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Author Topic: AC hum are easily heard due to the present power adaptor  (Read 764888 times)
OBiSupport
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Posts: 267


« Reply #20 on: March 22, 2011, 10:40:24 am »

Customers who use a cordless phone base station connected to the OBi device are not affected.  From our observation the majority of customers use a cordless phone with their OBi and are not affected in any way / do not observe this issue.

Although Obihai has tested a multitude of handsets at all price point and construction quality levels which do not exhibit an audible hum, it has been observed that in rare occurrences, some corded phones will experience an audible hum on the telephone handset to which the OBi device is connected.

It has been observed by some members on this forum, that using a 12V linear power adapter gets rid of the observed hum.

Here are the specifications of the power adapter Obihai Technology provide in the original packaging:
US, EU & UK Style Prongs:
Input: 100V-240V- 0.6A 50/60Hz
Output: +12V=1A Max - Center Positive


AU Style Prong:
Input: 220V-240V- 0.3A 50/60Hz
Output: +12V=1A Max - Center Positive


Obihai will not warrant the failure of a device which does not use the switching power adapter included with the original packaging.  

Due to wide-reaching environmental / regulatory policy the use of a 12V linear power supply as part of the original packaging (and specification) is not possible.

However, at the customers' own risk, a linear (or switching) power adapter which matches the above mentioned Output rating and fits the physical barrel connection could be used with the OBi.  Again, this is neither advised nor supported by Obihai. Obihai will not provide a warranty for devices used in this manner.



« Last Edit: March 22, 2011, 05:20:53 pm by OBiSupport » Logged
Gogyroswin
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« Reply #21 on: March 26, 2011, 02:29:33 pm »

I have the same issue with my corded Nortel 9417CW.  It has been there since day one with the Obi.  I tried switching line cords, resetting the phone, etc.  Never did I associate it with Obi's power supply as the phone and adapter are so far away from each other.  Interesting.  I guess I won't try the other power supply method as it will void my warranty.  Angry
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swbrains
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« Reply #22 on: May 04, 2012, 11:10:25 pm »

Quote
Customers who use a cordless phone base station connected to the OBi device are not affected

I realize this thread is quite old but I want to leave my experience on this same topic as I think it's relevant.  I have the Obi110 and a fairly new Panasonic KX-9321 2-line cordless DECT 6.0 phone with a cable company phone line on line 1 and the Obi110 on line 2. I have had some type of hum/noise on line 1 that is fairly loud since installing it, so this issue is not isolated specifically to corded phones and does affect (at least in my case) a cordless phone.

I first noticed that unplugging the Obi connection (line 2) from my phone allowed line 1 (cable co phone line) to be clear with no hum.  Plugging in the Obi connection again introduced the noise, so I knew my problem was likely Obi related.  I tried various cables including 2-wire vs. 4 wire in each port of the phone, homemade CAT-5e phone cables but nothing helped.  Researching Obi110 and hum/noise, I ended up in this thread.

FWIW, I am in the U.S. using 120V electrical service.

I tried moving the Obi power adapter from a simple unfiltered power strip into a nearby UPS -- no difference, the noise remained.

I found a Netgear router switching adapter in the closet with output at 12V, 1.5 Amps, correct polarity.  As soon as I swapped out the Obi power adapter and replaced it with the Netgear adapter, the noise on line 1 was gone.  I put the Obi adapter back on and the noise returned on line 1, so I went back to the Netgear adapter again and it's clear. So I will stick with that adapter as it has adequate amperage capacity (1.5A) above and beyond the stock Obi adapter.

Anyway, I just wanted to add my experiences and let you know that my case also resolved with a different power adapter.
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Everton
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Posts: 163


« Reply #23 on: May 05, 2012, 07:23:01 am »

Isn't the Netgear Adapter, with output at 12V, 1.5 Amps, outside of the OBi Adapter specification of 1.0 Amp Max output or it doesn't matter?



I found a Netgear router switching adapter in the closet with output at 12V, 1.5 Amps, correct polarity.  As soon as I swapped out the Obi power adapter and replaced it with the Netgear adapter, the noise on line 1 was gone.  I put the Obi adapter back on and the noise returned on line 1, so I went back to the Netgear adapter again and it's clear. So I will stick with that adapter as it has adequate amperage capacity (1.5A) above and beyond the stock Obi adapter.
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swbrains
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Posts: 4


« Reply #24 on: May 05, 2012, 07:42:16 am »

My understanding is that volts are "given" and amps are "taken."

