Bucket-brigade flanger with resonance, 1980 style

Pedal and tube amp circuits, solved part by part the way SPICE (the circuit simulator engineers use) does it, while you listen and watch. Turn the knobs, change any part, or tap a wire to put a probe on it.

How to use the bench

Every part is simulated. Nothing you hear is a recording.

  1. 1Pick a circuit

    Choose one from the menu, or type a name, maker or year in Find a circuit. The buttons under the menu switch between versions.

  2. 2Set the knobs and the input

    Turn the circuit’s knobs on the front panel. In the Input box, choose Guitar or Signal generator, and the note or chord.

  3. 3Press Play

    Press Play through the circuit to hear a picked note or chord. Play the string is the guitar by itself.

  4. 4Tap a part

    Tap any part on the schematic to change its value, or swap the transistor, tube or diode. The red numbers are DC voltages, and they update as you go.

  5. 5Tap a wire

    Tap a wire to put the probe there. The Probe graph and the spectrum show the signal there.

  6. 6Try a change

    Press Try it on a card under Try this to hear one change, before and after. Modify this circuit, below the schematic, adds or removes parts.

Good to know

Modeled after the Boss BF-2 Flanger.

An MN3207 bucket-brigade chip delays the guitar by 1.0 to 12.7 ms, and a triangle LFO sweeps its clock. Mixed back with the dry signal, the delay cuts a row of notches that move as the delay moves. Res feeds the delayed signal back in, so the notches ring.

Input

Add

Peak voltage from the pickup for each note. Strum hard and a single coil puts out a few hundred millivolts. When you play a chord, its strings share this level.

How it’s played
Tap a part to change its value, or a wire to probe it. To add or take out parts, open Modify this circuit, below. Red numbers are DC voltages to ground, not warnings. Scroll or drag sideways to see the whole circuit.
Modify this circuit Add parts, take them out, or put one in series with another, then hear what it does. Tap to open.

Pick what to do, then tap the schematic. Your changes show in purple. Any change can go on a switch beside the knobs, from the menu in its row under Your changes.

Add a part

Tap where each leg goes. Tap both ends of a part to put the new one across that part.

Change a part

With Remove a part on, tap any part of the pedal or amp to take it out, and tap it again to put it back. Tapping a purple part you added deletes it.

Turn on Add in series with a leg and tap a part. In that part’s box, below the schematic, pick which leg to lift and what goes in the gap, such as a resistor between a cap and ground or a stopper in front of a grid.

Change a wire

With Cut into a wire on, tap any wire. Pick a part from the menu and it goes in the gap, wired in. Volume pot puts a pot there with the input on one end, the output on the wiper and the other end to ground.

With Run a wire on, tap a leg, then where the wire goes. Drag any piece of a wire you ran, or of an added part’s lead, to square it up or move it.

Keep and share

Your changes stay in this browser, on this device, for your next visit. Nothing is sent to us. Anyone using this browser can see them. They’re lost if you clear your browsing data or use a private window, so save a file to keep a copy. A shared link carries the circuit after the #, a part browsers never send to a server.

Test tone for the graphs
The graphs use a steady tone. Play sounds a plucked string that dies away.

Input

pickup, unloadedat the pedal input

Output

at the amp input

Probe

Spectrum

Frequency response

What the curves mean

The ink curve is the response to a very quiet signal, from the generator to the probe. The blue curve is measured with pink noise at the level you set, like an audio analyzer. When stages clip, the blue curve pulls away from the ink one and the gray coherence line (right-hand scale) drops below 1. Then no single curve tells the whole story. Both use the signal generator, whichever Input tab is picked.

Output

Bias

every voltage and current at rest

What to listen for. IC1a boosts the treble above about 410 Hz and IC1b cuts it back after the delay, so the BBD’s hiss comes out lower. IC2a adds the Res feedback to the dry signal and drives a low-pass and the BBD. The chip holds 512 samples and moves them on one step each clock tick, so the delay is 512 over the clock rate. Two more low-passes smooth its steps. At the mixer the delayed and dry signals cancel wherever they’re half a cycle apart, so the notches sit one over the delay apart: about 500 Hz at the middle of Manual. Manual sets a voltage on Q8. Depth blends it with the LFO’s triangle, and Q6 and Q7 turn the blend into the clock chip’s timing current. With the knobs at their default settings the delay sweeps from 1.4 to 3.1 ms about 0.7 times a second. Rate runs up to 10.8 sweeps a second, and down to about one every 14 s by the parts’ values. The three trimmers are set as a factory-trimmed pedal would be, the clock at the service setting of 40 kHz with Manual at 0. The chip’s reset time rounds the clock off near 500 kHz at the top, a delay of 1.0 ms. The footswitch, its flip-flop, the LED and the effect switch Q4 are left out, so the model is the pedal with the effect on. Clock feedthrough isn’t modeled.

