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GB for Virtins MI Pro for RTX6001 autoranging/autoscaling & for soundcard end users
GB for Virtins MI Pro for RTX6001 autoranging/autoscaling & for soundcard end users
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Old 29th April 2020, 08:15 PM   #641
jan.didden is online now jan.didden  Europe
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Mine too, I did the mods after I bought it.

Jan
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Old 29th April 2020, 11:55 PM   #642
kevinkr is offline kevinkr  United States
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GB for Virtins MI Pro for RTX6001 autoranging/autoscaling & for soundcard end users
I still need to do the mods on mine, but it is reasonably close, and I found a lot of gains by preventing common mode noise from the switcher in my PC from getting back to the line.. (Medical grade isolation transformer) The NUC is much quieter than what it replaced. The RTX does not share the same power connection as the NUC or monitor.

I also have electrostatic shielding under the work space which is grounded to the RTX, these days I am able to work on phono stage designs and get good measurements with 5mV into the DUT, was always a problem before.
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Old 25th May 2020, 10:24 AM   #643
jan.didden is online now jan.didden  Europe
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Default XLR-BNC adapter

The RTX only has XLR inputs to the analyzer, so if you do single-ended measurements you need an adapter. These are standard products and most people have them in their parts box probably.

But there can be a catch, which I ran into. For XLR, pin 2 & pin 3 are the signal pins, pin 1 is the equipment chassis connection. You should never connect pin 1 to signal ground as this normally causes noise on the signal lines.

In XLR-BNC adapters one of the signal lines, normally pin 3, is interconnected to pin 1, opening up the possibility of ground loops and noise.
What to do?

Neutrik (as often) to the rescue. They sell XLR-BNC adapters that are un-assembled where you can wire the internal connections as you want, complete with a pair of stripped short wires! See the attached picture. I build up a pair with the central BNC to pin 2 and the BNC 'ground' tag to pin 3. (The BNC 'chassis' is isolated from the XLR shell). I kept pin 1 internally unconnected; when you plug it into the RTX it connects to the chassis through the shell, and that is how it should be.

When you look for these adapters on the Neutrik website, you won't find them (at least I didn't); you only find NA2MBNC, which is internally wired with pin 3 and pin 1 interconnected.
But Mouser sells the unwired version as NA2MBNC-UW (UW stands for un-wired). The female version is NA2FBNC-UW.

Jan
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Last edited by jan.didden; 25th May 2020 at 10:31 AM.
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Old 25th May 2020, 03:53 PM   #644
1audio is offline 1audio  United States
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GB for Virtins MI Pro for RTX6001 autoranging/autoscaling & for soundcard end users
Jan- On my cables I use 2&3 as a differential input and run pin one as a separate connection tied to the DUT's ground. The Chassis of the RTX is tied to power ground and you want to keep currents in that connection well away from the signal you are measuring.

I just built cables with appropriate connectors at the far end. The weakness of the RTX is the common ground on the source. As it is that becomes an additional ground loop if you aren't watching. If it were isolated then the remaining grounding problem would be resolved.
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Old 26th May 2020, 07:13 AM   #645
jan.didden is online now jan.didden  Europe
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Yes, I have similar cables. For next generation I would vote for both se and bal inputs and outputs.
The AP has output transformers (I'm sure you know), which nicely circumvents the issue, and still gets below -130dB source signal. Not sure we still know how to do that, and how to design xformers that allow that. For one thing, the transformer has a stable resistor wound within the primary that has the same value and the same tempco as the primary winding, which allows completely cancellation of the xformer distortion via positive feedback.
A lost art.

Jan
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Old 26th May 2020, 08:11 AM   #646
mbrennwa is online now mbrennwa  Switzerland
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GB for Virtins MI Pro for RTX6001 autoranging/autoscaling & for soundcard end users
I don't get it... why would you need SE inputs?
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Old 28th May 2020, 04:02 AM   #647
PaulBC is offline PaulBC  Taiwan
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I have two issues when using MI PRO v3.9.

