Hello--
I've got an Audio Note Kit 2.1 DAC which, when not playing music, produces a high pitched noise. If I play music, it stops. When I pause a track, there will be no high pitched whine for a second or two, but it always returns. It is volume dependent and I must turn the amplifier up pretty high to hear it. Currently don't have an oscilloscope to do any measurement, but will have a very basic one soon. In the meantime, I've used an online tone generator and the high pitched noise seems to be something like ~12 kHz.
There is a deactivated ANK forum that I have searched for help on this issue to no avail. Also consulted Brian, ANK proprietor, but did not have great luck with him on it. He basically offered to send me a new AD1865, then didn't, then said "this has only happened with 1 other kit and we have never been able to reproduce it."
So I'm here. If this is an inappropriate post on DIYAudio, please let me know and we can delete it.
The DAC can be broken into two halves: analog and digital. A single transformer feeds a digital and analog power supply.
The analog power supply is AN's "M2 power supply," which uses a 6X5 and an ECL82. This feeds into an output stage which uses two 6DJ8s.
The digital power supply is a basic Schottky diode bridge rectifier with (going by eye) an RC filter. This outputs at +/- ~9V to the pre-assembled DAC board. I do not have a schematic for the DAC board or the power supply, unfortunately. The DAC board features an AD1865N-K and a CS8414 Digital Audio Receiver chip.
The DAC board and the analog out board are transformer coupled via I/V transformers.
I use a Raspberry Pi with a JustBoom DigiHAT with Moode to stream via Qobuz.
Does anyone have suggestions for how to investigate this? As mentioned, I will have a basic oscilloscope available soon. Is there any way to determine if this originates via the digital or analog side?
Is this known behavior amongst DACs?
You can find images of the kit here:
Shared album - Kyle Karthauser - Google Photos
(Note that I am using a SS faux-tube rectifier in lieu of a 6X5 right now--6X5GT just died and I wanted to give one a shot)
Please let me know if any additional details on the issue or the DAC would be helpful.
Thanks!
I've got an Audio Note Kit 2.1 DAC which, when not playing music, produces a high pitched noise. If I play music, it stops. When I pause a track, there will be no high pitched whine for a second or two, but it always returns. It is volume dependent and I must turn the amplifier up pretty high to hear it. Currently don't have an oscilloscope to do any measurement, but will have a very basic one soon. In the meantime, I've used an online tone generator and the high pitched noise seems to be something like ~12 kHz.
There is a deactivated ANK forum that I have searched for help on this issue to no avail. Also consulted Brian, ANK proprietor, but did not have great luck with him on it. He basically offered to send me a new AD1865, then didn't, then said "this has only happened with 1 other kit and we have never been able to reproduce it."
So I'm here. If this is an inappropriate post on DIYAudio, please let me know and we can delete it.
The DAC can be broken into two halves: analog and digital. A single transformer feeds a digital and analog power supply.
The analog power supply is AN's "M2 power supply," which uses a 6X5 and an ECL82. This feeds into an output stage which uses two 6DJ8s.
The digital power supply is a basic Schottky diode bridge rectifier with (going by eye) an RC filter. This outputs at +/- ~9V to the pre-assembled DAC board. I do not have a schematic for the DAC board or the power supply, unfortunately. The DAC board features an AD1865N-K and a CS8414 Digital Audio Receiver chip.
The DAC board and the analog out board are transformer coupled via I/V transformers.
I use a Raspberry Pi with a JustBoom DigiHAT with Moode to stream via Qobuz.
Does anyone have suggestions for how to investigate this? As mentioned, I will have a basic oscilloscope available soon. Is there any way to determine if this originates via the digital or analog side?
Is this known behavior amongst DACs?
You can find images of the kit here:
Shared album - Kyle Karthauser - Google Photos
(Note that I am using a SS faux-tube rectifier in lieu of a 6X5 right now--6X5GT just died and I wanted to give one a shot)
Please let me know if any additional details on the issue or the DAC would be helpful.
Thanks!
Last edited:
The tubes are faulty, check the voltages around those.
Who puts tubes as the analog section in a DAC, except fanatics?
The fanatics of pure sound should have an analog source.
I take it the company has low volumes, and not doing well?
If you have analog outputs on the computer, experiment with different software, and use the output to an amp that takes analog inputs.
Who puts tubes as the analog section in a DAC, except fanatics?
The fanatics of pure sound should have an analog source.
I take it the company has low volumes, and not doing well?
If you have analog outputs on the computer, experiment with different software, and use the output to an amp that takes analog inputs.
Just a guess but perhaps the CS8414 is losing lock when no music is playing? When you have a 'scope available, check the MCLK out of the CS8414 and see if the frequency changes between playing and not playing music.
No idea if this is applicable at all, but a whine can be a mixing product between ultrasonic signals. For example, I remember an analogue mixing deck with a soft high-pitched whine that turned out to be due to voltage regulators oscillating at about 100 kHz, but all with a slightly different frequency. Each channel had its own regulators with too small decoupling capacitors at their inputs.
Eureka???
Marcel--
You may have figured it out. The schematic indicates that the capacitors near the L78S05 regulators should be 470uf, but the installed caps are 10uf.
🙁
The whine noise is actually audible with my head near the chassis. When I received my parts, more than a handful were not within spec according to the assembly manual. Again, if anyone is at all familiar with Audio Note Kits, this is a standard experience. I was assured that all substituted parts would function normally. Needless to say, at the time I assembled the kit, I knew very little about electronics. Since then I have "hit the books" and am working on my understanding of audio circuitry and components.
