Audio Amplifier Output Measurement Using Different Types of Oscilloscopes

How to measure audio power output using either an analog or digital scope.

[@Attic-Toy-Design]

That’s a lovely, simple and sincere video explaining clearly how to properly make the right thing from a sincere and professional electronic engineer. Like and subscribed straightaway. 3 Years old uploaded video!

[@raygianelli3612]

Thank you. You caught me at a bad time, though. Having to take a hiatus to prepare my house for sale.

[@Warclock07]

Thanks, I was looking how to calculate the watt and this formula gave exactly what I have expected.

[@tjsogmc]

Brilliant use of the dummy load. I have a 500 watt resistor but never thought about the banana clips and the scope loops. I'm going to make one like yours right away! Thanks for sharing.

[@raygianelli3612]

You're welcome! There's more than one way to do these. I have since moved on to 1,000 watt dummy loads, with a dual banana jack on the front and coax that goes directly to my distortion analyzer. Think about what you have for test equipment and tailor your dummy loads accordingly.

[@waynecummings5021]

That was really good in that you broke it down to better basics. I'm still confused how to connect the function/sound generator to the amp, then how the oscilloscope is connected. This helped a little clear that up, but I'm now off to look for a basic video that walks me through basic connection step-by-step. Got any ideas anyone please?

[@IronAgeAudioworks]

So many cool tools and toys!!!! Thanks for the video!

[@Hr.0ldenberg]

Deutsch, German: endlich mal jemand der genau versteht wie es funktioniert. Bisher war noch niemand auf KZbin in der Lage, es so darzustellen wie er es gemacht hat. Man braucht nur ein 1000 Hz Sinussignal , einen Lastwiderstand und ein Oszilloskop um die sinusleistung zu messen‼️‼️ Mit dem Taschenrechner ermittelt man den Rest.... Great Job, well done.. I do it since 40 jears like this! Greatings from Bremen, the Home of Becks Beer🙋🍺

[@raygianelli3612]

Vielen Dank, Herr Oldeberg! Das Ziel dieses Kanals ist es, das Wissen weiterzugeben, das mir von vielen großzügigen Menschen gegeben wurde, als ich aufwuchs. Jetzt ist es an der Zeit, das zurückzugeben. Wir freuen uns sehr über Ihre Kommentare!

[@DavidBrown-ez5jc]

Hey Ray so brilliantly done so I have Dlabs and uncle doug for valve stuff and now you wow this just gets better and better thank you so much I am absolutely buzzing David from uk

[@raygianelli3612]

Thanks so much for the kind words, David! So many people helped me out along the way, and as I get older I realize the importance of giving back. Hence this channel.

[@amitanaudiophile]

Nice upload sir

[@dawidstepnowski]

Great video, thank you very much 💚

[@capricorn839]

Thank you. You makes everything looks simple to understand !

[@raygianelli3612]

That's wonderful, as that's my goal!

[@amkp40technology]

Good work 👍🏻👍🏻❤️

[@emc8564]

Thanks Ray.

[@JohnUsp]

Excellent thanks.

[@montygore]

Good ideo. Thanks

[@bernardzertuche7376]

Thank you for your video Excellent tutorial Where can I find the heat sink you have on this video

[@raygianelli3612]

Well, I pulled those out of the dumpster at work. They came from an old Telco rectifier. But if you look around you can find heat sinks in old equipment of various types.

[@jimpalmer1969]

What was the frequency and power of the input signal? Your bench amp looks very clean. Both of the peaks started to clip at the same time.

[@raygianelli3612]

Frequency was 1 Khz, I don't recall what it took to drive it. Been a while!

[@g.fortin3228]

Hi Ray.. any change you might do a short video on the basic settings like the ms/ and triggering for the digital scope when you first turn it on and want to measure the volts to figure watts like this ? .. not knowing much about scopes I am finding my new digital one a little confusing. but even for analog I need the settings to help me get started. thanks!

[@raygianelli3612]

I'll see about doing so in the near future.

[@g.fortin3228]

@@raygianelli3612 That'l be just awesome! thank you. I'm just starting repairs/restore so i wont be at that stage for a while.. it'l be a slower but careful job.

