I wonder if it's possible to modify the technics servo to work with the extra mass. Can you get schematics for it?
Service Manual
You will find Technics SM at " http://www.vinylengine.com "
-and a lot of others...!
Arne K
You will find Technics SM at " http://www.vinylengine.com "
-and a lot of others...!
Arne K
DaveM a bunch of posts back.
If you add mass to the system I agree it is less likely to do harm. But the system is a feedback system (actually I think all turntable drive systems are, it just a question of what the feeback is, mechanical or electronic) and such has a responce that can vary from overdamped to oscillating and so if the designer has done his or her job correctly altering something is going to make things worse. I should not say worse I should say it will change things, it might be better for what you want.
For example a requirement of the designer might be fast start up time for say a DJ table, the DJ does not want sit around for the record to start spinning unless they have a lot to say, that might not be a requirement for an audiophile. Some DD could be on speed in a small fraction of a turn.
My point is that changing the mass/inertia is changing the system and you should be aware of it and possibly consider changing other things as well (time constants etc.) The manual would help here, but I would not expect it to explain the fine details much,been a long time since I looked at that manual, the technics motor drives seemed very reliable do not remember ever fixing a motor, other things. Fixing DD motor circuits was often a PITA because the platter often had to be in place which then usually blocked any access to the board. Good job most were reliable or had known fixes.
I'm rambling, but one more thought, since it is the inertia that matters one could design a heavier (or lighter - but most audiophiles seem to think bigger is better when it comes platters) platter with the same inertia (more mass in towards the center, less on the outside) for say 'sound' of the platter - that is keep your ideal rotational inertia for your system, and play with varying thickness or materials for damping, ringing (same thing sort of) concerns.
I'm stoppnig now before I write a 'white paper' on my turntable thoughts
Bill
If you add mass to the system I agree it is less likely to do harm. But the system is a feedback system (actually I think all turntable drive systems are, it just a question of what the feeback is, mechanical or electronic) and such has a responce that can vary from overdamped to oscillating and so if the designer has done his or her job correctly altering something is going to make things worse. I should not say worse I should say it will change things, it might be better for what you want.
For example a requirement of the designer might be fast start up time for say a DJ table, the DJ does not want sit around for the record to start spinning unless they have a lot to say, that might not be a requirement for an audiophile. Some DD could be on speed in a small fraction of a turn.
My point is that changing the mass/inertia is changing the system and you should be aware of it and possibly consider changing other things as well (time constants etc.) The manual would help here, but I would not expect it to explain the fine details much,been a long time since I looked at that manual, the technics motor drives seemed very reliable do not remember ever fixing a motor, other things. Fixing DD motor circuits was often a PITA because the platter often had to be in place which then usually blocked any access to the board. Good job most were reliable or had known fixes.
I'm rambling, but one more thought, since it is the inertia that matters one could design a heavier (or lighter - but most audiophiles seem to think bigger is better when it comes platters) platter with the same inertia (more mass in towards the center, less on the outside) for say 'sound' of the platter - that is keep your ideal rotational inertia for your system, and play with varying thickness or materials for damping, ringing (same thing sort of) concerns.
I'm stoppnig now before I write a 'white paper' on my turntable thoughts
Bill
Cobra2 - thanks for the link. Just looked at the SP10 mkII drive circuit quickly - looks like it could be played with if one was so inclined.
My inclination would be a syncronous motor, power oscillator, and belt - though isolating the mechanical motor noise from the platter bearing while keeping the two relatively positioned absolutely the same is the trick -
I know off topic you're talking about DD, just my 2¢
Bill
My inclination would be a syncronous motor, power oscillator, and belt - though isolating the mechanical motor noise from the platter bearing while keeping the two relatively positioned absolutely the same is the trick -
I know off topic you're talking about DD, just my 2¢
Bill
I noted on my Luxman PD-121 with the heavier masse, the speed actually slowed down when I place the needle on the record. I think it has open loop control. The heavier mass on my Technics SP-25 destabilized the speed, so it had closed loop feedback control. Either way, the DD turntables may not work well at non optimized platter weights.
Adding mass can be good,
but only if the bearing is designed to handle it. With a (too) soft endplate, friction will increase...
Arne K
but only if the bearing is designed to handle it. With a (too) soft endplate, friction will increase...
Arne K
pixpop said:
It's a high end myth, as there are many. Arm and cartridge have way more impact on sound. On VERY long sustained organ notes I prefer quartz direct drive.
I have modified a Akai direct-drive a long time ago, potted the alu platter almost full with soft-elastic podding to fight the ringing. But the player is still cogging, more then a belt drive i think.
