Noise Gen.

isak · Posted: Mon Jul 29, 2013 2:20 pm Post subject: Noise Gen.

Hi Yves and Guys.

ok, i build it, i think its ok but not perfect (my bad of course).
the white noise is more like high pass filter, no lows, only highs.
the pink noise is sound and looks more like the white noise.
do i miss something here?

in addition the output is very low, i see from the scheme that i can change the 470k - R34 and R27 and the 220k - R31 to what value you suggest me to change them?

cheer,
Isak.

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prgdeltablues · Posted: Tue Jul 30, 2013 1:30 am Post subject:

Try different transistors for Q2 - if the rest of your circuit is correct, you may just have picked one that doesn't produce a good white noise - they do vary. Go for quality of noise, not volume - you can adjust that in the amplification section as Yves illustrates.

Best to socket them Smile

Peter

isak · Posted: Tue Jul 30, 2013 2:10 am Post subject:

Thank you for replying.

I did socket Q2 just for that reason, I replaced Q2 now the output vol is ok but still looks like the above pics.
I think I have problem in the filter section? I know that pink noise suppose to be LP filtered, as you can see it looks like white noise, when the white noise looks like HP filtered for some reason.
So i guess that my circuite is not ok, what should I check first?

Pseudo · Joined: Jan 14, 2009 Posts: 2 Location: UK

The spectrums look OK to me. I notice the spectrum analyser is in third-octave bands.

Pink noise should be fairly flat when measured in octave bands as it should have equal power in bands that are proportionally wide.

White noise however has equal power in any band for a given bandwidth. So when measured with octave bands which are proportionally wide there will be more energy in higher frequencies, hence the graph shows the levels increasing at higher frequencies.

isak · Posted: Tue Jul 30, 2013 7:18 am Post subject:

thank you for replying.
After reading more I understand what your talking about, thank you for the input.

One more question if I may..
to increase the out put level do i need to increase or decrease R34 and R27?

Pseudo · Joined: Jan 14, 2009 Posts: 2 Location: UK

To get a greater output you'll need to increase R27 and R34

isak · Posted: Tue Jul 30, 2013 1:06 pm Post subject:

Thank you.