Noise Generator Design - Feedback and or help/advice

metal_head_82

Hey folks!

I'm currently designing a noise generator for my drum/percussion synth project.
I got a little circuit here and I'd like to hear what you think about it.

The frequencies it produces and the schematic are attached.

It's built from two transistors (build like an darlington pair) which produce some noise. They are connected to two gain stages, made of a TL072 OpAmp.

My current thoughts are, to exchange the first gain stage with another pair of transistors which will hopefully result in lots of gain and noise Wink

I could use one of the OpAmps to amplify the noise and the second to build a simple active LPF with POT to adjust the "color".

What do you guys think about that?
Please be kind... I'm new to all that electronic and DIY synth stuff. But any feedback or advice is highly appreciated.

(hopefully I did the schematic right... tried to draw it from breadboard Wink

)

noise_freq.jpg

Description:

The frequency range of my noisegen (measured)

Filesize:

15.85 KB

Viewed:

5022 Time(s)

noise_gen_1-2.gif

Description:

The (hopefully correct) schematic of my noisegen

Filesize:

10.68 KB

Viewed:

391 Time(s)

This image has been reduced to fit the page. Click on it to enlarge.

metal_head_82 · Posted: Tue Apr 20, 2010 3:13 am Post subject:

Hello again!

The design is nearly completed.
I simplified things and now I use one single OPamp and a single transistor.
Makes a lot more sense Wink

And now it puts out real white noise Smile

The schematic will follow as soon as I get hold of another problem:

I have a VCO in the circuit. But it bleeds into the noise. I sounds like there's a hipassed version of thenVCO output inside the noise. The sound is gone as soon as I disconnect the Pitch Pot from the VCO. Now I'm pretty stuck here.

Is there a way to stop the vco bleeding into the noise? I read something about decoupling and virtual ground on the web BUT I'm not quite sure how to get THAT into my circuit.

I have to say again that I'm new to all this... Could someone please point me into the right direction?

Thanks guys...

Rykhaard · Joined: Sep 02, 2007 Posts: 1290 Location: Canada

kkissinger · Posted: Tue Apr 20, 2010 8:25 am Post subject:

metal_head_82 · Posted: Wed Apr 21, 2010 2:05 am Post subject:

Thanks for the answers! thanks

But if I get the whole thing right I need a dual supply, right?
I'm currently using a 9V battery. Because I want this little thing for mobile use.

I will try to use a voltage divider and an OPamp to build a virtual ground. And then try buffering the ICs. If I'd do this now the ICs won't work.

So please tell me if I'm right with this... Dual supply + Buffering = Success???

Thanks

metal_head_82 · Posted: Wed Apr 21, 2010 3:47 am Post subject:

I made something up myself Smile

I simply use an OPamp to buffer the supply voltage. I just use the remaining amp of the TL072 which amplifies the noise to feed the VCO.
Maybe it's not THAT ULTIMATE solution but at least it works - and until now without problems Wink

Or do I have to be careful with such misuse of my OPamps???
What do you guys think about that?