Hi all,
I am using REW for RLC measurements and my soundboard is an ASUS Xonar D1 .
The output level is not enough for measurement of electrolytic capacitors bigger than 2200uF and I would like to ask here for help in finding a schematic/project for a small power amplifier (max. 3W) but with a very good linearity in the 10Hz - 100KHz domain .
Xonar D1 has 100 ohms output impedance and 3.6Kohms line input impedance.
A 4700uF capacitor has about 0.7 ohms capacitive reactance at 50Hz...
The original REW measurement circuit setup is here :
https://www.roomeqwizard.com/help/help_en-GB/html/impedancemeasurement.html
... and I think that I should use something like this:
Well, I think that I could use any ordinary amp that could cover the 10Hz-300Hz domain, in order to measure electrolityc capacitors (especially for ESR), but this will became uncomfortable : for small values of capacitance (< 2200uF) I should switch out the amp from the measurement circuit, and after that I must recalibrate the entire system 🙁
So, if anybody could help me with some ideas and schematics, I will be grateful!
Thanks and all the best!
Robert
I am using REW for RLC measurements and my soundboard is an ASUS Xonar D1 .
The output level is not enough for measurement of electrolytic capacitors bigger than 2200uF and I would like to ask here for help in finding a schematic/project for a small power amplifier (max. 3W) but with a very good linearity in the 10Hz - 100KHz domain .
Xonar D1 has 100 ohms output impedance and 3.6Kohms line input impedance.
A 4700uF capacitor has about 0.7 ohms capacitive reactance at 50Hz...
The original REW measurement circuit setup is here :
https://www.roomeqwizard.com/help/help_en-GB/html/impedancemeasurement.html
... and I think that I should use something like this:
Well, I think that I could use any ordinary amp that could cover the 10Hz-300Hz domain, in order to measure electrolityc capacitors (especially for ESR), but this will became uncomfortable : for small values of capacitance (< 2200uF) I should switch out the amp from the measurement circuit, and after that I must recalibrate the entire system 🙁
So, if anybody could help me with some ideas and schematics, I will be grateful!
Thanks and all the best!
Robert
Were you able to get flat gain and phase frequency spectrums for simplest loopback to either input channel with that soundcard? If so, then for the impedance measurement setup, were you able to get flat spectrums (after full calibration) with confirmation testing of say a short circuit at the DUT terminals, followed by a few example fixed resistor values (eg. 1, 10, 1k, 100k resistors) ?
Adding any extra amp is best done with a physically small and battery powered module, to avoid using mains powered equipment, and equipment that doesn't use a single node for input and output signal 0V (as that node is typically linked in the soundcard and any external noise in the 0V loop may contaminate the system).
Adding any extra amp is best done with a physically small and battery powered module, to avoid using mains powered equipment, and equipment that doesn't use a single node for input and output signal 0V (as that node is typically linked in the soundcard and any external noise in the 0V loop may contaminate the system).
Good evening and thank you for the reply!
@trobbins:
Well, for a 48KHz sampling rate, yes, between 30Hz and 22KHz. However, the phase trace is not too flat, especially after 10KHz:
@trobbins:
@trobbins:
As a matter of fact, I tested a small opamp powered by 2 x 9V batteries . Of course, is not what I need, but I didn't find any artefacts on the graphs.
However, I had an unpleasant surprise this evening.
I tried to use the sound card with Asio4All drivers, set for sampling at 96KHz. Here is the setup during calibration:
... and I obtained a very weird results after the calibration of soundcard process has ended:
Do you have any idea why the graph looks so ugly from 2KHz up ?
Moreover, I noticed another surprising fact.
I have never tried to use my sound card as a signal generator above 20KHz. So I tried to do this now (in this evening) and I found that the REW signal generator module does not allow settings above 20KHz! This, despite the fact that during the measurements, the graph shows that higher frequency signals can be generated.
I wonder if it is a limitation from REW or if it has to do with my sound card?
@trobbins:
Well, for a 48KHz sampling rate, yes, between 30Hz and 22KHz. However, the phase trace is not too flat, especially after 10KHz:
@trobbins:
Yes. If needed, I will upload a screenshot also.
@trobbins:
Well, thanks for the advice, I will keep an eye on this matter.
As a matter of fact, I tested a small opamp powered by 2 x 9V batteries . Of course, is not what I need, but I didn't find any artefacts on the graphs.
However, I had an unpleasant surprise this evening.
I tried to use the sound card with Asio4All drivers, set for sampling at 96KHz. Here is the setup during calibration:
... and I obtained a very weird results after the calibration of soundcard process has ended:
Do you have any idea why the graph looks so ugly from 2KHz up ?
Moreover, I noticed another surprising fact.
I have never tried to use my sound card as a signal generator above 20KHz. So I tried to do this now (in this evening) and I found that the REW signal generator module does not allow settings above 20KHz! This, despite the fact that during the measurements, the graph shows that higher frequency signals can be generated.
I wonder if it is a limitation from REW or if it has to do with my sound card?
I'd suggest any issues relate to your setup, and yes it can take some time and effort to remove poor settings, so best to use simplest loopback to confirm ok operation first - especially if not using standard ASIO, or using a soundcard that nobody else has used (ie. google for any references of its use). Your soundcard is old'ish and is a PC card with multiple channels, so try and find others who have been able to use standard ASIO driver and have settled on the configuration for channels. The card specs do indicate standard ASIO support and out to 192kHz sampling at 24bit, so I'd suggest try and get that basic loopback working for starters.