You are aware how DD motors work? It does sound like you have some serious confusions on where the coil drive signal comes from.
In the Pink Fish Media link the Phonosophie P3 turntable, which has stepper motor has good polar chart. Isn't it ? Don't know if it can be improved. If It can be, then it will be a good motor unit.
regards.
regards.
OK. Give us a detailed answer and no mistakes please. Within reason what was said is universal for the majority of AC motors. The idea being if one can by mass and how current is allowed to be drawn influence the initial switching from being abrupt we should get a bonus in sound quality. Due to the inductance of the motor some of that is a given. I dare say whatever one tries the set up of the drive system will dictate outcomes. So ignoring servos we have mass, voltage and waveform shape to help us. The thing I was trying to say is don't assume what the simple mecahniism gives is as simple as you think. As I said any fool can see this. To be that fool you have to think. What is the ideal rotational speed of the motor? What speed do you want? Are they one and the same? No they aren't. Therefore a big hole of a problem turns up. An analogy would be switching an engine of a car on and off to take the need for a gearbox away.
I don't know the top speed of a SP10. I would suspect 300 rpm. Thus to rotate at 33 1/3 means more off than on. I suspect as it reaches it's top speed the flutter is least ? It is working inside that compromise where we can make a difference ( take SP 10 to be a generic of 20 pole and 60 slots I think ). Over to you.
Well Technics, JVC, kenwood at least use DC servo motors. Rotational speed is controlled by DC voltage not by the waveform frequency. More to follow if I can be bothered to do what you could google for. Measurements DO NOT SHOW this abrubt switching you fuss about so maybe stop worrying.
https://www.youtube.com/watch?v=VXeicfJ-l3w
This shows a 78 mod. I have 2 x SP 10 somewhere. I must find the natural speed and do an oscilloscope grab at 33 1/3.
This shows a 78 mod. I have 2 x SP 10 somewhere. I must find the natural speed and do an oscilloscope grab at 33 1/3.
Denon DP-80 Manual - 2-Speed Direct-Drive Turntable - Vinyl Engine
The Denon is good reading.
I wish I had the block dia for these. I have a pile of Sony service manuals for their DD at my parents house. They might have a good description. Now if some are a DC motor with on off control I can't say. FG servo perhaps?
The Denon is good reading.
I wish I had the block dia for these. I have a pile of Sony service manuals for their DD at my parents house. They might have a good description. Now if some are a DC motor with on off control I can't say. FG servo perhaps?
This opens up the same questions. I must do my own tests. I must see how the reference signals look in reality. Should not be difficult and do current waveforms to see if my conjecture is right. It still seems right to me that anything that switches is AC and inductance comes into to it. Were it a brushed motor even then it might as the AC/DC universal proves.
https://www.youtube.com/watch?v=0PDRJKz-mqE
Quartz Controlled Vs. Servo Controlled - Meaning? - Vinyl Engine
https://www.youtube.com/watch?v=0PDRJKz-mqE
Quartz Controlled Vs. Servo Controlled - Meaning? - Vinyl Engine
try reading this Updated Technics SP10 quartz PLL drive Covers the details quite well if you CBA to register on VE to get manuals for everything. It is a good primer, and he understands control theory.
Thanks Dave/ Mr B 12.9 Hz @ 78 RPM. That's what I wanted to know. It's much better it works that way. I am slightly surprised the working frequency is that low and it says a remarkable magnetic circuit. My assumption and wrong is the circuit would become too inefficient magnetically to work that low. If so a coasting circuit would be needed. I am very happy to be wrong. However it raises a question. 5.5 Hz is a very low frequency as compared with the 1.8 Hz of the platter itself. Lets not forget the phases as that helps greatly.
A 24 pole stepper gives 250 RPM at 50 Hz and 300 RPM at 60 Hz. At 5.5 Hz it would give 27.5 RPM. That seems about right allowing for poles. The diagram in the link shows squarewaves. That conflicts with the text.
Now to the crunch. If a small resistor is inserted we shall see if the waveform truely is low distortion or is the very low output impedance shunting everything making it look low distortion? L165, that's a nice surprise. I don't know if Technics have a series resistor? Having established it is an AC synchonous 3 phase we truely can look at mass and waveform. Thank goodness Tesla principles are good enough for this problem. I won't eat my hat if wrong, but I feel 70% certain I wouldn't have to. I have to thank the late Richard Hay for teaching me how to measure amplifers. Did you know him Dave ( Ex Chew Magna near Bristol )? Switching transients shouldn't be a problem except if load changes dramatically. The only question being leading edge into the motor.
Linn Valhalla exactly the same. Distortion 0.1 % or better. Real distortion about 5 % into the motor. I have that as graphs. 5 % is not bad at all.
