Looking for an automated test for watts vs freq. My goal is to see how the watts change with a set input value across the freq spectrum. I am not sure what to select from the Automated Test Tab
I believe you can only do this at 1 frequency, typically 1khz, where you can plot the THD vs Output power. I think a future version of the software will allow the option of plotting THD vs Power, but for now, you can plot THD vs Frequency for multiple input levels, which you can equate to output power to a certain extent depending on how flat your frequency response of the amp is.
Amplifier Gain Varies with Frequency
This is the point of the measurements to determine how flat the frequency response is.
Frequency response can be easily done with the Frequency Response Generator at a fixed input level.
People almost always use dB for frequency response, not absolute watts (or volts or whatever). There is a measurement “Pwr Watts” you could use, oddly no “dBW” though.
(matt: that measurement should be watts lower case, the unit is lower case, the person its named after capitalized).
Volts would be nice to see.
It would also be terrific if the Automated Test would have a description of the test.
Hi @YamahaCA, with the QA40x app running, go to your browser and type:
http://localhost:9402/AutomatedTests
That should dump all the tests available with some more detail on each.
That link is incomplete and goes nowhere
Did you first start the QA40X application before using the link in your browser? I am trying it out at the moment and it works regularly. If the application is not started first, it does not work
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Thank you for your most kind assistance.
This information will be very helpful. It has already answered one of my points of confusion with the Settings File to Load. It would also be helpful to provide some recommendations on what parameters these should be set to, with a brief explanation on why.
The first line under the test title is a very minimal, i am sure a chapter could be written for further explanation but with a paragraph of details would go a long way.
I have asked this question several times and never seem to receive a clear reply if any: When the device under test was manufactured the engineers provide a test report and this is often found in the service manual. My question is what QA403 test can recreate these individual test and what parameters should be set.
In addition why is everything written based upon the QA401? That is like buying a 2024 car and the manufacturer provides a Owners Manual for a 1950’s model, wouldn’t you scratch your head and ask WTF?
This is a 70wpc integrated amp, 30db gain
Trying to run THD/PWR, will not complete the test series. Getting the message of input overload
What parameter do I have set incorrectly?
In addition: I have set the Load Impedance to 4.0 ohms, yet it displays 8 ohm why?
Hi @YamahaCA,
The displayed measurement tiles are using the impedance you set in the DBV options. The PwrThdVersusPower is using whatever you tell it to use for that graph.
When you specify Autoset Input Range, you are tellign the analyzer to make the first measurement at your minimum specified level (-30 dBV in your case) and with max full scale input (42 dBV). Your amp has a gain of 14 dB it looks like, so we might expect the first measurement is leave the analyzer at -30 dBV and arriving back to the analyzer at -15 dBV or so.
So, the first measurement should complete no problem. How many iterations is it getting through before you see the error?
Second, you are asking the input level to be set to 1 dB above the expect level. You might try to set that to 10 dB and see if it completes. The assumption by the plug-in is that the gain measured in the first step is consistent throughout the sweep. If that isn’t the case, then the overload could be legit.
If you do a run manually at the output level that is giving you trouble in the automated test, what do you see? It’s very important to ensure the measurement is making sense to you manually. If it’s not, then automating won’t help.
My question is what QA403 test can recreate these individual test and what parameters should be set.
What test specifically are you trying to recreate? A “test report” is seldom something that was generated automatically. And the spec provided for a product also includes margin the engineers think will be needed. That is, if you meaure the gain of your amplifier at 15.36 dB, you need to fall back to worst case analysis to arrive at your mean and sigma for gain. And then you publish that. The measurement is simply validating the analysis.
In addition why is everything written based upon the QA401? That is like buying a 2024 car and the manufacturer provides a Owners Manual for a 1950’s model, wouldn’t you scratch your head and ask WTF?
There’s a clear lineage between the products. Is there something factually wrong in the manual, or do you just wish the UI that looks different (but functions the same) was changed?
The amp has 30db gain
Not sure if this makes much sense but it is what I am observing:
I am beginning to think the issue has to do with the load Impedance. I set it for 4 ohm but as you can see during the test it is displaying 8 ohm and basing the test results upon that. So when it is stepping through the power band it is overloading the input and aborting the test. I have it set to automatically range the attenuator and I see this taking place. When it reaches 0 attenuation it has driven the amp into clipping, thus the distortion reaches its preset threshold and aborting the test.
If I change the -12 to say -15 the input signal becomes so low the watts drops to mw or uw, which results in garbage test results.
When i set the generator to 1khz i can increase the input value and watch the scope and see that it will run up to 30v before it starts clipping. That 30v into a 4ohm load should be around 80wpc. The display of watts on the QA says it is around 45wpc.
As i stated earlier they are both cars and they both have an accelerator and brake pedal. What further explanation could any one ask for. lol!
Hi @YamahaCA, yes, the two pictures you have shown are correct. You have specified for the measurement tile to use 8 ohms. Set that to be 4 ohms since you are using a 4 ohm load.
When you do that, the measurement tile will indicate the load as 4 ohms:
The load impedance in the plug-in is only used by the plug-in.
When it reaches 0 attenuation it has driven the amp into clipping, thus the distortion reaches its preset threshold and aborting the test.
Yes, there are two things to try here. First, you can set the full scale input to 42 dBV and disable Autoset. This will let you see the full run of the sweep so that you can see where the problems are creeping in without overload impacting your measurements.
Next, you can disable early abort. That might be hard on your amp (some amps won’t care), but it will also let you see where the problems creep in.
Since you were seeing the issue with Range, that suggests you should first set the input range to 42 dBV and disable autoset. Paste the resulting graph here when time permits.
