I few months ago without much time and some health issues I decided to buy a premaded headphone preamp and ended up getting a FidelityAudio (UK based company) HPA-100. I only had the chance to test it more seriously a few weeks ago and it's showing a slight humming that varies a bit with the pair of headphones used (but is always present). The worse case scenario is a very, very, and I mean VERY old pair of Onkyo headphones, they sound terrible per se and are circumaural.
Also to my surprise the humming is completely independed of the volume control and if I connect the headphones to other equipment's headphone outputs (preamp / power amp, even an old boombox!) this type of humming is not present with any headphones.
RCA sockets are connected.
I'm out of ideas and don't want to spend a fortune on shipping the unit around to them and back....
Can anyone help ?
Thank you!
Also to my surprise the humming is completely independed of the volume control and if I connect the headphones to other equipment's headphone outputs (preamp / power amp, even an old boombox!) this type of humming is not present with any headphones.
RCA sockets are connected.
I'm out of ideas and don't want to spend a fortune on shipping the unit around to them and back....
Can anyone help ?
Thank you!
Looks like the amp has an IEC power socket and may have signal ground connected to safety earth. Try some source that is known to have a floating ground - like most any ordinary CD player or a mobile player or cellphone. (Or don't connect anything at all, or better short the input.) In short, anything but your computer.
If the hum does not occur with these other sources, the problem is a ground loop and needs to be addressed accordingly.
If the hum remains present whatever you do, it's probably inherent - either a power supply rejection problem or a defect. Nothing that should be present in a £350 amp, anyway. In this case I would suggest something like a Lake People G103-S.
Those old Onkyo headphones would not happen to be 8 ohm parts? They might just be the most sensitive of the bunch and hence show the issue most clearly.
If the hum does not occur with these other sources, the problem is a ground loop and needs to be addressed accordingly.
If the hum remains present whatever you do, it's probably inherent - either a power supply rejection problem or a defect. Nothing that should be present in a £350 amp, anyway. In this case I would suggest something like a Lake People G103-S.
Those old Onkyo headphones would not happen to be 8 ohm parts? They might just be the most sensitive of the bunch and hence show the issue most clearly.
I don't understand how this could be an inherent problem when this amp got a 5 star review on WhatHiFi ?!!
Thank you for your answers. I've tried with other sources that definitely don't have an earth connection on the mains socket, same result. Even without anything connected to the RCA sockets the humming is exactly the same.
One thing I remembered is that it has pass through RCA connections. Could the output connections be getting some signal internally.
So it's either the design or some bad part.
Here are some internal pics:
Thank you for your answers. I've tried with other sources that definitely don't have an earth connection on the mains socket, same result. Even without anything connected to the RCA sockets the humming is exactly the same.
One thing I remembered is that it has pass through RCA connections. Could the output connections be getting some signal internally.
So it's either the design or some bad part.
Here are some internal pics:
Thanks. Since this uses a toroidal should it still matter to twist the wires ?
Yes it's weird because I've taken it to other places including an hifi shop to test with other equipment and the hum was there, although not as pronounced TBH.
What about changing the voltage regulators, apart from probably lowering hiss, should it have any effect ?
Yes it's weird because I've taken it to other places including an hifi shop to test with other equipment and the hum was there, although not as pronounced TBH.
What about changing the voltage regulators, apart from probably lowering hiss, should it have any effect ?
is the capacitor marked in red supposed to be discoloured like it is?
An externally hosted image should be here but it was not working when we last tested it.
Well, I've sent it to them for repair and upgrade and the problem continues! The amp sounds even more amazing after the upgrade, but I'd like to get rid of this problem which, to be honest is only heard when there is no music playing. They said they couldn't reproduce the problem
Is it possible for this to happen only in my home / county /country or whatever... ?
Is it possible for this to happen only in my home / county /country or whatever... ?
Here's something that I found. If I have it playing from a source and turn the amp off without disconnecting the source it continues playing for a small interval of time, from the reservoir caps I suppose. Now if I repeat the same sequence but turn off the source before turning off the amp I should hear humming but I don't! It's gone right after I turn it off, instead of continuing for at least the same amount of time it would continue playing the music source.
So it must be transformer / power supply related.
So it must be transformer / power supply related.
You shouldn't have to re-engineer such an expensive amplifier.
There could be a defect or deficiency in your house mains wiring. Try taking it to somebody else's house, or to work, and see if the hum is still there.
It's not at all unusual (but very unfortunate) to find the ground wire for a building disconnected, or not wired properly.
There could be a defect or deficiency in your house mains wiring. Try taking it to somebody else's house, or to work, and see if the hum is still there.
It's not at all unusual (but very unfortunate) to find the ground wire for a building disconnected, or not wired properly.
@Fast Eddie D
There's a thread on another forum about humming on Leben cs300xs models, have you checked the price on those ?. It seemed to be cured with a power supply choke, so it was related to the design and it seems it was only apparent in certain situations. I'm considering giving that a try...
Thanks for the suggestions but I already tried those. Took it to another house. They even soldered a resistor to earth but there's no difference, actually it made it worse, causing more hum (maybe from a different source than the volume independant one) at high volumes, which in practice doesn't make a difference.
Ah and they also added a small resistance to the output, no difference!
There's a thread on another forum about humming on Leben cs300xs models, have you checked the price on those ?
. It seemed to be cured with a power supply choke, so it was related to the design and it seems it was only apparent in certain situations. I'm considering giving that a try...Thanks for the suggestions but I already tried those. Took it to another house. They even soldered a resistor to earth but there's no difference, actually it made it worse, causing more hum (maybe from a different source than the volume independant one) at high volumes, which in practice doesn't make a difference.
Ah and they also added a small resistance to the output, no difference!
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I tried another experiment. I used an old UPS wich has a battery (the old non switching ups versions...). Mains was disconnected from the UPS. There is still humming! But the sound of it seems to be a bit difference, around the same frequency range though... That discards the grounding issue hypothesis I think.
Could it be the transformer ?! I'm kind of hopeless here, I rather give them the benefit of the doubt but which on earth would it work well in the UK, where I resent it for test and repair/ upgrade, and not here where I am ?
I'm starting to think it's really a design issue, but again, how the heck did WhatHiFi gave 5 stars to something that hums by design ?....
Could it be the transformer ?! I'm kind of hopeless here, I rather give them the benefit of the doubt but which on earth would it work well in the UK, where I resent it for test and repair/ upgrade, and not here where I am ?
I'm starting to think it's really a design issue, but again, how the heck did WhatHiFi gave 5 stars to something that hums by design ?....
I've got a CTH headphone amp that hums like a bugger at work, where there's no filtering to AC versus at home where I have a DIY AC line filter / power conditioner, where it's whisper quiet. Similar to this: "DIY Hydra" Power Conditioner | 10 Audio
I'm sure you can purchase one for around $100 that will work sufficiently. The UPS you tried, was it plugged in when you tried it? or were you running from battery only?
D.W.
I'm sure you can purchase one for around $100 that will work sufficiently. The UPS you tried, was it plugged in when you tried it? or were you running from battery only?
D.W.
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