There is a massive contradiction in the text. It states that the frequency does not control the speed. Then why differrent frequecies to make different speeds ? I think I know what he means. I will have to play and see if the English can be made more meaningful. I suspect what he means is. If the load is changed voltage alone will restore the abillity to be synchronous ? That is as any synchonous that is being run at the lowest possible power level. If I am right this proves to be " any fool " you have to look at how it works. Don't take anyones word for it.
To quote.
The drive circuit consists of 3 identical power amplifiers. L165V PentawattTM power op-amps are a convenient solution, in a small package. A discrete transistor version - using something like TIP31/32 transistors would work just as well. The L165 saves PC board space and eliminates a few design steps, and costs no more than the equivalent disscrete transistors and their associated components. A TDA2040 'chip-amp' and its siblings would be drop-in substitutes for the L165V, at a higher cost, with no real advantage.
The required bandwidth of this stage is no more than a few Hz - actual drive waveforms for 33.3 rpm being 5.5 Hz, rising to 12.9Hz at 78 rpm. Being almost pure sinusoids (more on that later) they have no appreciable harmonic content, and amplifier stages require no remarkable performance characteristics.
The power amplifier section was to be built on the same printed circuit board as the linear power supply to eliminate any PCB interconnects involving heavier current wiring. But after I obtained a real chassis, I discovered there was not enough space insude to fit all the circuitry in. So the original Matsushita arrangement of an outboard power supply box will be used. The motor draws only a few tens of milliamps during normal running, and several hundred milliamps briefly at startup.
A 24 pole stepper gives 250 RPM at 50 Hz and 300 RPM at 60 Hz. At 5.5 Hz it would give 27.5 RPM. That seems about right allowing for poles. The diagram in the link shows squarewaves. That conflicts with the text.
Now to the crunch. If a small resistor is inserted we shall see if the waveform truely is low distortion or is the very low output impedance shunting everything making it look low distortion? L165, that's a nice surprise. I don't know if Technics have a series resistor? Having established it is an AC synchonous 3 phase we truely can look at mass and waveform. Thank goodness Tesla principles are good enough for this problem. I won't eat my hat if wrong, but I feel 70% certain I wouldn't have to. I have to thank the late Richard Hay for teaching me how to measure amplifers. Did you know him Dave ( Ex Chew Magna near Bristol )? Switching transients shouldn't be a problem except if load changes dramatically. The only question being leading edge into the motor.
Linn Valhalla exactly the same. Distortion 0.1 % or better. Real distortion about 5 % into the motor. I have that as graphs. 5 % is not bad at all.
There is a massive contradiction in the text. It states that the frequency does not control the speed. Then why differrent frequecies to make different speeds ? I think I know what he means. I will have to play and see if the English can be made more meaningful. I suspect what he means is. If the load is changed voltage alone will restore the abillity to be synchronous ? That is as any synchonous that is being run at the lowest possible power level. If I am right this proves to be " any fool " you have to look at how it works. Don't take anyones word for it.
To quote.
The drive circuit consists of 3 identical power amplifiers. L165V PentawattTM power op-amps are a convenient solution, in a small package. A discrete transistor version - using something like TIP31/32 transistors would work just as well. The L165 saves PC board space and eliminates a few design steps, and costs no more than the equivalent disscrete transistors and their associated components. A TDA2040 'chip-amp' and its siblings would be drop-in substitutes for the L165V, at a higher cost, with no real advantage.
The required bandwidth of this stage is no more than a few Hz - actual drive waveforms for 33.3 rpm being 5.5 Hz, rising to 12.9Hz at 78 rpm. Being almost pure sinusoids (more on that later) they have no appreciable harmonic content, and amplifier stages require no remarkable performance characteristics.
The power amplifier section was to be built on the same printed circuit board as the linear power supply to eliminate any PCB interconnects involving heavier current wiring. But after I obtained a real chassis, I discovered there was not enough space insude to fit all the circuitry in. So the original Matsushita arrangement of an outboard power supply box will be used. The motor draws only a few tens of milliamps during normal running, and several hundred milliamps briefly at startup.
Last edited:
One idea that comes to mind is a viscous bath to force the motor to work harder and force the voltage up. The motor almost needs nothing to do this except sealing it. My goodness so many advantages I can think of. It should sound remarkable as long as not pushing the voltage/ current too high. It will even cool the coils. The same oil as the bearing needs ( ATF ? ). Can I have a patent please? Doubtless well known already?
well in DD the coils are fixed so no idea what the oil will do.
Note here I am talking about classic technics/jvc/trio designs. The motor has an alternator inside it, with 3 coils at 120 degree spacing fixed to the stator and an iron cross with magnets at 90 degrees fixed to the platter. Often the coils are driven at about 50KHz and as the magnets swing past you get sinusoids out to drive the coils. Always ensures the right sequencing, frequency and waveform for minimum torque ripple.
What this also means is that the control system only needs to worry about the DC voltage to the coil drivers and the servo loop just adjusts that.
