I have just added a lead ring into the platter of the heavy Akai DD TT. Discovered it did'nt help much, still varying in speed (i can see this on the strobe) Sound is improved a very little, but i think its better to switch over to belt drive.
Have a cheap Dual 505/2, very light flimsy platter, but because of the belt its running more synchronical. I can also buy a pioneer belt drive for cheap at the local secondhand shop, maybe this is a better start-off for a decent high-end TT project, to put my diy arm on. http://img109.imageshack.us/my.php?image=armoq2.jpg
Have a cheap Dual 505/2, very light flimsy platter, but because of the belt its running more synchronical. I can also buy a pioneer belt drive for cheap at the local secondhand shop, maybe this is a better start-off for a decent high-end TT project, to put my diy arm on. http://img109.imageshack.us/my.php?image=armoq2.jpg
I recall seeing the cogging of an earlier DD turntable (a Technics) without its outer platter added. About every 90 degrees of rotation, a torque pulse from the motor would double the speed of the platter which would then immediately start slowing down until the next cogging pulse. It looked just terrible.
DD turntable unweighted rumble specs are also tremendously worse (by 20 db or more) than that of competent belt drive turntables.
DD turntable unweighted rumble specs are also tremendously worse (by 20 db or more) than that of competent belt drive turntables.
thoriated said:
http://translate.google.com/transla...&hl=en&ie=UTF-8&oe=UTF-8&prev=/language_tools
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Arne K
EMT made only one poor deck, the 928. It was the only belt-drive deck the company ever made. It is, of course, superior to toys like Linn LP12 and Thorens TD-125 (which it was based on). Then EMT made THE classic DD deck, the 950.
My point is, if you are going to compare different technologies, compare products of equal quality. Otherwise you aren't any better than the infamous showman Ivor Tiefenbrun--the P.T. Barnum of audio--who demonstrated that his deck was superior to a faulty DD deck.
Some other pretty good DD decks.
http://de.geocities.com/bc1a69/nakamichi_eng.html
My point is, if you are going to compare different technologies, compare products of equal quality. Otherwise you aren't any better than the infamous showman Ivor Tiefenbrun--the P.T. Barnum of audio--who demonstrated that his deck was superior to a faulty DD deck.
Some other pretty good DD decks.
http://de.geocities.com/bc1a69/nakamichi_eng.html
When i take off the platter, i see those anxious "jerks" in rotation too. There has to be mounted an enormous weight on the platter before the rotation velocity is equal enough to have a good enjoy of the analog music imo. The cogging (with platter again!) is also very unpredictable. Sometimes 1 minute equal, and the speed starts to vary, about 3 mm visible on the strobe/rotation!
Just set up the very simple Dual 505/2, shifted a OM10 needle in the original Dual (Ortofon) cart, and played music. Bought this one for Eu 3.50. This unmodified belt drive has less hearable wow than the Akai DD. The Akai DD itself is not faulty, a 2nd has the same cogging. For simple diy still belt drive is a very good solution, and i assume the Linn is not that bad, just as Thorens. And when there is a magnetic coupling, such as Transroter uses, it is even better. http://www.audiopaul.nl/images/transrotor/mdrive.jpg
The PS for the Akai DD should be modified, i only changed the 33 1/3 speed pot into a 10 turn precision one. I leave it now because the Akai DD has not the best drive design, i know that now. Maybe an EMT is better. When Akai added a lot more poles on the magnet it would be much better DD.
Just set up the very simple Dual 505/2, shifted a OM10 needle in the original Dual (Ortofon) cart, and played music. Bought this one for Eu 3.50. This unmodified belt drive has less hearable wow than the Akai DD. The Akai DD itself is not faulty, a 2nd has the same cogging. For simple diy still belt drive is a very good solution, and i assume the Linn is not that bad, just as Thorens. And when there is a magnetic coupling, such as Transroter uses, it is even better. http://www.audiopaul.nl/images/transrotor/mdrive.jpg
The PS for the Akai DD should be modified, i only changed the 33 1/3 speed pot into a 10 turn precision one. I leave it now because the Akai DD has not the best drive design, i know that now. Maybe an EMT is better. When Akai added a lot more poles on the magnet it would be much better DD.
