Project: Avenger Rim drive with BLDC motors & Class AB Amp

Re: Project: Avenger Rim drive with BLDC motors & Class AB A

Postby vienna acoustics » Sat May 23, 2020 2:13 am

An interesting article of Anatoly Markovich Liknitsky on idler drives and their superiority -in his Opinion - over the belt drives, translated with google from Russian

"Why is an idler drive better than a belt drive? If you focus only on reducing rumble, the Belt really has an undeniable advantage. After all, he has more flexibility than a movie. True, this is true only as long as the passage of vibrations along the second path is not taken into account. If we compare these drives with a predisposition to detonation, then all the advantages are on the side of the idler drive. It remains only to answer the question, what bothers us more: rumble or detonation? I personally am of the opinion that rumble is an unfortunate hindrance to the perception of music, while detonation of sound, especially low-frequency (with modulation frequencies below 10 Hz), even inaudible, destroys the integrity of music to the ground. It is because of this integrity that an idler drive should be preferred. I’ll try to explain why the idler drive has advantages in terms of detonation. In a belt drive, the moment of inertia of the disk and the moment of flexibility of the belt (rotational flexibility) form a low-pass filter [6] of the second order, which frees the rotation of this disk from irregularities. The source of irregularities can be a drive motor, as well as mechanical transmission elements of this rotation (idlers, belts, gears, etc.). It would seem that cleaning rotation from irregularities is very useful if you do not take into account that due to the absence of losses in the belt, a pronounced resonance is formed with a Q factor of 20-30 at the cut off frequency of this filter. This resonance, as it turned out, does not weaken, but rather enhances the irregularity of rotation. Due to insignificant mechanical disturbances in the drive, caused, for example, by slightly uneven friction in the axis of the rotary disk or by slightly varying thickness of the belt, a rotational “swing” of the disk occurs at the frequency of this resonance. We call this phenomenon, similar to the rotational oscillations of a pendulum in a mechanical watch, rotational resonance. Swinging of the disk in a belt drive is usually observed at frequencies of the order of tenths of a hertz and therefore causes low-frequency destructive music detonation of sound. For similar reasons, the actual, that is, not weighted, low-frequency detonation of sound in the B1-01 Electronics player reaches 0.5%. It can only be reduced by damping rotational resonance. However, in a belt drive, this damping is practically not feasible. Nobody has yet succeeded in making a flexible belt with the necessary internal attenuation, and adding viscous mechanical resistance to the axial bearing of the rotary disk, although partially correcting the situation, will increase the load on the drive motor to unacceptable limits. Trying to solve this problem, some companies tried to apply a belt, inflexible in the longitudinal direction, for example, waxed cotton thread, and immediately faced a new problem: how to hold such a belt in tension? After all, without tension, he will not be able to rotate the rotary disk and in the end it will simply fall down. The way out of this predicament is to pull the thread with a passive idler held by a spring or elastically suspended by a drive motor. By the way, in a similar way, that is, with the help of a thread stretched by a spring, the unit of variable capacitors was rotated in the radios of the 30s. But what have we come to? A thread drawn by a spring is a thread with flexibility introduced into it, and without mechanical losses! So, it turns out that we are back to where we started. The “inflexible belt” turned out to be a beautiful myth, which allowed for one audio season to hide the problem of the belt drive under the carpet. There is also rotational resonance in the idler drive, however, it is well damped and therefore does not enhance the detonation of sound. Good, that is, critical resonance damping is achieved in this drive in a natural way, due to the successful combination of flexibility and mechanical resistance of the rubber ring nozzle on the idler. No wonder the drive of this type was originally called friction."
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Re: Project: Avenger Rim drive with BLDC motors & Class AB A

Postby theeng » Sat May 23, 2020 10:54 am

VA,

Regarding the inability to dampen the system with a belt-drive, check-out the heroic engineering that Techdas uses to dampen the platter/system for their belt drive https://techdas.jp/pages/air-force-one-premium2/, . The debate as to which design belt, rim or direct is better will continue. Each has its pluses and minus, and each can be engineered and manufactured to achieve desired results. The greater the platter mass/moment of inertial the less affected it is by the belt hysteresis (going from tension to relaxation), and belt tension has an effect, as does the contact force of the rim drive. However, it should be noted, that similar to Techdas, Basis who also uses belt drive, both use very heavy patters, and the flat-belt precision for both is considerably higher than the simple round-cord O-ring. But both of these top belt-drive designs are heroic with equally breath-taking cost. And, there may be the catch - cost. Absent cost no object; each design has some a cost-effectiveness; as well as easy of use.

