An independent audio output for your computer


Walter W9KJO in writing to the list says,

” The yellow wire on the volume control does not have enough audio for my Signal Link to work with.  I have to reconnect to the 3.5mm Audio Out jack and turn the volume up about half way.  which is too loud for my headphones so I need to install a second 3.5mm for my Head Phones.  

“I would be much better if I could find a way to get enough audio separate from the actual audio out to the 3.5mm jack.”

Clark Martin, KK6ISP replies “You could use the second audio amp in U1.  The TDA2822 is a dual amplifier.”   He provides the following guide [with some additions from the editor for the sake of clarity].

Modifications to the µBITx to add a second audio channel for computer use 

  • Remove R75
  • Connect U1 pin 6 to VOL-H.  This will give you an auxiliary sound output that is independent of the volume control.
  • Connect the + terminal of a 470 µF, 16V electrolytic capacitor to U1 pin 3.
  • Connect the – terminal of the above cap to your auxiliary out mini jack.
  • Earth the auxillary out mini jack sleeve connection.
Additional Notes
  1. The 470 µF could very likely be much smaller, depending on the input impedance of your Signal Link.   Experiment, it won’t hurt.
  2. You may also want to add a resistor divider between the cap and jack to reduce the signal strength, depending on how much your Signal Link can tolerate.
  3. Considering the problem others are having with the TDA2822 you probably should add a resistor in series with the cap, unless you implement the resistor voltage divider, that will provide the same protection.
  4. Rather than use a voltage divider on the output of your second audio amp, you may want to incorporate a trimmer potentiometer between VOL -H and pin 6 of U1 similar to the primary volume control to set the auxillary audio output level.