This is a very basic circuit which consists of 2 parts
1st is the noise generator which is the first transistor with no collector connection
2nd is the bit which may look more familiar which is an AC common-emitter amplifier and this is just to bring the noise upto a usable level - I have taken a scope screenshot of what the noise looks like however it is an audible sound which is pretty useful for testing guitar fx or filters and other such things.
if you wish to learn more about the common-emitter amplifier the best source for information is "The Art Of Electronics" book - on page 77 almost the exact same amplifier circuit appears with explanation
you can of course experiment with different types of transistor in the noise section - i'm not sure how available the BC108s are now, I just happened to have a load of old ones, I hit it with a hammer to get a bit more noise out of it.
the best voltage I've found to use this at is 18volts however it does make noise at 9volts upwards
I think it sounds perfectly reasonable.... hahahaha... actually... perhaps the sound wouldn't be reasonable, but the design (in my obviously expert opinion) sounds good. White noise is something that I like to keep going for lots of reasons.
ReplyDeleteI liked this bit from your blog,
"I hit it with a hammer to get a bit more noise out of it."
THAT sounds very reasonable and applicable to loads of different things!
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I know it seems a bit weird but hitting it with a hammer does improve the noise you get out of it !
DeleteBrown Noise is bestest and Pink Noise is the gayest
Deleteyou're the gayest noise
DeleteHey Paul, here is a thought I had while looking at this, could you blend the output of this noise generator into a mic signal (actually making two and blending them into each of the two balanced lines might be cool) to essentially "crap-fi" it, ie make it sound like a shitty old radio, or like the vocal is going through a loudspeaker??
ReplyDeleteAlso just because I have totally no ability to figure out sarcasm etc on the interwebs, did you really hit the BC108 with a hammer??
I think you want a band pass filter to make that shitty old radio sound, what this circuit does is give you a white noise signal, they use them in synths though so I'm sure you can do something with it.
Deleteno, I wasn't being sarcastic, with this kind of circuit you're relying on the bad qualities of the transistor so I hit it a few times to get abit more noise out of it, however I do have thousands of these transistors so I was able to experiment in that way. I wouldn't say it will always yield good results.