There is no such thing as RMS Watts. Power rating is average, not RMS. Only volts and amps are RMS. And that is not an X on the scope probe. It is a multiply symbol. It is one times, not one ex.
Even some o-scopes that calculate the voltage for you, don't give it to you in RMS voltage and those that do may not give it as the default. You have to go into the menu to select RMS, or do the calculation from peak to RMS, for example.
Mean power - there's no such thing as RMS power (it's a mistake that a lot of amplifier manufacturers make, sadly). Assuming a sine wave, RMS voltage x RMS current = mean power. RMS voltage (or current) of wave is the equivalent DC voltage (or current) that would cause the same power dissipation in a load.
Still have to put a load on both channels even if your testing one at a time right ? nice little demo. learned a lot from you and a couple others, a valuable recource.
It's best to use load resistors on both channels as the capability of the power supply can affect power output when both channels are driven. Most power ratings will state something like "... both channels driven".
Thanks Aidan for the demo video, much appreciated. I once blew up a scope by attaching the negative clip of the probe to the wrong place, I no longer have that scope...expensive mistake.
When doing this one needs to make sure the negative speaker lead is not driven. One way to do this is to see if there is continuity between left and right negatives, common, whatever you call it. overall best way is to make sure the negative is tied to the center tap of the high voltage transformer windings (or ground, on grounded bridge amps like some Crown typologies.) If the negative lead is driven, you will attempt to drive the ground of your home.
You do a really excellent job of troubleshooting and diagnosing these incredible vintage receivers which I grew up with at about your age. I'm what you call a Heathkitnic, meaning I started building heathkits in about age 13 and really never stopped until they were no longer available and then I started collecting. All of my Heath kits are operating and are not trailer queens, I enjoy them everyday and they have never required repair. Do you know about and how advanced their products were?
I am using a function generator on my iPhone 12, out the lightning adapter to a 3.5mm stereo cable to RCA. There is quite a bit of ringing in the square waves however. I think it needs a better impedance match, perhaps a couple of 100 ohm resistors across the RCA outputs? Not that that would matter for the purpose of viewing clipping of a sine wave, but just pointing out using the phone generator has it's limitations. Cheers man
Good demo, but be mindful of truly balanced power amps though, where the negative of the speaker output is NOT at ground potential. You will either blow your scope, your amp , or both.
Does this approach give you an indication of distortion? For example, does the smoothness of the sine curve indicate low distortion? Or can I conclude if power is up to spec, the distortion is probably at spec too? Perhaps a different test, but power and distortion are hand in hand for performance.
This test doesn't give a good look into distortion. A distortion meter or spectrum analyzer are what you want to use for that. Expensive tools that I don't have....yet. xraytonyb just released a good video where he tackled a very odd distortion issue on a Marantz. Watch it when you have a minute. It's a good showcase of how those tools can help you: ua-cam.com/video/byijs873XVc/v-deo.html
I did not see anything in the spec sheets about those load resistors being non inductive. They should be non inductive design for audio load resistors from what I understand. Great video
Great video. Love it. I have 2 questions. 1st did the 69W is RMS or peak power? 2nd did those resistors are carbon or not? Because what I've heard that carbon resistor are better for testing those amps. Thank you.
