• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Impact of AC Distortion & Noise on Audio Equipment

solderdude

Grand Contributor
Joined
Jul 21, 2018
Messages
15,891
Likes
35,912
Location
The Neitherlands
My air conditioner affects my equipment. There`s a buzz in AMT on my Adam A77x speakers the AC is running. NO buzz on headphones though.
Both are driven by A90.
So I guess that in high gain amp distortion from AC power would be hearable, and should be seen on if someone would measure tweeter output of the amp. (A77x uses 3 amps, 1 per driver).

The issue is the groundloop created by the active speakers via mains (they are connected via mains as well).
Not dirty mains but common mode currents making it into the audio path. EMC filtering is not going to help here either as it is in the audible range and mains filters do nothing here.
Solutions:
Use a balanced connection or an audio isolation transformer (adds distortion but minimal) or maybe look at the mains wiring (ground used or not)
 

JohnYang1997

Master Contributor
Technical Expert
Audio Company
Joined
Dec 28, 2018
Messages
7,175
Likes
18,292
Location
China
All connections are balanced.
If that includes DAC to the A90 as well. Then it can be direct electromagnetic interference. If you can try to reduce the volume on the speakers and turn up the a90 to compensate for that.
 

solderdude

Grand Contributor
Joined
Jul 21, 2018
Messages
15,891
Likes
35,912
Location
The Neitherlands
All connections are balanced.

Are the speakers silent when the audio cable is not connected ?
Does it start to make noises as soon as you connect it to the A90 ?
When the A90 is connected and on but all inputs are disconnected does it still happen ?
 

kopczas

Active Member
Joined
Oct 6, 2020
Messages
260
Likes
154
Then it can be direct electromagnetic interference. If you can try to reduce the volume on the speakers and turn up the a90 to compensate for that.

The buzz is constant. I can reduce speaker volume to 0, and it`s still there. Level is always the same, from 0 to max volume.
 

kopczas

Active Member
Joined
Oct 6, 2020
Messages
260
Likes
154
Are the speakers silent when the audio cable is not connected ?
Does it start to make noises as soon as you connect it to the A90 ?
When the A90 is connected and on but all inputs are disconnected does it still happen ?


I haven`t investigate this that much. A90 as HP out is silent so I thought this does not come from preamp. I`ve just turned AC off.
 

JohnYang1997

Master Contributor
Technical Expert
Audio Company
Joined
Dec 28, 2018
Messages
7,175
Likes
18,292
Location
China
The buzz is constant. I can reduce speaker volume to 0, and it`s still there. Level is always the same, from 0 to max volume.
So....what if you short the audio input of the speakers? If you don't know how to do that, just unplug the speaker input cables. And see what happens.
 

RayDunzl

Grand Contributor
Central Scrutinizer
Joined
Mar 9, 2016
Messages
13,198
Likes
16,981
Location
Riverview FL
@amirm

Your distorted test wave:

1628182052943.png


Would it make a difference if the major distortions are near the peak, where most equipment will actually draw from the mains?

Does the test setup disturb the voltage on the Neutral?


My AC:

Here's a mains picture from my place a while back, voltage on Hot and Neutral:

170Vpk flat-top sine on the Hot wire and about 4Vpk on the Neutral, both referenced to Earth.


index.php



---

Probably not, but I had to ask, since that's the first thought I had.

As for stuff on neutral, I have 60Vrms on mine now, with the balanced power setup, so the neutral disturbance probably means nothing as well.
 
Last edited:

SDX-LV

Active Member
Joined
Jan 11, 2020
Messages
132
Likes
141
Location
Sweden
Sorry for not reading the whole thing.
While filtering AC mains power for self-powered audio devices is clearly nonsense, I wonder if small USB powered DACs are sensitive to noisy USB 5V power?

Specifically: Apple USB-C to 3.5mm dongle is known to be great in Amir's test, but it is made for battery-powered iPad, where USB power is essentially always very clean. I wonder if this specific Apple dongle and even similar dongles made primarily for phones are as capable to resist power supply noise as the desktop products made to work with desktop PCs and such?
 

H-713

Senior Member
Joined
Jan 24, 2021
Messages
379
Likes
666
@amirm

Your distorted test wave:

View attachment 145595

Would it make a difference if the major distortions are near the peak, where most equipment will actually draw from the mains?

Does the test setup disturb the voltage on the Neutral?


My AC:

Here's a mains picture from my place a while back, voltage on Hot and Neutral:

170Vpk flat-top sine on the Hot wire and about 4Vpk on the Neutral, both referenced to Earth.


index.php



---

Probably not, but I had to ask, since that's the first thought I had.

As for stuff on neutral, I have 60Vrms on mine now, with the balanced power setup, so the neutral disturbance probably means nothing as well.

That looks like the standard distorted waveform I'd expect to be caused by bridge rectifiers - not the effects of a dimmer. Note that the pulses on the neutral perfectly coincide with the flat-topping of the sinusoid on the hot.

Also, because I'm an analog scope nerd, mind if I ask what scope that is?
 

solderdude

Grand Contributor
Joined
Jul 21, 2018
Messages
15,891
Likes
35,912
Location
The Neitherlands
Why exactly shoud I add all that? Cause pluging my iron to mains causes transients there?

It is for making sparks smaller.
 

b4nt

Addicted to Fun and Learning
Joined
May 29, 2021
Messages
803
Likes
270
So that is from the Internet. I beleive dimmer noise ( @solderdude or any such "spakles") on mains lines will look like this:

DimmerNoise.PNG
 

solderdude

Grand Contributor
Joined
Jul 21, 2018
Messages
15,891
Likes
35,912
Location
The Neitherlands
@solderdude I think you have missed #293 and #299 (and see also #311)

299 see my reply #301

(sorry had to make and eat dinner for the fam... poffertjes )

311: You see the voltage waveform + current (voltage across N wire) in this plot. Can't say anything about the current because the neutral to ground resistance is unknown.
 

b4nt

Addicted to Fun and Learning
Joined
May 29, 2021
Messages
803
Likes
270
311: You see the voltage waveform + current (voltage across N wire)

The author of #311 may have to confirm. Current? He wrote:

Here's a mains picture from my place a while back, voltage on Hot and Neutral:

170Vpk flat-top sine on the Hot wire and about 4Vpk on the Neutral, both referenced to Earth.
 

solderdude

Grand Contributor
Joined
Jul 21, 2018
Messages
15,891
Likes
35,912
Location
The Neitherlands
So that is from the Internet. I beleive dimmer noise ( @solderdude or any such "spakles") on mains lines will look like this:

View attachment 145605

it could when the dimmer is set to turn on at 90 degrees phase shift with a high wattage lamp.
What will happen is the 'charging' of the reservoir cap is just very shortly interrupted. I don't think it will be visible on the DC voltage on the reservoir caps because there is too short a time to discharge.
One thing that could happen is some HF can occur because the diodes are temporarily switched on and off.
Depends on the snubbering of the transformer/rectifier.
 

solderdude

Grand Contributor
Joined
Jul 21, 2018
Messages
15,891
Likes
35,912
Location
The Neitherlands
The author of #311 may have to confirm. Current? He wrote:

Here's a mains picture from my place a while back, voltage on Hot and Neutral:

170Vpk flat-top sine on the Hot wire and about 4Vpk on the Neutral, both referenced to Earth.

Yes, as I already mentioned the voltage seen on the neutral is the current from the transformer that causes a voltage across the resistance of the wires in the house between neutral and ground. Most likely they are connected somewhere near the meter.
 
Top Bottom