Dover. I tried to get out of this thread by offering an olive branch since I sense that we are going nowhere.... oh well.
The argument that servos cause overshoot followed by a period of slowing and then repeat does not hold up to analysis. This pitch was likely put out into the market by BD manufacturers and it has taken root in the collective thoughts of the audio community.
We use servo control here almost daily on small and large machines. If they behaved as you describe the machine performance would be totally unacceptable in some cases destructive and dangerous. Servos are not fully on, fully off devices. They have response curves, gain, ramp rising and falling, dead band and frequency responce adjustments. These parameters are talored to the task. We tune then for this. Properly implemented they do not overshoot and as we apply then here they achieve a staggering level of accuracy. The same applies to DD and ironically this is proven by the scope tests I did on the Goldmund. You will recall I could see the music being played at the time on the scope, even treble information. If the servo was correcting, over shooting, correcting undershooting..etc, what I would have seen would be a series of square wave like pulses with little relation to the music as the platter acceleration/ decelleration time constant would smother the individual current draw/music waveform. (I have said before. A correct match of motor capability, platter inertia and controller) Say what you will about the Goldmund, but one feature it has is a very mechanically stable speed measuring system. This along with the servo iteslf was doing its job correctly. ( lets keep physical motor cogging out of this)
I hesitate to use the "spurious" word again, but while loop rigity, energy dissipation etc are topics dear to my heart, as you well know, they are spurious to the discussion on platter speed stability.
Wow and Flutter, stylus drag speed change. Yes I knew the moment I pressed submitt that this would draw a response. I will concede that they are both troublesome. That said as per my earlier post, stylus drag induced speed changes are below the threshold of measurement with the SP10 MK3 and most likely many other DD tt's. On the other hand the time line is ineffective in measuring your type B stylus drag because, by its very nature, its effect is transient and the time line is measuring an average.
Agree, quality power supplies are critical to the correct operation of....just about everything in our hobby.
Ketchup. I like your idea of using two tomearms. I think that the test disc is 10 inch diameter, havent seen one. So could it be placed on top of a LP? Use one arm to measure frequency and use the second arm to play music on the outer track of the LP. That would be intersting.
The argument that servos cause overshoot followed by a period of slowing and then repeat does not hold up to analysis. This pitch was likely put out into the market by BD manufacturers and it has taken root in the collective thoughts of the audio community.
We use servo control here almost daily on small and large machines. If they behaved as you describe the machine performance would be totally unacceptable in some cases destructive and dangerous. Servos are not fully on, fully off devices. They have response curves, gain, ramp rising and falling, dead band and frequency responce adjustments. These parameters are talored to the task. We tune then for this. Properly implemented they do not overshoot and as we apply then here they achieve a staggering level of accuracy. The same applies to DD and ironically this is proven by the scope tests I did on the Goldmund. You will recall I could see the music being played at the time on the scope, even treble information. If the servo was correcting, over shooting, correcting undershooting..etc, what I would have seen would be a series of square wave like pulses with little relation to the music as the platter acceleration/ decelleration time constant would smother the individual current draw/music waveform. (I have said before. A correct match of motor capability, platter inertia and controller) Say what you will about the Goldmund, but one feature it has is a very mechanically stable speed measuring system. This along with the servo iteslf was doing its job correctly. ( lets keep physical motor cogging out of this)
I hesitate to use the "spurious" word again, but while loop rigity, energy dissipation etc are topics dear to my heart, as you well know, they are spurious to the discussion on platter speed stability.
Wow and Flutter, stylus drag speed change. Yes I knew the moment I pressed submitt that this would draw a response. I will concede that they are both troublesome. That said as per my earlier post, stylus drag induced speed changes are below the threshold of measurement with the SP10 MK3 and most likely many other DD tt's. On the other hand the time line is ineffective in measuring your type B stylus drag because, by its very nature, its effect is transient and the time line is measuring an average.
Agree, quality power supplies are critical to the correct operation of....just about everything in our hobby.
Ketchup. I like your idea of using two tomearms. I think that the test disc is 10 inch diameter, havent seen one. So could it be placed on top of a LP? Use one arm to measure frequency and use the second arm to play music on the outer track of the LP. That would be intersting.