Posted by & filed under Noise, Projects, Synth DIY.

A pure white audio noise generator using an 8 pin PIC 12F675

This pages describes a simple digital noise source that produces pure white noise over the whole audio band – out to more than 40Khz, in fact. With filtering, you can derive pink noise and other colours. The circuit diagram included below was developed from the famous Polyfusion noise generator, and can produce white, pink and infra-red (low frequency) noise.

The noise generator 12F675 PIC microprocessor uses a dual LFSR algorithm which produces a pseudo-random stream of bits at over 90KHz. The bitstream shouldn’t repeat for 142 million years, but obviously I haven’t checked!

Replacement noise generator for Sequential Prophet 5 / Korg MonoPoly / Oberheim OB-X

I arranged the chip to be as close a replacement as I could for the notorious MM5837 digital noise generator which appears in early Korg MonoPolys, the Sequential Prophet 5, and the Oberheim OB-X. This chip has a very short LFSR (only 17-bit) which means that the noise it produces repeats every few seconds. This is audible, and has been described as sounding like a steam train puffing, rather than smooth white noise.

The only difference between the two chips (and one I couldn’t do anything about) is the supply voltage. This also means the new chip is quieter.

The datasheet includes some details about replacing the MM5837 in these synths.

Pinout Diagram

Pinout of MM5837 Noise Generator IC and modern replacement based on PIC 12F675

More details

A potential pitfall

The chip uses both the internal oscillator and the internal MCLR pullup. This combination causes problems with some PIC programmers. My own ICD2 clone complains that it doesn’t support it, and there are many reports online of problems with the JDM programmer. I programmed my chip successfully using the PICKit1 programmer, and it’s been reported to me that the P16pro programmer and Picallw software work too.

    Related Products

  • NOISE 1B Noise Generator

    The NOISE 1B is a simple digital noise source that produces pure white noise over the whole audio band – out to more than 40Khz, in fact. With filtering, you can derive pink noise and other colours. It only requires a +5V supply to operate. The chip was arranged to be as close a replacement as possible notorious MM5837 digital noise generator which appears in early Korg MonoPolys, the Sequential Prophet 5, and the Oberheim OB-X, amongst others. It can be used... Read more »...

    More Info Buy Now
  • PENTANOISE Noise Generator

    The PENTANOISE is a five channel digital noise source that produces independent pure white noise over the whole audio band. With only two resistors and two capacitors on each output, you can build five independent channels of analog white noise. Download the Electric Druid PentaNoise Generator Datasheet The datasheet includes the pinout diagram and application circuit.    ...

    More Info Buy Now

Leave a Reply

Your email address will not be published. Required fields are marked *