Download.

Parts and what they do

Stock values. Tap a part on the schematic to change it.

C39, 100 µF electrolytic
Bulk cap across the 9 V supply.
R34, 33 kΩ
Top of the 4.5 V divider. The op-amps, Q1 and the filters after the BBD work around this line.
R35, 33 kΩ
Bottom of the 4.5 V divider.
C25, 33 µF electrolytic
Filters the 4.5 V line.
IC6, 6 V
A 78L05 regulator with D9 in its ground lead, so its output sits near 5.6 V. Modeled as a steady 5.6 V source. It feeds the BBD’s bias trim, the LFO, Manual and the clock control, so none of them move as the battery runs down. The real BBD and clock chip run from it too. Their supply pins aren’t modeled.
C40, 47 µF electrolytic
Filters the regulated 5.6 V.
R40, 10 kΩ
Top of the LFO’s 2.8 V reference divider, from the 5.6 V line.
R41, 10 kΩ
Bottom of the LFO’s reference divider.
C29, 47 µF electrolytic
Filters the LFO’s 2.8 V reference.
R1, 1 kΩ
In series with the input.
C1, 47 nF
Input coupling cap.
R2, 470 kΩ
Biases Q1’s base from the 4.5 V line and sets most of the input impedance, about 450 kΩ.
Q1, 2SC1815
Input emitter follower. 2SC732TM-GR on the drawing. A 2SC1815 stands in, typical of the part.
R3, 10 kΩ
Q1’s emitter load.
C2, 1 µF electrolytic
Couples Q1 into IC1a.
R4, 47 kΩ
Input resistor of IC1a. Alone it sets a gain of one.
C3, 6.8 nF
With R5 it adds a second path into IC1a above about 410 Hz, so the treble going into the delay is boosted. IC1b cuts it back the same amount after the delay, which pushes the BBD’s hiss down.
R5, 10 kΩ
In series with C3. It holds the treble boost to about 5.7 times by 2.3 kHz.
R7, 10 kΩ
Biases IC1a’s + input at 4.5 V.
IC1a, RC4558
Inverting input stage with the treble boost. Its output feeds both the dry path to the mixer and the delay path. µPC4558C on the drawing. A 4558-class op-amp stands in, typical.
R6, 47 kΩ
IC1a’s feedback resistor.
C4, 100 pF
Rolls off IC1a above about 34 kHz.
R8, 220 kΩ
With C5, a treble path into IC2a. Above about 3.3 kHz it lifts IC2a’s gain slightly.
C5, 220 pF
In series with R8. 220 pF, hard to read on the drawing. The Aion redraw agrees.
R9, 82 kΩ
Input resistor of IC2a. With R12 it sets a gain of about 0.57.
C6, 47 nF
Couples the dry signal into IC2a. With R9 it cuts below about 40 Hz.
R13, 10 kΩ
Biases IC2a’s + input at 4.5 V.
IC2a, RC4558
Inverting mixer ahead of the delay. The dry signal and the Res feedback from after the delay add here.
R12, 47 kΩ
IC2a’s feedback resistor.
R11, 4.7 kΩ
In series with D3 and D4 across R12. On loud peaks the diodes conduct and the gain drops toward 4.7 kΩ over the input resistor, so the BBD isn’t driven past its range and Res can’t run away.
D3, 1N914 / 1N4148
One of the two limiter diodes. 1S2473 on the drawing. A 1N914 is the same kind of part.
D4, 1N914 / 1N4148
The other limiter diode, the other way round.
R10, 39 kΩ
Res feedback into IC2a. With VR5 it sets the most feedback Res can reach.
VR5, 22 kΩ pot, linear taper
The Res trimmer, inside the pedal. The factory set it just short of the pedal howling with Res full. In the model the loop stays short of oscillation over the trimmer’s whole travel, so it’s set near its low end, about 2.2 kΩ.
C7, 47 nF
Couples the Res feedback into IC2a.
R14, 10 kΩ
First resistor of the filter ahead of the BBD.
C8, 12 nF
From the filter’s middle to Q2’s emitter. With C9, R14 and R15 it makes a two-pole low-pass near 12 kHz, so less of the treble above half the clock rate gets into the BBD.
R15, 10 kΩ
Second resistor of the filter ahead of the BBD.
C9, 150 pF
Filter cap from Q2’s base to ground.
Q2, 2SC1815
Emitter follower that drives the BBD and closes the low-pass filter. 2SC1815 typical, for the drawing’s 2SC732TM-GR.
R16, 10 kΩ
