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 Forum index » DIY Hardware and Software
Simple Noise Source
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Zoomby



Joined: Aug 28, 2006
Posts: 18
Location: Germany

PostPosted: Fri Oct 20, 2006 12:33 pm    Post subject:  Simple Noise Source Reply with quote  Mark this post and the followings unread

Hi,
Posted Image, might have been reduced in size. Click Image to view fullscreen.

Would someone help me to fully understand this circuit?
What is the first capacitor for? I'd guess it's for smoothing the supply volage, but this would be silly in a noise oscillator?
The second RC is a Highpass to remove the DC amount, is it?

Bye,
Chris
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Blue Hell
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Joined: Apr 03, 2004
Posts: 20274
Location: The Netherlands, Enschede
Audio files: 143
G2 patch files: 318

PostPosted: Fri Oct 20, 2006 1:04 pm    Post subject: Reply with quote  Mark this post and the followings unread

Both assumptions are correct.

I can see a purpose for smoothing the supply when it's a part of a synth. Oscillators and LFO's tend to draw current from the supply in spikes, these could become audible in the noise when not filtered out, thus making it less random.

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yusynth



Joined: Nov 24, 2005
Posts: 1214
Location: France

PostPosted: Sat Oct 21, 2006 7:35 am    Post subject: Reply with quote  Mark this post and the followings unread

The 100uF cap is there to filter out the residual ripples of the power supply. Even though these ripples are small they are of the same order than the noise produced by the BC548. Because, this signal is strongly amplified by the OP amps (> x2000), the ripples can be heard and a strong hhum is superimposed to the noise "signal". Therefore this 100uF is there to tackle these residual ripples !
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Zoomby



Joined: Aug 28, 2006
Posts: 18
Location: Germany

PostPosted: Sat Oct 21, 2006 8:43 am    Post subject: Reply with quote  Mark this post and the followings unread

Thank you very much! It's clear to me now. Smile
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