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- #21
No, I think it will be fine.Pretty disappointing the USB low power mode has this problem. Do you think that with low impedance headphone, even at low volumes, fidelty is going to be good enough or just ok ?
No, I think it will be fine.Pretty disappointing the USB low power mode has this problem. Do you think that with low impedance headphone, even at low volumes, fidelty is going to be good enough or just ok ?
I did with the dashboard and it made no difference with or without.Could you test it as a DAC-only without an external power supply?
I think we had it a lot lower than that to get 2 volts.P.s. when using it as a dac with outputs from the RCA connections, volume control should be set to 90. 90.5 activates the output opamps.
In that case, from my memory of how Mr. Grace described that it works on Massdrop's forum during their first offering (ie 'drop'), there was a digital volume control that was attenuating the digital signal in play. Maybe that factors into the ultrasonic anomalies you observed? Dunno. Something to experiment with tho I imagine.I think we had it a lot lower than that to get 2 volts.
Performance is excellent in most of the measurements using that same setting. The tests that show poor results are due to ultrasonic tone at 40 kHz.In that case, from my memory of how Mr. Grace described that it works on Massdrop's forum during their first offering (ie 'drop'), there was a digital volume control that was attenuating the digital signal in play. Maybe that factors into the ultrasonic anomalies you observed? Dunno. Something to experiment with tho I imagine.
Indeed, they are. I am just spitballing if having the volume set to anything other than 90, i.e. unity gain for the output from the DAC chip, is a factor or source of that...Performance is excellent in most of the measurements using that same setting. The tests that show poor results are due to ultrasonic tone at 40 kHz.
The RCA line outputs are variable. For reference, a volume setting of "90" is "unity" on the volume attenuator and will result in an output level of 2Vrms for a full scale digital signal (0dBFS). The maximum output level with the volume at "99." is +14dBV (5.1Vrms)
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(this is a copy of a response to the same question on Head=Fi) The m9XX attenuator is a hybrid design. Most of the volume control duties are handled in the digital domain with 32 bit processing but there are two analog gain ranges. This allows a full 98dB of volume control range, preserves a very low noise floor for IEMs, and allows high peak output voltage for low efficiency planar magnetic phones.
I suggest that there may be a minor misconception regarding operating m9xx at an "optimal" volume setting. It is true that setting the volume above 90 raises the noise floor because it raises the gain of the output amplifier. However, the noise floor is constant from 90 all the way down to 0. At the volume setting 90, the digital gain control in the AKM DAC IC is set to 0dB / full scale. I think that it is incorrect to suggest that there is a compromise in signal integrity if the gain is set below full-scale. The digital gain control in the AKM DAC IC is at least as accurate as the volume control in FB2k or other player apps. The AKM DAC IC has a 32-bit datapath and the dynamic range is greater than any analog circuitry and loudspeaker combination you can connect to its outputs. Note too that the channel matching of a digital gain control is far better than a stereo potentiometer. Listeners are often distracted by a bias in perception that louder signals seem to sound better.
I like the way they've done the volume here. Pretty much digital to your standard 2v out for 0 db FS, and some useful analog gain which won't compromise SNR for those who could use more. I wish more devices worked like this.Indeed, they are. I am just spitballing if having the volume set to anything other than 90, i.e. unity gain for the output from the DAC chip, is a factor or source of that...
Massdrop's forum kinda stinks. It's hard to navigate. But I did get lucky with search. Here are some quotes from Michael Grace about the topic...
This is a post from another person ( Caleb Roberts ) on the topic...
All of this is only to say, there is at least some possibility that operating this unit with volume control at a setting other than 90 when using RCA out, 'could' be what is throwing those ultrasonic frequencies.
Perhaps I'm having trouble reading the inset, but it looks like enormous H2 at 32kHz with 40kHz gone.We have that large spike at 40 kHz. The more I increase the frequency, the taller it gets. To wit, the inset is at 16 kHz and by then the 40 kHz tone is at very high levels.
The frequency of the 40 kHz tone is not changing with source frequency. It is its amplitude that increases.
You might be right. Let me fire up the analyzer and check. For some reason when cutting and pasting the graphs in this mode, the AP software deleted the X axis labels after 20 kHz.Perhaps I'm having trouble reading the inset, but it looks like enormous H2 at 32kHz with 40kHz gone.
Good eye and good catch. There is no high 40 khz tone with the 16 khz input tone. It looks like high second harmonic as you said.Perhaps I'm having trouble reading the inset, but it looks like enormous H2 at 32kHz with 40kHz gone.
I don't know for sure. They seem correlated to me seeing how they both showed serious issues with higher bandwidth and higher frequency tones which they both share.I’m not sure I understand your explanation of the poor multi-tone performance @amirm, as the IM seems to be present right throughout the audio band. To clarify, are you of the view that these IM products within the audio band are actually the IM products of tones outside the audio band?
I like the way they've done the volume here. Pretty much digital to your standard 2v out for 0 db FS, and some useful analog gain which won't compromise SNR for those who could use more. I wish more devices worked like this.