I find your recourse to a web site to do basic calculations quite humorous. I recently performed this exercise to see what I was getting out of my bridged-to-mono power amps. My resistors weren’t as stout as yours and they got quite hot at full load. Using my scope I was seeing 155-160 Volts p-p which was at the limit of what my scope could supply. First step: Since we need the equivalent DC voltage for the power calculations, Vpp = 2*sqrt(2)*VRMS, rearranging terms VRMS=Vpp/2*sqrt(2). The sqrt(2) = 1.414, twice = 2.828; Vpp = 157/2.28 = 55.5 Vrms. Second Step: Ohms law states that V=I*R and that power, in Watts, P = I*V. I don’t know the current, but I do know the static resistance, and I know that (rearranging terms again) I = V/R, so P = (V/R)*R or P = (V)squared/R. The resistance of my ganged resistor pack is 7.5 Ohms as measured by my DMM, so plugging in my values: P = (55.5)squared / 7.5 = 3,082 / 7.5 = 411 Watts. For an amp rated at 350 Watts bridged into 4 Ohms. (A RadioShack MPA 250.) My resistors (two 25 Ohm + two 50 Ohm, all adjustable and mounted in parallel) were getting hot enough to cook a steak on after not much time. I set the VU meters to normal listening levels and calculated that it was consuming about 7 Watts. I’m grateful for the part numbers of your resistors and need to get some of them on order. You may find my calculations as humorous as I find your web searches, but it is how I learned things, only two formulas do you need to make a host of calculations V=IR and P=IV. Note: Wouldn’t publish the 411 Watts as an official rating, the exercise was to satisfy my curiosity about the capabilities of my amplifier, I would need to do a lot more verification of my setup before I would confidently publish power ratings.
If you square the voltage and divide by the ohms I think you can bypass the online calculator at least for this exercise. :)
Thank you for the very straight forward demonstration. Some of the more experienced techs who post videos should take note.
There is no such thing as RMS Watts. Power rating is average, not RMS. Only volts and amps are RMS. And that is not an X on the scope probe. It is a multiply symbol. It is one times, not one ex.
Even some o-scopes that calculate the voltage for you, don't give it to you in RMS voltage and those that do may not give it as the default. You have to go into the menu to select RMS, or do the calculation from peak to RMS, for example.
Mean power - there's no such thing as RMS power (it's a mistake that a lot of amplifier manufacturers make, sadly). Assuming a sine wave, RMS voltage x RMS current = mean power.
RMS voltage (or current) of wave is the equivalent DC voltage (or current) that would cause the same power dissipation in a load.
Awesome video and much appreciated. Been rebuilding both of my Pioneer and Marantz receivers and wanted to learn how to do this.
Still have to put a load on both channels even if your testing one at a time right ? nice little demo. learned a lot from you and a couple others, a valuable recource.
Not necessarily but I always like to
*You’re.
It's best to use load resistors on both channels as the capability of the power supply can affect power output when both channels are driven. Most power ratings will state something like "... both channels driven".
Awesome I like the idea of using a phone to generate a signal as I don't have a working signal generator yet.
Hi m8 is the procedure tge same for powered/active studio monitors?
Cheers
I work on consoles from the 60's , it was laughable what some manufacturers claimed for power outputs on their units
Great site - thank you. I am new to the hobby - what output voltage were you using on the function generator?
Thanks Aidan for the demo video, much appreciated. I once blew up a scope by attaching the negative clip of the probe to the wrong place, I no longer have that scope...expensive mistake.
Thank you for taking time to share your knowledge. I for one appreciate it.
fantastic channel!
Nice Demo as well as the watts output its very handy to find out when the Amp or Receiver starts clipping
When doing this one needs to make sure the negative speaker lead is not driven. One way to do this is to see if there is continuity between left and right negatives, common, whatever you call it. overall best way is to make sure the negative is tied to the center tap of the high voltage transformer windings (or ground, on grounded bridge amps like some Crown typologies.)
If the negative lead is driven, you will attempt to drive the ground of your home.
You do a really excellent job of troubleshooting and diagnosing these incredible vintage receivers which I grew up with at about your age. I'm what you call a Heathkitnic, meaning I started building heathkits in about age 13 and really never stopped until they were no longer available and then I started collecting. All of my Heath kits are operating and are not trailer queens, I enjoy them everyday and they have never required repair. Do you know about and how advanced their products were?
I am using a function generator on my iPhone 12, out the lightning adapter to a 3.5mm stereo cable to RCA. There is quite a bit of ringing in the square waves however. I think it needs a better impedance match, perhaps a couple of 100 ohm resistors across the RCA outputs?
