Aiyima A07 Max THD vs Frequency and Input with QA403 and Pico Scope
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- Опубліковано 18 чер 2024
- This video 'Aiyima A07 Max test set-up for QA403 Audio Analyzer'. I will show how I setup the testing for the QuantAsylum QA403. #QA403 #quantasylum #Aiyima #A07max
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HI Eddie, this was an excellent video, thank you so much.
Thanks for your feedback!
With all voltage feedback audio amplifiers you will always typically see approximately 10 times more THD+N from 1 kHz to 10 kHz, so if your amplifier has a THD+N at 1kHz of say
0.002% you will almost always see 0.02% at 10 kHz and typically 0.04% at 20khz.
The amplifier at the higher frequencies is simply running out of open loop gain at say 10 KHz, to improve this you normally need to increase your open loop gain at the higher frequencies or improve the local feedback around the output stage where most of the THD is produced. Also the rapid drop off in THD above 10kHz is normally produced by the Analyzer bandwidth. So try increasing the Analyzers measurement bandwidth to 44 kHz and you should see an improved accurate measurement at 20 kHz.
Or what could also be happening is the output filters on the Class D amp is coming in a little early.
Thanks for the great feedback! The bias can change the THD by making it more Class A than Class A/B. The THD of 0.04% is amazing and more feedback can reduce the dynamics. Marketing people love THD as so many people focus on the small numbers - which take away the focus from other much more meaningful specifications. Too much feedback is not a good thing. In fact, some love the no feedback systems - for a great reason. The bandwidth or resolution of my settings on the analyzer are less than 1 Hz. I did go to much higher resolution because the analyzer is capable - but saw no improvement in the measurement - but it took longer.
Great Video dude thank/s
Thanks so much! I appreciate you!
After years of music listening and countless gear, I pay little attention to THD anymore. I cannot hear the difference between gear with vanishing THD numbers vs gear with average THD numbers. But, what I can hear and what matters to me after 60 years of this audio obsession is the composition of the harmonics. The relative amplitude of each harmonic. Give me relatively high second harmonics, followed by a quick suppression of the third harmonic any day of the week. If this is the condition then the total THD will mean very little to me even if it is quadruple higher than that of gear having see-saw high odd harmonics. I will be listening to the gear with the higher THD. After the third harmonic, seeing the 4th, 5th, 6th, 7th, 8th, etc relatively the same is great, better still is to see the 4th higher than the 5th.
Thanks for this great feedback! You make some excellent points. I think the next video might be something more meaningful;)
great video excellent
Thanks so much!
There's something odd about the THD+N curves, as you noted. The variance vs signal level is one issue and the rapid drop off past 6kHz is another. But I wonder if these aren't test artifacts. My recommendation is to connect the TE output directly to the measurement input, no amp. Or a perfect amp, gain = 1, if you think of it. See what happens then. Because the amp has some gain, these signal levels will be different but I'd be interested if the 60Hz plus harmonics is still present and what their contribution is.
When the TE measures THD, how far out in frequency does it look ? Do you know what the amp output filter LPF is ? Either of these might explain the drop off vs frequency in the curves.
Lastly wrt audience and views etc, you present like an engineer. I say that being one, now retired. I had to be taught to do effective presentations. Yours is a technical channel. People viewing it expect to see the results but not every detail and misstep that produced them. Conciseness is a benefit. You, like I did, wander too much when some interesting-to-an engineer thought crosses your mind. Resist that, or edit it out. Have, if not a script, then a set of bullet points that the video is trying to convey. Then stick to them, at least in the first pass. If some oddities arise, note them but move on with the main story. At the end, or in another vid, then delve into the anomalies. As in amplifiers, linearity is much desired and appreciated. I say this because 30+ years ago I was "you", but presenting to management.
Thanks for the recommendations! I appreciate your feedback!
This may be completely wrong, but is it possible that the THD in the amplified noise itself is very low giving you a lower overall THD of the small signals since the noise is a higher percentage of the signal than it is when the signal level is increased?
Great question! This is really what we are looking for - is the noise just a low level noise or is it a function of the amplified signal? In the first case the SNR will get better with higher signals, but if it is a getting amplified - then it will increase with signal and SNR will stay the same - or possibly get worse.
Have you considered replacement of the filter cap ? I had problems with some of there other models and upgrades in power supply and filter caps always improved them . And op amp rolling , does that model have op amps? Great video as always brother
From the Aiyima A07 page ...
"Replaceable Op-Amp Chips:OPA2604AP, OPA2134, MUSEO1/02/03, LME49720NA, LM4562, AD827AQ, etc"
I guess we'll see in a future video what's actually installed.
Thanks for the great question! I'll show the parts inside once I get these basic measurements taken. I might consider modifying these amps to see if we can get improvements. I have a other amps that I want to test - some with the same chip set that this one has, so we can see if they have similar characteristics or if they are very different.
I'll try different OpAmps at some point as well - to see what differences we can measure.
I Just found the Asio update thanks to Nerijus at RAw-Cat channel. Excited to test stuff with REW
Please let us know what you learn;)