Using the QuantAsylum QA40x Audio Analyzer Pt. 1- Vintage Audio Review Episode #97

[@indiakilo3929]

Hi, I understand that if you want to use the + input (ADC side) single ended that you should terminate the other unused - input with a short in order to reduce noise and preserve linearity. At 05:00 you mention using a 50ohm terminator. Page 9 of the manual states that you will see thermal noise from the unused 470ohm input resistor, with a 50ohm terminator you may exacerbate that. I expect a loopback test will show any differences here. Just to cover it off, the output (DAC side) should be left open (floating) if you have a channel unused. Hope that's helpful. Enjoyed your video, helpful while I'm researching while my unit is on order!

[@vintageaudioreview]

For audio purposes the 50 ohm (or 75 ohm) termination acts like a short. I made my own short and there is no difference when using that or the loads, though sometimes you can get some strange noise changes and removing the termination on the - input and replacing it with another one solves the problem. You will not get good results w/out a termination or short on the - input. This is for measuring things like a preamp. When you are measuring a power amp (or intg amp or receiver) then the -input is going to be connected to the load/amps - terminal. For what I do- measuring mostly vintage gear, I don't care about thermal noise related things. I hope to do another video using the QA403 before too long. It is really a great instrument and I am sure you will agree once you get yours.

[@indiakilo3929]

@@vintageaudioreviewcool, thanks for sharing your experience!

[@vintageaudioreview]

@@indiakilo3929 you are very welcome!

[@boatanchoraudio6453]

Very nicely done. I'm looking forward to more videos. Idea: Perhaps you could get with Matt of QA and collaborate for a set of videos on using the QA40X, from beginner to advanced.

[@vintageaudioreview]

Thanks for watching and the suggestion. Based on the fact that there are limited videos on the wiki, I think that Matt has his hands full with all his products and supporting the forum, but I will reach out to him. If I do another video depends on the # of views which tells me if my subscribers like the subject. This one is doing ok, so there is a good chance. I would classify this 1st one as beginner. Advanced would be doing some automated tests...

[@GrzegorzMatusinski]

Great video, very informative. I am putting the QuantAsylum QA403 on my shopping list.

[@vintageaudioreview]

Thank you so much- It is a great tool and a bargain at the price.

[@curtislucka9954]

Great video and appreciate the time and effort it takes to produce these. I am using my QA403 more and more and am glad to see practical examples of how to use it. Looking forward to seeing more on the automated tests. Thanks again!

[@vintageaudioreview]

Thank you for the encouragement. It does take a lot of time to put these together. If the response it good I will do another video (Pt 2) later- maybe measuring a high power amp. So far the response has been good.

[@Douglas_Blake_579]

Nice ... Thank you. One question ... does it have safety checks built in for stuff like DC Offsets or High Frequency Oscillations?

[@vintageaudioreview]

Hi Douglas- Good question! It does not have checks for DC offsets that I am aware of- hopefully, that is a feature that could be added- that would be useful for sure. Same thing for the high frequency oscillations, though you will see the frequency response show an oscillation at times.....

[@Douglas_Blake_579]

@@vintageaudioreview Thank you Scott. So it's on us to make sure we're not hooking up an amp-in-trouble. That's fair. I presently do those checks manually anyway. Thinking it might be time to update my DIY distortion meter... Can't afford an AP box. This might be the way to go.

[@vintageaudioreview]

@@Douglas_Blake_579 Best money I have spent on a piece of test equipment, and really good support.

[@Douglas_Blake_579]

@@vintageaudioreview Good to hear. It's going to be a while, but It's on my shopping list.

[@jameswarren1831]

Thank you! If you choose an attenuation level to low it will automatically move it back to avoid damage? I watched QA's video where they had the 304 increase power as part of the test, will it stop the test if it goes beyond the allowable voltage input?

[@vintageaudioreview]

Thanks for the question. I am not familiar with the 304 that you mentioned. Maybe you meant the QA403? In just normal use, the attenuators do not go to the next step if the signal gets too high- it just distorts what you are seeing. It will not damage the QA40x unless you are near around 40vrms. It will start making the clicking sound I showed in the video when this happens- I am not sure what is going on then. Best to start off with max attenuation and decrease it until it starts clicking or you have the best snr or thd. If you do an automated test- which I did not cover in this video- you have the option of having an amount of attenuation added if needed.

[@jamesspurlock4481]

Very nicely done. I'm looking forward to more videos. Idea: Perhaps you could get with Matt of QA and collaborate for a set of videos on using the QA40X, from beginner to advanced.

[@vintageaudioreview]

Thanks for the comment and suggestion. Matt has pretty much told me to do videos on what I want. As I am active on the forums I get an idea what may be useful (IMHO). I was just thinking about that today- possibly measuring a speaker impedance or a high power amp measurement....