I love Behringer’s approach to tech and synths. The TD-3 is super affordable and performs like a charm. The community has quickly started modding the TB303 clone and I also decided to give it a simple mod: if there is something I don’t like, its cables! Also why use a 9V power wart, when there’s USB power.
I wanted to experiment with 18650 lithium ion battery cells that I will use in other contexts. The Sony 18650 VTC6 batteries that I am using deliver 3.7V on average and around 3000mAh. I would need charging electronics and then somehow try to make them deliver the 9V that the TD-3 expects.
My requirements were:
- all components are located in the TD-3
- battery is charged using USB or 9V while powering the device (USB preferred)
- when unplugged, deliver 9V for the device
- seamless plugging and unplugging (like a mobile phone)
- enough power for a day
After some research I found the TP4056 USB charging module and MT3608 step-up converter that seem to work almost perfectly. I am picking up USB Bus (5V) and deliver the 9V at the wart connector.
Here are some pics:
- It seems that the protection circuit of the TP4056 fires when switching on the TD-3. My tests with the KORG monologue do not show that power surge. The quick fix was to short-circuit BAT- and OUT- on the TP module, since the MT3608 includes a protection module anyway. But I would like to solve this before calling it a day.
- I am using the TP4056 OUT+/- as power delivery to the MT3608 even during charging. It works, but I suppose a better way would be to take the USB Vbus and OR it with the battery out using two Schottky diodes, or even better ideal diodes (like SM74611 with a super low loss).
- The 9V in connector needs to be desoldered (I am not using it anymore, but it would lead to problems if anyone connects the wart…).
- MT3608 draws power constantly (300µA) from the battery, even when the device is off. However, it should take a year to drain the battery before the undervolt protection circuit kicks in.
- I need to test USB power draw. It worked with all chargers that I tested and my iMac.
A nice coincidence: The charging LED is bleeding softly through the function LED of the TD-3 (exaggerated in the pic), so that I can see when charging is finished (red charging/ blue fully charge):
Parts cost is less than 10$ / 10€. I found on the following offerings on amazon.de:
WARNING: This is a prototype that I built for my own testing purposes and is not finished yet. Whatever you do to your device: It is your own responsibility. Batteries are dangerous, if not handled properly!
It would be nice if Behringer offered a battery add-on (granted, not everybody needs lithium in their devices). @gekart