Buzzing caused by bluetooth receiver only when DAC inactive

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brettstahlman

Audiophyte
Hello,
I have a 1Mii bluetooth receiver and a WiiM Mini wifi streamer connected to the same HTD audio system, located in my basement. When I connect both devices directly to the HTD controller, all is well. However, when I put the 1Mii bluetooth receiver upstairs, powered by a wall outlet, and connected to the HTD controller through CAT6 ethernet with a pair of audio baluns, there's a noticeable buzz through the speakers from the moment I turn on the amplifier until I start playing music, at which point the buzz disappears completely. Suspecting I'd created a ground loop by connecting the 1Mii bluetooth device to an outlet different from the one the HTD controller is connected to, I purchased the BESIGN ground loop isolator from Amazon, but it seemed to have no effect, leading me to wonder whether the issue could be something other than a ground loop. Note that the buzzing stops immediately when I begin playing music and returns a few seconds after the music stops, as though the DAC in the 1Mii device disables its outputs when not in use, allowing something else to drive that buzzing frequency. But what is the source of the buzzing? If it's A/C currents from the power supply induced in the ground loop why do they not persist when the DAC is active?

I'm assuming the BESIGN ground loop isolator uses some sort of transformer to perform the isolation, but if the induced currents are A/C, how does this work exactly? Wouldn't the transformer pass the A/C ground loop currents? Is there an easy way to try disconnecting the shield in one of the cables from the 1Mii bluetooth device? (I'm assuming the RCA cables are make-before-break, preventing me from simply plugging in part way...)

Thanks in advance,
Brett S.
 
highfigh

highfigh

Audioholic Slumlord
Hello,
I have a 1Mii bluetooth receiver and a WiiM Mini wifi streamer connected to the same HTD audio system, located in my basement. When I connect both devices directly to the HTD controller, all is well. However, when I put the 1Mii bluetooth receiver upstairs, powered by a wall outlet, and connected to the HTD controller through CAT6 ethernet with a pair of audio baluns, there's a noticeable buzz through the speakers from the moment I turn on the amplifier until I start playing music, at which point the buzz disappears completely. Suspecting I'd created a ground loop by connecting the 1Mii bluetooth device to an outlet different from the one the HTD controller is connected to, I purchased the BESIGN ground loop isolator from Amazon, but it seemed to have no effect, leading me to wonder whether the issue could be something other than a ground loop. Note that the buzzing stops immediately when I begin playing music and returns a few seconds after the music stops, as though the DAC in the 1Mii device disables its outputs when not in use, allowing something else to drive that buzzing frequency. But what is the source of the buzzing? If it's A/C currents from the power supply induced in the ground loop why do they not persist when the DAC is active?

I'm assuming the BESIGN ground loop isolator uses some sort of transformer to perform the isolation, but if the induced currents are A/C, how does this work exactly? Wouldn't the transformer pass the A/C ground loop currents? Is there an easy way to try disconnecting the shield in one of the cables from the 1Mii bluetooth device? (I'm assuming the RCA cables are make-before-break, preventing me from simply plugging in part way...)

Thanks in advance,
Brett S.
Ground loops are caused when the power circuit has measurable resistance between two (or more) pieces of equipment. Electrons, being the OCD little bastards they are, want everything to balance, so they look for a path that will accomplish this and the easiest place for this is on the audio cable. Hum is AC, the problem comes from directly connecting the equipment's power and signal paths. Break the audio path and the hum stops, so that's the reason transformers are used. Since audio is AC, transformers can do this without blocking the signal.

However, ground loops generally show as hum, not buzz.

I would bet that your baluns are close to a source of MRI or they don't isolate the input from the output. You can check these by moving the baluns away from their current location- if the buzz stops, look for the source- most likely, it's from a wall wart power supply.

If you want to check for isolation, connect a stereo cable to each and, with a short ethernet cable, check for continuity between L+, R+ and the shields. If you see continuity on any, use something else.
 
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B

brettstahlman

Audiophyte
Ground loops are caused when the power circuit has measurable resistance between two (or more) pieces of equipment. Electrons, being the OCD little bastards they are, want everything to balance, so they look for a path that will accomplish this and the easiest place for this is on the audio cable. Hum is AC, the problem comes from directly connecting the equipment's power and signal paths. Break the audio path and the hum stops, so that's the reason transformers are used. Since audio is AC, transformers can do this without blocking the signal.
But wouldn't the currents induced in a ground loop (e.g., by EMI from nearby wiring) also be AC? And if so, how are they blocked by the transformer? Is it because they're generally lower frequency than the audio signal?