That is, the volts sent to the device by the power supply must match the voltage the device's components were designed to operate at or the device's components will likely fail.   

On the other hand, the device will draw a particular number of amps during operation, so the power supply must be capable of providing AT LEAST that level of power, but not less.  If the device draws more power than the power supply can provide, the power supply will likely fail.  If the power supply is capable of providing more amps than the device will draw, there is no harm done to either the supply or the device.

At least that's my understanding...  Smiley
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ckdash
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Posts: 10


« Reply #25 on: May 07, 2012, 06:55:32 am »

Customers who use a cordless phone base station connected to the OBi device are not affected.  From our observation the majority of customers use a cordless phone with their OBi and are not affected in any way / do not observe this issue.
I have a DECT device connected to the OBI110, and it suffers from ac hum.
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Ogdensburg
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Posts: 3


« Reply #26 on: May 19, 2012, 07:17:19 pm »

I second that. I have same noise problem on my OBI202. Changed to a Netgear 12V 1.5A power supply bought from Amazon and the noise is gone immediately.

Here is the link where I get the power supply (The one Fulfilled by Amazon is what I bought ) just in case some one need it:
http://www.amazon.com/gp/product/B00746W4GG


Quote
I found a Netgear router switching adapter in the closet with output at 12V, 1.5 Amps, correct polarity.  As soon as I swapped out the Obi power adapter and replaced it with the Netgear adapter, the noise on line 1 was gone.  I put the Obi adapter back on and the noise returned on line 1, so I went back to the Netgear adapter again and it's clear. So I will stick with that adapter as it has adequate amperage capacity (1.5A) above and beyond the stock Obi adapter.

Anyway, I just wanted to add my experiences and let you know that my case also resolved with a different power adapter.
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TalkOutLoud
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Posts: 2


« Reply #27 on: June 10, 2012, 10:03:37 pm »

I have the same problem. It used to work great, but now, the hum is overwhelming. Swapping for another adapter with the same rating removed the hum as others have stated; however, I discontinued use as this apparently will void the warranty. So do I send the whole device back, or will Obi send me a new one? Please advise?
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Ostracus
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Posts: 576


« Reply #28 on: June 10, 2012, 11:13:47 pm »

There's suppose to be a firmware update that addresses the hum. Obihai can also replace your power supply. Open a trouble ticket with them.
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OBiSupport
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Posts: 267


« Reply #29 on: June 11, 2012, 11:23:42 am »

@TalkOutLoud

Please fill-out this form: http://www.obihai.com/supportTicketForm.php

Thank you
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sailing
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Posts: 89


« Reply #30 on: September 08, 2012, 01:06:46 pm »

Since there was a thread on this topic, I thought I would post to it. I recently bought an OBi110. I was very impressed with the ease of setup. When I plugged it into my home setup, there was a 60Hz hum easily heard on the phone. My home setup consists of phone wires run all over the house. After reading this thread, I decided to test the power adapter and determine the problem more specifically as to why the adapter is a problem.

The current adapter uses a switching regulator. This allows for a small light design instead of what has been refereed to as an analog adapter. The reason you do not want to substitute an analog adapter is because the output is generally unregulated. Depending on the line voltage, the output could vary from 12V to 16V depending on the adapter.

Looking at the phone lines with an oscilloscope and differential probe shows a 60Hz waveform that would be generated from the charging of the input capacitor of the adapter. This noise is being coupled to the output by the leakage current through the adapter. The leakage current is 14microamps which is low but with audio, not low enough.

To prove the problem is the adapter, I used a lab supply to supply 12V to the OBi. The 60Hz hum was gone. The lab supply has a leakage current of 2microamps.

The problem is what is known as common mode noise. In this case, the noise at the input of the adapter is coupled to the phone lines through the leakage current through the transformer. If there are long phone lines or they are near power lines, capacitive coupling completes the circuit. You then get hum. To further prove this I connected the 12V ground from the adapter through a 0.1uF capacitor to earth ground (that third plug on the outlet or in my case the electrical conduit). The hum was significantly reduced. In fact, I have to listen closely to notice it.

