External Power Supply Issues


New member
Hello, I am trying to communicate with a DFMiniPlayer using a Teensy4.0. I am powering the teensy with a 7805 regulator. However, when powering with the external regulator I just get a high pitched noise coming out of the speaker, with no music. I am using pins 0 and 1 on the teensy4.0 with Serial1 to communicate with the DFMini.
However when i power the Teensy with the USB port it works fine. I've attached both my schematic and code. Any help is appreciated.

#include <DFRobotDFPlayerMini.h>

DFRobotDFPlayerMini player;

void setup() {
  pinMode(12, OUTPUT);
  digitalWrite(12, HIGH);

void loop() {

Well the schematic does not show the power supply arrangements or decoupling for one thing. Where does the +/-15V come from for instance?

I do note the TL072 trying to drive 470nF through 16 ohms - likely to oscillate, opamps can't drive heavy capacitive loads without a fair bit of resistance to isolate them from it, more like 100 ohms than 16.

Also the speaker arrangement is strange with the transistor on the other terminal to switch it.

A TL072 doesn't have the clout to power a 2W speaker fully of course, it will distort heavily if overloaded. What impedance is the speaker? What is the purpose of Q1?
Just to be sure: are we talking about this module?
Why not try to get the basic arrangement to work first as shown in the WIKI? (speakers connected directly to the module)
And as @MarkT stated, how does your circuitry look exactly when powered by the external 5V?

I should've originally specified the op-amps are a LM1458N chip, which is powered by a 7915 and 7815 regulator.
PaulS, yes it is that module. Yes, I had it working in the basic arrangement, powered by USB. The speaker is 8Ω 2W.
I have said the circuit works fine when the Teensy is powered by USB, separate from the regulator, I know.
I know the transistor is redundant because I could simply use the play and pause commands on the DFMiniPlayer, I am planning on removing it.
So the basic arrangement worked on USB, good.
Did you try to power the basic arrangement also by an external 5V using a 7805? If so, did that work? If not, how did you connect the external 5V exactly?