Q2’s emitter load.
C10, 33 nF
Couples the signal into the BBD, so the chip’s input sits at the bias trimmer’s DC.
VR6, 22 kΩ pot, linear taper
The bias trimmer, inside the pedal. It sets the DC on the BBD’s input, about 2.8 V at the middle of its travel, which is how this file is set. The factory set it for the least distortion. The BBD’s range in the model is centered on 2.8 V, so moving the trimmer clips one side of the wave first.
C11, 1 µF electrolytic
Filters the bias trimmer’s wiper.
R17, 100 kΩ
From the bias trimmer to the BBD’s input. 100 kΩ, hard to read on the drawing. The Aion redraw shows 100 kΩ.
IC3, MN3207
The delay line, an MN3207 with 1024 stages. It holds 512 samples, so the delay is 512 over the clock rate: 12.7 ms at the slowest clock and 1.0 ms at the fastest. Its two outputs are drawn as one pin. The chip runs from the 5.6 V line, so its clean range is about ±1 V around 2.8 V.
R18, 56 kΩ
Load on the BBD’s output.
C13, 33 nF
Couples the BBD’s output into the filter after it.
R19, 330 kΩ
Biases the filter after the BBD, and Q3, at 4.5 V.
R20, 10 kΩ
First resistor of the three-pole low-pass after the BBD. It smooths the steps the chip puts out.
C14, 3.9 nF
First cap of the low-pass after the BBD.
R21, 10 kΩ
Second resistor of the low-pass after the BBD.
C15, 8.2 nF
From the filter to Q3’s emitter, the feedback cap of this low-pass.
R22, 10 kΩ
Third resistor of the low-pass after the BBD.
C16, 330 pF
Filter cap from Q3’s base to ground.
Q3, 2SC1815
Emitter follower that closes the low-pass after the BBD. 2SC1815 typical, for the drawing’s 2SC732TM-GR.
R23, 10 kΩ
Q3’s emitter load.
C17, 220 nF electrolytic
Couples Q3 into IC2b.
R24, 47 kΩ
Input resistor of IC2b. With R26 it sets a gain of one, turned over.
C18, 1 nF
Filter cap of IC2b’s low-pass.
R25, 22 kΩ
From the filter node to IC2b’s − input.
C19, 150 pF
IC2b’s feedback cap. With C18, R25 and R26 it makes another two-pole low-pass near 13 kHz.
R26, 47 kΩ
IC2b’s feedback resistor.
IC2b, RC4558
Low-pass stage after the BBD, gain of one, turned over. Its output is the delayed signal for the mixer and for Res.
C20, 220 nF electrolytic
Couples the delayed signal out of IC2b. Q4, the effect switch after it, is drawn as a wire: it’s on with the effect on.
R27, 1 MΩ
Holds the delayed signal’s line at 4.5 V.
C21, 47 nF
Couples the delayed signal to the Res pot.
Res, 50 kΩ pot, reverse audio taper
Res, 50 kΩ reverse audio. It sends part of the delayed signal back into IC2a, so the delay goes round again. The notches get deeper peaks between them and the sound turns metallic.
R28, 47 kΩ
The dry signal into the mixer.
R29, 27 kΩ
The delayed signal into the mixer. Smaller than R28, so it makes up for IC2a’s gain of 0.57 and the two come out near equal.
IC1b, RC4558
Output mixer, inverting. Where the dry and delayed signals are half a cycle apart they cancel: those are the notches. It also takes back IC1a’s treble boost.
R31, 47 kΩ
IC1b’s feedback resistor.
C22, 100 pF
Rolls off IC1b above about 34 kHz.
C23, 6.8 nF
With R30 it cuts IC1b’s gain above about 410 Hz, the reverse of IC1a’s boost.
R30, 10 kΩ
In series with C23.
R32, 470 Ω
In series with the output.
C24, 1 µF electrolytic
Output coupling cap.
R33, 100 kΩ
Holds the output at 0 V so the jack doesn’t pop.
R38, 100 kΩ
From the 2.8 V reference to IC5a’s − input.
C26, 10 nF
From IC5a’s − input to its output. It kicks the − input as the output flips, so each flip is sharp.
R36, 180 kΩ
From the triangle to IC5a’s + input. With R37 it sets the switch points about 1.06 V each side of 2.8 V.
R37, 220 kΩ
Positive feedback from IC5a’s output. It holds the output high or low until the triangle reaches the switch point.
