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I have a simple audio setup I am trying to build that consists of an op-amp board (OEP30Wx2), 2 speakers (Dayton Audio ND65-8), a steady 16V power supply (this op-amp requires 16V to drive 8 Ohm speakers at 15W) and a simple aux cable.

First setup was successful, I got clear loud sound coming from my drivers. Then I decided to introduce a 50K potentiometer since I want to build the speaker system into a case with a volume knob (attached to said potentiometer.)

Here is where things got dicey. The sound was definitely not right, things like voices was completely gone and it almost sounds like when an aux cable is broken and one channel was dead. I connected the potentiometer in the following manner:

enter image description here

Here is picture of my actual connections:

enter image description here

The first pair or wires (bottom pair in picture) is a screened audio cable that goes to my aux cable (audio source) that I've stripped the ends of and isolated left, right and ground and soldered it on to the aux cable.

The second pair of wires (top pair in picture) goes from the potentiometer to the op-amp and its connected to INL (left channel input), INR (right channel input) and AGND (audio input ground.) Note that on both wire pairs going to the potentiometer, I took their ground cables to the far left connections (ground connections in the first diagram I showed.)

I'm unsure where I connected the potentiometer incorrectly, and the "Common Ground" connection confuses me - the first cable's ground goes to the potentiometer's bottom connection and the second cable's ground goes to the potentiometer's top connection. Is that right?

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    \$\begingroup\$ That's not an opamp. "Voices gone" suggests you have inverted one channel and then summed to mono (the classic way of making a karaoke mix). But without a proper schematic I haven't a clue how. But no your potentiometer wiring doesn't sound right ... why doesn't it follow the sketch? \$\endgroup\$
    – user16324
    Commented Jul 27, 2020 at 18:08
  • \$\begingroup\$ i think that you are confused by the fact that the control contains two electrically separate potentiometers which are mechanically linked \$\endgroup\$
    – jsotola
    Commented Jul 27, 2020 at 18:10
  • \$\begingroup\$ The grounds from the two cables should be connected together and to both cournter-clockwise terminals of the pot. \$\endgroup\$
    – Peter Bennett
    Commented Jul 27, 2020 at 18:10
  • \$\begingroup\$ The picture is not clear and neither is your explanation, but ground wires of both cables must be connected together, it seems like you have not connected grounds. \$\endgroup\$
    – Justme
    Commented Jul 27, 2020 at 18:13

1 Answer 1

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enter image description here

Figure 1. Close-up of wiring. There is no sign of a ground connection between the black wires at the rear.

If my analysis is correct then you have done this:

schematic

simulate this circuit – Schematic created using CircuitLab

Figure 2. A schematic of Figure 1.

Connect the two grounds together at the potentiometer.

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  • \$\begingroup\$ Your pots are B which is linear. A volume control must be A which is logarithmic. The datasheet for the amplifier IC shows that the maximum undistorted output with your 16V supply is only 3W into each 8 ohm speaker. Your tiny speakers are shriekers because they produce no bass.. \$\endgroup\$
    – Audioguru
    Commented Jul 27, 2020 at 22:37
  • \$\begingroup\$ @Audioguru: I think this should have been posted below the question rather than below my answer. \$\endgroup\$
    – Transistor
    Commented Jul 28, 2020 at 7:24
  • \$\begingroup\$ You are correct indeed! My grounds we're not bridged. Also, I wrongly assumed that the red wire coming off my aux in put cable was the right channel but it was the left, so I created a mono audio channel by accident. \$\endgroup\$
    – Marnus Steyn
    Commented Aug 1, 2020 at 8:07

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