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Problems with impedance measurement
Problems with impedance measurement
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Old 8th March 2018, 04:11 PM   #21
sese317j is offline sese317j  Germany
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Default Way better

I now added a headphone jack to my measurement jig to measure with the headphone out of my behringer.

Click the image to open in full size.
The measurement of the 3R9 resistor looks a lot better compared to the one with the line level outputs, but still has the issue.

Click the image to open in full size.

Im now going to try to measure the impedance with the speaker hooked up to the amplifier.
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File Type: jpg cK02LM0.jpg (951.7 KB, 184 views)

Last edited by sese317j; 8th March 2018 at 04:14 PM.
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Old 8th March 2018, 05:30 PM   #22
mbrennwa is offline mbrennwa  Switzerland
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Quote:
Originally Posted by sese317j View Post
Im now going to try to measure the impedance with the speaker hooked up to the amplifier.
You won't get good data below 100 Hz.

Did you set the volume of the phones out to max.?

Do you have another soundcard to try? Maybe your computer has a built audio in/out?
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Old 9th March 2018, 03:21 PM   #23
sese317j is offline sese317j  Germany
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Default finally got a good measurement

Today i tried to measure the 3R9 resistor with the headphone out and mic in of my laptop and the measurement looks fantastic.

Click the image to open in full size.

So my final advice is not to use the behringer UCA 222 for impedance measurement, the headphone output on your computer is probably better for impedance measurements.

Thank you all for your helpful suggestions, now i can finally measure correct impedance curves.

Last edited by sese317j; 9th March 2018 at 03:31 PM.
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Old 25th March 2018, 02:18 PM   #24
Mario Pankov is offline Mario Pankov  Europe
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Problems with impedance measurement
Quote:
Originally Posted by Lojzek View Post
Mario, can this small Behringer sound card measure a resistor impedance to be a flat line or not, from start to beginning? Inductive audio resistors are not a problem, they measure ruler flat to 20 kHz.
Ralf already posted results before me, sorry was away. I may run one with mine, its modified and can deliver higher current, in short - yes it can be used but not in its stock form.
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Old 28th August 2018, 07:51 AM   #25
Mario Pankov is offline Mario Pankov  Europe
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Problems with impedance measurement
The rise in impedance below impedance peak is caused by this Behringer`s layout. It is DC coupled and has 100uF output capacitors on the headphone out (and the output RCAs). And they cause the rising impedance below Fs. Mod is easy - change the opamp to a better one (it has a 4560 inside which is glued to the PCB) like an AD8565, remove completely the output 47R resistors (short them) and replace the outptu caps with largest possible - I managed to fit 1800uF 6.3V Panasonic FR inside and when set at full power, the rise is gone even with 4 ohm drivers.
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Old 28th August 2018, 08:29 AM   #26
Lojzek is offline Lojzek  Croatia
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So it's sorted then. Very good.
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Old 28th August 2018, 09:13 AM   #27
giralfino is offline giralfino  Italy
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Mario, how are marked those components on the PCB?
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Old 28th August 2018, 12:32 PM   #28
Mario Pankov is offline Mario Pankov  Europe
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Problems with impedance measurement
Hi Ralf,

need to open my unit, I modded it (I have modded two indeed but the first one died in a motherboard failure which sent a surge through the USB port) some year ago. Will post details this evening once I get home.
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Old 28th August 2018, 09:12 PM   #29
Mario Pankov is offline Mario Pankov  Europe
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Problems with impedance measurement
I took mine apart. The resistors that are in series with the headphone amp output are R36 and R41 - both around 47R. You can short them. The caps are C15 and C16 to the opposite part of the PCB. Here you put the largest possible that can fit, these are 1800uF 6.3V Panasonic FR - pretty compact. You can also replace the headphone chip to an AD8656 without any modifications, will work fine (its made for low voltage rail) and sound better than the original one. Around EUR 3 from farnell.

And finally, an impedance measurement on a 8 ohm resistor after the mod. Note the decline in the region above 10Khz, at 20Khz the cursor showed 7.15 ohms on a 8 ohm resistor. Not sure of the cause - there are two inductors on the PCB which might be on the output but I didn`t go that far.

Despite its pretty good performance, it would be much better to use a USB interface that has no output capacitors or so, like the M Audio or Focusrite series.
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Old 29th August 2018, 08:09 AM   #30
giralfino is offline giralfino  Italy
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Thanks a lot!
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