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minimize audio interference
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Please be positive and constructive with your questions and comments.

minimize audio interference

by Leetmouse on Tue Aug 20, 2019 2:12 pm

Question,

I have a microphone that is power by a 9v battery that is plugged into a camera.
I made an adapter that would substitue the 9v battery with a 9v power supply
the audio coming from the microphone powered by the battery sounds great.
when I use the power supply and adapter, you can hear a buzzing noise in the background.
It is loud enough to be annoying.

Does anyone have any suggestions how to remove this noise? ferrite filters, grounding, etc.
both devices are not on the same power strip but both power strips are are connected to the same outlet.

Thanks in advance

Jim

Leetmouse
 
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Re: minimize audio interference

by adafruit_support_mike on Wed Aug 21, 2019 3:27 am

The noise is probably switching residue from the external 9V supply.

Most voltage adapters these days are made from switching converters.. basically switches that open and close quickly, followed by a filter that smooths the on/off pulses into something closer to a DC voltage. Switching converters are more energy efficient, lighter, and generally safer than the old transformer-based voltage adapters.

The problem is in the filtering. Good filters use lots of components, making them more expensive than just-sorta-okay filters. The companies that make voltage adapters are always tempted to reduce costs by using the worst filter they can get away with. That's especially true for consumer electronics, where the average user doesn't have the equipment or knowledge to test the output. It's a thousand times more true for low-price electronics from anonymous vendors in China, some of which are absolutely terrifying when you look at what's inside.

Assuming you have a medium-good adapter, try adding a large capacitor between the 9V and GND pins where they enter the board.

Adding ferrites between the external supply and the capacitor can help in extreme cases, but try just the capacitor on its own first. You really need an oscilloscope to know what effect ferrites have on a signal path.

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Re: minimize audio interference

by Leetmouse on Wed Aug 21, 2019 9:14 am

Thanks for the advice.

I suspected that it was being caused by the power supply so I was also trying to scare up an old transformer based psu and I found a couple but the output voltage was not consistent with what the the output claimed. which ended up being the case for all three psu's I had found. After testing the first one, I had thought I might have had a bad psu but after all three tested similarly, I though there was no way I had three bad units so I began to suspect that it was the nature of those devices.

which led me to this article.

https://learn.adafruit.com/power-supplies/transformer-based-ac-dc-converters.

Very informative.

Leetmouse
 
Posts: 10
Joined: Wed Aug 13, 2014 6:48 am

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