I often come across leaky and noisy PNP germanium transistors while testing them, so after reading Robert Penfold’s article on noise generator circuits some time ago, I decided to put them to good use. Rather than auditioning/abusing silicon transistors in reverse avalanche mode, you can get (better?) noise by using an otherwise throwaway germanium transistor.
Penfold mostly uses a discrete approach with the rather obscure BC650 for amplification. I was able to find BC650’s locally for a few cents, so I just followed his simple common emitter approach that requires only a single supply of 9 volts. I assume that you can replicate his approach to red, yellow, etc noise filtering using op amps, or substitute BC650 for a similar high gain transistor (mine had an hFE of about 820).
The stripboard follows the schematics in the article, but I added a volume control while, in my actual build, I increased the 1.2k resistor to 3.3k as I found the end volume of pink noise too high. You might want to adjust yours accordingly.
