I just wanted to thank you for your awesome phase shifter circuit design - it sounds great! Everyone I have showed it to agrees that it's one of the best phase shifters they've ever heard. We especially like how extremely the parameters can be adjusted to make dramatic, watery sounding effects. I had this vision of putting it into a hot pink clear acrylic enclosure with an 80's punk rock aesthetic - large aluminum knobs and those old embossed labels. With help from a friend, I was able to create this crazy enclosure. We added some blue LEDs and it looks really cool in low light. My terrible rats nest of a wiring job makes it look more frankenstein- like with the LEDs lighting it from underneath. I gave it to my boyfriend as a birthday present and he uses it all the time in his studio!
See more photos at Alison's Flickr Site
U1-A (and associated components) acts as both the input buffer and the mixer that combines the original signal with the phase shifted sigal via S2 (Four or Eight Stage Selector) and R15 (Feedback adjust pot). U1-B (and associated components) buffers the OUT-4 circuit point which is the output of the fourth phase shift stage. When using 8 stage phasing shifting you get a pseudo-stereo effect by connecting OUT1 and OUT2 to the inputs of a stereo mixing channel. If you change the gain of the input mixer BEWARE of too much feedback from the phase shifted signal. I have found that anything higher than a gain of 1 applied to the fed-back signal and you have an excellent candidate for an alarm system siren. So for example if you choose to change the op-amp gain setting resistor (R19) to 50K you should also change both R15 and R9 to 50K.
U2-A and U2-B (and associated components) combine to form a simple but effective low frequency oscillator. U2-B is an integrator that ramps up when U2-A (acting as a comparator)'s output is low and ramps down when U2-A's output is high. U2-A's output goes high when the voltage at its non-inverting input goes above the threshold voltage (ground) and overcomes the current flowing through hysteresis resistor R7. At that time the integrator begins to ramp low until the voltage at U2-A's non-inverting input goes below the threshold voltage (ground) and overcomes the current flowing through hysteresis resistor R7. At that point U2-A goes low and the cycle repeats. R16 controls the rate of the integrator by changing the voltage appearing at R17 and thus the current into (and out of) the integrator. R63 keeps the integrator from seeing ground (which would stop the LFO). If your LFO stops at the lowest setting you could increase R63 a bit (try 150 ohms, 200 ohms etc.). R63 is mounted on the panel. When closed, switch S1 (Tri Ramp switch) bypasses the rate set pot with a diode and a 1K resistor so that during the high cycle of U2-A the integrator ramps down very quickly. During the low cycle of U2-A (as the integrator ramps up) the rate control pot is in the circuit since the diode is reversed biased. You will see a rate shift when you switch from one wave to the other. The ramp will always be about twice the rate of the triangle wave since the integrator discharge is almost immediate in ramp mode.
U3-A and U3-B are used in the venerable voltage to exponential current generator. External voltage may be applied to control the phase shift of the unit. The LM13700s are all fed bias current via Q2 (2N3906 PNP) and the 20K resistors in series with their bias pin. The 20K resistors at the bias inputs help to equalize the current into the bias inputs so all of the sections track together pretty well. The phase shift sections are all the same as U4-A (and associated components). The transconductance amp in conjunction with C21 acts to shift the phase of the signal applied to the input (junction of R23 and C21). The angle of shift is dependent on the current flowing through U4-A (which is determined by the control current at it's pin 1 bias input). Each section takes as input the output of the previous stage and adds more phase shift. When this phase shifted signal is combined with the original signal in U1-A, cancellation of frequencies that are at (or close to) 180 degrees out of phase takes place and the characteristic phasing sound is heard. The more feedback applied (via R15) the more pronounced the effect. Several very noticable effects can be heard by experimenting with the settings of R10 and R15 interactively.
Although I used all .0047uF caps in the phase shift cells you can change this value (I tried from .001uF to .01uF) or even only change some of them to achieve different sounding phaser effects. Experiment have fun!
One last word... If you don't want to use all four LM13700s you can just use the first two (U4 and U5) and just take OUT4 back to feedback to the input mixer/buffer. However using all eight gives you more full cycle phase shifts per modulation cycle and is really... well stunning.
The Stop The Clicks Kludge is incorporated into the circuit and PC Board. NO KLUDGE NECESSARY ANYMORE See the original circuit for the history of this change.
The Increase Output Levels Kludge is incorporated into the circuit and PC Board. NO KLUDGE NECESSARY ANYMORE See the original circuit for the history of this change.
|Approx. Current Consumption|
|4||LM13700 Dual gm Op Amp(s)||LM13700||U4, U5, U6, U7|
|3||TL072 Dual Op Amp(s)||TL072||U1, U2, U3|
|1||1N914 or 1N4148 Sw. Diode||1N914 or 1N4148||D1|
|1||Potentiometer||100K Audio Taper||R4|
|2||Potentiometer(s)||100K Linear Taper||R16, R10|
|1||Potentiometer||10K Linear Taper||R15|
|5||Resistor 1/4 Watt 5%(s)||100K||R18, R21, R20, R12, R17|
|1||Resistor 1/4 Watt 5%(s)||43K||R3|
|13||Resistor 1/4 Watt 5%(s)||10K||R14, R5, R2, R9, R33, R36, R39, R41, R61, R60, R58, R55, R19|
|11||Resistor 1/4 Watt 5%(s)||1K||R31, R34, R37, R40, R51, R52, R53, R54, R8, R6, R1|
|1||Resistor 1/4 Watt 5%||1M||R13|
|9||Resistor 1/4 Watt 5%(s)||20K||R24, R26, R28, R30, R44, R46, R48, R50, R64|
|1||Resistor 1/4 Watt 5%(s)||270K||R7|
|1||Resistor 1/4 Watt 5%||2K||R22|
|16||Resistor 1/4 Watt 5%(s)||30K||R23, R25, R27, R29, R43, R45, R47, R49, R32, R35, R38, R42, R62, R59, R57, R56|
|1||Resistor 1/4 Watt 5%||430K||R11|
|1||Resistor 1/4 Watt 5%||100 ohm||R63 Mounted on panel|
|1||Resistor 1/4 Watt 5%||33K||R65|
|8||Capacitor Ceramic(s)||.0047uF||C21, C22, C23, C24, C25, C26, C27, C28|
|10||Capacitor Ceramic(s)||.1uF||C2, C4, C3, C6, C8, C10, C9, C13, C11, C15|
|2||Capacitor Ceramic(s)||22pF||C30, C31|
|3||Electrolytic Capacitor (s)||10uF||C20, C7, C16|
|1||Electrolytic Capacitor (s)||2.2uF||C29|