[@tenissabbalas]

Nice Video thanks. I think it will boost your views if you upgrade your camere.

[@raygianelli3612]

Agreed. I sent that one back shortly after I did this video.

[@TheSoundtec]

What was the Frequency voltage output from the generator. Thanks for this video

[@raygianelli3612]

Frequency was 1 Khz, amplitude was whatever was necessary to drive the amplifier to the edge of clipping.

[@Luke-12V]

good evening, 1khz is always used in this measurement? Thanks for the answer, and thanks for your videos👍👏🤩and I also wanted to ask if it is possible to connect the signal generator to the oscilloscope, without a separating transformer, thank you for everything.

[@raygianelli3612]

Hi Luke. Some manufacturers use 1KHz for their distortion spec. Some rate their products from 20Hz-20KHz. 1KHz is a good starting point. You can certainly connect your signal generator directly to your scope. Thanks for the thanks!

[@Luke-12V]

@@raygianelli3612 you are the best, thank you very much for your comments, nice day :-))

[@bernardzertuche7376]

I have a second question I’m not to familiar with digital or analog scopes , but wanting to learn more about their uses and functions . If I’m working on old vintage stereo equipment . Do I need a digital or analog scope? Or can I read audio signals from vintage equipment with both digital or analog scopes? Just want to make sure I buy the correct scope.

[@raygianelli3612]

You're best value will be older analog Tektronix scopes. They work well for this application. The new DSO's are amazing, but expect the prices to start out around the $300 mark. You can find good used Tek scopes nearer the $100 mark. Make sure that the scope is shown displaying a trace before buying. DSO's have an amazing array of measurement functions, and shine on low frequency signals. Their downside is having to dig through menus to access those amazing functions. And the DSO's at an affordable price are terrible in X/Y mode, which I use for my curve traces, determining if an FM tuner is actually putting out stereo and some FM alignment functions.

[@jesseyasaitis9036]

All these videos I've seen about measuring output wattage are all very good. However, no one has said what input voltage they are using to drive the preamp. Is it 20mv or 200mv?

[@raygianelli3612]

Jesse, it just needs to be enough to drive the amplifier to the edge of clipping. A CD player puts out close to 2 volts, just to give some perspective. The job of your preamplifier (or preamp stage in your receiver or integrated amp) is to drive the output stage with the necessary voltage for the desired volume. If you're testing a straight up power amp, just crank up your signal generator and watch the scope for visible clipping. 20mV would be good to test a phono input, but inadequate for a power amp.

[@jesseyasaitis9036]

@@raygianelli3612 Thanks!

[@timp9848]

Hi Ray Firstly thanks for another great video, as a beginner I am learning so much from you. I have a question regarding clipping, can you please explain when would you would consider an amp has a clipping issue, for example if an amp is rated at 100watts max, at what power output level would you consider a clipping issue and is it normal behaviour for an amp to clip at 100watts, is there a threshold?

[@raygianelli3612]

Clipping is what happens when you ask your amplifier to output more power than it can supply. And yes, a 100 watt amp could be expected to clip when asked to deliver in excess of 100 watts.

[@treadmillrepair754]

@@raygianelli3612 Hi Ray, Forgive my boldness, do you work fixing vintage audio gear for hobby? Or you earn money doing this? I ask you because fix vintage audio consumes a lot of time. In my case I earn money fixing High End Audio and motor controllers here in my country. I fix a lot of McIntosh and Audio Research both are American companies. Best Regards.

[@raygianelli3612]

@@treadmillrepair754 Ricardo, it's really just a hobby. I have a day job as a central office technician with a large telecom provider.

[@edwinhurwitz6792]

@@raygianelli3612 Except when it's a McIntosh amp! My 2105s have put out between 130 and 150wpc without clipping. Considering how hard they've been gigged, it's pretty cool. I really appreciate this video as I am going to buy some dummy loads and start experimenting with all my amps (mostly old Fenders aside from the Macs). It's exactly what I needed to see.

[@raygianelli3612]

@@edwinhurwitz6792 Thanks Edwin! Maybe I'll put my VHT (Fryette) power amp on the bench and see what it will do.

