On another forum I came across mods for a Michell Gyro/Orbe turntable, replacing the stainless steel ball bearing by ceramic, plastic, changing the suspension turrets to use rubber o-rings (like on SME turntables) and mods for the motor etc.
What got me thinking is changing the power supply for the motor, which I believe is a Papst 24v? motor. My power supply is perspex box with 2 transformers but it should be possible to build a quiet DC supply, amplifier and a PIC to play a digitised sinewave. A second sinewave albeit at a higher frequency could be used for 45 rpm so no need to move the belts on to the larger spindle.
I sure something like this has been done, the part I'm lacking is what voltage is required by the motor, (I don't understand why my power supply has 2 transformers). Hopefully someone can point me in the right direction.
What got me thinking is changing the power supply for the motor, which I believe is a Papst 24v? motor. My power supply is perspex box with 2 transformers but it should be possible to build a quiet DC supply, amplifier and a PIC to play a digitised sinewave. A second sinewave albeit at a higher frequency could be used for 45 rpm so no need to move the belts on to the larger spindle.
I sure something like this has been done, the part I'm lacking is what voltage is required by the motor, (I don't understand why my power supply has 2 transformers). Hopefully someone can point me in the right direction.
Can you take any photos? Early Papst motors are 3 phase devices, often driven by a single phase supply and a 'faking' capacitor.
I've not seen a 2 phase Papst motor, but many Premotec, airpax, and phillips motors are 2 phase designs.
There are two designs well known on this site that will produce the requisite frequencies:-
https://www.diyaudio.com/community/...e-generator-for-turntable-motor-drive.298018/
and
https://www.diyaudio.com/community/...generator-for-synchronous-motor-drive.365849/
Give us a bit more info and I'm sure lots of useful info will be forthcoming 🙂
In order to avoid any conflict of interests I am the UK and ROW distributor for the SG4 chip and pcb.
Good Luck
I've not seen a 2 phase Papst motor, but many Premotec, airpax, and phillips motors are 2 phase designs.
There are two designs well known on this site that will produce the requisite frequencies:-
https://www.diyaudio.com/community/...e-generator-for-turntable-motor-drive.298018/
and
https://www.diyaudio.com/community/...generator-for-synchronous-motor-drive.365849/
Give us a bit more info and I'm sure lots of useful info will be forthcoming 🙂
In order to avoid any conflict of interests I am the UK and ROW distributor for the SG4 chip and pcb.
Good Luck
I have identified the power supply as a Gyro power.
From what I gather, it is a more sophisticated version of the a phase shifted supply like this (dunno if you call that 2 or 3 phase, I'd call it 2 phase)
Yes indeed I found your post, but the challenge is to DIY, the simplest of PICs with DAC would do it, a pi pico is on overkill for what I would like to have.
From what I gather, it is a more sophisticated version of the a phase shifted supply like this (dunno if you call that 2 or 3 phase, I'd call it 2 phase)
Yes indeed I found your post, but the challenge is to DIY, the simplest of PICs with DAC would do it, a pi pico is on overkill for what I would like to have.
Hi 02, I think you have solved my problem. Many years ago I inherited a Michell turntable but my late uncle had done some "work" on it, resulting in bare wires emerging from the motor, and a missing motor power supply. He was a CPO radio operator in Australian ships in WWII and the wiring in those vessels might have been very rudimentary. Apparently so was his way of tackling a hum problem (my guess). Now I need to get the turntable motor going. It is labelled as follows:
PAPST MOTOREN KG
901 3520 001
HSZ 20.35-4-232 EeM-B112
24V 50Hz 22uF 6. -85
I hope your circuit above will do the job for me. I will build that and see how it performs. I have a couple of 22uF 100V capacitors intended for loudspeaker crossovers and one of those should be suitable. But could you please tell me what is the purpose of the PTC thermistor, and is it strictly necessary. Should it be in thermal contact (or proximity) with the motor? This turntable has a green push-on push-off switch on the motor mounting plate which I presume should be wired in series with the thermistor. Thanks in anticipation.