1. After I switched the channels in the ADC device setting dialog for RTX6001, i.e., channel A = R, channel B = L, the auto-ranger doesn't know the channels have been switched and keeps trying to change the range of the wrong channel.

2. I am trying to measure the THD+N vs. frequency for some USB DDC + DAC combinations. The USB DDCs I am measuring now are Musical Fidelity V-Link and TASCAM US-366. When I use the "THD-F" test plan, the signal generator always set the sampling frequency to 4KHz, therefore the THD vs. Frequency test will not go further than 2KHz.

Does anyone have similar issues? Thanks a lot.
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Old 28th May 2020, 05:05 PM   #648
VIRTINS is offline VIRTINS  Singapore
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@PaulBC

Thank you for your questions.

1. Your observation is correct. The [Setting]>[ADC Device]>"Analog Channel Configuration" function is inherited from ASIO which does not have input voltage range selection API. The original intention of this "Analog Channel Configuration" function is to allow the software to select data from any two channels out of up to 200 channels. We did not customize the input voltage range selection of RTX6001 for this function, because RTX6001 has only two input channels.

2. All the preconfigured Panel Setting Files (*.psf) and Device Test Plan (*.dtp) are samples only. You may need to modify them or create new ones to suit your own hardware configuration and test requirements. If you look at [Setting]>[ADC Device Database] and [Setting]>[DAC Device Database], you will find that RTX6001 is customized to support only a subset of sampling rates that are configured for a generic sound card. The PSF files of RTX6001 are thus not fully consistent with those of a generic sound card, in terms of sampling rates and voltage ranges.

The “THD~f” button in the third toolbar (called Hot Panel Setting Toolbar) will load a PSF file named “psf\RTX6001\THD+N_THD_SNR_Magnitude_vs_Frequency_ RTX6001.psf”. You can view this configuration via [Setting]>[Configure Hot Panel Setting Toolbar]. This PSF file will then load a DTP file named “THD+N_THD_SNR_Magnitude_vs_Frequency_RTX6001.dtp” . If you look at this DTP, the first step is to load a PSF file named “psf\RTX6001\THD_FFT65536_SR48000_FifthOrder_RTX60 01.psf”. This PSF file is configured using RTX6001 as both ADC and DAC devices. If the ADC or DAC device is not RTX6001, then it must be modified. To modify this PSF file, configure the ADC and DAC device to be used first via [Setting]>[ADC Device] and [Setting]>[DAC Device], then load the PSF via [Setting]>[Load Panel Setting]. Modify the ADC and DAC sampling rates, then save it via [Setting]>[Save Current Panel Setting]. If you change the PSF file name, then you will have to change the file name in the first step of the DTP as well.

Of course, you can also configure a brand-new DTP dedicated to your own hardware configuration and test requirements.
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Old 28th May 2020, 10:26 PM   #649
PaulBC is offline PaulBC  Taiwan
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Quote:
Originally Posted by VIRTINS View Post
1. Your observation is correct. The [Setting]>[ADC Device]>"Analog Channel Configuration" function is inherited from ASIO which does not have input voltage range selection API. The original intention of this "Analog Channel Configuration" function is to allow the software to select data from any two channels out of up to 200 channels. We did not customize the input voltage range selection of RTX6001 for this function, because RTX6001 has only two input channels.
@VIRTINS, thanks a lot for the detailed explanation.

Will you customize the input voltage range selection of RTX6001 for this function in the next release?

The performance of channel R is a bit better than that of channel L (at least for my RTX6001), therefore I prefer to do 1-channel measurements using channel R instead of channel L. However, the default channel A of IM PRO is channel L. That is why I need to switch the channels.

Thanks again.
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Old 29th May 2020, 06:49 PM   #650
VIRTINS is offline VIRTINS  Singapore
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@PaulBC
I see. In that case, you can probably sample both input channels and display the input Ch. B only. To do that, right click within any graph window and select [Display Ch. B Only] in the popup menu.
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