# wireless head set Hum sound help

#### frank55

Joined Dec 6, 2013
298
Hi guys i bought this wireless head phones,it works ok with batteries but it also has an input for 4.5 v dc power supply but it did not come with it,i have a few dc power supply i connect any of them and sound coming from the TV or any audio source has a background ground hum, and don't need to connected to source ,as long as i connect it to a Dc power supply ,is there anything i can do to over come this annoying hum riding with sound,it also has a few radio FM channels that don't do that only with audio source or without audio ? also with 2 ,1.5v batteries in the
set doesn't do it,but it eats batteries real fast , thanks in advance and have a marry Christmas

https://www.walmart.com/ip/Professio...phone/39461871

Joined Jan 15, 2015
6,987
Lends me to believe the external power supplies you have tried have poor filtering. You could always just try adding maybe a 100 uF cap and 0.1 uF cap across your DC input. That or invest in a good quality external 4.5 volt power supply.

Ron

#### Audioguru again

Joined Oct 21, 2019
5,206
A DC power supply is not supposed to produce hum but cheap ones do.
Maybe the headphones produce hum when powered from a DC power supply because the main filter capacitor in the headphones circuit is defective or is missing.

If it eats cheap old Chinese "Super Heavy Duty" batteries then try new modern Name-Brand alkaline batteries instead.

#### frank55

Joined Dec 6, 2013
298
Thanks guys ; i believe this headphones set is not well build , i don't think there is any power supply out there that it will work with it ,i tried a few good dc power supply and all do same,i even tried 5 volts dc coming out of the USB port coming out of my router and TV box and it did not even worked with hum or without,well i guess the manufacturer where i bought when i complained and asked to return it and get a refund,they right away did refund me and said also to keep it or donate it, thanks guys i'll try the 100uf an 01uf caps, have a merry Christmas you all.

#### MisterBill2

Joined Jan 23, 2018
13,185
To get rid of the hum from the power supply you can use an external filter capacitor. This will be connected across the power feed between the DC supply and the headphones power connection. The capacitor will need to be rated at least 470MFD and at least 10 volts. 1000 MFD would be better if it is available.

#### frank55

Joined Dec 6, 2013
298
To get rid of the hum from the power supply you can use an external filter capacitor. This will be connected across the power feed between the DC supply and the headphones power connection. The capacitor will need to be rated at least 470MFD and at least 10 volts. 1000 MFD would be better if it is available.
Thanks MisterBills2 , i already tried per instructions of member Reloadron;100 uF cap and 0.1 uF cap across your DC input ,but it did nothing ,i will try 470uf or 1000uf, i send a pic of scheme ,is this the way a should do it?

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#### MisterBill2

Joined Jan 23, 2018
13,185
Thanks MisterBills2 , i already tried per instructions of member Reloadron;100 uF cap and 0.1 uF cap across your DC input ,but it did nothing ,i will try 470uf or 1000uf, i send a pic of scheme ,is this the way a should do it?
YES, that is the way that I was intending it to be. You got it exactly right.
And if that is not enough, , adding a regulator to a higher voltage supply is another option. Do you have a meter to check the voltage and the polarity, because with a polarized capacitor polarity is very important.

Joined Jan 15, 2015
6,987
Yes, your drawing would be correct. While my 100 uF may have been a little low I would think 470 or 1,000 uF would remove any hum. Looking at a 6.0 VDC AC mains adapter (120 VAC 60 Hz Input) I see no discernible AC component on the output. AC coupled to my scope with vertical deflection of 5.0 mV/DIV. Judging by weight and appearance this AC adapter is likely a linear type using a transformer. If you can't remove the hum with additional filtering I have to wonder where it is coming from? The thing works with batteries, no hum.

Ron

#### frank55

Joined Dec 6, 2013
298
Yes, your drawing would be correct. While my 100 uF may have been a little low I would think 470 or 1,000 uF would remove any hum. Looking at a 6.0 VDC AC mains adapter (120 VAC 60 Hz Input) I see no discernible AC component on the output. AC coupled to my scope with vertical deflection of 5.0 mV/DIV. Judging by weight and appearance this AC adapter is likely a linear type using a transformer. If you can't remove the hum with additional filtering I have to wonder where it is coming from? The thing works with batteries, no hum.

Ron

Hi;Redoadron; i installed the 1000 cap in the line but same result,but i had an old PC power supply in my scrap and connected it to the 5 v dc line and much better,but it's kinda expensive on electricity to have a PC power supply for this,but if i have no alternative will use it and turn it off when it's not in use ,thanks and have a Merry Christmas

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#### TeeKay6

Joined Apr 20, 2019
572
Yes, your drawing would be correct. While my 100 uF may have been a little low I would think 470 or 1,000 uF would remove any hum. Looking at a 6.0 VDC AC mains adapter (120 VAC 60 Hz Input) I see no discernible AC component on the output. AC coupled to my scope with vertical deflection of 5.0 mV/DIV. Judging by weight and appearance this AC adapter is likely a linear type using a transformer. If you can't remove the hum with additional filtering I have to wonder where it is coming from? The thing works with batteries, no hum.

