Has anyone identified these distortions as thermal distortion? It should look striking, as it must be a H2 harmonic with -90° phase. For a standard 0.6 W axial wire resistor with a Tc of 50ppm this H2 calculates to -130 dB if 1 kHz sin max power applied. If 10% power applied it should be -150 dB.
Noise related numbers are not valid when using coherent averaging. That is why they are displayed in orange.
I used my dso scope with rms readings but used a 1x bnc to phono wire first with the scope set to 10x so ignore that reading.
Here ive used the correct 10x probe to measure 1vrms from the oscillator then connected it all back up, this is what I have now,
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please can you please switch on phase information for the distortion display, i want to compair that to my motu.
Before I make and post anymore readings I want to make sure my cables are 100% wired correctly, so please correct if any errors
Input from Victors Oscillator Phono to XLR connected at XLR end signal to pin 2 ground to pin 3
Input from Victors Oscillator Phono to STEREO TRS connect signal to Tip and ground to R
Measured signal from dummy load to AutoRanger MONO TRS signal to Tip and ground to Sleeve
Input From Auto Ranger to Motu MONO TRS signal to Tip ground to Sleeve
Input from Victors Oscillator Phono to XLR connected at XLR end signal to pin 2 ground to pin 3
Input from Victors Oscillator Phono to STEREO TRS connect signal to Tip and ground to R
Measured signal from dummy load to AutoRanger MONO TRS signal to Tip and ground to Sleeve
Input From Auto Ranger to Motu MONO TRS signal to Tip ground to Sleeve
Have a look at Wtnh's diagram in post one. This utilizes the balanced input of the MOTU. I can't get rid of the last bits of mains noise (probably needs to be shielded, 0.1% resistors etc.) but gets readings down to ~120dB THD. Xrk how about a nice little active unbal to bal converter with input attenuation and output clamping to protect our sensitive sound cards!
I use this one. It converts any bal/unbal input to bal output.
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For the Motu, such a converter is really a good recommendation. Asymmetric signals show high THD. I use a similar converter to measure asymmetric signals.
Shielding is important, as well as a potentail free power supply, therefore i use a LiO battery pack to operate it. OPA 1656 may be better in terms of noise and THD, but i did not test that.
Shielding is important, as well as a potentail free power supply, therefore i use a LiO battery pack to operate it. OPA 1656 may be better in terms of noise and THD, but i did not test that.