Going to order some new caps!
Marcel--
You may have figured it out. The schematic indicates that the capacitors near the L78S05 regulators should be 470uf, but the installed caps are 10uf.
🙁
The whine noise is actually audible with my head near the chassis. When I received my parts, more than a handful were not within spec according to the assembly manual. Again, if anyone is at all familiar with Audio Note Kits, this is a standard experience. I was assured that all substituted parts would function normally. Needless to say, at the time I assembled the kit, I knew very little about electronics. Since then I have "hit the books" and am working on my understanding of audio circuitry and components.
Going to order some new caps!
I've just installed the new 470uF caps. The noise is reduced somewhat, and I can no longer hear it with my naked ear next to the chassis. But it does persist. I will do a voltage check and attempt to measure the MCLK as well.
Another update: I removed a choke from the power supply module. Power supply for the tube output stage is CLC into a 6BM8 tube regulator setup. This has removed the high pitched whine from the comfortable listening section of the volume control of my headphone amplifier. I can no longer hear any noise at all from the DAC from my work desk, where I'm about 3 feet away. If I get close, however, I can hear noise from the main transformer (which is quite large). Unfortunately that will be hard to replace, as it's a custom TX that comes with the kit and has quite a few outputs on it.
Unfortunately have not been able to use the oscilloscope I mentioned earlier since my other posts. Maybe I will get one for Christmas?
Appreciate all the comments and advice up to this point. Just wanted to post an update.
Unfortunately have not been able to use the oscilloscope I mentioned earlier since my other posts. Maybe I will get one for Christmas?
Appreciate all the comments and advice up to this point. Just wanted to post an update.
I should have said in the post above that I was curious if the choke was a source of the whine I am hearing. With my ear close to the power supply section of the DAC with the cover off, it seemed plausible. Hence my decision to try and remove it.
2023 update:
I still have not resolved this issue. But after encountering tube oscillation in another build, I'm pretty certain that's what I'm dealing with. One set of 6922 I tried produced out-and-out oscillation, in fact--so bad that I can't even use them. As the sound appears to disappear when playing, I've just learned to live with it. It's barely audible at my listening position with no music playing. Eventually I need to revisit my build and see where I can shorten leads and insert grid-stopper resistors where needed. According to the schematic, there are 100 ohm grid resistors already in-circuit, which is mildly troubling. Since it's a PCB-based build, I am not certain how I am going to accomplish this, though I have seen people soldering ferrite beads onto socket/tube leads.
I still have not resolved this issue. But after encountering tube oscillation in another build, I'm pretty certain that's what I'm dealing with. One set of 6922 I tried produced out-and-out oscillation, in fact--so bad that I can't even use them. As the sound appears to disappear when playing, I've just learned to live with it. It's barely audible at my listening position with no music playing. Eventually I need to revisit my build and see where I can shorten leads and insert grid-stopper resistors where needed. According to the schematic, there are 100 ohm grid resistors already in-circuit, which is mildly troubling. Since it's a PCB-based build, I am not certain how I am going to accomplish this, though I have seen people soldering ferrite beads onto socket/tube leads.
Having a look at the info for this kit it seems it deliberately has no DAC reconstruction filter, which is bad news and easily accounts for beat frequencies mixing down to the audio band - shows a lack of basic engineering understanding if you ask me.
You very well could be right!
I drank some kool aid when I bought this.
Can I duct-tape a filter onto the AD1865 output?
I drank some kool aid when I bought this.
Can I duct-tape a filter onto the AD1865 output?
If the noise sounds a bit like a mosquito buzzing at your ears it can be digital noise.
If that is the case it can be coupled by the EMF emiited by the digital path to the analog path(s) or could be present due to a ground loop or insuficient decoupling capacitance.
Does the clock runs continuously?
If that is the case it can be coupled by the EMF emiited by the digital path to the analog path(s) or could be present due to a ground loop or insuficient decoupling capacitance.
Does the clock runs continuously?
It sounds exactly like the oscillation I have heard when working on amps with triode-strapped pentodes loaded with gyrators.
I've been told to try and hook an oscilloscope up to the AD chip to measure a few things but since my two kids have been born and are now aged 2 and 4, I barely have time for anything like that. The sound stops when I play music and then, after I pause the music, is silent for about 2-3 seconds before resuming.
I was told by the audio note kit guy (Brian, of dubious reputation), "That this has only happened a couple times," and had no advice on it.
It sounds great to me otherwise and it's not tough to live with for the time being.
I've been told to try and hook an oscilloscope up to the AD chip to measure a few things but since my two kids have been born and are now aged 2 and 4, I barely have time for anything like that. The sound stops when I play music and then, after I pause the music, is silent for about 2-3 seconds before resuming.
I was told by the audio note kit guy (Brian, of dubious reputation), "That this has only happened a couple times," and had no advice on it.
It sounds great to me otherwise and it's not tough to live with for the time being.
All part of the AN magic and most AN buyers even like it better because of the issues. Does this one have the SPDIF transformer at the input?
I have finally resolved the issue. The leads connecting the DAC to the so-called "I/V transformers" and then to the voltage gain stage were too long. I halved the lengths and no more whine.
Have been thinking of doing this for a while based on subsequent experiences, especially with Ale Bartola's gyrators. Finally found the time.
Thanks for everyone's contributions and time.
Have been thinking of doing this for a while based on subsequent experiences, especially with Ale Bartola's gyrators. Finally found the time.
Thanks for everyone's contributions and time.