[sdiy] prob with noise circuit?

[Dave Magnuson]

----- Original Message ----- 
From: "Pete" <23isgood at gmail.com>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Monday, May 30, 2005 4:03 PM
Subject: [sdiy] prob with noise circuit?


Hey everybody. I have been trying to get this circuit to work but I simply
don't understand why I get no sound out of it. This is out of Thomas Henry's
"Noise Generator Cookbook" In the book he mentions to use a, 2n2712 for the
transistor or a 2n3904. I am using a 2n3904. I built this basic circuit on a
breadboard, and im using a 1/4" jack for the output, and a 15v power supply.
Do I have to apply power to the pins of the 741? It does not specify to do
so. I attached a pic of the circuit. Im pretty much a beginner on this stuff
and trying to teach myself. I have rebuilt this thing a few times double
checking everything. According to the book there should be a good amount of
noise coming out of this thing. Is there something that I am not aware of
that im overlooking?

Thanks
pete
-- 


Hi  Pete,

You absolutely need to power the 741.   If the Noise book is anything like 
the E-Drum Cookbook, then the pinout should be in the back.   Opamps will 
ALWAYS need power.

Looking at the way the inverting input is tied to ground with a 1K resistor 
means you'll want a bipolar supply (+/-15V) not just +15 and ground.  If the 
1K resistor tied to a voltage divider (100K to V+ and 100K to GND), I'd say 
a single-ended supply would be fine.

Also, transistors used like this usually need to be selected for noise 
output.  Some 3904's will create a good noise level... some will be quiet. 
Expect to have to swap in a few different transistors before you find one 
that you like.

Dave