Matching low impedance headphones to a high impedance source

Discussion in 'General Electronics Chat' started by jaco523, Jun 8, 2010.

  1. jaco523

    Thread Starter New Member

    Jun 8, 2010
    5
    0
    I apologize in advance for my inexperience. :)

    I've started working on a [hopefully] simple project.

    I want to safely connect low impedance stereo headphones (16ohms) to a high impedance intercom (500ohm).

    Mouser has a 500ohm primary / 16ohm secondary audio transformer:
    http://www.mouser.com/ProductDetail/Xicon/42TM026-RC/?qs=LQJGOuQCHKSqrkgpQIuPNg==

    I believe I would need one transformer for each of the stereo channels. Ultimately I'd also like to also add a stereo pot for volume.

    I've googled extensively, but haven't been able to find an example of a similar circuit.

    could anyone provide some ideas on how to best build this circuit?

    Thanks!
     
  2. ELECTRONERD

    Senior Member

    May 26, 2009
    1,146
    16
    How many audio channels do you have?
     
  3. jaco523

    Thread Starter New Member

    Jun 8, 2010
    5
    0
    it's stereo, so L and R.
     
  4. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    A transformer might pickup mains hum if a power transformer is nearby. Also the step-down transformer will reduce the level a lot.

    Instead, you need a little stereo power amplifier like a TDA2822M. Use a 10k stereo audio-taper volume control.
     
  5. jaco523

    Thread Starter New Member

    Jun 8, 2010
    5
    0
    thanks for the responses.

    assuming i wanted to try a passive solution (without the amplifier) first, how would i go about wiring everything?

    is it as simple as connecting the line from the intercom to one of the primary(500ohm) leads, grounding the other primary, and then connecting one of the secondary leads to the headphone jack and grounding the other?

    or do i need some additional components? (resistors, capacitors, etc.)

    thanks, and sorry if my questions seem novice.
     
  6. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    As simple as that.
    Did you try the headphones straight to the intercom? That could also work, but might as well destroy the output of the itercom, especially when set to high volume.
     
  7. jaco523

    Thread Starter New Member

    Jun 8, 2010
    5
    0
    damaging the intercom is my main fear.

    is there a way to test the impedance of the headphones and the circuit before trying it with the intercom?
     
  8. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    How do you know that the intercom can drive 500 ohms? Speakers are not 500 ohms.
     
  9. jaco523

    Thread Starter New Member

    Jun 8, 2010
    5
    0
    aviation headsets are typically between 300 and 600 ohms. the specs on the intercom show 150ohms as the minimum. and if i understand it correctly, you won't damage an amplifier by presenting a higher impedance load.

    i was estimating 500ohms because the 500ohm/16ohm audio transformer was the closest i could find at mouser...
     
Loading...