Most likely has 3 North poles and 3 south poles. What's the radius of the outer ring of coils, and how big are they?
Do you see hall effect sensors? I'm guessing not, as these motors are probably driven with relatively pure sine waves.
I wonder about the two sets of coils and magnets. Seems like a lot of trouble just to get a tacho signal.
The outer coils aren't all that big. The laminations are perhaps 3/4" high and the coils are about 1/2" wide. The whole thing is about 4 1/4"" diameter.
There are more than three North and three South poles on the magnet. I very crudely tested by wiping the steel blade of a screwdriver around the inside of the magnet and found twenty places where it would stay.
No, I didn't see Hall sensors. The reason for three coils for the tacho is to try to increase the tacho frequency. Trying the same screwdriver trick, I found that the inside of the magnet was serrated. I think this may be a variant of the Studer/Revox trick where they use the leakage field from their (AC) capstan motor. Their 4" outer rotor motor has lots of little fingernail slots cut into it so as it passes near a single coil the flux changes rises and falls with the slots to give a nice high tacho frequency. Cunning.
There are more than three North and three South poles on the magnet. I very crudely tested by wiping the steel blade of a screwdriver around the inside of the magnet and found twenty places where it would stay.
No, I didn't see Hall sensors. The reason for three coils for the tacho is to try to increase the tacho frequency. Trying the same screwdriver trick, I found that the inside of the magnet was serrated. I think this may be a variant of the Studer/Revox trick where they use the leakage field from their (AC) capstan motor. Their 4" outer rotor motor has lots of little fingernail slots cut into it so as it passes near a single coil the flux changes rises and falls with the slots to give a nice high tacho frequency. Cunning.
Yeah, they've certainly been doing their homework.
I want to get one. Maybe someone has one they don't use and would part with for a reasonable price. Otherwise, I guess I'll have to watch for a good one on eBay. From what I've seen, folks tend to hang on to them though. ;-(
pixpop said:
If you only need a motor, without platter, and without electronics, make me an offer for my Technics SP10mkII motor.
Well, I actually need a complete unit, but I'll offer you $25 for your motor anyway (and I'll pay shipping, of course). I'm assuming you have reason to believe it's not dead.
Forgot the Beogram 8000 schematic at work 
Dont have a full manual on this one, only schematic and some data.
http://www.beocentral.com/products/bg8000
Best regards Kim Olesen
Dont have a full manual on this one, only schematic and some data.
http://www.beocentral.com/products/bg8000
Best regards Kim Olesen
The first thing you need to do is get the speed under control.
I'm assuming that you have the motor driver electronics from the VCR, as well as the motor. These work using a DC control voltage. The higher the voltage, the more torque, and the faster it spins.
You'll need to build a PLL. You feed a reference frequency into the PLL, along with tach pulses from the motor controller. The PLL will output a DC voltage that will increase or decrease the motor speed until it matches the reference frequency. A PLL exists inside the VCR, but I doubt you'd be able to find and separate it out.
You cannot just put a steady voltage on the control pin, as you will have no speed regulation. If the load changes, the speed will change.
You'll need to source a belt of some kind, and do some math to figure out what speed the motor should run at in order to generate 33.3 rpm.
If all you have is the motor, then you'll have to source a BLDC motor control chip, and get that working with your motor.
Some VCRs have two motors you could use: the head drum motor, and the capstan motor (The one that controls the speed of the tape through the machine). The drum motor has low torque and high speed. The capstan motor has high torque and low speed, which might be more suitable for a belt drive. It usually has a nice flywheel as well so the speed control should be easy.
pixpop and Cobra2: I have a naked motor stripped from a SP10mkII that was missing some external BBC electronics and I have an SP10mkII chassis that would need to be restored to the original Technics circuit to compensate for the lack of external BBC electronics (power supply and master clock). I didn't bother offering the chassis because I assumed that the freght would be prohibitive, but it might not be too bad. If this is of any interest I can email you tomorrow evening.
As I made the offer to pixpop and don't want to turn this into an online auction, he has first refusal of the naked motor at the price he offered. Converting currency on this amount will be expensive, so I suspect a barter deal is probably best.
As I made the offer to pixpop and don't want to turn this into an online auction, he has first refusal of the naked motor at the price he offered. Converting currency on this amount will be expensive, so I suspect a barter deal is probably best.
EC8010,
It probably makes more sense for me to find something closer to home, so I think I'll back out at this point. Go ahead and sell to cobra2 if he still wants it. I'm watching eBay for a complete unit that doesn't have to ship too far.
Thanks,
Neil
It probably makes more sense for me to find something closer to home, so I think I'll back out at this point. Go ahead and sell to cobra2 if he still wants it. I'm watching eBay for a complete unit that doesn't have to ship too far.
Thanks,
Neil
Apologies!
I haven't read all the five pages yet, but from what I know about the situation... DD turntables are bad if they have NEGATIVE FEEDBACK. The 'free floating' kenwood KD series DD turntables were fine. They had no feedback. Those were teh big corian based decks, the ones where you could put a seprate arm on. the KD 500, 550, and 600, I believe.