I was using a Linksys ATA before this without any issues. The Linksys uses a switching power supply adapter. Unfortunately the Linksys adapter has a 5V output so I could not try this adapter. I did measure the leakage current and found it to be about 1microamp. I suspect that if this adapter was 12V, there would be no hum when used with the Obi.

The problem with power is not unique to OBihai. Many companies that develop digital products don't think much about power until there is a problem. OBihai probably just chose the lowest cost adapter they could find. For a few bucks more they could sell an adapter that would eliminate this problem.

Some other information about the Obi. With the Obi powered and nothing plugged in, it draws about 130mA. With a corded phone off hook, about 200mA. So if you have an adapter rated at 12V and 0.5A or a higher current, the adapter will work just fine.
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QBZappy
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Posts: 2316



« Reply #31 on: September 08, 2012, 01:51:42 pm »

sailing,

Thanks for the info. You probably spent some time doing this. I suspect that you're not an accountant by profession.  Smiley
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Owner of the 1st OBi110/100 units in service in Canada & South America. 1st OBi202 on my street. 1st OBi1032 in Montreal.
RoJo
Newbie
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Posts: 2


« Reply #32 on: September 15, 2012, 05:38:18 am »

Power adapter that came with my OBI100 will buzz as soon as it is plugged into any power outlet with or without the OBI connected.  It can easily be heard from the opposite end of my bedroom.  It continues to buzz a few seconds after unplugging.  Guess it's off to to the store for a replacement--annoying.  Otherwise happy with the product.
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sailing
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Posts: 89


« Reply #33 on: September 15, 2013, 01:48:01 pm »

This is an old thread but the issues with 60Hz hum were never completely answered. I had the chance to investigate this issue and thought others would be interested. I am keeping this as short and non-technical as possible. The FXO and FXS ports are controlled by integrated circuits (IC) from Silicon Labs. (I have an ob110.) The specifications of these ICs show good suppression down to 200Hz. Below 200Hz there is no specification. I would assume that at 60Hz, the suppression is much less so if your power lines can inject enough hum into your phone lines, it will be heard. The choice of these ICs were not a bad one. I would guess, that to have designed these devices with the same suppression that the old phones had, would have raised the price. Other analog telephone adapters (ata) I have used did not have this problem. I don't have any of these units to compare what they did to eliminate this problem but I suspect they used transformer coupling.

Running telephone wires all over the house means they run past power lines. Capacitive coupling will cause the injection of the 60Hz current. To actually hear the hum, the injected noise on the phone line needs a path back to earth ground which is through the power supply (wall wart). The power supply has current leaking through it continuously. It is only about 10 microamps but if this leakage is eliminated, there will be no hum.

Comparing a few wall warts, they all had about the same leakage current. Inside, there is a capacitor connected across the transformer. This is where all the leakage is from. There are agencies that specify the amount of electromagnet interference (emi) allowed. All electronics must meet these requirements. This cap is there for this reason. With this cap removed, my phone lines are dead quite. Don't even think about opening one of these wall warts unless you know what you are doing.

On a previous post, I had said if you tie the 12V negative output from the power supply to earth ground through a 0.1uf capacitor, the hum would be reduced. It will be but I will recommend against this unless you put voltage transient protection across this capacitor to earth ground and the phone line inputs to earth ground. You would have to know what you are doing to rig something like this up. The reason I don't recommend tying only the 12V negative to earth ground, is that under the right conditions, you could cause a failure of the phone port. Just like the 60Hz hum is injected into the phone line, if a transient, lets say due to a lightning strike on the power lines not far from your house, will induce a large voltage that will also couple into your phone line. Over 200V could be induced on the phone input to the Obi. If the negative output of the power supply is being held at earth ground, the voltage rating of the ICs will be exceeded and you will get a failure.

If you have a wall wart with the proper power supply and a ground plug on it, don't use it. The ground plug ties the 12V negative to earth ground creating the same problem described in the previous paragraph.

A non-intrusive way to eliminate this leakage current is to use an isolation transformer. The transformer rating should be 15VA or higher.

Most don't have this problem. You need to drive the phone lines in your house from the Obi, you probably have many extensions and the phone lines run past the power lines numerous times.
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