EMT 950 for a lot of $$, it went to Taiwan. So curious, all those well build European stuff is all drawn away to the far eastern, just like all Philips LHH 1000 CDP's.
http://cgi.ebay.co.uk/SUPERB-EMT-95...R_W0QQitemZ110025630712QQihZ001QQcmdZViewItem
http://cgi.ebay.co.uk/SUPERB-EMT-95...R_W0QQitemZ110025630712QQihZ001QQcmdZViewItem
I play with the old Dual 505/2 for a few days now, OM10 cart.
Very nice to hear no wow anymore. I think the bearing of the DD is demolisched too. (standard brass bush with stainless spindle and steel ball on steel plate)
Btw listened to the Dual's TT with an LP on with stethoscope: what a huge feedback of sound though whole TT.
Very nice to hear no wow anymore. I think the bearing of the DD is demolisched too. (standard brass bush with stainless spindle and steel ball on steel plate)
Btw listened to the Dual's TT with an LP on with stethoscope: what a huge feedback of sound though whole TT.
"DirectDrive" still alive
Whenever people talk about direct-drive turntables, one of the most popular websites on the topic they refer to is the "directdrive" page but due to the shut down of geocities, it is no longer operative. Luckily, someone has transported all the information to a new site so people can still continue to read about the direct-drive genre. Everything is the same as before except the website is "GEOCITIES.WS" not "GEOCITIES.COM", whatever links you had before, just change geocities.com to geocities.ws and will work the same. Please keep in mind that some info is dated regarding market price of used turntables. My favorite is the DirectDrive Museum in browsing all the products from the DD golden age (mid 70's to early 80's) from different brands. Enjoy!
geocities.ws/bc1a69/index_eng.html - Welcome at DirectDrive
.
Whenever people talk about direct-drive turntables, one of the most popular websites on the topic they refer to is the "directdrive" page but due to the shut down of geocities, it is no longer operative. Luckily, someone has transported all the information to a new site so people can still continue to read about the direct-drive genre. Everything is the same as before except the website is "GEOCITIES.WS" not "GEOCITIES.COM", whatever links you had before, just change geocities.com to geocities.ws and will work the same. Please keep in mind that some info is dated regarding market price of used turntables. My favorite is the DirectDrive Museum in browsing all the products from the DD golden age (mid 70's to early 80's) from different brands. Enjoy!
geocities.ws/bc1a69/index_eng.html - Welcome at DirectDrive
.
direct-drive German style
Don't forget the smaller sibling, Brinkmann Bardo. Same gut minus the Oasis plinth. I prefer the Bardo's look better. Very cool construction!
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Don't forget the smaller sibling, Brinkmann Bardo. Same gut minus the Oasis plinth. I prefer the Bardo's look better. Very cool construction!
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Serious & nice. A lot of years ago DD was the real high-end, If I don't remeber bad a Denon TT was superb.
To ships passing in the night... Thats what you want in a TT. Motor vibratons over there and the business end over here. DD's ignore these rules
As nice as the Brinkman is, Belt drive still has the edge at isolating your needle.
No suspension means bass freqs. will still upset your expensive baby !
David
As nice as the Brinkman is, Belt drive still has the edge at isolating your needle.
No suspension means bass freqs. will still upset your expensive baby !
David
This whole idea of direct drive turntable lacks motor isolation is rather misguided. The whole turntable has only ONE moving part, the platter. And it runs at 33rpm, which is half hertz! It vibrates as little as belt-drive whose platter also runs at 33rpm. So where is the vibration coming from. In fact, belt-drive tables often employs a spinning motor as fast as up 1800rpm in many vintage tables, that's 30Hz - yeah, you can hear it. In fact, belt-drive requires even more attention to isolate the motor than DD. It's such a cliche to criticize the DD genre just based on that notion. Yes, DD has cogging issue but can be minimized or eliminated with quality motor and electronics. But the notion that just because direct drive has motor underneath the platter is automatically susceptible to motor vibration or worse than belt-drive is one of the myths in knocking the DD genre. It has been repeated ad nauseam. I have many direct-drive turntables that I cannot even hear or felt any vibration whatsoever with a stethoscope. I, however, had many belt-drive tables having motor vibration leaking through the plinth and into the platter bearing and tonearm, if the motor is built inside the plinth. Once again, DD has its own issues just like any technology but motor vibration is NOT an issue in a quality model.
