Can someone advise on how to deal with a new low frequency hum/buzz.

[Roy Slough]

I have a very basic setup, for mixing songs. A laptop using three monitoring methods.
DT770 Pro headphones plugged in to the 3.5mm audio jack of the laptop
A goodmans sound bar plugged into the 3.5mm Audio jack 
My Stereo system (Nad amplifier) connected via a USB behringer audio interface UCA200
I also have a Behringer UM2 USB audio interface which I use mostly as an input device but can be used as an audio output.
None of these produce any hum when connected directly (as mentioned above)

Switching between monitoring methods currently involves plugging in the new method and switching the output in cakewalk (from audio to USB) .
So for Xmas I got a Behringer HA400 HEadphone amplifier with 4 outputs, with the aim of simplifying switching between.

I can connect all the monitor methods (headphones, Soundbar, stereo system) and power the HA400 = no hum.
As soon as I connect the HA400 to the laptop either via the audio jack OR either of the USB interfaces there is a low frequency hum/buzz. (to describe the hum/buzz, In a live environment I used to occasionally get similar hum connecting my guitar to the amplifier depending on the venue we were performing at)
This only occurs as soon as the 3.5mm jack OR USB plug touches the laptop and continues even when fully plugged in. All the volume controls are a zero on the HA400

It isn't there when the HA400 is powered up and connected to any/all of the monitors only when the HA400 is connected to the laptop, so I assume a potential ground loop problem, however all these devices are plugged into the same 4 way extension socket   so the laptop and the HA400 should not have a ground loop issue (Both do have AC/DC adaptors)
I do not believe it is the audio cable from laptop to HA400 as I have tried 2 different cables (same result) and it also is there when the connection is via USB.

Any thoughts or advice please.
Thanks

 

[mettelus]

Also check proximity to any digital/electrical interference (any powered equipment not necessarily "connected" but in close proximity, particularly a cell phone). The USB cable itself is an antenna, so interference may be getting through the shielding.

If you do not use that USB port often, it may also be a dirty connection (this one is uncommon). That will typically clean itself by plugging/unplugging the port several times, but I would do that with the equipment unpowered (since USB can carry power itself and not good practice to cycle a live connection).

The AC adapters may also be feeding each other being in close proximity, so a quick check of unplugging the laptop and running it on the battery may also shed light on the source of the issue.

[Mr No Name]

try using a different plug further away, the cable probably isn't shielded.

[Amberwolf]

Do the laptop ac adapter and the new item ac adapter have grounding plugs?  If not, it isn't an outlet-caused "ground loop". 

If one or both has no ground pin on the ac adapter, then do they both have polarized plugs? (and if they have detachable cords, on *both* ends of the ac cords to the adapters)?  (so that they can only be connected to the AC source in one way)  If it's possible to plug one in either way, try it the other way.  Some devices are not "isolated", and use the neutral side as ground, *and* connect that internally to the negative rail of the DC output, which can cause problems of various kinds.  If the plug is not polarized, it can also lead to worse hum when the neutral-wired side of the system is connected to the hot side of the outlet.   (this "shouldn't" matter, electrically, but it often does). 

 

Does it happen when the laptop is not connected to it's ac adapter, or when the new item is not connected to it's ac adapter (assuming it can operate without it, some can and some can't)?

If it stops when one of them is not connected to teh outlet, then it's likely that one or both have the neutral connected to the DC side ground, and it's allowing AC noise to pass thru into the ground.  Since it didn't happen until you added the new item, it's probably the new item's adapter causing the problem.

 

Since the new item doesn't cause the problem under every test condition so far, it's unlikely that the new item has bad or insufficient capacitors allowing AC noise to pass thru to the DC side, but it could still be that, and a replacement ac adapter that's functioning correctly would fix this issue. 

 

Alternately, if you are electrically-DIY-capable, you can wire up a battery power source for the new item, using an old unused ac adapter's cord that has the same plug as the new item to connect the battery(ies) to the device instead of the actual ac adapter.   That eliminates all possible issues with the ac adapter (grounding, faulty caps, etc).  

[Roy Slough]

On 12/30/2024 at 6:33 PM, Amberwolf said:

Do the laptop ac adapter and the new item ac adapter have grounding plugs?  If not, it isn't an outlet-caused "ground loop". 

