Need Help "Short Circuit Measurement i not Valid"

[biogesic]

Hi all, I trying to make the jig for the impedance measurement but Im stuck with calibrating because I always have this error... I dont know what seems to be the problem.. I followed this diagram

 

[John Mulcahy]

The diagram looks wrong, laptop headset inputs usually have a mono mic input and a stereo headphone output and so are not useable for impedance measurement, which requires a stereo input.

 

[Bernard]

Hi all, I trying to make the jig for the impedance measurement but Im stuck with calibrating because I always have this error... I dont know what seems to be the problem.. I followed this diagram View attachment 64937View attachment 64938

Hi,
The diagram posted comes from the "Audio Judgement" website.
You need to read the author's article Measure Thiele Small parameters using free software - Audio Judgement and to watch the "Part 2 : UPDATE video".
It should work.

 

[biogesic]

The diagram looks wrong, laptop headset inputs usually have a mono mic input and a stereo headphone output and so are not useable for impedance measurement, which requires a stereo input.

yes Iv seen part 2 but still got the same results. Im using an external soundcard

 

[biogesic]

The diagram looks wrong, laptop headset inputs usually have a mono mic input and a stereo headphone output and so are not useable for impedance measurement, which requires a stereo input.

Thanks, I was following the diagram for the cable and using this external soundcard for the input and output.... also tried this diagram from the site and also gives me the same error....

 

[trobbins]

Have you confirmed basic loopback measurement is ok from your designated output to separately each designated input ? That should confirm that you have assigned the inputs and outputs in REW 'Preferences' control correctly.

 

[biogesic]

Have you confirmed basic loopback measurement is ok from your designated output to separately each designated input ? That should confirm that you have assigned the inputs and outputs in REW 'Preferences' control correctly.

tried swapping loopback but still have the same results and cant go thru number 2 cal.

 

[trobbins]

Were you able to do a frequency measurement sweep from the designated output, looped back to the designated input, and see a flat-line amplitude and phase response, and where that frequency response changed levels as the output signal level was varied using soundcard settings? And similar for other input channel, and similar for when the input gain control is varied on the soundcard?

 

[John Mulcahy]

For the soundcard use line in and headphone out. Both require stereo jack plugs.

 

[biogesic]

For the soundcard use line in and headphone out. Both require stereo jack plugs.

I managed to solved the issues and successfully getting it to work for few weeks and yesterday I cleared cal and tried to calibrate again but now I get lots of errors and cant get pass 1st cal and cant get the input levels the same...

 

[John Mulcahy]

If that's the open circuit calibration the level should be almost the same on both inputs, which suggests a wiring problem since the measurement input should be getting the same signal as the reference input, just from after the sense resistor.

 

[biogesic]

If that's the open circuit calibration the level should be almost the same on both inputs, which suggests a wiring problem since the measurement input should be getting the same signal as the reference input, just from after the sense resistor.

you're right, I checked the board of my sound card and found out damaged joints , fixed it and its working now.... thank you...

 

[paul_timber]

Hi everyone,

I have the same problem with the impedance calibration in rew. I´m using an external soundcard (Behringer UCA 202) ,which i slightly modified, the Arta Box and an old Pioneer A-604R. At the moment I´m not using a microphone, but that should not be any problem. The open circuit calibration works great, but if i make a short circuit calibration, I get an error. Has anyone any idea how I could fix this? I really tried everything and I still have no clue why it´s not working.

 

[John Mulcahy]

Follow the REW instructions for calibration, leave the box in impedance mode and do not change any settings on it.

 

[paul_timber]

Follow the REW instructions for calibration, leave the box in impedance mode and do not change any settings on it.

Thank´s for the reply.

I read the instructions again, followed it step by step, but I get the same error again. :/

I also check if the wiring is correct and i could not find any error.

 

[John Mulcahy]

Something must be set up wrong. When you do the short circuit measurement the load is shorted, so the measurement input is connected to ground through that short while the ref input gets a direct feed from the output. Since the image you posted shows both inputs have almost exactly the same level the measurement input can't be shorted to ground or the sense resistor isn't in circuit.

 

[paul_timber]

Something must be set up wrong. When you do the short circuit measurement the load is shorted, so the measurement input is connected to ground through that short while the ref input gets a direct feed from the output. Since the image you posted shows both inputs have almost exactly the same level the measurement input can't be shorted to ground or the sense resistor isn't in circuit.

I just measured with a multimeter if the sense resistor is in the circuit and it is. I also check if the wiring of the arta box is correct and I couldn´t find any mistake.

Is there any easy solution without the arta box? If there is one and it would work, i would know, that the problem is the arta box.
Or maybe you have any other idea, why it´s not working?

 

[John Mulcahy]

The minimum circuit is shown in the help, there is very little to it. For it not to work as you have it set up either the switches are in the wrong position (the box should be in impedance mode and on, NOT in cal/off) or something is wrong in the wiring. It should be pretty straightforward to check that when you short the leads where the thing you plan to measure will be connected that you have a good connection to ground right back to the measurement input.

 

[andro]

Hi,
Ive got the same problem with my setup.
My soundcard is the Behringer UCA202 and I use a circuit for impedance measurement only. No switches or frequency response related components to simplify my setup.

I tried to switch around every single hardware input and output as well as probably every "preferences" setting.
Java drivers also didnt help here. I do still guess that it is a software issue?
My circuit is wired correctly, I checked multiple times now. Just a 27.15Ohm Rsense with two voltage dividers before and after the Rsense with diodes for soundcard protection. And a 1k resistor for ground to digital ground decoupling. Thats it.

I would be greatful if anyone could recommend a fix for my issue ;D

 

[John Mulcahy]

My circuit is wired correctly

Evidently something is not correct. How could a short-circuited input have an input level of -30 dBFS?

 

[andro]

Evidently something is not correct. How could a short-circuited input have an input level of -30 dBFS?

Thank you for your fast answer.
I have not short-circuited the inputs themselves, only the outputs from the load connection.

Short circuit cal:

This is my current setup. If I have misunderstood the measurement, a correction would be very helpful or if the circuit does not work like this, that would also be good to know.

 

[John Mulcahy]

Same question basically, with the load shorted the "Cinch out left" should be connected to ground through the parallel combination of 920R and 1.4k, yet the input is seeing -30 dBFS signal level. Your load ground terminal should be connected to the same ground as the inputs, not passing through the 1k earth bleed.

 

[andro]

So should I remove the 1k working resistor and bring the masses without resistance to the same potential? This will probably cause problems with the potential difference between the amplifier and the sound card.

 

[John Mulcahy]

You can't make these impedance measurements if your load doesn't share a common ground with the interface, the interface is trying to sense the voltage across the load.

 

[andro]

Okay, I have connected both grounds, but the automatic circuit breaker in the amplifier doesn't seem to like that. I get clicking noises every second from the amplifier with simultaneous spikes in the REW input graph. The input resistance on my circuit is 4.5kOhm, i.e. the inputs are not short-circuited. I can't say whether it's due to the Class D amplifier, maybe you need a Class AB or something similar?
What is the minimum circuit for the impedance measurement to work? I will build a new circuit if that is the only way to fix this mess.