It's clearly visible in the spectrum without APU in my measurement.
yup
It's clearly visible in the spectrum without APU in my measurement.
I will try changing the VRdiv Vref and re-measure when I have time to see if it has any effectThanks a lot for confirmation @trungdtmc. So my measurement seems not to be flawed.
On both D-6s that I measured the left channel did show the THD-vs-level hump more pronounced than the right channel. I might just measure my third unit the next days to see if this is consistent across all three units.
I'm wondering why the DO400 (1x ES9039Pro) does not show this. The output of each of the stereo channels of the DO400 is the average of 4 DAC outputs of that 8-channel chip. In case the phenomenon is related to limit cycles in the SD-DACs that occur at this level, these limit-cycles would very likely be somewhat different on the 4 merged channels due to tolerances and noise. Each internal channel only contributes 1/4 of the amplitude, so this could provide ca. 12dB attenuation. compared to the D-6s.
If merging of several channels alleviates this hump, e.g. the SMSL RAW MDA-1 or DO100 Pro (2x ES9039q2m, but likely very similar analog stage) should show this hump at the same digital drive level, but ca. 6dB less pronounced.
I might as well try to dig deeper into the noise floor of the DO400 - perhaps a hump will then also become visible.
Any other "dual ES9039q2m" based DAC would be welcome to be measured.
Do you mean the AVCC divider (the resistive voltage divider that makes ca. 3.67V that gets buffered and provides the analog supply voltage AVCC to the output stages)?I will try changing the VRdiv Vref and re-measure when I have time to see if it has any effect
No, i mean this VRDo you mean the AVCC divider (the resistive voltage divider that makes ca. 3.67V that gets buffered and provides the analog supply voltage AVCC to the output stages)?
These are modified on my units in order to get the AVCC down to the recommended nominal value of 3.30V.
Ok. got it.No, i mean this VR
yup, i also just thought of that vref because 9038Q2M hump is affected by it.Ok. got it.
But wouldn't that only adjust the offset at the XLR+/- pins (the RCA is the difference, so it will stay close to 0mV anyway)?
As far as I figured out (see attached pdf) the output stage that SMSL uses is quite straight forward. They do not apply the common-mode "noise" cancellation proposed in one of the datasheets (see attached png) and as a consequence they need an offset adjustment. But to my understanding this should not really have an effect on the DAC chip. Of course adjusting this Vref away from the common-mode voltage of the DAC chip outputs will introduce some DC current into the DAC chip outputs.
Disclaimer: I can't guarantee my schematic extracted from the D-6s is correct, but I'm relatively confident it is correct
There was something related to the operating point of the output stage I remember. The DC current introduced into the DAC chip outputs (when adjusting Vref away from AVCC/2) may indeed have an influence on the SD-modulator.yup, i also just thought of that vref because 9038Q2M hump is affected by it.
Yes, you can.This might be a stupid question, but can I (and should I) connect the XLR to V3 monos and the RCA to a subwoofer?
I'm interested in hearing how!Yes, you can.
There are better ways to create a 2.1 setup, but it'll totally work.
Using the D-6s this way will send identical signals to both the Sub and your main speakers.I'm interested in hearing how!
So you would get a miniDSP Flex and use that as the DAC instead of SMSL D-6s? My plan was to just use the crossover dial on the back of the subUsing the D-6s this way will send identical signals to both the Sub and your main speakers.
Better results can be achieved if you can modify each signal independently, like for example with a miniDSP 2x4 or miniDSP Flex.
I think @staticV3 rather meant that with advanced filtering with one of the miniDSP devices you have more flexibility to achieve a good transition between mains and sub.So you would get a miniDSP Flex and use that as the DAC instead of SMSL D-6s? My plan was to just use the crossover dial on the back of the sub
Ideally I'd like to exclude the low end entirely from the bookshelves and let the sub handle that exclusively - but the price to do that with miniDSP products is as much as an AV receiver which can do the same thing and more, which I struggle to justify!I think @staticV3 rather meant that with advanced filtering with one of the miniDSP devices you have more flexibility to achieve a good transition between mains and sub.
If you want to run the mains full-range and use the internal filtering of the sub, your proposal to wire the amplifiers for the main speakers with XLR and to connect the sub via the RCA jacks sounds very reasonable. The outputs of the D-6s are both active all the time, so this is a straightforward way to connect both.
I'm all for it! I just can't find (or rather, I'm not aware of) a reasonably priced solution that will fit on my desktopThe low frequency roll-off is different depending on if the bookshelves are ported (24dB/octave) or closed (12dB/octave) cabinets, you can use the roll-off of the bookshelves as high-pass filter. If the sub filter is adjustable in frequency and the filter order (24 vs. 12dB/octave) does match, this can work properly.
The drawback of course is a higher distortion due to the bookshelves having hard times when you hear louder. Having a HP-filter well above the LF roll-off of the bookshelves relieves them from this stress.