Thank you! I was just a bit worried, as I recently saw another thread here that said that measuring output impedance by hand can be inaccurate, and I'd rather be as accurate as possible.
I'd like to know how to measure output impedance on my (and friend's) devices, specifically for headphone gear, and the headphone output on various receivers. I think I have all of the tools that I would need, but if someone could give the down low on what I would need as far as equipment, and what tools I would need to measure the output impedance as accurately as possible, that would be amazing. Also, I assume that I would need to actually be playing something through the headphone out, so what would be the best sound to play?
"By measuring the output voltage with no load, and with a known load, you can calculate the output impedance. This online calculator makes it easy. The no load voltage is the "Input Voltage", R2 is the known load resistance (don't use headphones), the Output Voltage is the loaded voltage. Click Compute and R1 is the calculated output impedance. This can be done using a 60 hz sine wave file (Audacity can create such a file), a Digital Multi Meter (DMM), and a 15 – 33 ohm resistor. Most DMMs are only accurate around 60 hz. Play the 60 hz sine wave file and adjust the volume for about 0.5 volts. Then attach the resistor and note the new voltage. For example, 0.5 volts with no load, and 0.38 volts with a 33 ohm load gives an output impedance of about 10 ohms. The math is: Zout = (Rload * (Vnoload - Vload)) / Vload " - NwAvGuy@Arnold B. Krueger So Arny, you strike me as the kinda guy who has a 15 - 33 ohm resistor right on hand; might you please do us a big favor and measure your current Yamaha or Denon receiver's headphone output impedance? I know lots of people besides myself would be curious to know the results even though they would only be specific to that particular AVR. Thanks.
https://en.wikipedia.org/wiki/Output_impedanceThe accuracy will be limited only by how well you can measure the voltage and impedance, which with even a $25 multimeter should be very accurate. For best results, use a resistor, not a pair of headphones as the load.
Quote from: saratoga on 06 July, 2015, 12:03:41 PMhttps://en.wikipedia.org/wiki/Output_impedanceThe accuracy will be limited only by how well you can measure the voltage and impedance, which with even a $25 multimeter should be very accurate. For best results, use a resistor, not a pair of headphones as the load.I have an analog multimeter from the 70s, does that count?
I also have a really nice digital oscilloscope. I watched a youtube video where the guy in the video was using an oscilloscope, would that be more accurate than the multimeter, or should I stick with the one I have/buy a digital one at the hardware store?
Sure, cheating is fine, if your known resistor's value translates to a more specific headphone jack output impedance value you can then verbalize to me so I can start doing some numbers cruching on a specific value other than "it's bad". I can't do 1/8th rule calculations using the numerical value of "bad" now can I?
Thanks Arny, so as I understand it the 470 ohm resistors are wired in series from the positive terminals of the AVRs speaker outputs and you estimate the output impedance for the headphone jack to be around 470.1 ohms.Fixing this with an intermediate buffering amp like a Fiio connected to the headphone out to establish a nice low output impedance for one's headphones seems inelegant and like a visual eyesore to me. Have you ever explored building a simple, passive voltage divider network like this guy discusses on the lower half of the page underneath the simplistic method AVRs use which he first discusses, or have comments on it?
What about instead of attenuating the unneeded power into heat, using resistors or pads, we use an autoformer? There are expensive volume control companies which do it this way which I can't justify the cost of, but then again there are also less expensive ways to buy an autoformer meant for tapping the speaker outputs of an audio amp which are more affordable.
Transformers require careful engineering to avoid adding audible nonlinear distortion (particularly at low frequencies) and frequency response aberrations.