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Topic: Headphone amplifier hums with nothing connected (Not even power) (Read 5616 times) previous topic - next topic
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Headphone amplifier hums with nothing connected (Not even power)

I recently bought a Sony PHA-3AC headphone amplifier/DAC , this model was originally issues as the PHA-3 with a large Li-Ion battery for portable use. Sony for some reason decided to not include the battery for the European version, hence the "AC" behind the name.

I have recently found out, that when using the balanced connections for headphones and switching to "line out" (this should cut off the headphone output) the right channel of the amplifier begins to hum. Now the strange thing is, that the hum will continue even when nothing is connected, not even the power supply: I can plug in the headphones, and walk through the room, the amplifier mostly stays quiet, but as soon as I come near any electric device, or touch it with either the amplifier or the headphone cable, the hum/buzz is back.
If I put the amplifier down on a wooden cupboard that holds most of my equipment: soft hum, If i put it down on top of a CD-player or amplifier , slightly louder hum.
Sometimes touching the case of the amplifier will make the hum go away, most often it will not.

If I power down the amplifier when it is quiet, I cannot repoduce the hum after I disconnect it, but if I power down the amplifier when it IS humming, it will continue doing so, even after I switch from "line out" to "headphone out" , which would normally cut off the hum.

Now my question is: Is it conceivable in any way that a headphone amplifier without a battery could make the Sennheiser HD600 hum while not connected to any powersource or other device? (Extreme senstivity to EMI, Induction,  poorly shielded 3rd party headphone cable etc.) Or is it more likely that Sony just substituted the large LI-Ion battery for a smaller one, most likely so they did not have to change anything else with regard to power/charging scheme? (They did not even bother to remove the "charge" LED, which sometimes comes on after I power down the amplifer after using it.)

Headphone amplifier hums with nothing connected (Not even power)

Reply #1 –
Is there some kind of time limit, i.e. if it is humming with no power connected does this eventually stop or does it continues for hours or days?

Headphone amplifier hums with nothing connected (Not even power)

Reply #2 –
Quote from: pdq on
Is there some kind of time limit, i.e. if it is humming with no power connected does this eventually stop or does it continues for hours or days?


I've not tried it longer than an hour or two, humming stays, I could try an entire night.
Something that has ocurred to me is that the Sony PHA-3AC's left balanced output is most likely the amplifier also used for the unbalanced connection. The balanced connection is using tip for + and ring for - with sleeve unconnected, and the  unbalanced connection is using a standrad TRS headphone configuration. I am not too tech-savvy, but I could imagine that this could lead some contamination. Maybe the small currents often present on the outside of audio equipment can leak into the signal circuitry through the headphone cable  and chassis. This is probably enough current to generate some noise even without another power source. (Although this would not explain why i also get some buzzing when putting the PHA-3AC simply on the same shelf, unless the shelve's paint is slightly conductive, wich sounds far fetched to me)

Headphone amplifier hums with nothing connected (Not even power)

Reply #3 –
Quote from: The Dutch Guy on
I recently bought a Sony PHA-3AC headphone amplifier/DAC , this model was originally issues as the PHA-3 with a large Li-Ion battery for portable use. Sony for some reason decided to not include the battery for the European version, hence the "AC" behind the name.

I have recently found out, that when using the balanced connections for headphones and switching to "line out" (this should cut off the headphone output) the right channel of the amplifier begins to hum. Now the strange thing is, that the hum will continue even when nothing is connected, not even the power supply: I can plug in the headphones, and walk through the room, the amplifier mostly stays quiet, but as soon as I come near any electric device, or touch it with either the amplifier or the headphone cable, the hum/buzz is back.


I take it that the internal battery is the source of power.

Seems like the problem could be EMI, and a logical step might to to perform similar testing in other locales, perhaps even many miles away.  When you test, remove all other electronic devices from your person.

The source could be a radio transmitter or industrial process involving RF.

Quote
Now my question is: Is it conceivable in any way that a headphone amplifier without a battery could make the Sennheiser HD600 hum while not connected to any powersource or other device? (Extreme sensitivity to EMI, Induction,  poorly shielded 3rd party headphone cord...


The cords going into a headphone amp from another device with a headphone jack, or coming out of a headphone amp to a pair of headphones involve such low impedances that noise pickup should never be a problem, shielded or not, except perhaps in a strong RF field.