From your posts, it is obvious that you took a lot of effort to stiffen the mechanical design so that it would not drift from vibration. But, when you get your 3-axis vibration measurement working, I would be curious to see the affects of time to see if there is any effects from thermal expansion on the system. Consider taking a cut shortly after startup, then after the first record side, and then final after a few hours of normal play operation - the short period of time when the platter stops to change a record should provide some time for cool-down - we are probably talking microns, but when the opinion is that very very low frequencies have an impact - microns may matter. I always allow my belt-drive to run for about 10-minutes before play to get the mechanical system to warm-up.

Just some thoughts, and Stay Well,

Neil
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Re: Project: Avenger Rim drive with BLDC motors & Class AB A

Postby vienna acoustics » Sat May 23, 2020 11:09 am

Hi Neil,

I agree with what you wrote and this is the reason that I like so much the belts driven Rim drive. I think that in a way, it consists of the golden section between the pure belt and pure idler driven turntables. For this reason I had invested so much on this turntable and drive system. By the way i had auditioned Techdas AF 3 and didn’t like it at all. Also I had the chance to listen to Reed Muse 3C which operates either as an idler or as a belt driven turntable and it was a joke .

I will not fail to publish the results with the accelerometer’s measurements as soon as I will receive the parts.

At the meantime I have installed the Class AB amplifier to the rim drive controller. This Amplifier is high biased.
From the beginning it made a subtle but noticeable difference. The accuracy and musicality, I think that they are improved. The improvements are more present when listening to recordings with violin, bass and piano.

It’s incredible how every part of the drive system is affecting the sound reproduction.

By the way the Operating temperature makes a significant difference, both on the sound and the speed stability. At the beginning of the listening session there is a very slow speed variation (33.331 to 33.336 rpm) and the controller applies a correction every seven-eight revolutions. After about 10 minutes the turntable’s parts are getting warmer and the speed variation is getting even more slow and very narrow (33.333-33.334) with the most of the time locked on 33.333 rpm and it takes several minutes to see a speed correction
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Re: Project: Avenger Rim drive with BLDC motors & Class AB A

Postby Golear » Sat May 23, 2020 5:43 pm

Very interesting.

But I'm not sure I understand what Liknitsky wrote. Is he saying that the the belt is pulled as it comes towards the motor and is relaxed as it has gone past the motor? And this soft-coupling is useful in that it can isolate vibration from the motor (rumble), but undesirable because it introduces a periodic variation in rotation of the platter which causes "detonation"?

What is detonation? Is it "distortion", "wow and flutter", or "speed variation"? Or something else?

What is the frequency of this rotational resonance? Is it in the tenths of Hz?

Will this rotational resonance be transferred to the rubber that goes around the rim drive? It seem so, but this is damped.... Is this what he is saying? (If this is the case, then the idler unit and turntable have to damp the resonance.)

Thanks

PS: I've looked at the insides of a Garard turntable. On the model that I looked at, the idler is underneath the platter and the axis of rotation is horizontal. So the mass of the platter presses down on it.
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Re: Project: Avenger Rim drive with BLDC motors & Class AB A

Postby vienna acoustics » Sat May 23, 2020 11:18 pm

Golear, I think he is referring, with the term detonation, to the right timing and how this is degraded with belt driven turntables. It is a fact that with the wrong timing the music is not coherent and ‘.....destroys the integrity of music to the ground....’ as he is correctly writing, please see my P.S at the bottom of this post.

It seems that many turntables manufacturers have identified the importance of the precise right timing and have introduced stiffer materials for belts, improved bearing systems (heated low tolerance shafts and bushings, highly engineered air bearings, diamond polished shafts etc), sophisticated speed controllers with better motors, which are providing, as a system, the right timing, low noise, low vibration, smoother rotation and stable speed. In this forum I have read about some users’ attempts to use thread instead of belts too on an attempt to improve timing and speed variations coming from the belts.

Initially with the EPDM rim drive belts only, later by adding the sapphire +Si3N4 to the turntable and rim drive, having the shaft and shaft bearing sleeve re-machined to high precision and then diamond polished, then by adding the Eagle+Roadrunner to drive the Hurst motors and currently with this project, I have managed not only to reduce noise and vibration but to reach a more precise timing.

I wrote earlier at this thread how the precise timing elevated my sound and the listening satisfaction/experience:

QUOTE:
A sophisticated well designed speed controller besides the speed accuracy and stability, is providing the most important factor ....the timing.

