Removing switchmode power supply noise - diyAudio
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Old 21st April 2002, 02:02 AM   #1
ih is offline ih
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Join Date: Dec 2001
Location: Sydney, Australia
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Unhappy Removing switchmode power supply noise

I have a Rod Elliot P3A amp running here, hooked up to my computer - which recently has been replaced with a laptop.

The problem is, running off mains power, a LOT of noise is picked up by the amp due to the power supply. It's not as bad when I'm running the machine at full load, but then I get the good ol' CPU fan, which is rather noisy itself. And that doesn't completely eliminate the noise, either.

There's an RF shield thingy on the power supply lead already. I'm planning to replace my current input cable with a shielded one, but I'm not confident that it'll make a whole lot of difference, since I can't make the noise go away by moving the cable and power supply around.

Things are almost perfect running off batteries - there's *tiny* bit of noise if I turn the amp right up, but I can hear the worst of it if I stick my ear against the keyboard anyway, amp or no amp.

At the moment, my current solution is to have the output level from the computer as high as possible, and the volume control on the amp as low as possible, but the noise is still quite noticeable, particularly in quiet passages.

Does anyone have any more ideas?

Oh - one other thing I forgot to add. If I set the amp's volume control to minimum, there's still some noise. I'm not sure how that's happening, since it's contained within a steel rack case and uses shielded wiring internally.
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Old 25th April 2002, 08:18 PM   #2
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I had the same problem. My CD-ROM in my computer has both an analog and digital outputs. When I enabled the analog input and disabled the digital input in the mixer console, it starts hissing. Then I enabled the digital input and disabled the analog. The hissing stops. A/V recievers and other multi-inputs amplifiers have this problem when they are connected to CD players. My A/V reciever recommends to disconnect the wires that is coming from the CD player for best sound quality. Though I only have my computer connected to my A/V receiver.

I think you already know that using shielded wire is best for audio hook ups. Try using shielded wire from your sound card to the amplifier if you didn't. Also re-organized the wires inside the computer.

Next you could buy a silent and a much better power supply. I'm sure you know which brands to buy so I don't have to list them.
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