Hello Coolerooney,
Based on the way you describe your design, it appears there is a chance that you may not be aware, that record grooves are cut with variable pitch, varying from .002" to .010" for grooves containing audio and .011" for banding grooves. (grooves between selections) If I am wrong, I sincerely apologize.
In tone arm designs that are driven by a motor, the motor runs at a constant speed to keep up with a groove pitch of .002" and the servo increases the motor RPM from there should the groove pitch increase. therefore the motor never stops turning. The servo is separate from the motor drive circuitry.
Record cutting lathes have been using that principle for decades referring to it as "base pitch". Rainer Horstmann seems to think he invented it.
In your design, the tone arm needs to be able to pivot by a small degree in order to allow the error detecting sensor to activate the servo.
If your error detecting sensor has an accuracy of 1 degree for instance, I would play the tone arm from -1/2 degree to +1/2 degree from true tangency. that way the off-tangency error is never more than 1/2 degree.
Sincerely,
Ralf
Hi Ralf
You are correct g.p.i. varies from record to record
A fixed speed on the motor does not work. The 200 gpi nr is an average
You are correct again that an arm needs play, otherwise the sensor sees no deviation, the grooves would just skip under the stylus
The motor is controlled by the sensor and only sends drive signal when ertor is detected -a reverse mode: on until OFF trigger is detected (overshoot instrad of undershoot
Have some ideas on where to measure, needs a bit more thought
Hope to get this well below 50 microns
Have some stuff on order via Ali, we’ll see
Best
Coolerooney
You are correct g.p.i. varies from record to record
A fixed speed on the motor does not work. The 200 gpi nr is an average
You are correct again that an arm needs play, otherwise the sensor sees no deviation, the grooves would just skip under the stylus
The motor is controlled by the sensor and only sends drive signal when ertor is detected -a reverse mode: on until OFF trigger is detected (overshoot instrad of undershoot
Have some ideas on where to measure, needs a bit more thought
Hope to get this well below 50 microns
Have some stuff on order via Ali, we’ll see
Best
Coolerooney
Ralf,
Reading your post again, I see I missed a distinction you make on the base pitch
Hmm- my initial thought/calc is that to “make the distance” 17k steps/sec are required.
The trigger will undershoot due to sensitivity, then make up, repeat
There is no base pitch now planned- if 0,127 mm (200gpi’s) is needed, then 20% of that should be no issue (I hope) The base pitch would help in reducing stop&go of the arm, but depends on the gpi’s of the record at hand. May need an “amplifier” to boost the sensor signal to get it right.
Reading your post again, I see I missed a distinction you make on the base pitch
Hmm- my initial thought/calc is that to “make the distance” 17k steps/sec are required.
The trigger will undershoot due to sensitivity, then make up, repeat
There is no base pitch now planned- if 0,127 mm (200gpi’s) is needed, then 20% of that should be no issue (I hope) The base pitch would help in reducing stop&go of the arm, but depends on the gpi’s of the record at hand. May need an “amplifier” to boost the sensor signal to get it right.
Last edited:
A motorized active arm like this has a fundamental shortcoming. It sensors the position of stylus, then, it corrects tracking errors. So, all the corrections are made after tracking errors happened. Although I don't have chance to listen to AVDesignhaus Dereneville, a 40k arm, I suspect the perform level of it.
Nonsense.
There are servo systems and then there are servo systems. The state of the art in servo technology makes possible a well-designed servo system that will move the arm with audibly imperceptible motion and tracking error. If you are afraid of servo systems then you should also be afraid to fly in an airplane. If you have taken a trip on a modern fly-by-wire commercial airliner then you have entrusted your life to the smooth operation of numerous sensor and servo control systems, all of which guided you safely to your destination without even causing a ripple in the coffee on your tray table. If you have driven a newer model automobile and engaged the smart cruise control then you have enjoyed the benefit of a servo system that can maintain your vehicle speed better than you can with your foot on the gas pedal. If you have watched a ballet, then you have seen the sensor and servo control system of the human brain make the body hold perfect balance.
The “motorized active arm like this has a fundamental shortcoming” argument is a tired relic. I find it refreshing to see new, out-of-the box thinking from people like Ralf and Coolerooney. I have some interesting servo control stuff of my own to post, but I’m saving that for a new thread.
Ray K
Ray,
Is there a delay between sensor and motor? If the needle is NOT bended, the sensor detects nothing. So, if the sensor detects bending, the bending of stylus already exists.
If it is audibly imperceptible motion and tracking error, this is another matter. Does anyone claim he can hear tracking errors from a pivot arm? If no-one can claim he can hear tracking errors from a pivot arm, linear arm is completely real nonsense. Do you agree linear arm is nonsense?
Can anyone claim he can hear the bending of a stylus? I don't think so.
Jim,
Is there a delay between sensor and motor? If the needle is NOT bended, the sensor detects nothing. So, if the sensor detects bending, the bending of stylus already exists.
