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Old 19th July 2012, 06:31 PM   #21
miklos is offline miklos  Canada
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A kind of Hysteresis Synchronous Motor was used in tape recorders (Reel to Reel and the early table top cassette machines) and possible in record players, before the on set of the Direct Drive TT's. Not much torque on start up, but pretty hefty while running. In the pictures is one such Akai 14W motor, obs. the smooth rotor.
In connection to the subject ,some links:
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Attached Images
File Type: jpg Hysteresis Synchronous Motor.jpg (95.3 KB, 101 views)
File Type: jpg Smooth rotor.jpg (74.5 KB, 96 views)
File Type: jpg Label.jpg (81.6 KB, 98 views)
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Old 20th July 2012, 02:05 AM   #22
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Nanook,you are right,pulling the paltter needs less torque,I have tested this on this TT.

I replaced the original motor by a small stepper motor,the vibration noise disappeared in stead of stepper self-noise,even I put the stepper into a cast aluminium box.This noise just like the printer head moving noise.New problem cameIt seems that I have to select other type motor,maybe a synchronous motor in photocopy.

I made a new belt by PU wire(can be heat melted & jointed),this new belt can keep in same position on platter while running.

Some new pics
Move the motor out of base
RTT-1.jpg
Machined half groove to keep new belt
Rtt-2.jpg
New belt is running steady
Rtt-3.jpg
PU wire
Rtt-4.jpg
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Old 21st July 2012, 07:11 PM   #23
Nanook is offline Nanook  Canada
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Default which stepper? How to implement

The 7.5 motors I have are Thomson/Airpax P/N M82101-P1, 5VDC, 20Ω/coil. These are a 6 wire stepper and came from a photocopier or scanner.

Remember 6 wire steppers need to be fed both a sine wave (channel A) and a cosine wave (channel B) with the appropriate motor voltage to work (too high and you burn the coils). So 4 wires must be connected to a 2 channel amp. The other pair of wires must be connected together (channel A common and channel B common) for a 6 wire stepper.

I guess you could use a PIC or even a DSP to create the sine and cosine waves. You could also feed the motor a square wave, using PWM (I think).
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Old 21st July 2012, 07:34 PM   #24
Nanook is offline Nanook  Canada
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Default and speed accuracy...and a fool proof motor controller

Quote:
Originally Posted by Nanook View Post
. The closest I get to a 33 1/3 RPM reading on my Oracle is to within .01 RPM (33.34 RPM, which I can live with), so accuracy is +/-.005 RPM or about .015%. Try measuring that accuracy with anything else except a frequency counter and a test record. I'd also suggest testing the speed while playing a record if using a laser tach.
To clarify: the old Alexandria uses a Pabst "flat" or "pancake" style motor driven with a DC power supply. I have a re-plinthed Sugden BD-1 "kit" tt running straight from a wall plug. It has been verified to run at 33.33 using an AC outlet. Previously it ran too slow so I used some stretchable artist's tape to build up the pulley and drive it with a nylon thread at fairly high tension. It worked, but started to unwind , thus I tried several wraps of Teflon tape (for thread sealing pipe), and it has continued on for years.

For compete idiots like me, using a DSP might be the the simplest (or one of the simplest) methods possible to generate a good signal. Looking at the mini-dsp (as on diyaudio), even I could manage to get get this thing running reasonable well. If you use 60Hz (or 50Hz) pulley and platter then you can generate the correct frequency to run the motor at the correct speed of 300 RPM (or 250 RPM). Then get yourself some kind of amplifier (maybe a T-amp?) and a pair of small wattage step-up transformers to get the required voltage.

Another option might be the use of a 2 channel PWM controller from an RC car. The motors from RC vehicles don't spin slow enough, but the controllers are very good and can be inexpensive.
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Old 22nd July 2012, 11:01 AM   #25
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I replaced the motor again,a cassette deck DC motor this time,its running silently and steady. Belt was replaced by teeth wire,and the LT tonearm was updated to GOLDEN version

DC MOTOR SET
TTT0.jpg

GOLDEN Version LT tonearm
TTT2.jpg

TTT1.jpg

Heavy adjust tool

TTT3.jpg
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Old 22nd July 2012, 09:29 PM   #26
Nanook is offline Nanook  Canada
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Default EB: I see you have other tts...

...have you modified them too? What are they?

Glad you have found the source of the noise issues and changed the motor. I would still seriously consider rebuilding the original motor (most likely just dirty from dust even in an original sealed box). Then buy or fabricate some motor grommets. I might still suggest a very heavy top plate made from non-magnetic stainless (some stainless is magnetic, so if buying SS then best to get non-magnetic type) or good old steel plating.

I imagine that if speed stability is good right now you have listened to the combination. How much can you say about the level of enjoyment you experience?
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Old 23rd July 2012, 01:56 AM   #27
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Nanook,I have another 2 DD TTs,LUXMAN PD370 and MRANTZ 6170,I did not modify them because they can spin steadily.LUXMAN PD370 is with VDS system,but this function is invalid because the disk seal rube has aged,but its sound is good with original heavy platter.

Yes!I also think heavy top plate can damp more vibration,I will try it.Maybe stone plate is another choice.

I played different condition vinyls including some with scratch, luckily,the cartridge can move form beginning to end smoothly on every records.The sound is good as using PD370,maybe better? You know,as a DIY lover,we normally enjoyed the whole DIY process more than the result,is it right?
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Old 23rd July 2012, 02:11 AM   #28
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Default DIY PLL speed controller for DC motor?

I will try further modification on speed control,the sensor is as following picture,it can generate 180 pluses every turn.Nanook,do you have any ideas on this?

TTT4.jpg
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Old 23rd July 2012, 07:04 AM   #29
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A short piece playing video of “Tea For Two”,the audio is lack of bass because I record the video by DC

http://www.flickr.com/photos/45199188@N03/7627131070/

Last edited by eaglebear; 23rd July 2012 at 07:17 AM.
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Old 25th July 2012, 12:58 AM   #30
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I recorded a piece of music named “Blue Tango” by this combination and converted it to mp3 format,here is this music flash playing address:
http://player.56.com/deux26_117522164.swf
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