The XLR inputs are the microphone inputs and they have the lowest noise and distortion, so those are the ones to use. The TRS inputs are the line/instrument inputs and they have higher noise and distortion.
However note that the line/instrument inputs have high input impedance, which can be quite a bonus if you then use 'oscilloscope' 10:1 or 100:1 probes that are designed to work into 1Megohm inputs. Using such a probe increases the peak input voltage capability, and reduces loading on certain DUT circuits - all very handy for certain types of benchwork.
It depends. For pure noise measurements this is true. But for THD-measurements of hi-level amp outputs the line-inputs are your choice.
I have soundcard issues.
Do I use the same soundcard txt file I use for speaker measurements?
I'll read through this thread tomorrow.
Do I use the same soundcard txt file I use for speaker measurements?
I'll read through this thread tomorrow.
You might be seeing noise from your desktop SMPS leaking into the UCA202. If you have a laptop try that and run it on battery power to see if this goes away?
You are running a loop back right? Output of UCA202 to input on front.
You are running a loop back right? Output of UCA202 to input on front.
Hi Mkane77g,
It would be helpful if you show us your setup or at least a sketch or block diagram of the connections and type of equipment and all things in signal path. What is oscillator? What is dummy resistor? Is there a voltage divider? Etc.
I am having a hard time understanding what you did and how it’s connected and what you are trying to measure. An FFT without background info is not helpful for debugging.
Here is how you could describe it to give us the info we need, for example:
“I have an XYZ amp with a 100W wirewound 8ohm dummy load and load is connected to balanced inputs of a UCA202 sound interface via a voltage divider similar to one shown in Post number ABC, using 10k/100k resistors and two 4.7uF caps. The UCA202 is connected to Win 10 desktop PC via USB. PC is powered from wall plug and same outlet strip as the amp. The uCA audio output RCA is connected to the amp input with RCA cable through a preamp model IJK with gain set about 6dB. The preamp is powered with 12v Class 2 wall wart and is ungrounded to mains. Using a Fluke ABC DMM I measure 0.25Vrms input into the amp and 2.5Vrms output at the dummy load. I am exciting the amp with 1kHz sine wave using built in generator in REW.”
Of great interest is how are things grounded?
It would be helpful if you show us your setup or at least a sketch or block diagram of the connections and type of equipment and all things in signal path. What is oscillator? What is dummy resistor? Is there a voltage divider? Etc.
I am having a hard time understanding what you did and how it’s connected and what you are trying to measure. An FFT without background info is not helpful for debugging.
Here is how you could describe it to give us the info we need, for example:
“I have an XYZ amp with a 100W wirewound 8ohm dummy load and load is connected to balanced inputs of a UCA202 sound interface via a voltage divider similar to one shown in Post number ABC, using 10k/100k resistors and two 4.7uF caps. The UCA202 is connected to Win 10 desktop PC via USB. PC is powered from wall plug and same outlet strip as the amp. The uCA audio output RCA is connected to the amp input with RCA cable through a preamp model IJK with gain set about 6dB. The preamp is powered with 12v Class 2 wall wart and is ungrounded to mains. Using a Fluke ABC DMM I measure 0.25Vrms input into the amp and 2.5Vrms output at the dummy load. I am exciting the amp with 1kHz sine wave using built in generator in REW.”
Of great interest is how are things grounded?