Hey everyone
I can see how seriously you, as audiophiles, are thinking about him.
But please re-read his post.
He's not trying to do something like recording where he can't afford to fail. I don't think he would want his daughter to have to seriously stare at a level meter and adjust the ADC level to match the level of each piece of vinyl before listening.
The DAC that receives BT may not only be used to play vinyl, but also listen to CDs and other digital sources. If she switch from vinyl playback with 24dB of peak level margin to another digital sources, she'll hear a blast.
I think he just wants to casually provide her with a better sound than she currently has.
I am posting this with such intention.
We need to know how geeky we are, myself included.😀
I can see how seriously you, as audiophiles, are thinking about him.
But please re-read his post.
He's not trying to do something like recording where he can't afford to fail. I don't think he would want his daughter to have to seriously stare at a level meter and adjust the ADC level to match the level of each piece of vinyl before listening.
The DAC that receives BT may not only be used to play vinyl, but also listen to CDs and other digital sources. If she switch from vinyl playback with 24dB of peak level margin to another digital sources, she'll hear a blast.
I think he just wants to casually provide her with a better sound than she currently has.
I am posting this with such intention.
We need to know how geeky we are, myself included.😀
@mason_f8 Correct, though I do appreciate everyone's input, even if it sometimes misses the mark.
This is not, by any means, a critical/audiophile application. I guess that should have been obvious from the start when I mentioned bluetooth. 😆
The "VU" meters are first and foremost for aesthetics. I thought they might also come in handy so she could have a visual indication of how close to clipping the signal to the ADC is. If they aren't really suitable for that, it's not a big deal.
I set the speakers up for her already, but I'm still waiting on some bits and pieces for this project. I did notice that the BT connection for the speakers has noticeably lower gain than the analog or optical inputs, so there's even less headroom to play with. She will only ever use BT, but there is still a small risk of abrupt volume increase when switching from the phono BT connection to her phone.
This is not, by any means, a critical/audiophile application. I guess that should have been obvious from the start when I mentioned bluetooth. 😆
The "VU" meters are first and foremost for aesthetics. I thought they might also come in handy so she could have a visual indication of how close to clipping the signal to the ADC is. If they aren't really suitable for that, it's not a big deal.
I set the speakers up for her already, but I'm still waiting on some bits and pieces for this project. I did notice that the BT connection for the speakers has noticeably lower gain than the analog or optical inputs, so there's even less headroom to play with. She will only ever use BT, but there is still a small risk of abrupt volume increase when switching from the phono BT connection to her phone.
I was finally able to wire things up and do some testing today. For testing on the receiving end, I'm using an XQ-50 Pro BT receiver, modified BRZHIFI MA12070 Class-D amp, and a pair of JVC S-M3 speakers.
I borrowed a "Poison - Open Up and Say... Ahh!" record from a friend. I figured that should be pretty "hot" compared to most of what my daughter will play (Taylor Swift, etc.). I connected my scope to the output of the phono pre and played one side of the record all the way through a couple times. The maximum RMS value recorded was around 0.93V, and the maximum Vpp value was almost 5V. The record isn't exactly pristine and I didn't clean it first, so there were some pops here and there.
The sound coming from the speakers was pretty good IMO (music selection notwithstanding). Even with the clicks/pops that obviously exceeded the input limit of the ADC, there were no crazy, unexpected noises and the speakers didn't go up in flames. I did have to turn the amp up quite a bit more than if I had something like my phone connected though. There was also more hiss, but I think some of that is from the test configuration.
I'm tempted to increase the sensitivity of the ADC, but as it sits right now, it has about 7dB of headroom. Probably shouldn't reduce that any further.
I borrowed a "Poison - Open Up and Say... Ahh!" record from a friend. I figured that should be pretty "hot" compared to most of what my daughter will play (Taylor Swift, etc.). I connected my scope to the output of the phono pre and played one side of the record all the way through a couple times. The maximum RMS value recorded was around 0.93V, and the maximum Vpp value was almost 5V. The record isn't exactly pristine and I didn't clean it first, so there were some pops here and there.
The sound coming from the speakers was pretty good IMO (music selection notwithstanding). Even with the clicks/pops that obviously exceeded the input limit of the ADC, there were no crazy, unexpected noises and the speakers didn't go up in flames. I did have to turn the amp up quite a bit more than if I had something like my phone connected though. There was also more hiss, but I think some of that is from the test configuration.
I'm tempted to increase the sensitivity of the ADC, but as it sits right now, it has about 7dB of headroom. Probably shouldn't reduce that any further.
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Oh, and a question about noise and grounding. There was a LOT of noise before I connected a wire from the turntable ground to the phono pre ground. There is still some noise like I said before.
The turntable, pre, and ADC/BT are all powered from a separate 2-prong switching supplies. Should there be a ground wire running to the AC outlet earth at some point?
The turntable, pre, and ADC/BT are all powered from a separate 2-prong switching supplies. Should there be a ground wire running to the AC outlet earth at some point?
Music signals are said to have Gaussian properties, similar to white noise.
RMS is the standard deviation σ, and if estimate three times that (that is, 3σ), there is a 99.7% probability that the peak will fall within the range, so the RMS is 0.93V and the peak value is 2.5V, which is close to that.
For switching power supplies, a common mode filter may be useful on the secondary side.
In the case of wall warts, many of them do not have a very high switching frequency, so a device with high inductance may be effective.
RMS is the standard deviation σ, and if estimate three times that (that is, 3σ), there is a 99.7% probability that the peak will fall within the range, so the RMS is 0.93V and the peak value is 2.5V, which is close to that.
In many cases, connecting the earth of the AC outlet creates a loop with the signal line's GND, so the problem may not change or get worse.
For switching power supplies, a common mode filter may be useful on the secondary side.
In the case of wall warts, many of them do not have a very high switching frequency, so a device with high inductance may be effective.
Project complete. Set everything up for her today. She's extremely happy with it, which makes me happy. It sounds pretty good IMO. Well, as good as the Edifier speakers can sound (not too impressed with them).
I think I could have reduced the headroom just a tad, but I guess it's better to have a little too much than not enough. Connected the power button LED to the BT connection status output of the BT transmitter. Works great. Also made up a set of custom cables in white to match the theme.
Thank you all for your comments and insight!
I think I could have reduced the headroom just a tad, but I guess it's better to have a little too much than not enough. Connected the power button LED to the BT connection status output of the BT transmitter. Works great. Also made up a set of custom cables in white to match the theme.
Thank you all for your comments and insight!
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Excellent visually compatible industrial design, in a compact and rugged enclosure. Careful craftsmanship, with great functionality as well; wow! A++
David
David