Noise Generator Circuit

Thread Starter

Đorđe Jocić

Joined Aug 15, 2019
14
Hello there, how are you all doing?

I started experimenting with Zenner diodes recently, and decided to try and make a simple audible noise generator - as shown in the attached circuit below. While it does work, LM386 IC overheats after several seconds and white noise turns into a high pitch sound.

Any suggestions? Thanks in advance!

:)
 

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Audioguru again

Joined Oct 21, 2019
6,673
Your LM386 was damaged because you did not read its datasheet. Your circuit had many missing parts.
It needs a 100uF supply bypass capacitor, a 0.33uF input capacitor, a 20k volume control, its pin 2 connected to ground, a 47nF and 10 ohms zobel output network, a 220uF output capacitor, an 8 ohms speaker and your C2 should be 10uF.

The datasheet for the LM386 shows that with a supply voltage higher than 9V the IC gets hotter but does not produce more output power. But your zener noise source might not work with a 9V supply.

The TDA2003 is obsolete and has not been made for many years.
 

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jeffl_2

Joined Sep 17, 2013
74
And it's white noise. In most audio applications (even most that AREN'T test/instrumentation) what you generally want is "pink" noise, that's like white noise that passes through a filter that decreases the amplitude 3 decibels per octave of bandwidth, that gives you equal noise power in each octave. There are circuits that do this (for example http://www.techlib.com/electronics/pinknoise.htm) but they aren't all that accurate. What I usually do for instrumentation is I just grab a pink noise MP3 file (like https://www.audiocheck.net/testtones_pinknoise.php) then I stick it in the memory of the cheapest MP3 player I can find (try https://www.ebay.com/itm/USB-Digital-Portable-MP3-Music-Player-LCD-Screen-FM-Radio-Support-32GB-TF-Card/272215771816?_trkparms=ispr=1&hash=item3f61530aa8:m:mmDlArr-p4Y5TsffWIbxcSAenc=AQAEAAACgIQvEcHUrT7nmUC3yY5qbPyaBN1nJEDYW8MyypsJPgXKZDjcxlp6P77HrmYz4BAV/nPvnKK2RS/gkmeGE/ncyQbqrGSyCfV1/6own0sW7FdqOs5Jpv3BMOVLwWi7HeznoYVhxDP2C0TquEEpUliMgNTVcONf6+ROPdkaKxYSspKRhDwwU4INZxziHjpDN98XxZGkk1enMtYGy4P+Z6t4Q3R4TrbZq3uDF8h1OpaM9+SxF+vab0hSAAI/d4ISkgybV+juis3lgp9BLavWpBJFhnPdoq9NKyWgAZeAZ7WpGKYf5cSLz7scDJKOrSuxPwKB4Rb5sPIoESt4XiTmActw/MeUwKLKm7ufE4E51AR+nzSDZVCoFefg+uMgoTzFRqASG+rqC0CvEAdEXuzSjrbTnyCDkA6cyrlPabEu+CpkclROWdSe+o6cTiQi6cjQb0RSbQlWpb9OjEfskXV1XRx1EQ47PKD8KV0/NaGdZxF59SGSvOlO+SeLNTacKDi6pDDYO3Dus0CVfnnD7W5LmGSO1B6SHZJi+L4IyfM2vRS7g/uBDm3D1MJjksINvhCxpHgCcNAjdUnqnLmTRciOmaalYIbLB/BtiOrP7jragbWnA4VJ11h24ahtDDEvivIe2FyYml1sjagPc3cKwzQpEjI1vT7E8eS/P9TNYnqYNX4Jar003rovpcUCuF8WHjaCtz6++4Z3a1TcpCljXqGtwzpfE3gwH/PQtRP9EKx3DezpPos2W2DAx76KEAGRhx0iVFL3omUEeSK3Xl0JQTgIoePFkTJVvCgKFHN9gGoia1ylZ6glsT7WYVfBgRaZklrJDuj4WCsvDce4alUzo9PGVkYXurw=&checksum=272215771816c6ff69e3a439404691a5c1e055c2eaa2), you don't need a very large memory chip at all because you can just set it to loop. If you want to connect the output to an LM386 to power a speaker it should work fine. If you're going to use the speaker output to do what used to be called "acoustivoicing" you need a REALLY precise speaker setup and an instrumentation-quality microphone, which are both well beyond the scope of this article! (But you CAN get a free app called an "RTA" or real-time analyzer, that will run on any smartphone and THAT gives you the analysis part, the little microphone in the phone itself often works OK, if anything it's generally the body of the phone with its "sound slots" that screws things up, or you can just use an external mic.)
 

AnalogKid

Joined Aug 1, 2013
10,986
LM386 IC overheats after several seconds and white noise turns into a high pitch sound.
Your circuit is missing the Zobel network, and R-C network connected to the output. It is on all of the datasheet schematics. It prevents high frequency oscillation, something that will overheat and kill the chip.

ak
 
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