I use a super expensive power source, or maybe a battery (if I wanted to carry the turntable like a Walkman)? Absolutely not, because I know the drive’s performance charts and understand where the deviations come from — not from the power source. Case closed. In this instance, the power supply I use is good enough and is not the bottleneck.
This is where things can get interesting. There’s an entire industry of various motors: synchronous, asynchronous, brushed, brushless, etc. I have a collection of these, both cheap and expensive Swiss gadgets, but I don’t use them in turntables (as I mentioned, it’s not about the most expensive but the best-suited components). In short, the motors used in BennyAudio turntables are BLDC (brushless three-phase DC motors). This is also stated in the specifications.
BTW How many motors should a turntable have? Ideally, NONE! If someone invents a motorless drive, they’ll win a Nobel Prize. Every motor (literally every single one) generates vibrations, which are the hardest thing to combat in a turntable. So, how many motors do I use? One and only one, and it will stay that way! Only one motor can guarantee the best possible parameters. The best results in this category worldwide confirm this. Even the most expensive turntable in the world has one motor! Why do some use more motors? You’d have to ask the designers of those machines. The reasons vary but are certainly not correlated with rotational quality.
Should the motor be integrated into the plinth or stand separately? There’s a holy war over this, and of course, everyone believes that the standalone motor is better. I disagree — it’s not about where the motor is but whether the designer has addressed the negative effects of the chosen solution.
Motor in the Plinth Pros:
● Fixed position, i.e., constant distance from the platter.
● Controlled belt tension through the choice of belt material, length, and cross-section.
● Ease of use (no need to move the motor back and forth).
Cons:
● Vibrations easily transfer to the plinth, then to the platter and tonearm. If the designer can mount the motor in the plinth so that it is absolutely quiet and doesn’t transmit vibrations, then we have a ready solution.
Motor Outside the Plinth Pros:
● Vibration control — a motor outside the plinth does not transmit vibrations to the platter and tonearm, unless the designer is exceptionally clueless.
● No other significant pros.
Cons:
● Properly positioning the motor to achieve correct belt tension — I don’t expect the average user to understand the concept of proper belt tension, which is crucial for rotational quality.
● The need to monitor the motor’s position (it can shift towards the platter).
● Long drive belt — a long belt resonates like a string, adding another dose of vibrations transmitted to the platter. Belt resonance is directly dependent on length and tension. If the designer can create an external drive that is always positioned correctly, provides constant belt tension, and uses the shortest possible belt, then we have an ideal drive. Modestly, I point to the drive in the Odyssey turntable.
Does a turntable with a motor outside the plinth sound better than one with the motor inside? If poorly designed, then yes (see above). If well-designed, it makes no difference.
Briefly, the controller must be matched to the motor, period.
This is my crown jewel — a microcontroller-based unit that I programmed myself. My modest programming experience resulted in just over 1000 lines of code. What does this microcontroller do?
● Checks the processor’s serial numbers (in case someone tries to copy the gadget to another microcontroller). If they don’t match, the device won’t start. Access to the code is also locked — it’s a black box.
● Checks the status of buttons or knobs and lights them accordingly.
● Remembers the last speed settings (value for the digital potentiometer).
● Ensures soft start and stop of the drive — to avoid belt wear and bearing strain. The start time in the Immersion model is about 7 seconds, in the Odyssey up to 20 seconds. No need to push the platter by hand, which is important.
● Provides variable motor torque after reaching the correct speed.
● Primarily, it independently controls speed accuracy in an open loop and makes corrections. No external device communicating with the motor is needed to temporarily catch the correct speed. In the case of BLDC motors (and possibly others), constant speed control is necessary because the motor tends to accelerate after a brief startup. Corrections are made at a 12-bit level at 3.3 volts. Those curious can calculate the level of a single increment.
This result is from many hours of observation and research. The pulleys are made with an accuracy of up to 5 microns (measured on the motor’s rotation).
I use custom-cast belts with a round cross-section made of several different materials. In the Immersion model, it’s EPDM and NBR (both included). In the Odyssey, it’s a different material and cross-section. Historically, chloroprene belts performed best, but they had to be glued and sometimes came apart. They are now obsolete.
Belts significantly impact rotational quality and have a crucial task — compensating for the variable linear speed of the drive shaft relative to the platter axis caused by motor vibrations. For this reason, flexible belts should be used instead of so-called rigid ones. Regarding “rigid” belts, there are often misconceptions. In the case of rigid materials like steel, reducing the cross-section of the element minimizes the transmission of shock waves between individual elements — a good example is common spikes. This theory does not apply to drive belts because they are not rigid but non-stretchable, which is different. A non-stretchable belt — regardless of its cross-section — beautifully transmits vibrations (speed variations) from the motor to the platter. I avoid such belts.
Bearing and Platter
These elements are made as a single set. The method of making the bearing and platter involves long-developed technology closely related to machining principles, specific machinery, and materials. In machined elements, it is crucial to make them from a single setup. Those familiar with turning and CNC will know what I mean. In any case, the bearing requires manual polishing after production — a task I do myself, and the technology took quite a while to develop. The effect is both visible and audible.
The bearing must be properly lubricated — there’s no room for improvisation. The lubricant, in this case, oil with appropriate parameters, must be suited to the working conditions, materials, and clearances. Here’s a secret: achieving smooth rotation isn’t about eliminating friction in the bearing. It’s not about having the platter spin for two days, as that doesn’t guarantee good performance. Remember, under working conditions, there’s a record on the platter and a needle dragging over it with variable force, trying to disrupt the platter’s steady rotation. This must be countered, and one element of the defense system is the proper oil and constant, so-called fluid friction.
What about magnetic suspension, magnetic transmission, air cushions, batteries, 4×4 drives, etc.? For those you’ll have to ask someone else.