Recently, Teenage Engineering released the PO-80 Record Factory, which is a rebranding of the Japanese Gakken Record Maker kit. It is a really neat record player that can also cut custom records. One problem I had with it is that it only plays 33RPM and 45RPM, but we had a lot of 7″ 78s I wanted to play on it, so I fixed it.
Most cheap record players use the same 5-pin motor module which is a DC motor with a speed controller built in. This particular one uses the EG530SD-3F. By wiring 3 of the pins in different ways, it will automatically play at constant speeds of 33RPM, 45, RPM or 78RPM. The 33 and 45 are basically the two built-in speeds, which is what this kit uses. To add the functionality of 78RPM, you can add a resistor to the circuit.
There wasn’t a detailed datasheet explaining what’s inside the motor, but rather many listings for this motor had the following instructions.
Adjusting Method:
- When the changeover switch reaches 33, use a small flat-blade screwdriver to adjust the resistance of the L hole of the motor, and the normal disc is 33 revolutions per minute.
- When the changeover switch reaches 45, use a small flat-blade screwdriver to adjust the resistance of the H hole of the motor, and the normal disc is 45 revolutions per minute.
- When the transfer switch reaches 78, use a small flat-blade screwdriver to adjust the resistance on the PCBS board. The normal disc is 78 revolutions per minute.
Luckily I found someone online who had taken one apart and described the controller circuit. This, along with the “official documentation” to get in the resistance range was all that was needed to make the simple hack. The official info is as follows:
For this hack, I needed a way to add in the resistance for when I wanted to play 78s, but I had to be able to completely remove the resistance to use the 33 or 45 speeds. For this I just found a JST connector, but any female wire connector would work. I soldered the wires of the JST connector to the motor based on the link above. I made sure my wires were long enough to reach out the side the connector for the record cutter extended to.
For the resistor, the only info I could find online were several schematics showing the use of a 300Ω potentiometer so you can adjust it, however, I only had a 5k so I threw a 1kΩ in parallel with it to get me somewhat within the range. The actual resistance needed is around 160Ω but it is nice to have the knob for adjustment. I intentionally left the resistor leads long so I could use them to plug into the JST connector. Notice that for this, you only need one side and the center lead from the potentiometer.
The final result looks pretty clean. It’ll look cleaner when I throw some heatshrink on the potentiometer. Again, this is only used for playing 78s so when playing the other speeds I disconnect the potentiometer and store it in the box the record player came in. Check the video out below.