Current chips for this synthesize the sine wave, but the 70s way is proven and reliable, albeit slightly more expensive in wound parts. These days you use hall sensors for position detection.
Given this drive method is used in machine tools I cannot find information on pre-distortion of the drive to reduce torque ripple effects (note fed up with use of cogging). There are twisted stator designs, but few of those used in turntables and certainly not in the sort we are looking to enhance on this thread.
Note here I am talking about classic technics/jvc/trio designs. The motor has an alternator inside it, with 3 coils at 120 degree spacing fixed to the stator and an iron cross with magnets at 90 degrees fixed to the platter. Often the coils are driven at about 50KHz and as the magnets swing past you get sinusoids out to drive the coils. Always ensures the right sequencing, frequency and waveform for minimum torque ripple.
What this also means is that the control system only needs to worry about the DC voltage to the coil drivers and the servo loop just adjusts that.
Current chips for this synthesize the sine wave, but the 70s way is proven and reliable, albeit slightly more expensive in wound parts. These days you use hall sensors for position detection.
Given this drive method is used in machine tools I cannot find information on pre-distortion of the drive to reduce torque ripple effects (note fed up with use of cogging). There are twisted stator designs, but few of those used in turntables and certainly not in the sort we are looking to enhance on this thread.
Just been checking on ebay for things that are cheap and interesting for the brave
JVC L-A55 currently £5. Should be standard green motor
Garrard DD75 currently £20.
Denon DP2000 currently £5, but not working properly. Might be a simple recap job. bit of an oddball as 2 phase drive with simple cap phase shift.
And a few cheapish SL-5s
Lenco's are sadly going up week on week as would like a rim drive to complete the set .
JVC L-A55 currently £5. Should be standard green motor
Garrard DD75 currently £20.
Denon DP2000 currently £5, but not working properly. Might be a simple recap job. bit of an oddball as 2 phase drive with simple cap phase shift.
And a few cheapish SL-5s
Lenco's are sadly going up week on week as would like a rim drive to complete the set .
John was a very very nice man. Remember his Star Wars R2D2 I think was the name? Not the gold fellow ( CP30 ? ).
Nigel, I really do not know where you are coming from ? Industrial mechanics perhaps ?
I can demonstrate a good wow/flutter at 16 2/3rds RPM on a Technics.
I can demonstrate a good wow/flutter at 16 2/3rds RPM on a Technics.
I have a Garrard DD 75. Nothing special. I might be able to test it.
The JVC I would buy if as good as Colleen's L3-E.
The Denon sounds more like a synchronous than usual.
BSR HT 70 might beat a Lenco. As with the Lenco the arm might be more OK than it looks as a way to try it. The platter was made as far as I know at Birmingham Master Casters suppliers of old to Linn. BSR and Linn were very close as friends. BSR was at one time the worlds largest producer of turntables. 6 million units a year if I am right ? Linn LVV arm was a BSR. Mr Itto supplied ADC/BSR.
BSR McDonald HT70 3 speed turntable For Sale
The JVC I would buy if as good as Colleen's L3-E.
The Denon sounds more like a synchronous than usual.
BSR HT 70 might beat a Lenco. As with the Lenco the arm might be more OK than it looks as a way to try it. The platter was made as far as I know at Birmingham Master Casters suppliers of old to Linn. BSR and Linn were very close as friends. BSR was at one time the worlds largest producer of turntables. 6 million units a year if I am right ? Linn LVV arm was a BSR. Mr Itto supplied ADC/BSR.
BSR McDonald HT70 3 speed turntable For Sale
Nigel, the title of this thread is " Technics SP-10/SL-1200 alternatives " How are you contributing to this ? Maybe you should go and start your own thread ?? 😉
It's to see no matter how unlikely if anyone has missed cheap ways to get a bit more from these decks. I suspect to get below - 70 dB was the quest.- 67 dB might have more verve. Having said that Colleen's JVC already has a LP12 beaten on verve. Forget wow and flutter, it seems to be excellent anyway. So we have torque and vibration sweet spot to find. My guess is we can get a little more. To slightly load the motor viscously really says to me I must try it. I would be so surprised if it didn't work. Verdier said much the same although not about this type of motor. Verdier was a sucessful designer going back years. His famous turntable was at first a DIY article in a magazine. Verdier said drag is a valuable tool. He reasoned if the drug or whatever was 10 times greater than the stylus load then dynamic wow can not happen. As the Technics motor will magically compensate the sound could leap to giant killing standards. Hope rather than a prediction. It's on the cards it could. One thing I suspect true is the Technics 1210 will react to the music albeit not greatly. Load it up with some drag and it should be cured.
Doing a bit of research it was David Gammon of Transcriptors who designed and first built it and it was later made under licence by Michell.
- Status
- Not open for further replies.