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)

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

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 »

Wavetable Oscillators

Posted by & filed under DW series, Korg, Oscillators, PPG, Synth DIY, Wave.

This page is an overview of two techniques for creating wavetable oscillators. Contents DDS – Korg DW series and similar Variable sample rate – PPG Wave and similar DDS – Korg DW series and similar The Korg DW series use a DDS oscillator scheme. Korg called it ‘DWGS’ for ‘Digital Waveform Generator System’ in the 80’s style of inscrutable acronyms, but in reality it is a single cycle of digitally stored waveform that can be played back repeatedly. It uses a counter… Read more »

Roland Juno DCOs

Posted by & filed under Juno, Oscillators, Roland.

This page is a brief look at the technology of the Roland Juno series digitally controlled oscillators. These are an interesting hybrid design. Although digitally controlled and digitally stable, the oscillator produces a true analogue output, even for ramp waves, rather than the typical staircase waveform produced by feeding an incrementing count to a DAC or from a wavetable. Here we will look at how this is done. Contents General Scheme Master Clock Counters Waveshapers Sub-Oscillator Sawtooth PWM Frequency accuracy… Read more »