IC5a, TL022
The LFO’s switch. Its output is a square wave, high or low. Half a TL022, on the 5.6 V line.
Rate, 250 kΩ pot, reverse audio taper
Rate, 250 kΩ, a variable resistor between the square and the integrator: all of it at 0, the slowest, none at full. Its taper is hard to read on the drawing. Reverse audio, as the Aion redraw shows.
R39, 1.5 kΩ
What’s left of the Rate path at full turn. It sets the top speed.
C27, 33 µF electrolytic
One of two 33 µF caps back to back, about 16.5 µF with no polarity. The integrator’s timing cap.
C28, 33 µF electrolytic
The other 33 µF timing cap.
IC5b, TL022
Integrator. It ramps up and down as the square flips, making the triangle that sweeps the delay. Half a TL022, on the 5.6 V line.
Manual, 50 kΩ pot, linear taper
Manual, 50 kΩ linear. It sets the base clock rate, so the base delay.
R42, 68 kΩ
From the Manual wiper to Q8’s base.
R43, 150 kΩ
Pulls Q8’s base up toward 5.6 V.
R44, 470 kΩ
Pulls Q8’s base down. With R42 and R43 it sets Q8’s range, about 1.0 V to 4.3 V on its emitter.
Q8, 2SC1815
Emitter follower for the Manual voltage. 2SC945-P on the drawing. A 2SC1815 stands in, typical.
R45, 4.7 kΩ
Q8’s emitter load.
Depth, 50 kΩ pot, linear taper
Depth, 50 kΩ linear, between the triangle and Manual’s voltage. At 0 only Manual sets the delay. At full only the triangle does.
R48, 220 kΩ
Turns the Depth wiper’s voltage into a current into Q7’s base node.
C32, 22 µF electrolytic
Smooths the control at Q7’s base. It rounds the triangle, and at fast Rate settings it narrows the sweep.
VR7, 470 kΩ pot, linear taper
The clock trimmer, inside the pedal. The service setting is 40 kHz with Manual and Depth at 0. Set here to its middle, for 40.3 kHz.
R46, 330 kΩ
With the trimmer it sets the current through Q6.
Q6, 2SC1815
Wired as a diode. Q6 and Q7 are a current mirror, and the current from R48 through R47 lifts Q7’s base above Q6’s. Each 26 mV more makes Q7 pass about 2.7 times the current. 2SC1815 typical, for the drawing’s 2SC945-P.
R47, 4.7 kΩ
Between the mirror’s two bases. The control current through it sets how far Q7’s base sits above Q6’s.
Q7, 2SC1815
Pulls the timing current out of the clock chip. More current, a faster clock and a shorter delay. 2SC1815 typical, for the drawing’s 2SC945-P.
R52, 4.7 kΩ
From Q7’s collector to the clock chip’s timing pin.
IC4, MN3102
MN3102 clock chip, drawn as its timing pin. The current Q7 pulls sets the clock rate, and the 47 pF timing cap C30 is the part’s timing cap field. Q5, D6, R49 to R51 and C31, which reset the cap each cycle, are inside the box. The law is set so the clock runs at the service setting of 40 kHz with the trimmer at its middle. Each cycle also loses a fixed reset time, about 1.1 µs, while the cap empties, so the top rounds off near the service note’s 500 kHz.

About this version

As drawn
As drawn. The BBD, the clock control and the LFO run from the 78L05’s 5.6 V. The op-amps work around 4.5 V. Transistors and op-amps typical of the parts named.

How this tool works. Every part is an equation, and the whole circuit is solved several times per audio sample: 192,000 samples a second while you drag a knob, 384,000 once you let go. Transistors use Ebers-Moll with gain, leakage, Early effect, base resistance, junction capacitance and temperature. Their charge storage is set at the bias point, close for small signals and rough while they switch hard. Tubes use Koren’s equations fitted to each datasheet, plus grid current. Diodes are exponential junctions with series resistance. Presets are typical of each type. Caps are ideal, and the battery or HT is a voltage behind a resistance.

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