[@Submarine_SeXJ]

When I use the regular ground reference oscope probe on the + and - terminal on the amplifier I get a reading that looks like 2 AC sine waves wth at are 180° out of phase. Would a differential probe help this?

[@raygianelli3612]

I don't know how I missed this but I did. Often this is an adjustment of the triggering on the scope. If you're still having this issue please contact me via email. My email address is available under the ABOUT tab.

[@bugsyjonesband]

that was very helpful. I'm ready to attack my stack. Thank You !!

[@raygianelli3612]

Your Marshall stack? 😁

[@bugsyjonesband]

@@raygianelli3612 stack of stereo amps !! Although actually, I’m a Fender guy

[@raygianelli3612]

@@bugsyjonesband I went through Fender, Marshall and Mesa before finally settling with VHT/Fryette before hanging it up due to the late hours and age catching up with me. Going into work Monday morning looking like Keith Richards wasn't helping my career any. 😁

[@bugsyjonesband]

I don’t gig anymore either. Last amp of first choice was a ‘64 P.R.

[@raygianelli3612]

@@bugsyjonesband I had an olde blackface Princeton Reverb that a buddy bought at a yard sale in pieces for $5. He gave it to me, and the only issue with it was the diode in the bias circuit was bad. Sold it for an obscene profit!

[@JohnUsp]

Next video explains how to use your THD analyzer ;)

[@raygianelli3612]

Good idea!

[@dans8935]

Yes! Please do a video about THD!

[@tomadams6685]

Interesting, I haven't seen that equation for finding rms. I use the peak voltage times .707 to get rms

[@raygianelli3612]

Perfectly valid method. There's more than one way to calculate the RMS voltage. I did a web search and found one page that multiplies .7071 for peak, and .35355 for peak to peak. The reciprocal of .35355 is 2.83, so dividing by that yields the same result. Just be sure to center the trace on the scope to get an accurate peak level.

[@maorienteg]

Ray, are the volume controls maxed out when doing this measurement?

[@raygianelli3612]

Really doesn't matter. If the volume controls aren't maxed then the signal generator output needs to me increased. It's all about pushing enough signal into the amp's input o get to the edge of clipping.

[@maorienteg]

Ok, thank you, I get it now.

[@brettbarnett9823]

Hi Ray.. Thanks for this video. I want to ask a question. I have an 8ohm dummy load box. I put bnc connectors on it to tap off the box and run to an o-scope. I take regular coax bnc cable. Female to female and run directly to my digital scope. The most I get before the SX-980 starts clipping is 2.64 RMS according to the scope. Am I missing something? I know regular probes have x1 and x10 switches. Is my scope setup wrong? I should be getting a lot higher RMS reading with this unit. Should I be multiplying that 2.64RMS by 10?

[@raygianelli3612]

Try measuring with your DMM on AC volts and see what you get. If it's significantly higher (and it should be) dig around in the scopes vertical setting and see if it's set up for X10.

[@brettbarnett9823]

​@@raygianelli3612The setting on the scope was set for 0.1. Set it for 1.0 and got the correct 26.4 RMS reading for the output. 87 watts per channel on this bad boy. :) Thanks for learning me!!

[@zoltankecse991]

Hi. Sorry for the question. :) The 2.83 what you used for devide what is that number? 1.41 per channel or not?

[@raygianelli3612]

Hi Zoltàn. Questions are welcomed here! An oscilloscope screen has a grid on it, and the grid's vertical axis reads out in volts peak to peak. In order to calculate RMS volts we must divide that reading by 2.83. This converts the peak to peak reading to RMS volts. Make sense?

[@zoltankecse991]

@@raygianelli3612 Ohh yes,yes I already understand. Thank you very much. :) BIG LIKE.

[@generationbehindhifi]

Where can I get a 500 watt or 1000 watt dummy load resistor? The highest one Parts Express sells is 200 watts. By the way, nice video! It's much appreciated!

[@raygianelli3612]

Thanks! Do a search for 8 ohm braking resistor. They've gone up in price since I got mine, but then what hasn't?