This site explains it better than I can.
Not having suspension is a design issue, not the inherent problem of direct-drive. The owner can always put the table on an after market suspension platform. Suspended belt-drive can have speed issue due to the motor and platter bearing not rigidly coupled. DD does not have that issue.
I see this is an old thread, but it's got some good stuff in it. As an engineer (analog and digital electronic design, embedded programming) I've thought about DD design for many years, so here's some of my thoughts.
I wonder if part of DD's alleged problem is the bearing has the weight perfectly balanced on it (except for a slight offset from the force of the stylus), and if there's any way for the platter to rock back and forth, even microscopically, it probably will. A belt drive pulls the platter shaft horizontally against the upper sleeve bearing (the one that holds the shaft vertically, as opposed to the lower bearing which holds the weight), making sure it maintains full contact on one side of the bearing. Thus the belt tension prevents (to use an old Rockwell/Chrysler/GE term) side fumbling.
If the platter edge has a flat vertical surface suitable for a belt, this could be tested by adding a belt and idler pulley to add this side force.
A low-distortion three-phase sine generator can be made easily enough with analog circuitry, but would be better with a small microcontriller A DSP is easier, but at these low frequencies a microcontroller should be fast and powerful enough. A numerically controlled oscillator in software can create phase-locked waveforms at any frequency, meaning you could set the speed to within a thousanth of an RPM of whatever speed you wanted and it would still be phase locked to a quartz crystal.
The precision is in the sensing of speed more than anything else. Detecting a line of the strobe as on the rims of some platters would be good, as it's a much higher frequency signal than the magnet poles in the motor, or other magnet/hall effect sensors that give only a few pulses per revolution.
For best speed control the drive coils should be 90 degrees ahead of the magnet poles, and the current varied to vary torque. Detecting and maintaining that 90 degree phase should be the job of a properly programmed microcontroller.
I suspect most DD designs (see my test below) use "full current" all the time to the coils and with no load the platter magnet poles are virtually in phase with the drive coil signals, but a slight increase in friction will change the phase, even though the platter stays in sync, the magnet poles start to lag the drive signals. This is a "first approximation" design.
I've got a couple of DD TT's I've been playing with lately, a Technics 1300 and a and a Pioneer PL-L800. With a strobe disk on the platter, things are nice and stable, and the "quartz lock" light is on. But I can drag my finger lightly on the platter edge and see a small but significant shift in the strobe pattern (it jumps back a little, but then maintains speed), yet the "quartz lock" light stays on on both of these tables. I haven't even tried this with playing an LP, as I have no doubt it would be clearly audible. I doubt a stylus would ever have that much drag, but it may still be enough to audibly slow the platter. IMHO this is an inadequate design.
And as for a fault, it may be in a specific DD TT's design rather than a faulty component.
I wonder if part of DD's alleged problem is the bearing has the weight perfectly balanced on it (except for a slight offset from the force of the stylus), and if there's any way for the platter to rock back and forth, even microscopically, it probably will. A belt drive pulls the platter shaft horizontally against the upper sleeve bearing (the one that holds the shaft vertically, as opposed to the lower bearing which holds the weight), making sure it maintains full contact on one side of the bearing. Thus the belt tension prevents (to use an old Rockwell/Chrysler/GE term) side fumbling.
If the platter edge has a flat vertical surface suitable for a belt, this could be tested by adding a belt and idler pulley to add this side force.
I was shocked about 12 years ago when I read that Technics turntables used square waves for their DD motors. Since the '70's when I had first heard of direct-drive turntables I assumed they all used sine waves to drive the motor. With square waves t's not a bit surprising there's "cogging" going on. A three-phase motor with sine wave input generates constant torque (just as a three-phase generator with all three phases equally loaded will generate constant power). With some other waveform, the torque will likely vary during the cycle of the input waveform.