PAPST MOTOREN KG
901 3520 001
HSZ 20.35-4-232 EeM-B112
24V 50Hz 22uF 6. -85
I hope your circuit above will do the job for me. I will build that and see how it performs. I have a couple of 22uF 100V capacitors intended for loudspeaker crossovers and one of those should be suitable. But could you please tell me what is the purpose of the PTC thermistor, and is it strictly necessary. Should it be in thermal contact (or proximity) with the motor? This turntable has a green push-on push-off switch on the motor mounting plate which I presume should be wired in series with the thermistor. Thanks in anticipation.
Michell also offers a more sophisticated psu for the (ac) Pabst motors, namely the gyropower qc. I haven’t yet come across a diy alternative but would be quite keen as the michell unit is rare and expensive.
Yes, the PTC can only be for over-current protection. But if the transformer is well chosen it should limit the current available. If the PTC is there to control switch-on surge it will take a second or two to heat up from cold by which time the motor will be up to speed and the surge will be a thing of the past. Or perhaps these motors have a habit of pulling somewhat excessive current due to insulation degradation in the windings without it being obvious and therefore the PTC is a precaution against things getting hot and smoky. Or it might be intended to produce a gentle acceleration of the motor at switch-on although the inertia of the motor mass should do that. I will build a temporary PSU in accordance with 02GF74's circuit and measure the current drawn by the motor, and that will allow selection of the appropriate PTC value. PTC thermistors are not commonly available and choice is limited.
When a asynchronous motor is not running, for example because of a missing, open or shorted phase shifting capacitor or a mechanical block the motor current increases six to tenfold. After a short time the motor windings get damaged due to this high temperature. A PTC is a good measure to limit the current. Both mechanical blockage or capacitor problems is something which is not unimaginable.
However, if the PTC is getting warm during normal use the engineers decided to limit the current during normal operation. The speed of this motor type is controlled by the frequency and much less by voltage. During start-up the motor might produce extra torque due to the higher voltage. Which is then reduced one the motor is running.
The latter option seems bad design practice to me. There is slip between the mains frequency and the rotor speed and the slip does increase with reduced voltage.
However, if the PTC is getting warm during normal use the engineers decided to limit the current during normal operation. The speed of this motor type is controlled by the frequency and much less by voltage. During start-up the motor might produce extra torque due to the higher voltage. Which is then reduced one the motor is running.
The latter option seems bad design practice to me. There is slip between the mains frequency and the rotor speed and the slip does increase with reduced voltage.
Today I had to drive to an electronics shop on the other side of the city to buy a 230V to 24V adapter (transformer enclosed in a housing) with secondary current of 1.87A (I am guessing the current requirement of the motor). And two PTC "fuses" rated at 1.85A hold current and 3.7A trip current. The PTCs are intended for loudspeaker protection but likely to be the type of PTC that 02GF74 had in mind when he sketched his circuit. I will use one in the 24V AC line to the motor and back it up with a conventional 2A fuse connected in series. I might need to change the PTC device to one of higher current rating after I get some meter readings on the bench. I will come back with the results of my endeavours.
I connected the motor and associated parts in accordance with 02GF74's circuit. The motor sprang into life, rotating silently and apparently very happily at maybe 1500 RPM although it might be 3000. I don't have a method of measuring the speed of rotation. Using that circuit and my new over-adequate transformer the AC applied to the motor was around 26.5 volts with a current consumption of 350mA. I placed a 5 ohm 5W resistor in series with the green wire and that brought the voltage down to 24.3V and the current to 300mA. I am very happy with that. Nothing is getting hot or showing any sign of distress after the motor has been running on the bench for 30 minutes. The 5 ohm resistor has warmed up to about 45 degrees C but I can hold it between my fingers without discomfort so it's not going to melt anything. 02GF74's circuit suggests a current consumption of less than 400mA so I can cautiously conclude that all is as it should be. I will trot off to the local electronics shop and buy a different PTC device to suit the 300mA current draw and add a conventional fuse of perhaps 750mA in series with the 24V line as an added precaution. Next steps are to mount the motor and other bits properly into the turntable (keeping the transformer as far away as I can - it has long leads) and to get the strobe LED operating although the latter is not absolutely necessary. Thanks to 02GF74 and to other contributors who have shown interest and willingness to assist.