MFOS SL MiniSynt White Noise Problems

ultramar1976 · Joined: Aug 17, 2014 Posts: 2 Location: Argentina

Hello everyone.
Two weeks ago I have this problem.
Just the white noise generator does not work.
The circuit is perfectly fine. The PCB without problems, short or cold solder joints. Probe nearly 20 2N3904 transistors.
To have a transistor as the base voltage of transistor -9V.
In the emitter -3,5V.
The support page says MFOS emitter voltage must be positive.
Insist the circuit is good, in the legs of the TL074, have the correct voltages.
Now, if I quit the transistor, I have the following voltages:
Pin of Base: -9V
Pin of Emitter: + 6V
The web in MFOS say those must be the values (but with the transistor placed)
I saw out there that lowering R100 4.7M would rise less volume but nothing.
No longer is more to do.
Thanks for the help!

elmegil · Posted: Sun Sep 21, 2014 8:51 am Post subject:

Have you measured the AC frequency of the emitter, or looked at it with an oscilloscope? A DC measurement when it is actually generating noise is not necessarily going to be meaningful, and could be different from that 6V.

Jack Gull · Joined: Oct 23, 2014 Posts: 6 Location: Italy

Have you verified that the transistors were placed in the correct way?

Anyway, when i built my SLMK2 noise generator i built the circuit on a breadboard and tested i think five different transistors with two o three trannies per kind. As is natural they all sounded differently, with different noise volume and tone. I found that the 2n3904 had a very weak volume *if* it started producing noise at all. infact only one of the four 3904 i tested was able to produce noise.

I suggest you try different transistors. Now i am using a BC208A but somthing happened and the noise has very deep basses, which result in blipping. BC108 might be a good choice, though.