Impedence 101 ?

I

imecho40

New member
I encountered a problem that I dont quite understand.I read,and searched for info about impedence mismatching,but quite honestly dont know enough to really understand what is happening. I can take my sons portable jam box,and connect from the headphone jack to the line in on the sound card and burn him a cd. the quality is not outstanding,but he seemed pleased with it. I tried to do the same for my wife with some old lp's,and the results were awful.
The stereo system used is a Soundesign circa 1985. It has a receiver/tape deck/equalizer unit with an external turntable mounted in another compartment.
From my reading here,I think I might have some type of impedence mismatch. Though,I dont understand why the jambox worked,and the stereo system didnt. Would one of those in-line transformers do the trick?. any thoughts would be greatly appreciated....Thanks......:)
 
More data needed. What output did you use on the combo stereo and what exactly do you mean by 'awful'?

There are really only 3 basic impedance levels to worry about.
Line level (high)
Instrument level (med)
Mic level (low)

That is a gross simplification but it will work for matching up most gear's in/outs. You may be using the mic input on the sound card or a powered out on the stereo.

For best results use a Line Out or sometimes called a Tape/Record Out and connect that to a Line In. Headphone jacks can work but there is an extra amplifier in the circuit so the sound is not all that clean.
 
The sound had some bits of audio in it,but for the most part it sounded like static,distortion,interference,etc.Basically like something was connected where it should not have been.The stereo output that I used was the headphone jack. I did not try the speaker out connection as I will have to get some additional adapters.BTW,the sound coming from the headphones is pretty good if I can just clean it up...........Thanks
 
Well:

- Don't use the speaker output. It's way too hot, and could actually blow an input that's expecting a line-level signal.

- Yeah, there would be an impedance mismatch between a headphone out and a line in. Headphones have an impedance of something in the 50-300 ohm range, or even lower. Line ins have an impedance in the thousands of ohms. The heaphone voltage level and and line level are in the same range, though. How an output responds when you run it with the headphone load removed and a high-impedance line input in its place seems to depend on the characteristics of the headphone amp.

- That said, I can't say I quite understand why it would matter what the signal source is. I would have thought the headphone output from a receiver should have more-or-less the same characteristics, whether the signal started out from a tape deck, or a radio, or a turntable, or a CD player.

- The immediate signal from a vinyl turntable is quite different from the output from a tape deck. That's why you have to connect a turntable to a phone preamp. But any receiver that has an input marked "phono" has a phono preamp.
 
Ah. I just re-read the original post. I hadn't realized that you were looking at the headphone out from two different devices: Device A (a jam box) and Device B (a stereo receiver).

It's possible the headphone out from Device B just won't work unless it's running into a headphone load.

See if you can find a line out from the stereo receiver. If you've got jacks that are supposed to go out to a tape deck, those should be good.

If there's no line out, try experimenting with the level, if you haven't already: start with the headphone volume turned way down and turn it up gradually to see if there's a level where it works. If not, I would probably just forget about trying to use the headphone out from the stereo receiver. Get something else to play the turntable through: either an old stereo receiver or a standalone phono preamp.
 
Thanks for the response.Sometimes it can be difficult to understand what it is someone is trying to say.Yes, the stumbling block was two different headphone jacks,one for each device.you referenced an old stereo ,or a stand alone phono. How old is an old stereo?......lol
 
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