The best mod i did was the replacement of the simple carbon film 20k speed-pot into a 10 turn precision-one (against cogging) but it still coggs. Did only the 331/3's
It went through my mind, due to the low rotation speed of DD motor, it's very sensitive to little differences manufacturing preciseness. A little variation of coil-orientation in the stator, or magnetic field orientation in rotor, this can cause speed variations also, but cogging?
Oh and yes Elso, you like quartz control....
The best mod i did was the replacement of the simple carbon film 20k speed-pot into a 10 turn precision-one (against cogging) but it still coggs. Did only the 331/3's
It went through my mind, due to the low rotation speed of DD motor, it's very sensitive to little differences manufacturing preciseness. A little variation of coil-orientation in the stator, or magnetic field orientation in rotor, this can cause speed variations also, but cogging?
Oh and yes Elso, you like quartz control....
Quartz
- another use for a kwak-clock! 😉
I do not agree with your term "cogging", "flutter" is commonly used for quick speed-variations, "wow" for slower speed-variations.
If you have variations, there must be a fault or something worn...
Arne K
- another use for a kwak-clock! 😉
I do not agree with your term "cogging", "flutter" is commonly used for quick speed-variations, "wow" for slower speed-variations.
If you have variations, there must be a fault or something worn...
Arne K
The electronic PCB seems very simple, no quartz (nor PLL?) There is no feedback. (When i brake the platter a little and then let it go, it shows an overshoot in speed)
Pcb has a lot of transistors and some chips. Have 2nd Akai DD TT (got it for free from a neighbour!) exchanged the platter to check for flutter, but still does. So the electronic could be improved i think, but what parts could be modified on it. Caps? Extra mains filter? I can swap from original to modified to check improvements.
Another strange thing: Downloaded and printed a strobe from the internet to check flutter. (enjoythemusic,freestuff, 100Hz,33 1/3) After checking discovered the speed itself is not corresponding with each other.
phn said:
This should be quite obvious - because of the program dependent drag from the stylus, feedback type of DD coupled with light platters don't sound that good.
I find it difficult to isolate the drive system as far as the final sound is concerned. Yes, cheap DDs seem to have a common sonic signature which is subdued in the more expensive models.
FWIW during the last 10 years i've only had two DD tts - a trio l07 which i hated and a Dual 701, which within the limitations of it's arm and plinth was very enjoyable. The problems of the Trio were probably not related to the drive system. It was ridiculously overdamped, the total opposite of Linn's philosophy of efficient energy transfer and as a result it couldn't play a tune to save its life. Of course, i should have tried driving the Trio by belt from an external motor for a proper comparison of drive methods but it's sound showed so little promise i never bothered.
tubee said:
Printers don't print exactly to scale and often have different scaling X and Y, so the disc won't be exactly circular.
Surely light platters are part of the system in cheap dd systems
i.e the error generated by the speed sensor relative to the reference
frequency must be able to be corrected almost immediately by increased power supplied to the motor . therefore any change in load
could cause this error signal to be generated , I can see why changing the mass of this type of drive could make things worse not better!
The system generally lends itself to hunting as opposed to high mass
platters and elastic drives f=ma (newton)
i.e the error generated by the speed sensor relative to the reference
frequency must be able to be corrected almost immediately by increased power supplied to the motor . therefore any change in load
could cause this error signal to be generated , I can see why changing the mass of this type of drive could make things worse not better!
The system generally lends itself to hunting as opposed to high mass
platters and elastic drives f=ma (newton)
Overdamped
Too often are platters, bases/plinths beeing damped to death...
In the case of the Trio, (I want it!!!), it was done so by engineering, but can be "un-done" by using different platter-mat, and; modify the arm-board coupling & material. Any other motor-drive would change nothing, or possibly worsen the design.
Arne K
Too often are platters, bases/plinths beeing damped to death...
In the case of the Trio, (I want it!!!), it was done so by engineering, but can be "un-done" by using different platter-mat, and; modify the arm-board coupling & material. Any other motor-drive would change nothing, or possibly worsen the design.
Arne K
Admittedly, my printer isn't as accurate as it was, but when I bought it second-hand thirteen years ago, it was perfectly capable of printing to the exact dimensions specified by Autosketch, so a circle wouldn't have been a problem.
I've found that I can spot wow by looking at a strobe disc illuminated by a precision strobe light. It was sufficient to show why there were BBC strictures about swapping platters between different Garrard 301s - I could see wow with the wrong platter.
I've found that I can spot wow by looking at a strobe disc illuminated by a precision strobe light. It was sufficient to show why there were BBC strictures about swapping platters between different Garrard 301s - I could see wow with the wrong platter.
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