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PX-560 headphone jack - output impedance


swistak

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Hi,

This might me useful for people interested in the technical side of digital pianos or headphones.

I measured the output impedance of the headphone out in my PX-560. It's about 4 ohms. I think it's a good or even very good result considering it's not a product specialized in driving headphones.

If you wonder what it is about, you can check the following links. It appears that the general consensus is that lower output impedance is better and you want it to be at least 8 times lower than the impedance of the headphones. However, some people seem to prefer how their headphones sound with high output impedance. If that is the case, I believe adding impedance is far easier than removing it.

http://nwavguy.blogspot.de/2011/02/headphone-amp-impedance.html
http://www.innerfidelity.com/search/node/output%20impedance

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  • 3 weeks later...

Turning the speakers off doesn't change anything in the measurements.

 

I have one more data point. The maximal output voltage on open circuit is about 1.18 Vrms. It's not extremely much, but not bad either. It should be enough to drive headphones with low impedance and reasonable sensitivity. There's another article from nwavguy that I can recommend: http://nwavguy.blogspot.de/2011/09/more-power.html

Max voltage + output impedance combined with relevant headphone specs and one of the formulas from the article gives you enough information to calculate the peak SPL.

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  • 2 years later...

Just noticed this topic, after trying to do some research. The PX560 specifies the output impedance as 200 ohms, I'm wondering how you came up with such a low measurement for the PX160 but now you've got me thinking-most headphone outputs on keyboards are not that low-4 ohms is more of a speaker measurement, and is even low for that, most pro speakers are 8, even 16. So I tried a whole bunch of my headphones in my PX560-should sound similar to the PX160, same sound engine. I have tested, so far, my AKG K52s, a cheap set of closed-back Maxells designed for Walkman and other consumer stereo mp3 players etc, and a set of cheap earb uds that came with one of my cheap Chinese tablet computers. Guess which one had the best response-more high end, good soundfield etc. The cheap Chinese earbuds! This leads me to believe that as low as the impedance for the stereo headphones is, it will actually sound better with cheaper earbuds, and I'm not sure  why. Impedance is not resistance-and cannot be measured with a simple multimeter as it is a reactance measurement must be done under a resistive load. See:

 

http://www.zen22142.zen.co.uk/Theory/inzoz.htm

 

And as I am posting some info elsewhere to someone who is not getting good fidelity from his PX160 headphone jack, I am now checking out all my phones on all 3 PX's, I will post results.

 

 

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Assuming the manual's spec of 200 ohm impedance here were my results-all with AKG headphones with the PX560...

 

AKG 240M-old version made in Germany, 600 ohms-very clear sound but 600 ohms requires a headphone amp with the PX560-had to crank volume all the way and was still pretty hard to hear.

AKG K301-older large diaphragm studio monitors rated at 120 ohms-much better results-very neutral sound but plenty efficient-only had to turn volume up about halfway to get fairly loud monitoring. frequency response-piano was very clear, good high end and slightly rolled-off bass (these are monitors) but still very realistic sound.

AKG K300-pretty much same results as K301, same impedance, same clear soundfiled and good frequency response.

AKG K52-rated 32 ohms. Very efficient, louder volume at lower volume setting than preceding, but not as good a frequency response overall. Definitely not as good in the high end.

So my quick results seem to indicate-the closer you are to the impedance of 200 Ohms, of course depending on the quality of your phones-the manual must be correct, you will better be able to duplicate the piano sound the Casio was designed for.  I don't know what the typical impedance is for cheap or even high-end earbuds are off the top of my head, but I have had OK results with both, certainly nowhere near as good as the big AKG cans.

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Double-checked the PX160-apparently you are right swistak, the reason I hesitated-I have never seen any electronic equipment with this low an impedance. MY PX350 is 170 ohms, my PX575 is 200 and my PX560 is also rated 200 and judged on some fresh listening comparisons with 4 different AKG cans, this seems accurate without actually measuring anything, just listening tests.

 

My next question then, is this. How is it possible to get any kind of good sound out of the PX160 headphone jacks? The lowest impedance headsets I've seen are earbuds, and these are usually at least 16 ohms, with a few spec'ing slightly lower.  I would guess, without having the PX160 to test, the audio results with any typical headphone would be pretty awful-I can't imagine the high end response could be there at all, unless you use audiophile earbuds but I may be wrong.  Is it an error in manufacture? I recently replaced the headphone jackboard on my PX560, it is the same part as the PX160, and it works well with 4 different AKG cans and several other lower-end headsets, but all of my phones are rated around 120 ohms, some a little lower and the AKG240 is the older 600 ohm version, even that works but no volume.  Obviously there is something in the circuit design giving this 3-4 ohm spec. I would be very interested to know about this if anyone else can weigh in here, as I have just posted to another recent PX160 owner who is getting bad results through the headphones and have been trying to help discover why this is so. Very important for those of us who must play through headphones and have invested in getting that wonderful Casio AIR piano sound, and it is, with the right cans!

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Another puzzler-checking my manuals for the CDP-230 and 235, the headphone impedance spec is yes, 3 ohms. So again, I have to wonder-this is such an extremely low impedance based on many of musical instruments-I would think this means that this is an extremely efficient headphone output, capable of driving even the lowest impedance earbuds but will this have an audio effect with typical cans rated at anywhere from 32 to 120 or so?  I would definitely be interested to know from a design point of view, as I've never seen any keyboard rated this low for the headphones, but then many of my modules, recorders and keys don't even give that spec, I've checked at least 6 different manuals.

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Wild guess: an LM386N could be used as headphone amplifier. It's designed to drive 4 ohm speakers. 

If they have used this 1970 IC to drive the headphone outputs, it's possible that the output impedance is low. Without a schematic is of course a wild guess, but given the fact that these IC are really cheap and rugged, I'm not surprised that they have used them.

 

 

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Since the headphone jack also acts as a switch for the speakers-could it be the headphone jack is running off the same circuit as the speakers? This would be closer to a typical speaker impedance. This would certainly be cheaper to manufacture rather than a separate circuit with 2 different impedances, but not by much. But then, I would be surprised this works with phones at all since it might be equivalent to hooking your headphones directly to a speaker connection, not a good idea....and after spending quite a bit of time going over websites and my and my electronics manuals it is possible provided very little power is needed to drive the speakers. As the CDPs are rated higher than milliwatts needed for phones, I think 4 watts per speaker side, this is still a puzzler. I wouldn't care but as i said earlier, I am trying to help another Privia owner who is not getting good fidelity from his phones, and the low impedance of the CDP might be the reason why. I wish Mike Martin would weigh in, but I don't want to PM him if another user can shed some light on this.

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I give up. Apparently as low to zero ohms is the new normal, based upon the preponderance of people trying to plug in higher impedance headphones into their ipods and wondering why it doesn't work. Guess Casio is going along with that ipod standard. But then, look at the PX manuals-those specify 170,  200 ohms output impedance. to repeat, I give up!

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