0

I have a DFPlayer and I want to connect the output of this device to an audio station (which has a jack stereo input - aka aux).

It is unclear for me what the difference is between DAC_R, DAC_L and SPK1, SPK2. From the research I did, both of them are analog signals. SPK is bigger.

Is DAC_R a signal from 0 to +Vcc, and DAC_L a signal from 0 to Vcc, whereas SPK1 and SPK2 are only working together as there is no GND?

I tried to connect DAC_R and GND as an input in station, and I also tried to connect SPK1 and GND and seems like it's working but I have no idea if it is good or no.

The plan is to send this signal via a long cable so I was searching for the proper output so that I can amplify it with a TPA3118 amplifier.

enter image description here

ocrdu
  • 8,705
  • 21
  • 30
  • 42
Cătălina Sîrbu
  • 127
  • 6
  • 1
    But you said in your previous question which signals you intend to use, they were correct, and then you did not use those signals. Why? – Justme Nov 10 '22 at 22:38
  • I think the question is clear enough: what is the difference between the two outputs, and how is GND related to both. I want to proper understand how this device works, because I have some problems which I'm trying to solve. – Cătălina Sîrbu Nov 11 '22 at 07:02
  • Maybe you should ask about those problems instead? They may be unrelated to how this module works. – Justme Nov 11 '22 at 10:00

1 Answers1

2

The DFPlayer data sheet table 2.2 and application circuits section describes the pins.

DAC_L and DAC_R are the ground-referenced outputs to earphones or amplifier from the decoder chip. These are used to connect stereo audio via 3.5mm TRS or RCA connectors. Typical modules should have these AC coupled. Some modules have a bias resistor to ground, some don't, and rely on the next device to bias it suitaly, which usually is ground. They are also summed to mono for the separate speaker output amplifier chip.

SPK1 and SPK2 are outputs from the separate amplifer chip to drive a speaker directly. SPK1 is the speaker positive and SPK2 is the speaker negative. The typical amplifier used on these modules is a 8002 which has a bridged output, so neither pin is ground. When no sound is playing, both pins will have the same voltage in reference to ground, which is chip supply voltage divded by 2.

You can simply measure with a multimeter what are the idle voltages on DAC pins to know how your specific module works. If it does not idle at 0V, it might be best to externally connect resistors to ground, and if the DAC pins still do not idle at 0V, you need separate AC coupling capacitors before the 0V bias resistors.

Justme
  • 127,425
  • 3
  • 97
  • 261
  • Thanks for the fast reply. " If it does not idle at 0V, it might be best to externally connect resistors to ground, and if the DAC pins still do not idle at 0V, you need separate AC coupling capacitors before the 0V bias resistors." I am aware I don't know exactly how to do this. Could you please provide a little schematic? – Cătălina Sîrbu Nov 11 '22 at 11:39
  • Why is it able to go like SPK1 with GND on left channel input of station and SPK2 with GND on right channel of station, and still hear music? (expecting SPK2 for example as is the inverted signal to hear bad or not at all) – Cătălina Sîrbu Nov 11 '22 at 11:40
  • That is because SPK1 contains a non-inverted mono sum with half-supply DC bias with respect to ground, and SPK2 contains an inverted mono sum with half-supply DC bias with respect to ground. So you will hear it, as both are mono signals, but the one will be phase inverted from the other. You can likely hear the effect, but unless you know how to interpret what you hear, you likely would not know what the problem is. Fortunately the AUX input removes the DC offset so that generally is not a problem, but you are not supposed to drive speaker level signals into AUX anyway. – Justme Nov 11 '22 at 14:28