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 »