[@generationbehindhifi]

@@raygianelli3612 Hey Ray! I finally got my test bench setup with a 500W braking resistor (4 ohm) but have a few questions. Do you mind watching this video that I made just for you showing my testing parameters and some of the questions I have? I appreciate your time! Thanks! kzbin.info/www/bejne/onO3p5yvr6p5hJo

[@sergeys6263]

Автор крут невероятно!

[@raygianelli3612]

Спасибо Сергей! Я просто пытаюсь передать все то, чему меня научили многие другие щедрые люди. Обучение сохраняет остроту нашего ума по мере того, как мы становимся старше, поэтому никогда не останавливайтесь!

[@sergeys6263]

@@raygianelli3612 А мы учимся у вас... Приятно общаться с умным профессионалом.

[@roberthudson8235]

Where did you get your heat sink ? I have the same load

[@raygianelli3612]

Dumpster diving at work. It came from a big telecom rectifier that was parted out.

[@zoltankecse991]

Hi. here i go again. :) I have an simple DDS signal generator. (fy3224s) Can you tell me what is the amplitude level to set for sine wave? ( I know the frequency is 1kHz) But how many volt needs to set for the pa amplifier test with the DDS generator? I've many PA amp and i just want to test the output power and the signal. Thank you.

[@raygianelli3612]

There's no magic number here. The key is to slowly bring up the amplitude until the visible onset of clipping, then back it down just until the clipping ceases. That's your maximum output.

[@scott7305]

When you calculate the output power using the multimeter method, why do you square it? Thanks, have been trying to do this before and have not gotten an accurate measurement.

[@raygianelli3612]

Scott, I must admit I don't know why you square the voltage, only that it's what Ohm's Law prescribes. I never even had high school math, so it's admittedly a weak point.

[@scott7305]

@@raygianelli3612 Alright. Thanks!

[@kubockferre5532]

hi what voltage you send on generator to test

[@raygianelli3612]

Enough to drive the amplifier to the edge of clipping. It varies so there's no one answer. The scope will let you know when you're there.

[@sivaganesh4519]

I have 500 watts RMs Passive speaker. My amplifier is Behringer NX-6000D. According to the manuals 1600 watts per x2 at 8ohms. The Max VP value at amplifier Dsp software shows 160Vp. Kindly advise me on the calculation, how much VP should i set to my Speaker Thanks

[@sivaganesh4519]

​@Ray Gianelli

[@jennyminskey4086]

Hello, I have a high frequency noise in my home. What instrument can I use to locate where it is coming from? Thank you!!

[@raygianelli3612]

Hi Jenny. I love questions that make me think, and the questions I get here never disappoint! I would look for a free audio spectrum analyzer smartphone app. You should be able to find one for either iOS or Android. This will not only tell you what the frequency is, but the amplitude will tell you when you are getting nearer to the source. Hope this helps, Ray

[@jennyminskey4086]

@@raygianelli3612 Hello, I downloaded 2 different ones. They had different readings. I dont know how to do the amplitude yet, but I will try! Thank you so much for the input. I believe it is a "mosquito" anti loitering device, but cant figure out how find it!!!

[@campion05]

If that is a stereo amplifier, doesn't the second channel need a load also while the other is under test?

[@raygianelli3612]

It doesn't need a load to prevent damage, unless it's a tube amp. There may be a small difference is power measured, since most amps are rated as "both channels driven".

[@Ryyderdie]

could you not just hook an oscilloscope onto your speaker leads while the amp is also connected instead of using a dummy load?

[@raygianelli3612]

No, the volume would be ear shattering, and you'd run the risk of damaging your speakers as well.

[@ariaaudiophile]

Does it matter watt power of Dummy Load? Thanks

[@raygianelli3612]

Really depends on the power of the amplifiers you're testing. The ones I have now are rated at 1,000 watts each. But I used smaller ones for years without issue. You can exceed the rating for BRIEF periods, long enough to verify an amp puts out full power without clipping.

[@ariaaudiophile]

@@raygianelli3612 Thanks for reply. Resaon i'm asking is i have tested few amps and power always comes to around 50watts but i know amp has 3 times more power, than i checked my dummy loads and they are 50watts. I think that could be a problem.

