Measuring the power of an amp, with an oscilloscope

[SIY]

I found those cheap gold anodised Chinese resistors to actually have no appreciable inductance up to 30kHz. I was incredibly surprised considering their low cost. They were better in that respect than my high powered, supposedly 'non-inductive' load resistors I'd been using for years.

Same experience.

 

[Bow_Wazoo]

For my measurement I use the following oscilloscope.

https://www.amazon.de/Rigol-Oszilloscope-kostenlose-Triggerungen-Dekodierungen/dp/B089WHC4MK/ref=asc_df_B089WHC4MK/?tag=googshopde-21&linkCode=df0&hvadid=447446356765&hvpos=&hvnetw=g&hvrand=3418173028879204469&hvpone=&hvptwo=&hvqmt=&hvdev=m&hvdvcmdl=&hvlocint=&hvlocphy=9044738&hvtargid=pla-931201814138&psc=1&th=1&psc=1

I realize that these measurements are far from professional, but this whole gimmick serves only the purpose, of making clear to some completely misguided people, that the power you demand from an amplifier, depends essentially on how, how loud, and what you listen to.
I, for example, like to listen very loud EDM, with Harman curve, and make every bet, and that it is now only an estimate, that I will demand the amplifier loose two watts per channel..

 

[fpitas]

Reminds me of the old saying, "When all you have is a hammer, every job is a nail".

 

[fpitas]

For my measurement I use the following oscilloscope.

https://www.amazon.de/Rigol-Oszilloscope-kostenlose-Triggerungen-Dekodierungen/dp/B089WHC4MK/ref=asc_df_B089WHC4MK/?tag=googshopde-21&linkCode=df0&hvadid=447446356765&hvpos=&hvnetw=g&hvrand=3418173028879204469&hvpone=&hvptwo=&hvqmt=&hvdev=m&hvdvcmdl=&hvlocint=&hvlocphy=9044738&hvtargid=pla-931201814138&psc=1&th=1&psc=1

I realize that these measurements are far from professional, but this whole gimmick serves only the purpose, of making clear to some completely misguided people, that the power you demand from an amplifier, depends essentially on how, how loud, and what you listen to.
I, for example, like to listen very loud EDM, with Harman curve, and make every bet, and that it is now only an estimate, that I will demand the amplifier loose two watts per channel..

If you have peak capture that would be most instructive. Non-technical people don't realize that music has enormous power peaks, 20dB and beyond. Obviously in a perfect world you won't shave those off

 

[Bow_Wazoo]

Presumably it would be easier, and better if I use my sound card to measure, right?

FFT Analyse Freeware Download - ROGA Instruments

FFT Analyse Software kostenlos – FFT Analysator Freeware – Spektrumanalyse Software kostenlos Wenn Sie auf der Suche nach einer professionellen FFT-Analysesoftware sind, mit der Sie Ihren PC in ein voll ausgestattetes Messinstrumentarium verwandeln können, ist Visual Analyzer das richtige...

www.roga-messtechnik.de

 

[HarmonicTHD]

Presumably it would be easier, and better if I use my sound card to measure, right?

FFT Analyse Freeware Download - ROGA Instruments

FFT Analyse Software kostenlos – FFT Analysator Freeware – Spektrumanalyse Software kostenlos Wenn Sie auf der Suche nach einer professionellen FFT-Analysesoftware sind, mit der Sie Ihren PC in ein voll ausgestattetes Messinstrumentarium verwandeln können, ist Visual Analyzer das richtige...

www.roga-messtechnik.de

Or an audio interface. Just be careful you don’t blow it and that’s why I would use an audio interface so the damage is contained ;-)

As software I recommend to use REW or Multitone Analyzer (both free) and programmed by forum members.

 

[Bow_Wazoo]

Thank you. Are these vst plugins?
But can I also determine the used / called power of the headphone amplifier in this way? Would then my dummy load parallel to the line in the audio interface?

 

[Bow_Wazoo]

Is 16bit/48khz enough?

 

[antcollinet]

Thank you. Are these vst plugins?
But can I also determine the used / called power of the headphone amplifier in this way? Would then my dummy load parallel to the line in the audio interface?