I've had 4 of them from that series. Not my favorite but the consensus among the audiophile crew was and is that the non-feedback design was and is superior. Similar characteristics to a belt drive unit, in terms of a ALCK of 'micro cogging' of the motor...leading to superior temporal characteristics presented to the listener.
Beware the KD series though, inspect the bearing closely before purchase. They have a tendacy to collapse.
I haven't read all the five pages yet, but from what I know about the situation... DD turntables are bad if they have NEGATIVE FEEDBACK. The 'free floating' kenwood KD series DD turntables were fine. They had no feedback. Those were teh big corian based decks, the ones where you could put a seprate arm on. the KD 500, 550, and 600, I believe.
I've had 4 of them from that series. Not my favorite but the consensus among the audiophile crew was and is that the non-feedback design was and is superior. Similar characteristics to a belt drive unit, in terms of a ALCK of 'micro cogging' of the motor...leading to superior temporal characteristics presented to the listener.
Beware the KD series though, inspect the bearing closely before purchase. They have a tendacy to collapse.
reading backward to page 3.
Reading, I find reference to self made platters etc. If machining, be aware that Linn has found that the platter can have severe resonance alleviated to a large extent...by taking a full month to machine.
The way Linn does it, is they only machine a small amount of the platter at one given time. then put it in a rack, pick up the next platter, etc.. do a bit more, move on to the next platter..etc..etc. One month to machine each platter. They don't allow the metals to heat.
This kills the hard 'bell' resonance that would normally be in the platter. Pick up a linn platter and tap it. You'll see that it resonates far less than you would expect. A different frequency, character and duration to that bell ring.
The main bearing, sleeve, thrust plate, and platter are all machined and matched together..and are only available as a set, if one part is damaged.
Reading, I find reference to self made platters etc. If machining, be aware that Linn has found that the platter can have severe resonance alleviated to a large extent...by taking a full month to machine.
The way Linn does it, is they only machine a small amount of the platter at one given time. then put it in a rack, pick up the next platter, etc.. do a bit more, move on to the next platter..etc..etc. One month to machine each platter. They don't allow the metals to heat.
This kills the hard 'bell' resonance that would normally be in the platter. Pick up a linn platter and tap it. You'll see that it resonates far less than you would expect. A different frequency, character and duration to that bell ring.
The main bearing, sleeve, thrust plate, and platter are all machined and matched together..and are only available as a set, if one part is damaged.
Re: reading backward to page 3.
Man, that's complete madness. There is such a thing as coolant one can use to keep the platter and the tool cutting it from heating up during machining. Also, repeated re-clamping of a job is a great way to introduce errors in concentricity and flatness.
Oh, and I think that it's only the KD 500/550 that had this floating feature you speak of. The KD 600/650 had a phased locked loop.
And, yes, my KD 650's platter (without its mat on) rings like a bell.
Max
KBK said:
Man, that's complete madness. There is such a thing as coolant one can use to keep the platter and the tool cutting it from heating up during machining. Also, repeated re-clamping of a job is a great way to introduce errors in concentricity and flatness.
Oh, and I think that it's only the KD 500/550 that had this floating feature you speak of. The KD 600/650 had a phased locked loop.
And, yes, my KD 650's platter (without its mat on) rings like a bell.
Max
The proof inthe pudding is that you can barely get an LP12 platter to ring, at all. What exactly that translates to, is well, a thing to be figured out. 🙂
What does that 'micro cogging' sound like? Can you describe it?
What is the bad effect that negative feedback has on a turntable?
It has to do with how the human hearing machanism works. We hear like a diode and in time, with level peaks being the critical point. So, we principally only hear the positive edge transients, in time.
If you think of how a horn speaker works, you find it has a very high amount of distortion to it's negative part of the waveform, but the positive edge is treated well, if you have designed a good horn. When you analyse the components of exactly why such a high amount of distortion of the negative wave corelates to the human perception of a horn's sound (positive!), you see that the timing, level, and placement of a transient becomes critical to satisfy human perception. The exact envelope of the frequency range of that warble or jitter (it has relation to digital jitter and it's perception) plays a part in it's perception as well.
Belt drive could sound as bad or worse than DD, but not that often, which is suprising to some. It all depends on how the platter speed is controlled/maintained by each differing technique. Ie, the nature of the distortion.
If you think of how a horn speaker works, you find it has a very high amount of distortion to it's negative part of the waveform, but the positive edge is treated well, if you have designed a good horn. When you analyse the components of exactly why such a high amount of distortion of the negative wave corelates to the human perception of a horn's sound (positive!), you see that the timing, level, and placement of a transient becomes critical to satisfy human perception. The exact envelope of the frequency range of that warble or jitter (it has relation to digital jitter and it's perception) plays a part in it's perception as well.
Belt drive could sound as bad or worse than DD, but not that often, which is suprising to some. It all depends on how the platter speed is controlled/maintained by each differing technique. Ie, the nature of the distortion.
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