Quote
Or is it more likely that Sony just substituted the large LI-Ion battery for a smaller one, most likely so they did not have to change anything else with regard to power/charging scheme? (They did not even bother to remove the "charge" LED, which sometimes comes on after I power down the amplifer after using it.)


Li battery physical size should not make a difference as long as sufficient voltage is available under load. Even small lithium batteries are capable of providing a lot of juice, just for a shorter period of time.

Headphone amplifier hums with nothing connected (Not even power)

Reply #4 –
Thing is, Sony says there is no battery in the model I have , there's no sticker on the box or the device indicating it has a Li-Ion battery, which would be mandatory in the EU I believe, and yet the amp is able to hum without anyhting connected to it. I did some more testing and there definately has to be physical contact or very close proximity between the PHA-3AC or the headphone cable and another device to generate the hum.
There is some AC onto the casings of my stereo components (No grounded wall sockets around), not enough to be obvious, but I do get a little sting when I touch a heating pipe with one hand and my stereo with the other.

Headphone amplifier hums with nothing connected (Not even power)

Reply #6 –
Yes I found that review too, but there are several others contradicting that.
I think I'm just going to return it while I still can, too much uncertainties, I've read elsewhere that the amp won't turn on when the battery is empty (It wants to charge first), and if Sony just replaced a large practical battery with a small one to circumvent some weird EU law without having to completely overhaul the power supply, chances are I'm going to end up with an unusable amp once the battery dies from being constantly hooked up to AC. (Or from me not using it for a few months and it dropping below its lowest allowed voltage)

Too bad, it took a while to find an amplifier with all the functions I need.

If anyone has any sugestions for a Headphone amp/ DAC with analog inputs, USB input, Optical or Coax , (preferably switchable with a switch) Line out, low output impedance and no noise, turn-on/off pops etc. feel free to chime in.

Headphone amplifier hums with nothing connected (Not even power)

Reply #7 –
Quote from: The Dutch Guy on
<br />Yes I found that review too, but there are several others contradicting that. <br />I think I'm just going to return it while I still can, too much uncertainties, I've read elsewhere that the amp won't turn on when the battery is empty (It wants to charge first), and if Sony just replaced a large practical battery with a small one to circumvent some weird EU law without having to completely overhaul the power supply, chances are I'm going to end up with an unusable amp once the battery dies from being constantly hooked up to AC. (Or from me not using it for a few months and it dropping below its lowest allowed voltage)<br /><br />Too bad, it took a while to find an amplifier with all the functions I need.<br /><br />If anyone has any sugestions for a Headphone amp/ DAC with analog inputs, USB input, Optical or Coax , (preferably switchable with a switch) Line out, low output impedance and no noise, turn-on/off pops etc. feel free to chime in.<br />
<br /><br /><br />


the help guide mentions a battery that won't work unless the AC usb power is plugged(dunno if it's some lost in translation thing or maybe just something done to get clean power for a specific part?

Headphone amplifier hums with nothing connected (Not even power)

Reply #8 –
Quote from: castleofargh on
the help guide mentions a battery that won't work unless the AC usb power is plugged(dunno if it's some lost in translation thing or maybe just something done to get clean power for a specific part?


Thanks! I thought I read the entire thing but it appears I skipped this bit.... 
This sounds pretty conclusive, and it actually warns about excesssive discharge, indicating the device will not function once the battery dies.

Back to the store she goes then!

I do wonder why they did this, the USA version is almost 70 grams heavier, and needs to charge up to 6 hours, i've never seen mine charge longer than 40 seconds, so the battery must be tiny. I've read speculations that it could have to do with some new EU transport rule for Li-ion batteries but mobile phones , tablets and other headphone amps sell with a big Li-ion battery in the EU. (And there's still a Li-ion battery in the PHA-3AC)
I had thought myself that it could have something to do with the decibel limits on portable devices in the EU, but that still doesn't explain why other portable amps are being sold in the EU.

Headphone amplifier hums with nothing connected (Not even power)

Reply #9 –
Assuming you're Dutch and can read German, here is an interesting user feedback on amazon.de
This German client finally bought a model with battery in Japan

Headphone amplifier hums with nothing connected (Not even power)

Reply #10 –
Read the amazon.de reviews, actually thought about importing a Japanese model (Although I would probably go with the PHA-2, don't need balanced connections or 1 gazillion kbps DSD/DXD256), but I really don't like having a Li-ion battery in a device that doesn't actually use it for portability: In my experience they are usually the first components to fail.

It appears half the people buying this amplifiier are returning it because it doesn't have a battery, and the other half because it does.