However, ground loops generally show as hum, not buzz.

I would bet that your baluns are close to a source of MRI or they don't isolate the input from the output. You can check these by moving the baluns away from their current location- if the buzz stops, look for the source- most likely, it's from a wall wart power supply.
This could be an issue. The baluns are near the TV and the wall outlet that powers it and the bluetooth receiver. I'll try moving it around later today to see how that changes things. Will also try moving the ethernet/balun setup to the basement on the same power supply as the HTD controller to see how that affects things.

If you want to check for isolation, connect a stereo cable to each and, with a short ethernet cable, check for continuity between L+, R+ and the shields. If you see continuity on any, use something else.
Do you mean there might be a short between the shield and the signal wires or just a resistive path that shouldn't exist?

Also, do you have a theory as to how the activation of the DAC eliminates the buzz? (And does the DAC's control over the buzz provide a clue as to the source of the buzz?)

Thanks, Brett S.
 
highfigh

highfigh

Audioholic Slumlord
But wouldn't the currents induced in a ground loop (e.g., by EMI from nearby wiring) also be AC? And if so, how are they blocked by the transformer? Is it because they're generally lower frequency than the audio signal?


This could be an issue. The baluns are near the TV and the wall outlet that powers it and the bluetooth receiver. I'll try moving it around later today to see how that changes things. Will also try moving the ethernet/balun setup to the basement on the same power supply as the HTD controller to see how that affects things.



Do you mean there might be a short between the shield and the signal wires or just a resistive path that shouldn't exist?

Also, do you have a theory as to how the activation of the DAC eliminates the buzz? (And does the DAC's control over the buzz provide a clue as to the source of the buzz?)

Thanks, Brett S.
The ground loop can occur is a car, too., Ever hear a car stereo that whines with the pitch of the whine rising and dropping with RPM? That's a ground loop and it's caused by the same thing, called a 'Potential difference' or 'Difference in Potential', meaning "Voltage can be measured when a meter is connected to two devices". Doesn't matter if it's AC or DC, the voltage needs to be measurable (more than about .1V).

Not a short, the resistance is on the power wires, between one piece and another.

Again, ground loops usually cause hum, not buzz. Buss is usually caused by RF or EMI.
 
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brettstahlman

Audiophyte
The ground loop can occur is a car,m too., Ever hear a car stereo that whines with the pitch of the whine rising and dropping with RPM? That's a ground loop and it's caused by the same thing, called a 'Potential difference' or 'Difference in Potential', meaning "Voltage can be measured when a meter is connected to two devices". Doesn't matter if it's AC or DC, the voltage needs to be measurable (more than about .1V).

Not a short, the resistance is on the power wires, between one piece and another.

Again, ground loops usually cause hum, not buzz. Buss is usually caused by RF or EMI.
So I guess the thing I still don't understand is how the DAC is able to eliminate the buzz when it's active. My theory is that whatever generates the buzz acts like a source with high output impedance. When the DAC is inactive, its outputs are floating (high-Z), but when the DAC switches on, its relatively low output impedance easily overpowers the buzz "source", effectively eliminating the noise it generates. Does this make sense?
Thanks, Brett S.
 
highfigh

highfigh

Audioholic Slumlord
So I guess the thing I still don't understand is how the DAC is able to eliminate the buzz when it's active. My theory is that whatever generates the buzz acts like a source with high output impedance. When the DAC is inactive, its outputs are floating (high-Z), but when the DAC switches on, its relatively low output impedance easily overpowers the buzz "source", effectively eliminating the noise it generates. Does this make sense?
Thanks, Brett S.
An open/un-terminated input circuit acts like an antenna when it's input connections aren't shorted to ground.
 
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brettstahlman

Audiophyte
An open/un-terminated input circuit acts like an antenna when it's input connections aren't shorted to ground.
So does anyone know whether there are any relatively inexpensive streaming devices that pull their outputs low when they're not playing music? Otherwise, I guess I'll either have to stop using the audio over ethernet approach or make sure everyone who uses the device always remembers to start the music before enabling the zone on the amplifier, and conversely, to disable the zone before stopping the music. This constraint wouldn't be so bad if the software controls for those 2 actions were in the same app, but they're not.

