Behringer TD-3 Rechargable Battery Mod Prototype

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:

Schematic
TP4056, the version with protection circuit, micro USB port is unused
MT3608 with a multi-turn potentiometer to adjust Vout to 9V precisely. Turning the pot to the left multiple times will eventually show 9V on Vout.
Soldering finished
Cables fit nicely through the prepared holes
Finished battery module
Fitting room
Works like a charm: way more than ten hours of power while playing a song and powering the headphones

Issues:

  • 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

About Grischa Ekart

I am a DevOps consultant writing about Docker, Kubernetes, AWS, IT, strategy, management, mobility, business cases, apps, consumer electronics and MBA education. Talk to me on Twitter: @gekart.
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