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 Forum index » DIY Hardware and Software » Developers' Corner
noise, where does it come from?
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mrand



Joined: Mar 30, 2014
Posts: 56
Location: Yukon and London Ontario

PostPosted: Mon Jan 22, 2018 8:04 am    Post subject: noise, where does it come from? Reply with quote  Mark this post and the followings unread

Sometimes when I build janky perfboard prototypes, they suffer from a problem of issuing loud hiss/static, till I hit it, then the noise goes away for a while, but gradually creeps back. I've had this in old synths too. It must be from bad solder joints or connection problems, but can anyone talk about why it results in hiss? I'm sure there are many possible reasons, so not looking for an answer, but there is probably lots for me to learn from any discussion on the subject.

Another type of noise that I'm interested in is the type I often see at mixer inputs where the incoming signal is breaking up and noisy, until you increase the signal level and it "breaks through" the bad connection, then you can operate for a while at the lower level, till the noise eventually creeps back.

Any comments welcome!
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JovianPyx



Joined: Nov 20, 2007
Posts: 1629
Location: West Red Spot, Jupiter
Audio files: 191

PostPosted: Mon Jan 22, 2018 10:12 am    Post subject: Reply with quote  Mark this post and the followings unread

This is a good question and the answer is pretty much "everywhere".

1) Any high impedance input can allow antenna action to introduce radio frequency noise from the environment. The higher the gain, the more likely noise will find it's way to annoy.
2) "Thermal noise" is generated in resistors (and wires because they are in fact resistors), semiconductors and other parts.
3) Noise can be introduced magnetically, especially when mains wires are not carefully laid out and kept away from high gain circuits.
4) Resistive connections that should not be resistive. Such as bad solder joint, loose connector or plug/socket, a switch that is worn out can have resistive internal contacts. Dirt build up on contacts exposed to the air, again sockets and plugs. IC pins that are in sockets can have corrosion chemistry which may come from the air itself.
5) Improperly designed op-amp circuits may not include necessary oscillation damping parts (usually just a capacitor). The RF oscillation that results is a source of noise.
6) Being close to a high power RF transmitter can introduce noise even in properly designed circuits (given enough power).
7) Bad grounding and ground loops are one of the most common sources of noise. Something as simple as a PSU ground wire attached to a front panel with a screw that is not fully tightened.

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