I've got a couple DC brushless capstan motors from a couple VCRs.
One requires a + voltage on the control pin to vary the motor's speed.
The other pulls the control pin up to 9Vdc.
I'd like to build a speed control circuit.
The motor that requires the + voltage may be easy as I can maybe use the control circuit I used with a VCR video head motor.
The motor that pulls the control voltage high has a control range of 2.133Vdc at 0 RPM to 3.70Vdc at max RPM.
The circuit I used for one motor.
Now if the voltage on the control line won't affect this circuit, I suppose that I could build the exact same circuit to control the speed unless there's a better circuit that uses the tach frequency.
The only thing is that circuit depends on the amplitude of the tach signal changing and both motors keep the tach signal at the same amplitude. Plus that circuit uses a transformer I cannot get anymore.
I used a variable power supply on the control wire and that works good so that circuit may indeed work, however the amplitude of the tach signal varies slightly once per revolution.
One requires a + voltage on the control pin to vary the motor's speed.
The other pulls the control pin up to 9Vdc.
I'd like to build a speed control circuit.
The motor that requires the + voltage may be easy as I can maybe use the control circuit I used with a VCR video head motor.
The motor that pulls the control voltage high has a control range of 2.133Vdc at 0 RPM to 3.70Vdc at max RPM.
The circuit I used for one motor.
Now if the voltage on the control line won't affect this circuit, I suppose that I could build the exact same circuit to control the speed unless there's a better circuit that uses the tach frequency.
The only thing is that circuit depends on the amplitude of the tach signal changing and both motors keep the tach signal at the same amplitude. Plus that circuit uses a transformer I cannot get anymore.
I used a variable power supply on the control wire and that works good so that circuit may indeed work, however the amplitude of the tach signal varies slightly once per revolution.
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Might be interesting, I'm just doing that but scrapped complete drive circuit and using only motor:
https://www.diyaudio.com/community/...eded-with-motor-and-drive.412984/post-7795028
https://www.diyaudio.com/community/...eded-with-motor-and-drive.412984/post-7795028
Either that or I'd have to build a motor base to mount the motor on to keep it totally separate from the record changer.
I'd then build a bottom for it all to sit on to where I won't have to worry about the belt tension changing.
The belt would then go around the edge of the platter.
I'd then build a bottom for it all to sit on to where I won't have to worry about the belt tension changing.
The belt would then go around the edge of the platter.
I glanced at your topic earlier and what you're doing is nice.
I'll look at it more in depth later today.
I'll look at it more in depth later today.
I decided to try that circuit on one of the capstan motors.
While it does work the tach signal doesn't seem to vary in amplitude as much as it does with the video head motor so this circuit wouldn't work unless the control voltage would change more at the output of the OP-AMP. That said the circuit was designed for a higher tach signal amplitude than what the capstan motor puts out so it's likely that it would work better if I increased the tach signal.
That said the speed adjust pots do alter the speed of the motor.
That said there is a circuit being talked about on the forums that does provide a real stable drive frequency which can be fed to three amps to drive a motor and it doesn't require a tach signal to keep the speed constant. So that might be a better option given the capstan motors have a relatively high torque. Plus I wouldn't be limited to a driver chip that likely hasn't been made in years and that requires a PLL loop to keep the motor speed constant under varying loads.
One thing about it is if I were to use the capstan motor with my 45 player I can use an o-ring for a belt and since I used the brass replacement drive wheel that uses two o-rings, I can remove the o-ring that goes against the motor shaft and place the o-ring belt there which will go around the capstan motor pulley. I can then place the motor such that the belt provides the tension needed for the drive wheel to properly contact the platter and then remove the spring that applies the pressure and taping it inside the cabinet so that I don't misplace it.
While it does work the tach signal doesn't seem to vary in amplitude as much as it does with the video head motor so this circuit wouldn't work unless the control voltage would change more at the output of the OP-AMP. That said the circuit was designed for a higher tach signal amplitude than what the capstan motor puts out so it's likely that it would work better if I increased the tach signal.
That said the speed adjust pots do alter the speed of the motor.
That said there is a circuit being talked about on the forums that does provide a real stable drive frequency which can be fed to three amps to drive a motor and it doesn't require a tach signal to keep the speed constant. So that might be a better option given the capstan motors have a relatively high torque. Plus I wouldn't be limited to a driver chip that likely hasn't been made in years and that requires a PLL loop to keep the motor speed constant under varying loads.
One thing about it is if I were to use the capstan motor with my 45 player I can use an o-ring for a belt and since I used the brass replacement drive wheel that uses two o-rings, I can remove the o-ring that goes against the motor shaft and place the o-ring belt there which will go around the capstan motor pulley. I can then place the motor such that the belt provides the tension needed for the drive wheel to properly contact the platter and then remove the spring that applies the pressure and taping it inside the cabinet so that I don't misplace it.