If one or both has no ground pin on the ac adapter, then do they both have polarized plugs? (and if they have detachable cords, on *both* ends of the ac cords to the adapters)?  (so that they can only be connected to the AC source in one way)  If it's possible to plug one in either way, try it the other way.  Some devices are not "isolated", and use the neutral side as ground, *and* connect that internally to the negative rail of the DC output, which can cause problems of various kinds.  If the plug is not polarized, it can also lead to worse hum when the neutral-wired side of the system is connected to the hot side of the outlet.   (this "shouldn't" matter, electrically, but it often does). 

 

Does it happen when the laptop is not connected to it's ac adapter, or when the new item is not connected to it's ac adapter (assuming it can operate without it, some can and some can't)?

If it stops when one of them is not connected to teh outlet, then it's likely that one or both have the neutral connected to the DC side ground, and it's allowing AC noise to pass thru into the ground.  Since it didn't happen until you added the new item, it's probably the new item's adapter causing the problem.

 

Since the new item doesn't cause the problem under every test condition so far, it's unlikely that the new item has bad or insufficient capacitors allowing AC noise to pass thru to the DC side, but it could still be that, and a replacement ac adapter that's functioning correctly would fix this issue. 

 

Alternately, if you are electrically-DIY-capable, you can wire up a battery power source for the new item, using an old unused ac adapter's cord that has the same plug as the new item to connect the battery(ies) to the device instead of the actual ac adapter.   That eliminates all possible issues with the ac adapter (grounding, faulty caps, etc).  

Wow a lot of info there.....
OK The HA400 does not have an earth pin on it's adapter (it is plastic) the laptop adaptor does have an earth pin.
The HA400 does not work without power.
The hum goes away if I unplug the laptop ac adaptor.
I have tried plugging the laptop adaptor into different sockets around the room but all produce the hum.
I have also tried plugging the HA400 into different sockets around the room but all produce the hum.
When I unplug the HA400 ac adaptor the hum slowly disappears but I guess this is just the residual current in the ac adaptor fading away.

The laptop can only run a few hours without power so this isn't really a solution

As the hum disappears when the laptop ac adaptor is unplugged what does this indicate?
Would a different adaptor for the laptop produce different results or is it the interplay between the 2 ac adaptors?

Thanks again for the help 

[mettelus]

4 hours ago, Roy Slough said:

The hum goes away if I unplug the laptop ac adapter.

This could be the adapter(s) interfering with each other, but may also be a shielding issue with the laptop internals (pretty rare case). Do both adapters have ferrite beads on them? Again, all cables are antennas and can transmit as well as receive interference if not properly shielded. Another thing to try to test that specifically is to get the wiring from those two adapters as perpendicular to each other as possible (even if coiled up, this gives the lowest interference... same as a single coil guitar pickup in front of an old CRT monitor), or even play with the wiring orientation while monitoring the hum so see if close proximity in parallel makes the hum louder. If those adapters are feeding off each other, also bear in mind the HA400 may have the weaker shielding (i.e., the bigger transmitter)... the diameter of the outside of the cabling is a sometimes an indicator of how much shielding is on a cable. Ferrite beads can help mitigate interference issues with cabling, but they are not always 100%.

Is that hum also getting into the DAW if you record (or input echo) something? If so, you can put something like Voxengo's SPAN on the signal and instantly see what it looks like (as well as how loud it is when moving wiring around). AC hums are going to have a dominant hum at 50/60Hz (depending where you live) and probably a tail of harmonics/partials on them.

[Glenn Stanton]

like a guitar foot pedal collection, DC powered equipment (or low powered AC) - you might look into getting a high quality power supply (or a few) to reduce the noise into your system. a single source of DC (many of the higher end units have multiple voltages and current ratings) should help.

most "wall wart" type power supplies are crap - a simple bridge rectifier and an inductor for some spike management, and even laptop power supplies don't have much filtering.

running all devices (as noted by amberwolf) off a single grounded power strip, keep your power and audio lines aligned (avoiding ground loops) and prefer the lowest noise outlet you can find (no other equipment as this can have other systems feeding noise).

[Mr No Name]

you might find a solution here. https://hiphopmakers.com/best-free-noise-reduction-vst-plugins

[rsinger]

7 hours ago, Roy Slough said:

The hum goes away if I unplug the laptop ac adaptor.
I have tried plugging the laptop adaptor into different sockets around the room but all produce the hum.
I have also tried plugging the HA400 into different sockets around the room but all produce the hum.

Have you tried both plugged into the same socket or using a surge protector or extension cord with multiple outlets? That should solve a ground loop.

[Amberwolf]

13 hours ago, Roy Slough said:

OK The HA400 does not have an earth pin on it's adapter (it is plastic) the laptop adaptor does have an earth pin.
The HA400 does not work without power.
The hum goes away if I unplug the laptop ac adaptor.

