DIY Stompboxes > Building your own stompbox

typical phaser lfo waveforms?

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PRR:
> what should the output waveforms be biased at?

They come out of the LFO at whatever the LFO wants to give you.

They go into the controller "centered"(*) around whatever you consider "mid-scale".

If you use a 400V 12AX7 VFO (the lovely Fender tremolo) and a DBX VCA (20mV control), you will have to pad and shift a lot. Controlling JFETs, you may need a few volts but "centered" a little below the bias, which may be zero or half-supply depending on the audio design.

(*)Since pitch and amplitude are log scale, and many controllers are linear, the notion of "centered" "mid-scale" may be considerably skewed.

Much of the real "art" is finding VFOs and controllers which fit together sweet. The McConkey plan makes a linear triangle, but then semi-LOGs it, so that a linear controller (BBD?) gives LOG frequency-- smooth "pitch" instead of linear Hz.

Processaurus:
Hey Karl, does your tap tempo chip's pulse width knob make the sine wave into a hypertriangular sine wave, or make it lopsided, approaching a sawtooth?  If the former is the case, I think it will work out well for a phaser project I'm getting around to.

MoltenVoltage:

--- Quote from: Processaurus on December 29, 2009, 11:04:53 PM ---Hey Karl, does your tap tempo chip's pulse width knob make the sine wave into a hypertriangular sine wave, or make it lopsided, approaching a sawtooth?  If the former is the case, I think it will work out well for a phaser project I'm getting around to.

--- End quote ---

By "pulse width knob", you are talking about the Duty Cycle Control.

It doesn't make a "hyper triangular" waveform.

Instead, it adjusts the relative playback speed of the first and second halves of the selected waveform.  When you look at a duty cycle adjusted sine wave on the scope, it is skewed sort of like a sawtooth wave, but it is much more rounded.  The eleven (11) Duty Cycle ratios correspond to the most common musical subdivisions, and let you make the LFO swing. The relative length of the first half is indicated by the numerator, the overall length by the denominator: 1/8, 1/6, 1/4, 1/3, 3/8, 1/2, 5/8, 2/3, 3/4, 5/6, 7/8

You can always get a pure triangle wave by programming a sawtooth up > sawtooth down, 2 step sequence.

We can program a custom chip with an order of 100 units.  Mathematically, the "hyper triangular" waveform looks like its just the repeated bottom half of a sine wave.

Lurco:
rectify a sine?

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