Hey guys, I need a little help understanding how to go about doing this. I recently got a Yamaha MT50 Multitrack Cassette Recorder and learned that it plays cassettes at 9.5 cm/s which is twice the speed of regular cassettes (4.75 cm/s)
So at first I used a potentiometer to change the motor speed and I added a bypass switch. The issue there is that the voltage is too unstable and since the speed of the motor wavers, the cassettes are nearly unlistenable. So I thought that I could use an Arduino to do the job instead but I don’t entirely know what they are capable of so I wanted to ask if this is even possible:
This is it right now. You can see the mod in the top right.
I want the Arduino Nano to take the voltage coming into the motor and either step it down to a defined amount, or let it pass through unchanged depending on the position of a switch, also if it could light up an LED when the switch is on that would be great (that would go where the pot is). I’ve already got an SPDT On-On switch in the deck
I actually used an oscilloscope and found out that the motor is very stable, even when i added a capactior to improve stability further. It seems the the MT50 is just not meant to record at lower speeds. Maybe its the head, or a mechanical problem with this deck. Luckily regular recordings on it sound great.
I ran across a similar discussion on the subject of repair on the SONY WM D6C, I got the speed-governor circuitry well explained to me by Valentin @ Stereo2Go here. The Stereo2go forum has more discussions about speed and some suggestions for circuitry pop up from time to time.
Valentin writes:
"There are 3 basic types of motor governors:
the most simple and widespread is one that takes a feedback signal from measuring the current of the motor (higher current means higher load);
the second type is what SONY used in its first walkman (the TPS-L2): a motor that contains an FG coil that picks up the speed of the motor shaft directly: it’s a much more accurate feedback mechanism, but it’s the motor speed that is regulated, not the capstan speed;
the thrid type is the one used on DD (a more complex direct drive system is used in DAT, VCRs): there is an FG coil directly on the capstan to read the capstan speed and adjust the motor speed accordingly;"
I tried some modifications and without any form of speed-feedback (even #1, current sensing) the motor will slow down, but be wobbly.
The Arduino option is considered and discussed theoretically (again, Valentin):
“Arduino looks like an interesting option, but creating a digital feedback loop (suppose we read the FG signal with ADC<which is not a good idea as it’s slow> and output PWM to the motor) will add signficant delays in the system. It can be done, but you need a really fast processor to be able to do the “correction” in real time.”
