Impedance Matching: Do Headphones == Microphones?

Factual Questions
1
      • In consumer-grade audio equipment, is it acceptable to use a double-ended line to run the headphone output of one player to the microphone jack of another recorder (as long as volume levels are at reasonable levels)? - DougC
2

That’s going to be the hard part. The headphone output is a much higher amplitude than the mic input wants to see. If there is a line-out on the player I would use it.

3

It depends on the equipment, but generally speaking that’s a bad idea. What Diver probably meant is that the voltage output of the headphone jack is much higher than a line level output. I forget the specifics, but yes, there are also impedance-matching problems. If you want to post what specifically you’re trying to do, maybe we can suggest other methods.

4
      • I want to record directly from some audio equipment that has no line-outs, only headphone jacks. Is there an adapter to allow this? - DougC
5

Here… add sizing ior splitting adapters as needed

6

I’ve recorded from a headphone jack before, and didn’t have any problems.

“Impedance mismatch” shouldn’t be an issue, since a low impedance source (headphone jack, which is probably a few ohms) is driving a moderately high impedance load (the line level input, which is probably around 10,000 ohms).

But you must be careful about voltage level. “Line level” is typically around 1 V, and a headphone jack can source more than that. So you’ll probably have to attenuate the headphone signal. There are three options:

  1. If there’s a dedicated volume control for the headphone jack, simply turn it down to a low setting.
  2. Purchase a patch cable with in-line adjustable attenuator. I know Radio Shack used to sell one. Not sure if it still does.
  3. Build your own adjustable attenuator using a potentiometer (one per channel).
7

Ditto. Though I was using AUX IN jacks on the record device rather than a MIC input. Would that make a difference?

8

Yeah, Crafter_Man, I realized I had my numbers backwards. DougC, just be careful with keeping the levels low, otherwise you may toast the input circuitry of the recording device. You may want to get an attenuator anyway, to give you a little more volume flexibility.

And KtK, Aux In is probably a line input, as opposed to a mic input, so you probably didn’t have to turn down the output signal as much. Should be OK. (Crafter_man?)

9

Right – an “AUX” input is most likely a line-level input.

There’s not much concern about blowing stuff up here… even if you directly connected the headphone output jack to the line level input, the worst that would happen is that it would sound like crap (lots of clipping & distortion). If you have an in-line attenuator or dedicated volume control, simply turn it down until it no longer clips/distorts.

10
      • Well, after getting really really bored I actually RTFM, and it turns out the thing has three different types of input, but only two input jacks: one is a mini mic jack, and the other is an optical-in/out, but also a regular line-in/out… It’s a Sony MZ-R700DPC minidisc recorder, by the by.
  • That particular Radio Shack line is mono only though, and I want a solution that supports stereo. I know it records stereo because I did the headphone/mic thing and could hear the separate channels upon playback. - DougC
11

I’ve used a headphone out from a cassette deck as a source before with no problems. I ran it through a mixer though before sending the signal to my computer. You don’t need a mixer. Just make sure, before plugging anything in, that the headphone level is all the way down, and that the recording level on the md is all the way down. bring everything up by increments until you get a good level. It’s probably better in the end to have the source signal as hot as you can stand rather than have the source low and the recording level on the md maxed.

12

It seems alot of people are confusing something.

Many recording devices have two different inputs for recording.

Mic input and Line level. They are NOT the same.

Line level usually expects from half a volt to maybe a couple of volts peak voltage levels.

Mic inputs expect voltages on the order of a millivolt or maybe less.

Hooking a line level out to a mic input is pretty much guaranteed not to work. Headphone out hooked to a mic input just might work if the volume level is set low enough (just barely off of zero).

Headphone out hooked to line level in should work pretty well somewhere around mid range volume for the headphones.

With an attenuator pad in the neighborhood of 500:1 or 1000:1 you could probably hook line level or headphone out to mic in without too much problems.

If you have a choice between mic in and line in, always use line in if you are not using a mic for the input source. The additional amplification of the signal by the mic input to get the signal up to a “line level” always adds “some” amount of noise.

Hope that makes sense.

13
      • Actually, the mic jack says “MIC JACK (plug-in power)”. What’s the “plug-in power” bit mean? - DougC
14

Plug in power is a feature used by many new recording devices. Quiet simply put, your recording device supplies a small amount of power to the microphone element. This allows your recording to be much more sensitive than a regular microphone. Technically this style of microphone is called an Electret Microphone.

I would not hook a headphone out or line out to this type of mic input. This is designed for Electret Mics only.

15

Scotth is right - don’t try to connect between a headphone output jack and a microphone input jack. Connect to a line-level input.

So the Radio Shack device is for mono only? You’ll have to buy two of them, then. Plus you’ll have to purchase a stereo male plug (to plug into the headphone jack). Cut-n-splice everything together, and you should have something that works…

16

If that’s the case just get a stereo mini plug (headphone out) to stereo mini plug connector (aux in) and go to town. Adjust the headphone output levels as needed for a clean recording.

6’ Shielded Cable

$3.99 Reg. Price Brand: RadioShack -
Cat.#: 42-2387 Model: 42-2387
This shielded cable can be used as an extension cord. Shielding preserves signal strength and guards against interference, or “hum” - 1/8" stereo phone plugs at each end - Length 6 feet