Ron
Perhaps from common mode? Unless the wall-wart has a ground pin it likely has substantial 60Hz common mode noise on the output. That might account for why a grounded PC supply is better.

#### MisterBill2

Joined Jan 23, 2018
13,185
It may also be that the wall wart used has only a half wave rectifier, possibly a bad diode or broken solder connection. So quite probably finding a different wall wart would give better results. The worst case, because of more work and expense, would be to get a higher voltage supply and use an IC regulator, such as a 7806 linear device. With a 12 volt supply it should not deliver any hum.
OOPS! I looked at that setup of mine and I see that the capacitor is 4700MFD, not 470. That may explain why it works.

Joined Jan 15, 2015
6,987
Perhaps from common mode? Unless the wall-wart has a ground pin it likely has substantial 60Hz common mode noise on the output. That might account for why a grounded PC supply is better.
I sort of think a grounded PC supply is overkill for a set of $30 Walmart headphones. The thread starter already mentioned having tried several supplies with no joy. I thought that a little unusual. They do work with batteries though. Ron #### MisterBill2 Joined Jan 23, 2018 13,185 I sort of think a grounded PC supply is overkill for a set of$30 Walmart headphones. The thread starter already mentioned having tried several supplies with no joy. I thought that a little unusual. They do work with batteries though.

Ron
Indeed! Grounding is only suitable for some problems, for others it is at bet a waste of effort. Because we know that the phones work hum free on battery power we also know that the hum is from the power supply. And unfortunately we have no information as to what the TS can do and what measurements they can make. Also it is not clear how much of our explanations the TS can understand.

#### frank55

Joined Dec 6, 2013
298
Indeed! Grounding is only suitable for some problems, for others it is at bet a waste of effort. Because we know that the phones work hum free on battery power we also know that the hum is from the power supply. And unfortunately we have no information as to what the TS can do and what measurements they can make. Also it is not clear how much of our explanations the TS can understand.
thanks guys you are the best,i also tried a 3vdc connected to the batteries connectors same result,also tried my Netgear usb 5 v port and Android TV box Usb and a whole bunch of USB chargers same result,i don't even know how to open this thing without being afraid to brake it ,it has no screws, i don't know how this guys can build such of a crap thing and call it professional? i'm goinmg to try the 4700 uf ,last try,i'm fad up with this crap thing, i should known better, and reed reviews on amazon about this thing that trash it all the way, normally i don't fall for this,but even smart and knowledge people fall for it, luckily it came out for free,thank you all for trying for help, if i find any solution to this hum crap i will post,

#### MisterBill2

Joined Jan 23, 2018
13,185
The assembly may be a snap-together type that is cheaper to build and impossible to service. Unfortunately there is a whole realm of "Design for Assembly" thinking that may actually reduce the cost to produce a product but make it impossible to ever service or repair.
One more option not mentioned yet is to build your own adequately filtered power supply. There are hundreds of designs available and at least 12 of them for the exact voltage and current that your application requires. Just be sure to use an adequately isolated transformer with no current leakage between the mains (primary) and the output connection.
Both the "schematicsforfree" website and the "Free informationsociety" websites have power supply circuits available. There are lots of others, but these are the ones that I am familiar with.

#### frank55

Joined Dec 6, 2013
298
The assembly may be a snap-together type that is cheaper to build and impossible to service. Unfortunately there is a whole realm of "Design for Assembly" thinking that may actually reduce the cost to produce a product but make it impossible to ever service or repair.
One more option not mentioned yet is to build your own adequately filtered power supply. There are hundreds of designs available and at least 12 of them for the exact voltage and current that your application requires. Just be sure to use an adequately isolated transformer with no current leakage between the mains (primary) and the output connection.
Both the "schematicsforfree" website and the "Free informationsociety" websites have power supply circuits available. There are lots of others, but these are the ones that I am familiar with.
Thanks mate and have a Merry Christmas

#### Rich2

Joined Mar 3, 2014
242
I built an amplifier years ago. The input had an IC for altering bass/treble and loudness which I added later, but with it came an annoying humm. I tried all sizes of capacitor to no avail. In the end I cured it completely by putting a 1 ohm resistor in series with the chips power supply. Can't remember if it was before or after the smoothing capacitor though

#### MisterBill2

Joined Jan 23, 2018
13,185
I built an amplifier years ago. The input had an IC for altering bass/treble and loudness which I added later, but with it came an annoying humm. I tried all sizes of capacitor to no avail. In the end I cured it completely by putting a 1 ohm resistor in series with the chips power supply. Can't remember if it was before or after the smoothing capacitor though
That resistor in series converted the one section filter into a two section filter, and that is what it took. A multiple section filter will usually be more effective than a single section filter.. It might work for the headphone system as well..

#### MisterBill2

Joined Jan 23, 2018
13,185