If it is audibly imperceptible motion and tracking error, this is another matter. Does anyone claim he can hear tracking errors from a pivot arm? If no-one can claim he can hear tracking errors from a pivot arm, linear arm is completely real nonsense. Do you agree linear arm is nonsense?
Can anyone claim he can hear the bending of a stylus? I don't think so.
Jim,
Last edited:
A ballet dancer is a perfect example to illustrate my view. If he or she wants to raise his or her leg, his or her brain directs his or her movements BEFORE it even happens. A perfect system for a linear tone arm! Can modern sensor do that?
In general, is AI that perfect to depict a human system today?
In general, is AI that perfect to depict a human system today?
You are making the mistaken assumption that all servo controlled linears rely on stylus deflection as a feedback signal. All the ones I am familiar with rely on the motion of a pivoted carrier or arm tube being sensed. There is no side force on the stylus and there is no bending of the stylus. What servo arm are you talking about that does this?
Yes, there are people who claim they can hear tracking errors. The whole point is to get it below the threshold of audibility, a matter of YMMV. There are other advantages of linear trackers:
Turntable speed stabilty
No, I don’t agree a linear arm is nonsense. What I said was that your argument is nonsense.
Come on now, bending of a stylus from arm friction or skating effects can result in sufficient side forces to cause mistracking, which is very audible. You can’t hear that?
Good night.
Ray K
Does it matter? It is same to sensor bending of stylus or arm. The propose to sensor arm IS to avoid bending of stylus.
Ok. Now the question becomes as long as we don’t hear. It doesn’t matter or doesn’t exist. This is not right base for discussions. Some but only some, may claim they can hear tracking errors. How about other people? Who is right? Some may not hear the shortcoming of an active arm, but some may be able to. How about that?
I know you are a believer of linear arm. This was why I said that. Some of people can’t hear the sound quality of linear arm. It doesn’t mean linear arm doesn’t have the advantages over pivot arm. This is precisely my point. It doesn’t mean a motor driving active arm doesn’t have the shortcoming I mentioned above if you can't hear.
There are a lot of reasons to cause mis-tracking. Stylus bending is one of reasons. It IS mis-tracking. You can hear mis-tracking. You can NOT hear bending of stylus. You can hear mis-tracking, but you can't hear what reason to cause mis-tracking.
Last edited:
I said it before. It seems to me that ELP tracking system is a better one. It tracks the groove before stylus( reading laser heads for ELP). However, I guess that the laser heads for reading groove may be ok if they are slightly high or low and right or left( I can be wrong here), but not for a regular cartridge.
Last edited:
Since twenty years there are around autopilots who "learn" to anticipate the movements of a sail boat, certainly more complex than those imposed by the eccentricity and variability of the pitch. Able to steer much better than me, and also cheap.
If we work hard we can perhaps invent a completely automated servo turntable, and discs that do not have all these damn problems, fought for a lifetime: beautiful silver Discs ... and Compact too.
noCDplz
I'm joking, but to accept completely the spirit of vinyl is a more fascinating challenge, imho
If we work hard we can perhaps invent a completely automated servo turntable, and discs that do not have all these damn problems, fought for a lifetime: beautiful silver Discs ... and Compact too.
noCDplz
I'm joking, but to accept completely the spirit of vinyl is a more fascinating challenge, imho
One of my friends-audiophiles from another city happened to see and hear a Laser Disc player, the one which was re-designed and re-adjusted to play regular LP. A former leading engineer from one of the former military equipment plants developed that project: of how to remake and re-adjust LD player to play LP, and he has built several of them. Actually, it works well. So, I can conclude, that there are perfect servo control ans sensor systems, fast and precise enough to linearly track a record. And they were developed long time ago.
Last edited:
I am not against all servo control arms. However, in most of cases, these servo control arms become merely showpieces in reality. In my mind, the state of art for LP playing back is simple structure. Kuzma 4-point and SAT arms are two of perfect examples. Btw, Kuzma’s air line is the only air bearing arm I admire highly.
I really look forward to the new thread. I was once dismissive of servo arms due to my lack of knowledge and understanding of servo technology (and I have owned multiple servo arms that were poorly executed). Admittedly, servo circuit is just as intimidating as having to deal with air-bearing, which is more about its hassle than anything. At one point I thought absolute geometry trumps all other criteria. I was wrong. To me lack of skating force is one of the few things that's more important than just total tangential accuracy. Analog playback is a complex system of conflicting forces and a servo system is one way to deal with those issues. Obviously there are outrageously pricey servo arms that seem too white elephant for my taste so if someone can create a servo system that's simple, elegant, and diy-able, all the better. I have come around to agree with Conrad Hoffman's idea of using a good pivot arm as the basis and build a moving platform for it to slide 4 inches of groove area.
Thank you for your contribution to these threads, Ray.
Last edited:
Hello directdriver,
What C. Hoffman suggests in his post from 2010, has all been done decades ago, all the way back to the Rabco tonearm. I guess it's the "Tales of Hoffman."
Ralf