[Ptrick]

Hi there,

I would like some technical expertise to help me clear up something:

I have used the line-out of my PCDP's directly to drive my headphones (HD580s and SR60s), but was recently advised by another head-fier that this could be possibly damaging to both my headphones and the player itself, since line-outs are not designed to drive headphones and speakers as they look for much higher impendance loads (1000 ohms?). Therefore by running headphones directly out of the line-out, it could be overdriving them or something?

Sorry if I'm not technical in explaining this, since I don't know much about electronics, but could someone verify or add something to this?

Much appreciated!

Cheers,
P

 

[CaptBubba]

I don't think you could damage your headphones or the pcdp by doing so, but I do know that you are not getting the best sound you possibly could out of the pcdp because of the imperdence mismatch between the headphones and the line out.

Both the line out and your headphones are designed to work best when paired with certain impedence inputs/outputs. This means that the designers expected that the line out would be plugged into a line-in with a high input impedence (10-100k) and therefor designed it so that it would be at its optimum outputting into such a load. The HD580 are designed to be driven by a source with 0ohm output inpedence. Does any of this mean that you are damaging something? Highly doubtful, but it probably does mean you are not getting the sound the designers had in mind.

To give you an example, my ns-500v player worked just fine when my CHA47 had an input impedence of 4kohms. But after I raised it to 50kohms I noticed a big change in the sound, it was much clearer.

The SR60 is another story. I highly doubt that the line out can give anywhere near the amount of current that those need to function well.

Anyway, I would highly suggest you get an amp, even if it is a cmoy or a CHA47. The HD580 sound much better with an amp and allthough I have never personally heard grados I bet an amp would enhance that "grado sound" that everyone keeps talking about. Plus it would put your mind at ease about the impedence mismatch.

 

[Ptrick]

CaptBubba,

Thanks for the info! That clears things up so much. What you've noted about the Grados is certainly true, since the lineout I've used (Sony D-25s PCDP) makes the SR60s sound much softer in comparison to the HD580s.

But this leads to another (newbie) question... the impendance of the SR60's is rated at 32ohms, whereas for the HD580s it's 300ohms. Shouldn't this mean that a source requiring a higher impendance load would drive the lower impendance rated units better, ie. volume output is higher?

 

[CaptBubba]

Quote:

Originally posted by Ptrick But this leads to another (newbie) question... the impendance of the SR60's is rated at 32ohms, whereas for the HD580s it's 300ohms. Shouldn't this mean that a source requiring a higher impendance load would drive the lower impendance rated units better, ie. volume output is higher?

Generally the maximum amount of power is transferred when the impedences match.


A more detailed explination is that the line output is current limited. The HD580s don't need much current for a given voltage, while the SR60s need much more. This means that the HD580s get more power than the SR60s do. If the line out was volatge limited instead of current limited then the SR60s would be much louder than the HD580s.

You can play around with the following formulas to get an idea of this: Voltage=current * impedence and Power= current * voltage. Basically fix either voltage or current to some arbitrary value and see which headphone gets more power. Yes, sensitivities come into play here as well but you can kinda ignore that for now.

 

[ppl]

The Operating Instructions on my Pannasonic SL-SW860 says the Line out is to be used with Equipment having an Input impedance above 10K ohms. If i plug my MDR-7506's into the line out i get a faint volume but the Sony's have a 63 Ohm Impedance.