[@donepearce]

At some point it would be great if you can persuade people that the resulting power measurement is average, not RMS. RMS is only applicable to the voltage and current measurements.

[@raygianelli3612]

"RMS" watts has been a misnomer ever since the FTC mandated watts measured using the RMS method, which as we both know does NOT equal RMS watts. But the term has been entrenched for decades, so all I can do is not perpetuate it.

[@CarloTheAtheist2.1]

sir. is it possible to measure the watts of the amplifier at 8 ohms?

[@raygianelli3612]

Yes. You need to load the amplifier with an 8Ω load, a large wattage resistor is recommended.

[@CarloTheAtheist2.1]

@@raygianelli3612 thank you so much. i watch on other youtube channel and heard. there's such thing as a Dyno Amp to measure the watts of the amplifier too.

[@raygianelli3612]

@@CarloTheAtheist2.1 Holy crap, they want almost US $6,000 for that thing! Guess if I ever need to measure amps of 19,000 watts/channel, I'd have to consider it. But I've never seen an amp even close to that, so my money's safe for now. 😁

[@CarloTheAtheist2.1]

@@raygianelli3612 exactly! oscilloscope also can do anything.

[@robertoarruda2056]

Whats a calcule ? Equations ?

[@raygianelli3612]

I think you mean graticule, which is the grid on the face of an oscilloscope.

[@gervaiscurrie6675]

the amp might cilp - the osciiosope doesn't - what am I missing here?

[@raygianelli3612]

I'm not sure what you're referring to. The scope clearly shows the onset of amplifier clipping.

[@gervaiscurrie6675]

@@raygianelli3612 Was bit drunk here - will re-watch :-)

[@raygianelli3612]

@@gervaiscurrie6675 OK, now I'm just jealous! :)

[@doveshouse]

Why don't people ever mention amperage with regards to audio power (watts) or amplifier audio output?

[@doveshouse]

In your example would that be about an amperage of 8.4?

[@raygianelli3612]

We characterize amplifier power in watts. Watts are the product of voltage times current.

[@doveshouse]

@@raygianelli3612 I understand... It's just interesting that no one seems to be bothered by knowing or not knowing the measurement of the current (amperage). I suppose they just extrapolate current based on the ohms and voltage measurements?

[@doveshouse]

The signal running through speaker wire is electricity... And when people talk about electricity, amps or amperage often seem to be part of the conversation... But not when it comes to audio signal.

[@raygianelli3612]

@@doveshouse The problem lies in the changing of impedance with frequency. Your 8Ω speaker is rarely 8Ω.

[@jeffm2787]

Congrats on Not saying RMS watts.

[@raygianelli3612]

Why would I? There's no such thing.

[@jeffm2787]

@@raygianelli3612 Exactly.

[@tiromancino_tt]

l'oscilloscopio fornisce misure di frequenza molto precise ( 0,1% tipicamente) , mentre misura l'ampiezza con molto meno precisione ( 2% tipicamente)

[@raygianelli3612]

Gli oscilloscopi analogici non sono neanche lontanamente vicini allo 0,1% per la precisione della frequenza. Sono d'accordo sul fatto che la precisione verticale è di circa il 2% e dipende da quando è stato calibrato l'ultima volta. I DSO sono molto migliori in questo senso.

[@tiromancino_tt]

@@raygianelli3612 ho detto precisi , non accurati . vediti il video di come è possibile misurare, tramite un espediente, una differenza di fase di pochi gradi tra due segnali di 10O MHZ , con un vecchio ma ancora fantastico HP1740A

[@Submarine_SeXJ]

When I use the regular ground reference oscope probe on the + and - terminal on the amplifier I get a reading that looks like 2 AC sine waves wth at are 180° out of phase. Would a differential probe help this?

[@raygianelli3612]

It sounds like you may be measuring the output of a balanced amplifier, which floats the output above ground. Do a search on oscilloscope pseudo differential input. Using 2 probes without the ground clip you can safely make measurements of amps like this.

[@Submarine_SeXJ]

@@raygianelli3612 There's no info. Its a 4 channel amplifier from CT Sounds. CT150.4D. They're sending me a replacement and we'll see what the oscope showes with that.