I'll try to set this up neatly;


  • [BAT] 3.7V Lithium Battery (freshly charged to 4.2V, capacity is almost 10Ah)
  • [AMP] LM386 Based 200 Gain Audio Amplifier (input is 5~12V, schematic)
  • [VUP] Voltage Boost Converter (amazon link, datasheet for a similar board)
  • [BLT] Bluetooth Audio Board Thing (input is 3.7V, sourced from some random cheap chinese earbuds, can't find the board or a schematic anywhere)

Colorful diagram thingy of setup:

Wiring Diagram As you can see, the battery is wired to the input terminals of the voltage booster [VUP], and also to the bluetooth board [BLT]'s power inputs. The voltage booster [VUP] is set to output 12V, and is wired to the amplifier [AMP]. The audio output of the bluetooth board [BLT] is wired to the audio inputs on the amplifier [AMP].

This results in an amplified audio signal on the unwired terminals on the amplifier [AMP].

The Problem:

When both [AMP] and [BLT] are on the same source –– [BAT] ––– the bluetooth board [BLT] gets really hot, has pairing problems, and/or powers on and off and restarts (I haven't yet gotten any audio playing at all through the full setup).

I've tested them in every other scenario where they aren't on the same battery, and they work PERFECTLY fine, even together.

Some modifications to the setup I've tried testing that work:

  • Take out [BLT] entirely, and just wire a 3.5mm jack to [AMP]'s audio inputs, and plug the jack into something. (no bluetooth, but amplified)
  • Take out [AMP] (and/or [VUP]) entirely, and connect test speakers to [BLT]'s audio output instead of [AMP]'s. (bluetooth, but not amplified)
  • Disconnect [VUP] and [AMP] from the 3.7V [BAT], and connect it to a separate spare 9V battery, so that the power sources of [BLT] and [AMP] are completely separate (bluetooth AND amplified, but it needs two batteries instead of one)


Do I have to somehow "split" the power coming from the battery into two distinct sources? How would I go about doing this?


  • \$\begingroup\$ Did you measure the voltage of the battery when the setup is as shown in the colorful diagram? Also could you please re-try the 3rd scenario, but additionally connect (-) terminals of the batteries as well? \$\endgroup\$ – Rohat Kılıç Nov 24 '17 at 5:34
  • \$\begingroup\$ What changes on BLT , Vcc? or DC output bias on Audio output from AMP input causing latchup? Or is Audio - an active output and not intended to be grounded. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Nov 24 '17 at 5:37
  • \$\begingroup\$ Can you unplug the boost converter from everything and use a multimeter to check which input and output terminals are connected to each other? I wonder if this could be an inverting buck-boost converter. Unfortunately the amazon link doesn't specify. \$\endgroup\$ – user253751 Nov 24 '17 at 6:51
  • \$\begingroup\$ @immibis here's a chart of the voltages of different terminals connected together (i.imgur.com/nty92XK.png). \$\endgroup\$ – Poootaatoooo Nov 24 '17 at 21:46
  • \$\begingroup\$ Well that rules out my theory, it looks like IN- and OUT- are connected, which is fine and shouldn't be a problem. \$\endgroup\$ – user253751 Nov 25 '17 at 0:45

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