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Amp sending noise into motherboard?

Swing_Riffs

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I recently purchased an SMSL A0100 Class D amp for my home office to power my Pioneer SP-BS22-LR. Recently I noticed a hiss in my headphones connected to the PC only when the SMSL is powered on. When the SMSL amp is OFF the headphones are dead silent.

The SMSL A0100 is directly connected to the back of my PC via RCA cable. My ATH-m30x headphones are connected to front of PC tower via Apple USB-C to 3.5mm (dac/adapter).

Only thing I can think of is the A0100 is sending some voltage/noise through the motherboard via its RCA connection. Is this even possible? To be very clear this PC has been dead silent on the noise front with previous desktop Fiso amp which the A0100 replaced.

On a side note if I turn the volume the up on the A0100 amp to 80% with no music playing there is much more hiss going to my SP-BS22-LR than there ever was with my previous desktop Fiso amp. There is a clipping in the hiss too. Like as studder of sorts kinda hard to explain.

My top priority is to make sure my motherboard is protected and not receiving any voltage or interference. Any help is greatly appreciated.

I have 6 days left in my return window with Amazon. Maybe I should have bought a Yamaha A-S301 instead.

Thanks in advance!
 
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tonycollinet

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When you power the SMSL on/off, are you using a switch on the amp, or are you pulling the power out of the wall, or back of the amp?

Is the amp connected to the same power outlet as the PC?

At the moment, I'm thinking that the introduction of the amp has created a ground loop which is picking up interference either from the PC, or from the amp itself.

Can you plug the amp into the power right next to the PC power connection, and route the two mains cables close to each other. Also keep the RCA Cable as short as possible.

Do you have another DAC you can try to provide audio to the amp, rather than the analogue ouptut from the PC.
 

digitalfrost

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Both your PC and the SMSL have 3pin power plugs. Most likely a ground loop issue.
 
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Swing_Riffs

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Must of been a ground loop issue. I had the SMSL and PC plugged into a PDU that was plugged into a UPS. So I removed the SMSL from the PDU and plugged it into a Furman surge protector. The Furman is now plugged into a separate wall outlet. Hiss in headphones seems to be gone to the point of inaudible.

One follow up question. Is it normal to here a soft crack/pop when turning off an amp like this?

Thanks so much to both of you.

Did find a great video describing ground loop issues affecting audio equipment.

 

tonycollinet

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Must of been a ground loop issue. I had the SMSL and PC plugged into a PDU that was plugged into a UPS. So I removed the SMSL from the PDU and plugged it into a Furman surge protector. The Furman is now plugged into a separate wall outlet. Hiss in headphones seems to be gone to the point of inaudible.

One follow up question. Is it normal to here a soft crack/pop when turning off an amp like this?

Thanks so much to both of you.

Did find a great video describing ground loop issues affecting audio equipment.

well done on solving the problem.
 
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