Not plugins - standalone programs.

You need to connect your dummy load. Measure the voltage accross it (using your scope or a multimeter (multimeter with a 50 or 60Hz test signal) at full output power, then use a pair of resistors to divide that maximum amp voltage to the maximum input voltage of your line in device.

 

[antcollinet]

Is 16bit/48khz enough?

For power measurement? Yes.

 

[Bow_Wazoo]

The audio interface I want to use has a high-impedance input, which is actually intended for e-guitars. In addition, I still have a gain control on the device. Then a voltage divider on the dummy load shouldn't be necessary, right?

This is what I found earlier:

A DIY approach to distortion measurements for audio amplifiers

I imagine I am typical of many DIY audio enthusiasts in that I build something and hope that subjectively it sounds good. However, I am also curious about the objective measurements of the equipmen…

enjon.uk

Quote:
"The amp being measured needs to drive a load, so a dummy load simulating your speaker load needs to be made. All that is required is a resistor that has the same impedance as your amplifier and is rated to handle the amp’s power output. I chose a 8Ω 50W power resistor from RS Components. You may wish to heatsink this but I bolted it directly to a metal case. The dummy load can connect directly to the sound card but it is prudent to attenuate the signal before it reaches the audio interface. This can be achieved using a voltage divider and it was recommended that a 10:1 voltage drop would be suitable. I used 22K and 2.2K resistors as these were at hand. Make sure you get the resistors the right way round (see image below) or the ratio will be out. In true (mis) Adventures in HiFi tradition, I got them the wrong way round to begin with."

 

[antcollinet]

The audio interface I want to use has a high-impedance input, which is actually intended for e-guitars. In addition, I still have a gain control on the device. Then a voltage divider on the dummy load shouldn't be necessary, right?

View attachment 265408


This is what I found earlier:

A DIY approach to distortion measurements for audio amplifiers

I imagine I am typical of many DIY audio enthusiasts in that I build something and hope that subjectively it sounds good. However, I am also curious about the objective measurements of the equipmen…

enjon.uk

Quote:
"The amp being measured needs to drive a load, so a dummy load simulating your speaker load needs to be made. All that is required is a resistor that has the same impedance as your amplifier and is rated to handle the amp’s power output. I chose a 8Ω 50W power resistor from RS Components. You may wish to heatsink this but I bolted it directly to a metal case. The dummy load can connect directly to the sound card but it is prudent to attenuate the signal before it reaches the audio interface. This can be achieved using a voltage divider and it was recommended that a 10:1 voltage drop would be suitable. I used 22K and 2.2K resistors as these were at hand. Make sure you get the resistors the right way round (see image below) or the ratio will be out. In true (mis) Adventures in HiFi tradition, I got them the wrong way round to begin with."

Your line in will have a maximum allowed input voltage. If your amp output exceeds this, then it can potentially damage the interface.

Hang on...

Your guitar input when set to line has a maximum rated input of 20dBu - this is 7.7V - I would not exceed this.

GUTAR set to MIC/LINE
Nominal input level:
–40 dBu (When INPUT konb is
set to MIC)
+4 dBu (When INPUT knob is
set to LINE)
Maximum input level:
+20 dBu (When INPUT knob is
set to LINE)
Input impedance: 15 kΩ

 

[Bow_Wazoo]

Then it is better to use a voltage divider. Which values would be ideal for my voltage divider?
The LYR+ delivers 6watts per channel at 32ohm

 

[Bow_Wazoo]

I have made some mess, and therefore opened a separate thread for it

How to measure output Power of an headphone amp with REW

Could someone please explain to me, how I can use the REW to measure the power output of my amplifier? I want to measure how much power I'm asking my LYR+ to deliver, and when it starts to clip. As a dummy for my He-1000 V2 Stealth, I take a 30 ohm resistor. As interface Tascam US122 MK2...

www.audiosciencereview.com

 

[Bow_Wazoo]

Then it is better to use a voltage divider. Which values would be ideal for my voltage divider?
The LYR+ delivers 6watts per channel at 32ohm

Doesn't really matter.1 :10 is already okay

 

[audio_tony]

You can find some useful information regarding hardware and software for audio test & measurement on this site.