OP
johny_2000
Senior Member
- Thread Starter
- #61
Correct. I noticed the same 240Hz peak on the battery pack.The only thing of interest I see in the plots are the slightly different mains spurs. For some reason the battery pack setup produced the largest peaks (at 4x, 240Hz) but is cleaner everywhere else. Of course all of this is irrelevant as it is 30dB below the RMS noise floor.
All these low-frequency peaks came from the ether through interconnecting cables. I measured the same thing without the ADI-2 DAC at all. In fact, as soon as any cables were connected to the active notch filter, it already picked up some low-frequency EMI from the environment. So this can be ignored when assessing the overall impact of power supplies.
That's right! I repeated these measurements several times with all three sets on different days and times.To double check, I often repeat the same measurement several times on different days, rigging up the tests again from scratch, and maybe it is slightly colder or warmer or the units haven't fully warmed up etc. +-0.5dB variance is nothing.
The graphs provided are the most representative of the results I saw during the tests.
An interesting proposal for future tests. Please draw a small schematic diagram of your proposals to better understand the conditions:May I suggest another measurement that would expose the effect of different mains leakage currents (the battery pack shouldn't have any), if you want to take the extra effort&time, that is?
- Add a 2-prong 12V/2A SMPS to the set of tested supplies.
- Leave the Intona in place to keep USB clean.
- Measure the unbalanced output of the RME with a normal unbalanced interconnect.
- Don't use the APU notch.
- Connect the shell/GND of the unbalanced interconnect at the receiving end at the ADC Iso to mains earth, to emulate an earth-grounded amp or similar. Alternatively, when using the original three supplies, connect the receiving end shell to the 2-prong supply, emulating an amp with such a supply.
- Play a lower level sine like -30dBFS, sort of a test signal the represents a quiet passages in music
- Look at the resultant SNR and spectra
- Connect the shell/GND of the unbalanced interconnect at the receiving end at the ADC Iso to mains earth, to emulate an earth-grounded amp or similar. Alternatively, when using the original three supplies, connect the receiving end shell to the 2-prong supply, emulating an amp with such a supply.