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I have an LG-V30 cellphone, which has an integrated headphone amp with two modes for audio reproduction depending on the headphones you plug in.

  • Normal mode for headphones under 50 ohm, low output, amp disabled.
  • High impedance mode for headphones over 50 ohm, high output, amp enabled.

I'm using Takstar 82 Pro headphones which according to the specs are 32 ohm (plus-minus 15%).

These headphones have a detachable cable, and I have two different cables, a short cable (1m) and a long cable (2m). When I plug the headphones with the short cable, the cellphone detects them as under 50 ohm, but when I use the long cable they're detected as over 50 ohm and the amp gets enabled, resulting in higher sound level and just better sound overall.

I have measured the apparent resistance of the cable by measuring the ohm between the tips.

  • Short cable: 0.4ohm
  • Long cable: 1.5ohm

Questions:

  1. Is it possible that the higher resistance of the longer cable is somehow fooling the phone into thinking the headphones are of higher impedance?
  2. Can I somehow add in-line resistors to the short cable to simulate the resistance of the longer cable, so I can use the headphones in high-impedance mode with the short cable?
  3. If so, which values would those resistors be?
  4. Will this mess up audio quality the way inline capacitors would?

Notes:

  • I am aware there are other headphones with higher impedance, but I want to use these specific model.
  • The behavior of the cellphone cannot be changed by the user.
  • My knowledge in electronics is somewhat basic, so be gentle :)
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  • \$\begingroup\$ Welcome to EE.SE. I think you can get what you want, but you need at least basic soldering skills. If you can solder in resistors of a specific value and wrap it up with electrical tape then we can help you. \$\endgroup\$
    – user105652
    Sep 1, 2018 at 22:35
  • \$\begingroup\$ Yes. I have a soldering pencil, flux, heat shrink tubes and basic understanding of how these things work. If you can help me with a crude diagram and resistor values I can build it. \$\endgroup\$
    – Joseph Sabido
    Sep 1, 2018 at 22:57

2 Answers 2

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You can try putting two 2.2 ohms resistors in series with the left-audio the right-audio connections - likely it will do the trick for you and should be pretty simple to do.

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  • \$\begingroup\$ Thanks. In which case do you use inline resistors vs resistors to ground? For example, in this headphone attenuator there are both. Why? diyaudioheaven.wordpress.com/headphones/… \$\endgroup\$
    – Joseph Sabido
    Sep 3, 2018 at 17:10
  • \$\begingroup\$ Some audiophiles will fuzz over matching impedances and such. In your case, you found that the longer cable has just enough extra resistance to trick the phone. Adding that as two discrete resistors can likely do the job for the short cable. \$\endgroup\$
    – Rolf Ostergaard
    Sep 4, 2018 at 5:59
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I figured out that double bouncing the headphone plug as you plug them in can trigger the higher output on my V30+

Slowly insert the plug until it's almost ready to snap in, as soon as the phone detects the headphones, let off a little and then push it all the way in... Works better than 50% of the time.

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