noise generator for 5V PS with output of about 1,2-1,5V

cypher · Joined: Dec 08, 2010 Posts: 12

Hi!
I was trying to make a simple noise generator based on two transistors (one with open emitor (I tried 2 different schematics)) and also another generator based on Zenner TL431, but I did not succeed yet. Its possible that the noise is simple just not amplified enough. I also tried to run the output to OP-AMP with gain approx 25x (maybe more will be necessary).
Also the transistor circuits were designed to run on 9-18V PS, so maybe this can also be a problem.

I will need it to produce the noise at the level of approx. 1,2-1,5 V. (a bit more that is the half of standard LINE level)
Can you please recommend some schematics of noise generator producing a relatively high noise level and usable on 5V PS.
Thanks a lot for any advice.
Greetings

Dan Lavin · Posted: Mon Feb 14, 2011 3:22 pm Post subject:

Check out the schematics for the Roland DR-110 drum machine. It runs on 6V. It is digital-based, but I think that's why it's used instead of the transistor method.

richardc64

cypher · Joined: Dec 08, 2010 Posts: 12

well I had some schematic with open emitor (insteed of collector), maybe this was the only problem...
Also you said that the gain should be lets say about 200 or so.
Will it give the output similar to "LINE LEVEL"? Because when I feed the line level audio signal (a bit less than 2V) to the VCF input, that is just the right level - working perfectly.
Thanks for now.
Greetings

cypher · Joined: Dec 08, 2010 Posts: 12

Hi.
Finaly I made a simple 2 transistor 9V noise generator working (cause I could not find 5V working OK).
I used the LM386 for amplification (with the max gain of 200) and connected a 8ohm small speaker directly to it (just for testing).

But now I have two questions:

a) I was just testing it from the batery - after several seconds the volume starts to fall down very fast. IMHO this is just because of the voltage from a 9V battery insteed of regular power supply. Am I right?

b) I found out, that the LM386 is putting out almost about 14V AC (according to multimeter) to the speaker. Its probably too much for my filter in (I need just 2V max). Should I just use lower gain - but then probably also the noise level will be lower. I need to keep the noise "level" in signal, but lower the overal amplitude to make it usefull for LINE-IN.
Should I use next op-amp gain lower than one after the LM386 or what will be the best solution to keep the "noise level (signal)" high but lower the output level to the LINE-OUT (approx. 2V)?

Thanks very much for advice.

Greetings.