Not that that would matter for the purpose of viewing clipping of a sine wave, but just pointing out using the phone generator has it's limitations. Cheers man
Thanks for the info I am building a guitar amp and the info is very useful.
Love this channel name! It always reminds me of getting frustrated like Ah F*** It!
Good demo, but be mindful of truly balanced power amps though, where the negative of the speaker output is NOT at ground potential. You will either blow your scope, your amp , or both.
Thank you for a very clear and concise explanation of amplifier output calculations
I love your customized decor, it's a nice touch!
I always learn a little more, really appreciate you sharing the knowledge 👍🏻
Thank you for this very interesting Videos
Very useful video
Thanking you
Thanks for this straight explanation
Very good thanks for that. 😎
Youv’e said nobody’s asking, but I’d like to see more on that Marantz 2230.
How about I do that one after the KR-5010?
Does this approach give you an indication of distortion? For example, does the smoothness of the sine curve indicate low distortion? Or can I conclude if power is up to spec, the distortion is probably at spec too? Perhaps a different test, but power and distortion are hand in hand for performance.
This test doesn't give a good look into distortion. A distortion meter or spectrum analyzer are what you want to use for that. Expensive tools that I don't have....yet. xraytonyb just released a good video where he tackled a very odd distortion issue on a Marantz. Watch it when you have a minute. It's a good showcase of how those tools can help you: ua-cam.com/video/byijs873XVc/v-deo.html
I did not see anything in the spec sheets about those load resistors being non inductive. They should be non inductive design for audio load resistors from what I understand. Great video
Great video. Love it. I have 2 questions. 1st did the 69W is RMS or peak power? 2nd did those resistors are carbon or not? Because what I've heard that carbon resistor are better for testing those amps. Thank you.
RMS and they are not carbon
Oh.. I didn't see the subject 😊.. Thank you for your reply. ❤
appreciate it
What about if I played Led Zeppelin to clipping through speakers. Would I get the same volts ? Nice video, thanks.
You would see the clipping but your voltage reading would be all over the place.
@@AHFixIt Ok thanks I guess one has to bite the bullet and shell out a hundred bucks for two resistors.
I find your recourse to a web site to do basic calculations quite humorous. I recently performed this exercise to see what I was getting out of my bridged-to-mono power amps. My resistors weren’t as stout as yours and they got quite hot at full load. Using my scope I was seeing 155-160 Volts p-p which was at the limit of what my scope could supply. First step: Since we need the equivalent DC voltage for the power calculations, Vpp = 2*sqrt(2)*VRMS, rearranging terms VRMS=Vpp/2*sqrt(2). The sqrt(2) = 1.414, twice = 2.828; Vpp = 157/2.28 = 55.5 Vrms. Second Step: Ohms law states that V=I*R and that power, in Watts, P = I*V. I don’t know the current, but I do know the static resistance, and I know that (rearranging terms again) I = V/R, so P = (V/R)*R or P = (V)squared/R. The resistance of my ganged resistor pack is 7.5 Ohms as measured by my DMM, so plugging in my values: P = (55.5)squared / 7.5 = 3,082 / 7.5 = 411 Watts. For an amp rated at 350 Watts bridged into 4 Ohms. (A RadioShack MPA 250.) My resistors (two 25 Ohm + two 50 Ohm, all adjustable and mounted in parallel) were getting hot enough to cook a steak on after not much time. I set the VU meters to normal listening levels and calculated that it was consuming about 7 Watts. I’m grateful for the part numbers of your resistors and need to get some of them on order. You may find my calculations as humorous as I find your web searches, but it is how I learned things, only two formulas do you need to make a host of calculations V=IR and P=IV.
Note: Wouldn’t publish the 411 Watts as an official rating, the exercise was to satisfy my curiosity about the capabilities of my amplifier, I would need to do a lot more verification of my setup before I would confidently publish power ratings.