Voltage-controlled digital oscillator VCDO1

Posted by & filed under Projects, Synth DIY.

A single chip 1V/Oct voltage controlled digital oscillator, with 20 waveforms in a scannable wavetable. The VCDO uses a PIC 16F1847 microprocessor to create a versatile and simple voltage-controlled 8-bit digital wavetable oscillator. All oscillator parameters are controlled by 0-5V control voltages. The chip has a native exponential control response, making interfacing with 1V/Oct control voltages very simple, even without an exponential convertor. Scanning through the wavetable with the Waveform knob. Sub Osc is a simple sine 2 octs down:… Read more »

Tap Tempo LFO (TAPLFO V2D)

Posted by & filed under Projects, Synth DIY.

This simple Tap Tempo LFO is based on the PIC 16F684. You can set the LFO frequency by tapping a tempo on a button connected to the chip, or by changing the Tempo CV. With this chip you can build tap tempo effects units or stompboxes, tap tempo controlled drum machines or tap tempo sequencer clocks. All of these are described in the datasheet below. The LFO can produce 8 waveforms, including a random (sample & hold) wave. All the… Read more »

Moog 911 ADSR Envelope Generator clone

Posted by & filed under Envelope Generators, Projects, Synth DIY.

A clone of a classic using my PIC code by J-P Desrochers Jean-Pierre Desrochers wanted to copy the response of the Moog 911 envelope generator using more modern technology. He asked me if it would be possible to tweak the response of my PIC envelope generator to do this, and I told him that it would, since the control mapping is stored in a table in the code. JP worked out the required table values and a front panel design…. Read more »

White Noise Source

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… Read more »

Practical LFSR random number generators

Posted by & filed under Noise, Synth DIY.

The linear feedback shift register is one of the most useful techniques for generating psuedo-random numbers. I’ve used this method for creating noise generators and as an element in the random modulation generators I spent a long time developing for my Protowave synth. If you’re not really clear how an LFSR works, have a look at one of the many pages online (links below). This page isn’t here for that. In short, an LFSR takes a series of bits from… Read more »

Voltage Controlled ADSR Envelope Generator (VC ADSR 7B)

Posted by & filed under Envelope Generators, Projects, Synth DIY.

A CEM 3312 / SSM 2056 clone using cheap PIC microprocessors This page describes a cheap clone of the CEM 3312 and SSM 2056 voltage-controlled envelope generator chips. Both of these chips include voltage control of A, D, S and R, but both include other inputs too. The CEM 3312 chip has a input which controls the final envelope output level. This is very handy as a voltage-controlled “envelope depth” when feeding the envelope to a filter, for instance. The… Read more »

CEM3320 Filter designs

Posted by & filed under Elka, Filters, OB-Xa, Oberheim, Pro-One, Sequential, Synth DIY, Synthex.

Like my SSM2044 page, this page is a look at how various synths implemented the CEM3320 filter, with the datasheet design as a reference standard. Whereas the SSM2044 is a dedicated lowpass filter, the CEM3320 is just a set of filter building blocks. In this respect, it is more like the earlier SSM2040. The CEM equivalent of the SSM2044 is probably the CEM3328, which is basically the same as the 3320, but wired up as a dedicated lowpass filter, thereby… Read more »

SSM2044 LP Filter designs

Posted by & filed under Filters, Korg, MonoPoly, Opera, Polysix, PPG, Siel, Synth DIY, Trident, Wave.

This page is a look at how various synths implemented the SSM2044 filter, with the datasheet design as a reference standard. I’ve redrawn all the schematics to make comparisons very easy. First, the datasheet design.   The datasheet suggests using the two differential inputs (+audio and -audio) as individual oscillator inputs for a two-oscillator synth (or synth voice). It also suggests that these two inputs should be provided with slightly different resistor values (68K Vs 100K) so that the oscillators… Read more »

Voltage Controlled LFO (VCLFO 9D)

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This voltage-controlled LFO is based on the PIC 16F684, which is a pretty basic chip. Nonetheless, this LFO has more features than your average LFO. For a start, it can produce 7 basic waveforms, and also includes a noise source. It can also morph its waveforms under CV control, well beyond basic PWM. There is an optional sample-and-hold module that can sample whatever is selected, the current waveform or the noise source. The LFO frequency, waveform selection, waveform distortion, and… Read more »

Direct Digital Synthesis

Posted by & filed under Oscillators, Synth DIY.

Direct Digital Synthesis (DDS) Direct digital synthesis is a common technique for generating waveforms digitally. The principles of the technique are simple and widely applicable. You can build a DDS oscillator in hardware or in software. A DDS oscillator is sometimes also known as a Numerically-Controlled Oscillator (NCO). How does it work? The most important part of a DDS oscillator is the ‘Phase Accumulator’. This is just a counter. For example, we could use a 16-bit binary counter: When the… Read more »