A low-distortion three-phase sine generator can be made easily enough with analog circuitry, but would be better with a small microcontriller A DSP is easier, but at these low frequencies a microcontroller should be fast and powerful enough. A numerically controlled oscillator in software can create phase-locked waveforms at any frequency, meaning you could set the speed to within a thousanth of an RPM of whatever speed you wanted and it would still be phase locked to a quartz crystal.
The precision is in the sensing of speed more than anything else. Detecting a line of the strobe as on the rims of some platters would be good, as it's a much higher frequency signal than the magnet poles in the motor, or other magnet/hall effect sensors that give only a few pulses per revolution.
For best speed control the drive coils should be 90 degrees ahead of the magnet poles, and the current varied to vary torque. Detecting and maintaining that 90 degree phase should be the job of a properly programmed microcontroller.
I suspect most DD designs (see my test below) use "full current" all the time to the coils and with no load the platter magnet poles are virtually in phase with the drive coil signals, but a slight increase in friction will change the phase, even though the platter stays in sync, the magnet poles start to lag the drive signals. This is a "first approximation" design.
I've got a couple of DD TT's I've been playing with lately, a Technics 1300 and a and a Pioneer PL-L800. With a strobe disk on the platter, things are nice and stable, and the "quartz lock" light is on. But I can drag my finger lightly on the platter edge and see a small but significant shift in the strobe pattern (it jumps back a little, but then maintains speed), yet the "quartz lock" light stays on on both of these tables. I haven't even tried this with playing an LP, as I have no doubt it would be clearly audible. I doubt a stylus would ever have that much drag, but it may still be enough to audibly slow the platter. IMHO this is an inadequate design.
These are different names for basically the same thing. A "brushless DC motor" is a combination of an AC motor with a DC-powered oscillator and driver circuit that sends AC to the motor. "Servo motor" means the motor has some speed detection device (maybe as little as one pulse per revolution, but that would be clearly inadequate for a DD TT motor) that feeds back to the electronics to have it keep the motor running at a constant speed.
It does fall into the definition of wow and flutter, but I've seen cogging used as the name for this specific issue in DD TT's, of the speed varying as the permanent magnet poles go over the electromagnet poles.- 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
And as for a fault, it may be in a specific DD TT's design rather than a faulty component.
Most ac syncronous motors for TT are at 300rpm, which translate nicely to 33rpm with the gearing at 1:9.00 (10mm pulley needs a 90mm subplatter to get 33.333 rpm)
Beltdriven table seems easier to design and build as the manufactur just can ploink down the motor with the rest. DD needs more careful manufacturing, and I suppose that most of them are too lazy with electronics. (!)
I loved the Brinkmann Bardo, it's a beautiful design and it have zero cogging!
If you look careful in the middle of the motor, you'll see a steelplate underneath, it's there to generate/increase the magnetic field between the magnet and rotors.
True, it's even easier to control such motors now.
I am playing with one, make a sinewave lookuptable, and then generate it,
but I need to understand the phase-thingy related to the frequency of sinewave. (BLDC need 60deg/phase, AC sync need 90deg/phase) I suck at math.
Well, I am not complete sure that you're correct, BLDC have 3 wires, and AC sync have two (or four?) wires. (I need to check the wikipedia...)
BLDC need 60deg/phase sinewave and AC sync. needs 90 deg/phase sinewave. That's the most bascale difference between them.
Beltdriven table seems easier to design and build as the manufactur just can ploink down the motor with the rest. DD needs more careful manufacturing, and I suppose that most of them are too lazy with electronics. (!)
I loved the Brinkmann Bardo, it's a beautiful design and it have zero cogging!
If you look careful in the middle of the motor, you'll see a steelplate underneath, it's there to generate/increase the magnetic field between the magnet and rotors.
Wow, is that better than a microcontroller? I want one!
True, it's even easier to control such motors now.
I am playing with one, make a sinewave lookuptable, and then generate it,
but I need to understand the phase-thingy related to the frequency of sinewave. (BLDC need 60deg/phase, AC sync need 90deg/phase) I suck at math.
Well, I am not complete sure that you're correct, BLDC have 3 wires, and AC sync have two (or four?) wires. (I need to check the wikipedia...)
BLDC need 60deg/phase sinewave and AC sync. needs 90 deg/phase sinewave. That's the most bascale difference between them.
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