As described earlier, the phase-shift L.F.O. circuitry found in tube amps is only capable of generating sine wave amplitude modulation. Further, these primitive L.F.O.s also possess another shortcoming—they lose gain at lower modulation rates resulting in a weaker intensity of effect (less depth to the tremolo) at slower settings. The original ‘Uni-Vibe‘ has a similar phase-shift L.F.O. configuration (built using transistors rather than tubes) and therefore also exhibits this drop-off of intensity as the oscillator begins to collapse. In hindsight it is easy to pick fault with these archaic old tremolo circuits, however it should be recognised that some of the designs being discussed here are over half a century old. In their time they were the state-of-the-art, cutting edge innovation.
Today, in the light of all that the knowledge and wisdom laid down by engineers at RCA, the great Leo Fender and more recent, staggering developments in electronics technology I realised the L.F.O. could be improved… a lot. My idea was to keep the benefits of an all-tube signal path, based on a grounded cathode stage (the same as the input stage in a Fender ‘Deluxe Reverb’ amp) and cathode follower (buffer) operating at amp plate voltages then sandwich my custom Raysistor in between the two tube stages—in short, an audio signal path based on archaic, vintage electronics. However, the control would be achieved using DDS (direct digital synthesis). DDS makes it possible to synthesise any type of analogue waveform. Sine, square, triangle, rising or falling ramps, pulse, arbitrary waveforms, that is, anything that can be imagined—now we’re really surfing!
But all these limitless possibilities can create chaos and confusion for a guitarist when attempting to dial in their favourite trem setting. So, in an effort to make things more straightforward and intuitive I decided to limit the Delta-Trem to three fundamental waveform shapes (‘Filament’, ‘Fluid and ‘Neon’) that could selected via a three-way toggle switch. These could then be morphed into radically different wave shapes using a ‘Shape’ knob. This, in combination with the ‘Width’ and ‘Rhythm’ knobs, makes it possible to sculpt a myriad of different L.F.O. wave shapes quickly and easily.
