• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). Come here to have fun, be ready to be teased and not take online life too seriously. We now measure and review equipment for free! Click here for details.

Review and Measurements of QuantAsylum QA401 Audio Analyzer

dreite

Active Member
Joined
Aug 10, 2018
Messages
281
Likes
271
Location
Bremerton, WA
#23
I second that question. Terminating inputs make sense, but I doubt the unit appreciates having its output shorted.
Well, they're not exactly shorted. He has 75 terminators attached.
I'm not exactly sure of the topology of the internal output interface, but in some cases a dual op-amp is used to generate both polarities and placing a big (dummy) load on one side could effect the operation of the other side, negatively.
I don't know that's the case here, but it did catch my eye in the photograph. :)

edit: I see these are dual OPA1612 op-amp sections with 47 ohm build-out resistors.

Dave.
 
Last edited:

amirm

Founder/Admin
Staff Member
CFO (Chief Fun Officer)
Joined
Feb 13, 2016
Messages
23,583
Likes
41,115
Location
Seattle Area
#25
56Vp-p looks too low even to test [email protected] amps. Is there any mistake about this number, maybe 56VRMS yet?
No, that is what it says on top of the box. And in the specs:

1566757785484.png


Using 4 ohm load, we can go up to 100 watts. So yes, it is a rather low limit.
 

amirm

Founder/Admin
Staff Member
CFO (Chief Fun Officer)
Joined
Feb 13, 2016
Messages
23,583
Likes
41,115
Location
Seattle Area
#26
Well, they're not exactly shorted. He has 75 terminators attached.
I'm not exactly sure of the topology of the internal output interface, but in some cases a dual op-amp is used to generate both polarities and placing a big (dummy) load on one side could effect the operation of the other side, negatively.
I don't know that's the case here, but it did catch my eye in the photograph. :)

edit: I see these are dual OPA1612 op-amp sections with 47 ohm build-out resistors.

Dave.
That's my bad. Four of the terminators had come with the unit and I must have blindly put them on when it first arrived (months ago). Fortunately it makes no difference as I just tested.
 

amirm

Founder/Admin
Staff Member
CFO (Chief Fun Officer)
Joined
Feb 13, 2016
Messages
23,583
Likes
41,115
Location
Seattle Area
#27
Can you test it for aliasing? That would be nice to know as well in a bit of test gear.
Hmmm. I can't figure out how! The horizontal axis in FFT is fixed at 20 kHz for 48 kHz sampling.
 

Blumlein 88

Major Contributor
Forum Donor
Joined
Feb 23, 2016
Messages
7,620
Likes
8,822
#28
Hmmm. I can't figure out how! The horizontal axis in FFT is fixed at 20 kHz for 48 kHz sampling.
Feed it a sweep that goes up to 80 khz. You'll see what shows up below 24 khz which is the aliasing you are interested in. That is what I did here.
1566759431521.png


You also could feed the ADC fixed tones above 28 khz (which will get aliasing below 20 khz) at a few frequencies and see what the ADC picks up. That would be easier to see in an FFT using the FFT part of the QA401 software.
 

amirm

Founder/Admin
Staff Member
CFO (Chief Fun Officer)
Joined
Feb 13, 2016
Messages
23,583
Likes
41,115
Location
Seattle Area
#29
@amirm My recollection is that FS input was 2 V rms. Why test at 0.7 v rms?
When I was testing it, the clipping indicator came on when I was messing with it which led me to believe without the attenuator it couldn't handle more than 0.7 volt. New value for 2 volt input below.

Can you test the noise floor modulation with 0dBFS (2 V rms) and - 60dBFS?
Here is 2 volt RMS:
QuantAsylum Analog Input QA401 2 Volt Input Audio Measurements.png


So performance drops about 3 dB or so from what I reported.

Here it is at 60 dB lower:

QuantAsylum Analog Input QA401 -60 dB Input Audio Measurements.png


So there is about 20 dB of noise floor modulation based on me eyeballing it at 1 kHz.

