Thanks for the feedback. I used qucs to draw the circuit. Here it is redrawn. What problem should I see with T_? I've built a pair of these into an Altoids tin, seems to work well, though I confess I don't know exactly why, just arrived at the design empirically.

 

I get that the Q1 base-emitter junction is reverse biased to create the noise source. Are you running the 2222 in reverse conduction mode for a reason? Actually, there is no DC bias at all on the base, so I don't know what is going on there.

ak

 

1. This thread has been inactive for over a year. Consider restarting it as a new thread. The moderators can help.

Thanks AK.
If the new replied was answered to and matched the issue then our Moderation Team might let it go, if it asked the same or similar question then we will take some different actions as let it go to replace the old TS when the old TS was gone for long, or split it to a new thread when the new post there was a little different, etc.

 

My GF of this ERA built the popular Electronics surf synthesizer here: http://www.preservationsound.com/?p=1864

It sounded pretty good.

 

I get that the Q1 base-emitter junction is reverse biased to create the noise source. Are you running the 2222 in reverse conduction mode for a reason? Actually, there is no DC bias at all on the base, so I don't know what is going on there.

ak

I am curious if anyone does know what’s going on.

 

I am curious if anyone does know what’s going on.

A photo of your build might help. You could simply have an error in the drawing.

 

A photo of your build might help. You could simply have an error in the drawing.

 

I am curious if anyone does know what’s going on.

Your circuit is a "variation" of the first schematic in post #4, but yours has some problems. The Q2 collector should be floating, and the T_ circuit is not correct. There are a couple of things it could be depending on the intent of the original designer. If you got this schematic off the web, can you post a link to the source?

ak

 

Your circuit is a "variation" of the first schematic in post #4, but yours has some problems. The Q2 collector should be floating, and the T_ circuit is not correct. There are a couple of things it could be depending on the intent of the original designer. If you got this schematic off the web, can you post a link to the source?

ak

I started with that circuit, but kept trying things out experimentally until I arrived at this, which does actually work quite well, producing a variety of noise characters as the pot is adjusted.

 

AK is correct, Q2 collector doesn't need to be grounded. Grounding the Q2 collector produces no audible effect, that connection can be omitted. This is such a basic circuit, but fun to mess with and explore transistor tweaking fundamentals as they cross into chaotic noise avalanche breakdown. I'm using this noise circuit, along with several oscillators and a bank of momentary resonant filters drive laser vectorscopes for a show tomorrow night.

P.S. Happy New Year!