Actually, the 1Mii's bluetooth receivers are good enough that even when they're in the basement, I seem to be able to stream from just about anywhere in the house, so maybe I'll just forget about sending balanced audio over cat6 for the time being.
 
highfigh

highfigh

Audioholic Slumlord
So does anyone know whether there are any relatively inexpensive streaming devices that pull their outputs low when they're not playing music? Otherwise, I guess I'll either have to stop using the audio over ethernet approach or make sure everyone who uses the device always remembers to start the music before enabling the zone on the amplifier, and conversely, to disable the zone before stopping the music. This constraint wouldn't be so bad if the software controls for those 2 actions were in the same app, but they're not.

Actually, the 1Mii's bluetooth receivers are good enough that even when they're in the basement, I seem to be able to stream from just about anywhere in the house, so maybe I'll just forget about sending balanced audio over cat6 for the time being.
I think you need to identify the RF source of this noise. Do you have dimmers on lights? Those can cause a lot of noise- shut off the lights and if it stops buzzing, replace the offending dimmer(s).

Why are you using cable to send the audio signal to other areas of the house when WiFi streaming works so well?
 
B

brettstahlman

Audiophyte
I think you need to identify the RF source of this noise. Do you have dimmers on lights? Those can cause a lot of noise- shut off the lights and if it stops buzzing, replace the offending dimmer(s).
It's next to a TV and wall socket, so I would guess that's the source.
Why are you using cable to send the audio signal to other areas of the house when WiFi streaming works so well?
Because WiFi streamers are ~3x more expensive than bluetooth... The Wiim Mini is a great WiFi streamer and has bluetooth as well, but the version with bluetooth is $99 and I'd probably need 4 to cover all the potentially simultaneous users. I was thinking that the $29 1Mii bluetooth receiver was a cost-effective option to permit 4 people to stream simultaneously. But as I said, the 1Mii's receiver is good enough that I could probably locate them in the basement without issue.
 
highfigh

highfigh

Audioholic Slumlord
It's next to a TV and wall socket, so I would guess that's the source.

Because WiFi streamers are ~3x more expensive than bluetooth... The Wiim Mini is a great WiFi streamer and has bluetooth as well, but the version with bluetooth is $99 and I'd probably need 4 to cover all the potentially simultaneous users. I was thinking that the $29 1Mii bluetooth receiver was a cost-effective option to permit 4 people to stream simultaneously. But as I said, the 1Mii's receiver is good enough that I could probably locate them in the basement without issue.
Don't expect great performance from items that cost $29.

The outlet isn't likely to be the source- as I wrote, the wall wart power supply is more likely.

Bluetooth has limitations WRT the number of users who can connect to one device. Look into the Miccus piece- it can be used as a transmitter or receiver, has optical in and out and the range is excellent.
 
B

brettstahlman

Audiophyte
Don't expect great performance from items that cost $29.

The outlet isn't likely to be the source- as I wrote, the wall wart power supply is more likely.

Bluetooth has limitations WRT the number of users who can connect to one device. Look into the Miccus piece- it can be used as a transmitter or receiver, has optical in and out and the range is excellent.
Our home environment has a non-negligible amount of noise pretty much all the time: e.g., hum of laptop fan, HVAC system, outside traffic. In such a decidedly non-studio-quality environment, I'm not sure that the passable sound I get from the 1Mii isn't close to the point of diminishing returns. But the Miccus looks impressive. I may look at upgrading if I notice limitations with the 1Mii.

Ah... I wasn't familiar with the term "wall wart", but now that I am, I'm wondering whether I should try a better power supply more suitable for audio than the cheap phone charging ones I typically have on hand...
 
highfigh

highfigh

Audioholic Slumlord
Our home environment has a non-negligible amount of noise pretty much all the time: e.g., hum of laptop fan, HVAC system, outside traffic. In such a decidedly non-studio-quality environment, I'm not sure that the passable sound I get from the 1Mii isn't close to the point of diminishing returns. But the Miccus looks impressive. I may look at upgrading if I notice limitations with the 1Mii.

