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Old 11th May 2017, 07:21 AM   #1
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Default Single ended discrete HP amp - question about earthing

Hi, I built a single ended headphone amplifier some time ago. I also built a low noise discrete linear Power Supply for it... I'm using HiFiMan HE400s headphones and iFi iDSD nano as source. Music is streamed either from laptop or HTPC from a NAS with 2x4TB HDDs...

I am struggling to get to the bottom of an earthing issue and need some advice. I am an experienced electronics engineer but still I have run out of ideas on how to resolve this issue...

The PSU case is earthed, there is a IEC RFI filter input... Does it make sense to disconnect that earth and only earth the common 0V output of the headphone amplifier or leave that floating also?

Thanks in advence for any advise offered!
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Old 11th May 2017, 07:30 AM   #2
Mooly is offline Mooly  United Kingdom
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Welcome to diyAudio

You haven't actually said what the issue is... I take it that it is a hum or a buzz getting into the audio.

A stand alone headphone amp like you show should be silent when fed its correct working voltage and with nothing (or perhaps just shorting plugs) connected to the input.

That has to be the first check, as external grounding issues shouldn't figure in that scenario.
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Old 11th May 2017, 08:09 AM   #3
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by tomskirurin View Post
........................The PSU case is earthed, there is a IEC RFI filter input... Does it make sense to disconnect that earth and only earth the common 0V output of the headphone amplifier or leave that floating also?

Thanks in advence for any advise offered!
If you have Mains power, then the Protective Earth (PE) wire MUST be directly and mechanically connected to the Enclosure/Chassis.
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Old 11th May 2017, 08:38 AM   #4
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Is the headphone amplifier case referenced to signal return (0V)? It's hard to see in your photograph, the RCA sockets are insulated from the chassis, that could be the problem
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Old 11th May 2017, 11:28 AM   #5
AndrewT is offline AndrewT  Scotland
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Originally Posted by scottjoplin View Post
Is the headphone amplifier case referenced to signal return (0V)? It's hard to see in your photograph, the RCA sockets are insulated from the chassis, that could be the problem
the amplifier will work without an enclosure. Thus it does not need to be connected to the enclosure.
The enclosure is there to attenuate interference and keep your fingers on the outside.
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Old 11th May 2017, 11:32 AM   #6
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We are yet to be told exactly what the problem is, I'd like him to try it anyway
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Old 11th May 2017, 11:55 AM   #7
Mooly is offline Mooly  United Kingdom
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Quote:
I am struggling to get to the bottom of an earthing issue and need some advice. I am an experienced electronics engineer but still I have run out of ideas on how to resolve this issue...
I read it differently in that there was an operational issue affecting the correct working of the PSU and amp.

A little clarification is needed from the OP methinks
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Old 11th May 2017, 06:27 PM   #8
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Thanks all for your advice... To clarify...

The amp works just fine i.e. it is very fine sounding as you would expect from a SE amp

The earthing issue is one of hum, the mains lead does have an earth. Maybe I can try one that only has live & neutral? I must say I have tried a couple of approaches already... Connect the earth to numerous 0V points in the circuit, inputs / outputs etc.

Is there a methodology to getting to the cause as I say I am experienced as an electronics engineer - but I must have missed the lessons about correct grounding in an audio system
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Old 11th May 2017, 08:09 PM   #9
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Any piece of mains powered equipment that you have built yourself must have it's chassis connected to mains protective earth (PE) see post #3. Have a look at this http://hifisonix.com/wordpress/wp-co...-Autosaved.pdf
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Old 12th May 2017, 01:33 AM   #10
Calvin is online now Calvin  Germany
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Hi,

are the RCA connectors mounted insulated to the chassis, or do they happen to contact the chassis?
Where is the trafo positioned?
Are You sure that You got a hum loop through the wiring or could it be emi due to proximity of the trafo?
Is there another device with IEC inlet connected .... such like the HtPC?
Have You tested a 10R-50R resistor between PE and circuit 0V?

jauu
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