If it's a ground loop issue, then a workaround is to get one of those old adapters for plugging a grounded device into a two-prong outlet.   You're suposed to then run the wire from the adapter to a ground somewhere else, but in your case you can't do that because it will cause the hum.   The ground is a safety feature to prevent electrical shock.  I expect that you probably won't have an issue with that, but you should be aware that without a ground the risk exists if certain types of failures happen inside the power supply.  

 

Like this kind of thing

https://www.amazon.com/JACKYLED-Listed-Grounding-Adapter-2-pack/dp/B06XTHWYPK

though I don't know anything about that specific one (I have a couple ancient ones kept in a drawer for various things, including stuff like this). 

 

If you have a multimeter, you can test if the HA-adapter connects the neutral of the ac side to the - side of the dc out; this could cause the hum.   Can't do much about it beside replacing it with a different one that doesn't do that. 

 

Edited yesterday at 01:10 AM by Amberwolf

[Roy Slough]

Thanks Guys,  my head is spinning with all the info.

I should point out I am in UK so US style adaptors are not relevant.

The Sound Bar speaker I use has a ferrite on it's power supply but neither of the others have (laptop & HA400). 

Using a different audio source (e.g. an mp3 player) connected to the HA400 = no hum. The hum only appears when I connect the HA400 via an audio lead (or via USB interface) to the laptop. i.e. I can have the sound bar,headphones etc. connected to the HA400 everything powered on = no hum until linked to the laptop.
(I was mistaken in the earlier post running the laptop on battery still has hum when linked to HA400)

The hum occurs as soon as the lead (audio or USB) comes into contact with the laptop

This was always intended to be a low cost solution to unplugging and switching, I don't really want to invest more money in this, my resources would be better directed elsewhere.  
 

[Mr No Name]

 

Press Play

[mettelus]

3 hours ago, Roy Slough said:

I should point out I am in UK so US style adaptors are not relevant.

This actually adds to potential issues, since you are also running at 230VAC there, correct? If those adapters are not specifically designed for 220VAC, the adapter you are using to bridge the wall wart to the outlet is critical (not sure how you are plugging them in?). Even some gear with a 115/230 switch may still be designed for 115, so the wall wart transformer is humping to deal with a 230VAC feed (can you feel/hear the transformer hum on the HA400 adapter?). IF that gear wants 115, you definitely want an intermediate power strip solution that is designed to step that down 230 to 115 (and "power condition" as well). I suspect more the HA400 is the culprit if you can replicate the hum with the laptop on the battery. That might be worth reaching out to Behringer about, since you may be lucky to get a design engineer involved.

[Sock Monkey]

This was an issue for me years ago ( 2005)  as I have always used a laptop for my backing tracks. It was fine on battery but a very noticeable hum through the PA the minute you plugged the laptop in to AC. 

I was told to simply break off the ground pin so I did. The hum was gone. Great!  A month later the power supply was toast! A buddy who is smarter than me explained why it happened and it was due to the missing ground.  Luckily the laptop was new enough that I managed to by a new one from Acer. This was pre Amazon days. But it was like $180  ouch! 

This forced me to use an audio interface with balanced outputs.  This was is the days when drivers sucked and it would bonk out on me and I'd have to re boot mid show! 

My next Laptop and Asus the hum was not  as loud  but it was still annoying.   

That's when I bought a Radial Trim Two DI box made for Laptops. I don't need an interface and it is passive.  Dead quiet.  

https://www.radialeng.com/product_category/multimedia-di    

 

Edited 15 hours ago by Sock Monkey

[Roy Slough]

Thanks, I have reached out to Behringer to see if they have any good suggestions.

The HA400 power supply accepts Voltage from 100 - 240V, I cant hear/feel any hum on the AC/DC converter itself.
Using an MP3 player as the audio source for the HA400 produces no hum,  even with everything plugged in and powered up = only when HA400 audio input touches Laptop.

The Radial Trim two looks lovely but is way out of my budget for this.

[mettelus]

Another side thought to keep in mind is the return window for the HA400 if still active. One-off issues with electronics will typically occur very early on during regular usage, so if that window is still open you may also have return/replace or outright return as an option if you cannot close the loop on this.

As mentioned early on, a common power strip for all devices that steps down 230 to 115 would be worth trying if you have one available (or could borrow one to test). I *think* everything you mentioned can be run off 115, but not sure.

Edited 1 hour ago by mettelus