Ah... I wasn't familiar with the term "wall wart", but now that I am, I'm wondering whether I should try a better power supply more suitable for audio than the cheap phone charging ones I typically have on hand...
Just don't believe the marketing BS about power supplies that make the sound much better- they don't.

If you bundled your cables, undo that. Never bundle audio or video cables with power cables.
 
B

brettstahlman

Audiophyte
Just don't believe the marketing BS about power supplies that make the sound much better- they don't.

If you bundled your cables, undo that. Never bundle audio or video cables with power cables.
I had a professional low-voltage wiring company do the wiring when the house was built, so I can't really tell how close the audio and power wires are in the wall. Hopefully they knew better than to bundle them, but I honestly haven't been impressed with the way they did some of the stuff I can see, so I guess I don't really know...

But even if the power and audio wires are kept separate, it seems like there's always the potential for ground loop issues whenever you have multiple streamers connected. So is it always recommended to use ground loop isolators with any audio equipment you connect? And are the relatively inexpensive ones you can buy for cars on Amazon effective, or is there a big difference between them and the pricier ones?
 
highfigh

highfigh

Audioholic Slumlord
I had a professional low-voltage wiring company do the wiring when the house was built, so I can't really tell how close the audio and power wires are in the wall. Hopefully they knew better than to bundle them, but I honestly haven't been impressed with the way they did some of the stuff I can see, so I guess I don't really know...

But even if the power and audio wires are kept separate, it seems like there's always the potential for ground loop issues whenever you have multiple streamers connected. So is it always recommended to use ground loop isolators with any audio equipment you connect? And are the relatively inexpensive ones you can buy for cars on Amazon effective, or is there a big difference between them and the pricier ones?
I don't know where you're located, but if you want to do some snooping for yourself, you could buy one of these- doesn't need to be this one, but they can be found for $20 if you search. Make sure the one you buy has a jack for phone or network cable, too. It's called a 'cable toner' and you would use the wand separately, to listen for the buzz.

1653322032536.png
 
B

brettstahlman

Audiophyte
I don't know where you're located, but if you want to do some snooping for yourself, you could buy one of these- doesn't need to be this one, but they can be found for $20 if you search. Make sure the one you buy has a jack for phone or network cable, too. It's called a 'cable toner' and you would use the wand separately, to listen for the buzz.

View attachment 56198
That looks similar to a $50 one I had in my Amazon cart but never pulled the trigger on. I was thinking of using it to tone out the speaker wires in the ceilings where I still haven't installed speakers. The low-voltage contractor left me hand-scrawled "maps", which don't have enough measurements on them to give me more than a moderate degree of confidence on where to cut into the ceiling. I initially got a toner for around $20, which I returned because it didn't seem to be selective enough for the purpose. But in retrospect, maybe I was getting a lot of false positives from power lines because I neglected to cut the breaker?
 
highfigh

highfigh

Audioholic Slumlord
That looks similar to a $50 one I had in my Amazon cart but never pulled the trigger on. I was thinking of using it to tone out the speaker wires in the ceilings where I still haven't installed speakers. The low-voltage contractor left me hand-scrawled "maps", which don't have enough measurements on them to give me more than a moderate degree of confidence on where to cut into the ceiling. I initially got a toner for around $20, which I returned because it didn't seem to be selective enough for the purpose. But in retrospect, maybe I was getting a lot of false positives from power lines because I neglected to cut the breaker?
Toning speaker wires in order to ID them is another reason for having one of these. The probe is the other main use- any electromagnetic interference in the audio range will be found and I have used mine many times for sniffing out noise sources. I wish they had been easier to find when I was doing car audio because it would have saved a lot of time.

BTW- if a cable is completely hidden and you don't want to crawl into the attic, you can make the toner louder by NOT connecting both clips to two wires and clipping one lead to a metal object. I have used the braces on my ladder, pipes, etc. It makes these things scream and it's far easier to find the cables.

You need the breaker ON- the power supplies and other sources won't make the noise and the equipment needs to be able to operate.

I'm not trying to prevent you buying a ground loop isolator, I just want to let you know that buzz is usually interference, not a ground loop. If it actually involves grounding, it's usually bad grounding.

Again, if you have dimmers for the lights, many can and do cause buzzing. Go close to the dimmers with the want and check for buzzing- it will become louder as you approach the source.
 
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