Also note that there is no compensation for FFT window for the voltmeter. It shows 1.89 volts with Hann window even though the input is 2 volts. Flat top window fixes that but of course screws up the FFT. AP software compensates for this.
 

amirm

Founder/Admin
Staff Member
CFO (Chief Fun Officer)
Joined
Feb 13, 2016
Messages
23,583
Likes
41,115
Location
Seattle Area
#30
Feed it a sweep that goes up to 80 khz. You'll see what shows up below 24 khz which is the aliasing you are interested in. That is what I did here.
View attachment 31973

You also could feed the ADC fixed tones above 25 khz at a few frequencies and see what the ADC picks up. That would be easier to see in an FFT using the FFT part of the QA401 software.
There is no way to get a cumulative graph like that from QA401 software. It is just a free-running FFT for each FFT window worth of audio samples. So such a sweep just shows what is there at that moment and then erases quickly.
 

Blumlein 88

Major Contributor
Forum Donor
Joined
Feb 23, 2016
Messages
7,620
Likes
8,822
#32
There is no way to get a cumulative graph like that from QA401 software. It is just a free-running FFT for each FFT window worth of audio samples. So such a sweep just shows what is there at that moment and then erases quickly.
The fixed ultrasonic tones should still work. Play a fixed tone at 30 khz and see how much is in the FFT at 18 khz. So on and so forth.
 

Blumlein 88

Major Contributor
Forum Donor
Joined
Feb 23, 2016
Messages
7,620
Likes
8,822
#33
If you find yourself limited by the QA401 Analyser software, you can always fall back to ASIO401 with your analyser of choice. (Full disclosure: I wrote that driver.)
So that would let you use it with REW, Virtins MI or various other software. Sounds like a good addition.
 

March Audio

Major Contributor
Manufacturer
Joined
Mar 1, 2016
Messages
4,601
Likes
5,054
Location
Albany Western Australia
#35
When I was testing it, the clipping indicator came on when I was messing with it which led me to believe without the attenuator it couldn't handle more than 0.7 volt. New value for 2 volt input below.


Here is 2 volt RMS:
View attachment 31974

So performance drops about 3 dB or so from what I reported.

Here it is at 60 dB lower:

View attachment 31975

So there is about 20 dB of noise floor modulation based on me eyeballing it at 1 kHz.

Also note that there is no compensation for FFT window for the voltmeter. It shows 1.89 volts with Hann window even though the input is 2 volts. Flat top window fixes that but of course screws up the FFT. AP software compensates for this.
Thanks @amirm that confirms my own experience.
 

restorer-john

Major Contributor
Joined
Mar 1, 2018
Messages
3,466
Likes
6,557
Location
Gold Coast, Queensland, Australia
#36
It appears to be a fantastic little unit for medium powered amplifier testing/repair or development. Along with the production line capabilities it's just insane value.

As for the interface design mimic, I love it. My bench is covered in real instruments and I like the look of a virtual set of buttons and lights.

:)
 
Joined
Jan 22, 2019
Messages
64
Likes
31
#37
I waited a long time for this test. Fortunately, my $ 50 ASUS sound card is a little better than the QA. The best and cheapest method is still a pure oscillator and a notch filter.
 

audio_tony

Active Member
Joined
Feb 24, 2019
Messages
137
Likes
128
Location
Leeds, UK
#38
I waited a long time for this test. Fortunately, my $ 50 ASUS sound card is a little better than the QA. The best and cheapest method is still a pure oscillator and a notch filter.
Which Asus sound card do you have? I have the Asus Xonar Essence STX, and my figures don't quite match the QA401.

I also have the Asus Xonar DX and that's ever so slightly inferior to the Essence (as one would expect) although in value terms the DX is fantastic value.

THD figures below. SINAD in my case is raised by the amount of 50Hz I have floating about.

2nd harmonic -127dB = 0.0000447%
3rd harmonic -121dB = 0.0000891%
5th harmonic -134dB = 0.00002%

WaveSpectra_Asus.png
 
Joined
Jan 22, 2019
Messages
64
Likes
31
#39
I think it is a Asus Xonar DX. Or DX2? You should increase the FFT buffer higher than 32k and the level -2 or -3 dB below 0dB.
 
Top Bottom