Because of this, we can't get equal charge and discharge times. 1, the timing capacitor charges through two resistances, R A + R B, but only discharges through R B. e., what percent of the time is it "on" and what percent "off"? Getting an uneven duty cycle from a 555 oscillator is easy it's getting equal on and off times that takes a little doing. The LDR may beĪ separate component or part of a photocoupler assembly.įor greatest flexibility, it's desireable for a tremolo to offer control of the duty cycle of the controlling signal, i. That the effect is operating, while LED2 excites photocell LDR1. Of Q2 and therefore the brightness of the LEDs. As the voltage of the control signal rises and falls, so does the bias on the Potentiometer R11 sets the quiescent bias of Q2.
Switch S2 feeds the selected control signal to modulator transistor Q2, through High input resistance of the MOSFET isolates the timing capacitor from the modulator,Īnd it outputs an exact replica of the charging voltage across R7. The triangle waveĪt pin 2 controls the gate of Q1, a MOSFET connected as a source follower. The edges of the waveform, which helps suppress audio ticks. R5-R6, which sets a suitable level to feed the modulator. The square wave output at pin 3 feeds voltage divider Use of the triangle wave without lousing up the charging of the cap. Wave from the output of the flip-flop, and the triangle wave at pin 2 resultsįrom the charging and discharging of the capacitor. The flip-flop is cleared, theĭischarge path is closed, and the charging cycle starts again. When the voltage on the cap is down toĪbout 1/3 of V+, comparator U1 changes states. The capacitor now discharges to ground through R BĪnd the drain-source of the transistor. When U2's output goes low, flip-flop FF toggles and turns on field-effect transistor Q. See, this will happen when external capacitor C charges to that level through resistors R AĪnd R B. Op-amps U1 and U2 areĬonnected as comparators the chip's internal resistors bias U2 such that its output willĬhange states if the voltage at the inverting input is greater than 2/3 of V+.
1 shows the internal components of the chip inside the dotted lines, with the externalĬonnections and components that make it run as an oscillator. For those who have never poked inside this chip, here's a look and an explanation of what goes on:įig. The CMOS version is used here for its low current drain. The Tremulous Bear gets its time-tick from a somewhat unusual setup of the popular 555 timer. This redesign is similar in conceptīut much easier to build. If youīought the kit, here's a link to the instructionĪn early version of the Tremulous Bear originally appeared in the August, 2001, issue of Gernsback's Poptronics magazine. This article describes a perfboard version forĪdvanced builders and includes technical details on how the pedal works. The LFO is an interesting design you get choice of triangle or square wave and lots of room for hacking and mods. It does all of the good things you would expect of a modern, flexible trem: traditional Fender-style chop, subtle background quavering and weird modulations. The Tremulous Bear The Tremulous Bear is a boutique-quality tremolo that can be constructed from
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