Music from a turntable with the right timing is live, coherent and palpable. A turntable with the right timing will provide the right instruments sustains, articulation, more detail, musicality and resolution. With the right timing the spatial information and ambience of the live event is successfully transferred to the listener.

@J_Perkins, with his Upcoming upgrade will experience soon the accurate timing feeling and together with the low noise, low vibration BLWS motor will also experience the effortless flow of music.

The moment I had experienced the effect of accurate timing, I was amazed and I couldn’t believe the improvement degree of my turntable and the unbelievable improvement of the listening experience and feeling. Since then I have listened to many turntables but none that could replace my current Avenger Reference and what the Rim drive is providing.

UNQUOTE

FYI, I can turn my Rim drive into belt drive within seconds by removing the flywheel and by installing a center aluminum pulley. In this way the motors small belts are turning the center pulley which is then driving the magnetic driving platter through two belts. Instantly the magic, the coherence, the torque feeling, the palpability, the naturalness , details, and realism are lost, together with all the spatial information. The dynamics are suffering too; and I can see too that the music’s integrity is suffering.
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Re: Project: Avenger Rim drive with BLDC motors & Class AB A

Postby Mr_Putty » Mon May 25, 2020 12:45 pm

Vienna acoustics,
Having read the Project upgrades and your precise observations about sound and timing improving musicality of your system, I have a question and an observation based on my Prime TT. First the observation. My motor pod vibration has improved with use to where it can barely be felt anywhere. I recently changed the motor pod and TT feet to the HW40 set from VPI. I noticed a slight audio improvement throughout the audio spectrum. I like the lower center of gravity of the table and the new “look”. And I got to thinking about belt drive timing or motor cogging or chatter (again) at a very small scale. As a test of doing something different I decided to fill the depression of the motor belt-drive pulley with modeling clay (it never hardens). The weight of the clay was 5.43 grams, and is just proud of the pulley top. I like the result, confirmed on several records, with more realistic instrument decay and tone presentation I had not noticed before. Now the question. While this is good for my setup, are there moving part recesses you can test in your setup for further noise reduction, using clay (or X material)? I don’t know if I just got lucky with the additional mass on the pulley or if the clay is reducing vibrations that were bad or a combination of both. I can think of no other reason for the improvement, but its definitely audible through my speakers.
:idea:
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Re: Project: Avenger Rim drive with BLDC motors & Class AB A

Postby vienna acoustics » Mon May 25, 2020 1:40 pm

Dear Mr. Putty,

As I am getting deeper into this hobby I am realizing that there is no Voodoo but pure physics.
This is the reason that I have ordered 3 axis accelerometers and purchased the ARPA software in order to be in a position and quantify, with real objective measurements, what a change will introduce into the system and consequently into the sound.
Bill Carlin was very generous and kind to make for me an instructional video on how to take precise measurements with this software and wire these sensors.

What you have achieved I have witnessed it too with the higher mass aluminum pulleys.
As per the materials, there are some people who have spent thousands of hours to study the acoustical and vibration physics behind them, for example this guy who has inspired many others https://qualia.webs.com/plinthbuilding.htm check the section with turntables. What Phoenix Engineering is for electronics (he has made a very good plinth too) this guy is for materials and plinths.

What I have learnt for sure Is that voids is not a good thing at the turntables world.

As soon as I will receive my sensors, besides the rim drives measurements (with different motors, pulleys, bearings, thrusts and belts) I will write on my next project too.
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Re: Project: Avenger Rim drive with BLDC motors & Class AB A

Postby vienna acoustics » Tue May 26, 2020 12:22 am

Yesterday evening I stayed till very late, listening to music. I just couldn’t stop.
Besides the enriched music attack, the right timing, stable speed, low noise and vibration I am realizing that the listening experience has so much improved also due to the correct pitch, which is providing the integrity of the original music notes as they were performed and recorded. Incorrect speed leads to incorrect variable pitch which affects the notes. An affected note can sound as Sharp instead of Flat and vice versa, thus differently from the performed note. In extreme variable speed and pitch conditions the notes are completely different. This affects not only all the instruments but the vocals too.

For those who may think that this might be of lesser importance, see this video of how differently a flat note is sounding comparing to a sharp note, practically is a different sound. Imagine now, this happening throughout the track with all the instruments and vocals.... far from the HiFi essence...

https://youtu.be/f-8cb_HYycQ
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