Noise suppression problems attempting to to mate power amplifier with PC power supply.

[kevinmount]

Hello!

My name is Kevin, I am an engineer based in the UK. This is my first post on here.

I am developing a 7.1 power amp to fit inside a PC tower. I want to power it from the PC supply. I am having problems with the horrendous amounts of noise coming from the supply.

I have tried several ways around this (LC/LR filters etc) to little avail. At the moment I am using a "Bumper" 10A power line noise suppressor designed for automotive use. It has reduced noise somewhat but not enough. I should add, when the amp is powered by a "wall wart" supply, it all works very well indeed.

I am thinking of trying a low-noise LDO regulator next. Does anyone have any experience or knowledge of this kind of thing?





Thanks.

 

[Martaine2005]

Hi Kevin, you might want to try a ground loop isolator rather than a power line noise suppressor.
Use it at the audio input.
I have several for a mobile disco and they work great.

Martin

 

[kevinmount]

Hi Kevin, you might want to try a ground loop isolator rather than a power line noise suppressor.
Use it at the audio input.
I have several for a mobile disco and they work great.
View attachment 51376
Martin

Thanks Martin. There are four 2-channel audio inputs. How many of these would I need?

 

[Martaine2005]

That would depend on what audio signals you have as inputs.
Are you using all 4 inputs for different audio devices?
I use an audio mixer with only one main output. But I use one for each laptop output to the mixer.

Martin

 

[kevinmount]

Each 2-channel input goes to an on-board 2-channel power amp.

 

[Martaine2005]

Yes, I understand that.
Are you using each input with a device? ie, ipod on input 1, iphone on input 2, ps4 on input 3 etc.

Martin

 

[kevinmount]

No, this is an 8-channel (7.1) surround sound amp.

One input is front left/front right.
One input is side left/side right.
One input is rear left/rear right.
One input is centre/sub.

 

[Martaine2005]

Ok, but you still need an audio input from a device.
Do you have a pre-amp or sound card connected?.
How is this connected to the computer?.

Martin

 

[kevinmount]

Most PCs now have a "sound card" built-in to the motherboard, as does my test computer.

 

[Technomaniac]

I have had considerable experience with interference. When using shielded cables, the shield is often the return for the signal, and any interference induced into the shield is added to the signal. You have to make sure that the shields are connected at ONE END ONLY. That way there cannot possibly be any current in them. Run separate return wires. We encountered severe interference when automating 35mm movie projectors for the theatre at Yeppoon on the coast. In that case we used a woven braid OVER another woven braid, (insulation between) and one braid connected to ground at one end, the other braid connected to ground at the other end. Ideally shields must be earthed at ONE END ONLY. Any shield current is either added to the signal owing to the fact that the shield is in series with it, OR the current in the shield can induce interference signal into the inner (live) wire.

 

[Bluejets]

To add...the shield is normally required to be connected only at the source end.

 

[Technomaniac]

With exceptions. We had experiences with long microphone cables run out in the open, which were picking up AM radio stations. We found it better to earth the shields at the amplifier end. We converted any single core shielded cables to twin core, and disconnected the shields at the microphone end. One inner core as the return. I think the shield is probably best grounded at the end which is best grounded.

 

[Bluejets]

With exceptions.

Never ever seen that exception.