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Hi, I did some measurements of my Buffalo III build with a R&S UVP analyzer. The setup is: Buffalo III, Placid HD 1.0 (modified as per infos on this forum to get rid of ripple), Trident 3.0 + 22uf to eliminate ringing, AVCC latest version, 8-channel mode, i2s isolated, all channels driven with 1kHz sine wave. Note, that control ic was removed and there was no external control, and thus ess chip was running on hardware defaults. For the measurements, only on output channel was connected. IVY III, Placid HD BP 1.0 (same mods), IVY modified with 0.1% resistors to compensate for 8-channel mode as per integration guide. I took the following measurements: - buffalo output directly connected to analyzer, 44khz and 48khz (no ivy connected) - ivy output to analyzer, 44khz, 48khz, 96khz - one measurement with 0 input signal The results, well, not bad, but after seeing Miero's results (at http://mr.ieero.com/pub/...r_Audio_Buffalo_III_DAC/) I was hoping for somewhat better, at least 3rd harmonic content seems to higher than I'd like. Does this seem reasonable? Any idea improving on 3rd harmonics? Thanks, igy Edited by user Saturday, September 5, 2015 7:52:22 PM(UTC)
| Reason: Not specified igy137 attached the following image(s):  buf 1khz buf 44k.png (22kb) downloaded 34 time(s). buf 1khz buf 48k.png (25kb) downloaded 20 time(s). ivy 1k 44k.png (28kb) downloaded 22 time(s). ivy 1k 48k.png (28kb) downloaded 29 time(s). ivy 1k 96k.png (20kb) downloaded 19 time(s).You cannot view/download attachments. Try to login or register.
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Can you reconfigure analyzer to smaller bandwidth? Because if you are using 200kHz range, then it has limited dynamic range according to the UPV datasheet. Dynamic range: - analog, bandwidth 22 kHz/40 kHz/80 kHz ... 120 dB - analog, bandwidth 250 kHz ... 100 dB Source: https://cdn.rohde-schwar...n_0758-1306-12_v0500.pdf
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Hi Miero, I used 20k bandwidth on all these measurements, am I missing something? BTW, have you done measurements directly using the buffalo outputs? It'd help finding the root-cause, to see if this distortion is coming from the buffalo itself, or it's the ivy which should perform better? igy Edited by user Sunday, September 6, 2015 7:56:13 PM(UTC)
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I'd highly appreciate some reply from TPA.
I'm mainly interested in the expected 3rd harmonics level without using an I/V stage.
Meanwhile I tried different things to see if I could reduce it somehow:
- replacing the transformer with a 80VA model,
- increasing placid hd C2/C3 value to 100uF,
- using shorter cable between placid hd and bufiii,
- checkig with another audio analyzer
Still, I have the same values, with 1kHz 0dB I2S input: 3rd harmonic level at -80dB, (2nd and all other harmonics are at least 20dB lower).
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Can you check voltages (and possible oscillations) on the AVCC?
Output from ES9018 chip should be determined by AVCC with "zero" at half of AVCC voltage.
Try also different signal levels - if the -80dB is relative to signal.
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I'm using a brand new, latest version of AVCC, which I checked upon arrival, I saw no signs of oscillation, the voltages were also ok. (I was actually not that happy seeing that the previous AVCC was having quite some ripple, after I already had to 'patch' the Placid HDs, again, because of some ripple...)
Meanwhile I also put back the original microcontroller, to check if running with it would help reducing artifacts, but in fact the 3rd harmonic just stayed there as it was... I'm pretty clueless, where to go / what to check to identify, where does this distortion is coming from.
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Rank: Member
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Other ideas:
- check if played signal does not contain that 3rd harmonics
- try to decrease input signal by -1dB if something changes
- check balanced outputs
- check if problem persist on the other digital channels #2-#8
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