The output is mono on both headphones and internal speaker, despite the new connector being stereo.


I only have a mono audio source, and the new socket has dedicated pins for the L/R channels + loads of other switches I'm not 100% confident about how to use.

How would I wire it so that even without that LM4875 with the sense pin I can do an automatic switchover between jack and speaker? The speaker is a very small 2W 8Ohm one.

The new audio jack

schematic of the jack socket

The original circuit I'm trying to replicate looks like this: original speaker and headphone circuit

  • \$\begingroup\$ Can you edit your question to explain whether or not you are using it as a mono output jack and switching a mono internal speaker? Also, if for headphones or input to an amplifier you would need to attenuate. Thanks. \$\endgroup\$
    – Transistor
    Commented Mar 2 at 19:28
  • \$\begingroup\$ Thanks @Transistor. I just updated the page. Aren't R20 and R11 used for attenuation? \$\endgroup\$
    – lupolucio
    Commented Mar 2 at 21:46

2 Answers 2


The new jack can be wired identically to old one.

Tip and ring are L and R audio. Detect 1 is tip switch. Sleeve is ground.

  • \$\begingroup\$ Brilliant. What I'm just missing now is how to wire the speaker. I won't be using the LM chip so I'm not sure the current configuration would be able to turn it off when headphones are plugged. \$\endgroup\$
    – lupolucio
    Commented Mar 2 at 22:00
  • \$\begingroup\$ @lupolucio It depends what chip you will be using instead. The LM4875 needs a signal for detecting headphones to drive either the speaker or the headphones correctly. If you want to use another chip, you need to show which chip it is or how anything is connected to it. \$\endgroup\$
    – Justme
    Commented Mar 2 at 22:22

If the headphones are truly mono and you want to directly connect things like it's 1965, then here is how we did this. I edited your own images:

schematic of amplifier, speaker, and headphone jack

None of the other connections are used. If you lied about the headphones, you can tie pin 3 and 7 together at the jack to send audio to both ears.

I looked for an illustration to best show how it works, and I found this right here on EESO:

action shot of headphone plug interrupting speaker circuit

That fancy new jack reflects a few decades' improvements...

  • Stereo (added circuit on pin 3)
  • Integrated microphone (added circuit on pin 2)
  • Chips with sensing line (repurposed switch on pin 6)
  • Operating systems that believe they know how to redirect the audio better than we do (additional switch on pins 4 and 5) This switch also opens when a plug is inserted.

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