Analog delay with a compander and a 4096-stage bucket brigade on 12 V, 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 Ibanez AD-80 Analog Delay.

A 4096-stage bucket brigade delays the signal by about 15 to 270 ms. An NE570 compressor ahead of it and an expander after it keep the chip’s hiss down, three-pole filters on both sides keep the clock out, and Repeat sends a share of the delay back in.

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. IC101a lifts the treble up to about 21 dB before the compressor, and IC101b cuts it the same amount at the output, so the dry signal comes through flat and the hiss added in between drops. The compressor halves the signal’s range in dB, the bucket brigade delays it, and the expander doubles the range again. A three-pole filter before the chip and two after it cut above about 3 kHz, so each repeat is darker than the last, and darker still at long delays, where the clock runs slower. Delay Time sets the clock from about 138 kHz (15 ms) to 7.5 kHz (273 ms). Repeat sends some of the delay back into the compressor, and near full the repeats run away. Blend’s wiper is grounded: toward DELAY it shorts the dry signal, toward DRY the delay. The footswitch, its flip-flop and the FET switches are left out, so the model is the pedal with the effect on.

Download.

Parts and what they do

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

C140, 100 µF electrolytic
Filter cap on the 12 V line after IC105, the 78L12 regulator. The regulator and the two 9 V batteries are drawn as the supply.
R156, 10 kΩ
Top of the 6 V divider.
R157, 10 kΩ
Bottom of the 6 V divider. Both op-amps work around it.
C139, 47 µF electrolytic
Filters the 6 V line.
C102, 47 nF
Input coupling cap. With R102 the corner is about 7 Hz.
R101, 1 kΩ
In series with IC101a’s + input.
R102, 510 kΩ
Biases IC101a from the 6 V line and sets the input impedance near 510 kΩ.
IC101a, TL022
Pre-emphasis stage, non-inverting. Gain 1 for the lows, rising above about 1 kHz to 11 (21 dB) near 10 kHz, so the treble goes through the delay louder than the hiss. TL022 values.
R103, 10 kΩ
IC101a’s feedback resistor.
C103, 470 pF
Across R103. It rolls the lift off above about 34 kHz.
R104, 1 kΩ
With C104 it sets where the treble lift starts and how far it goes (1 + 10 k / 1 k).
C104, 15 nF
Pre-emphasis cap. With R103 the lift starts near 1 kHz.
C105, 1 µF electrolytic
Couples IC101a into the compressor.
IC102 (1 to 8), NE570 (one half)
NE570 half wired as a compressor. The input goes in at pin 6, and the gain cell and rectifier listen to the output through C110. Every 2 dB change at the input is about 1 dB at the output, so quiet parts go into the delay louder.
C107, 470 nF electrolytic
The compressor’s rectifier cap. With the chip’s 10 k it sets how fast the gain follows the level, about 5 ms.
R106, 36 kΩ
Half of the compressor’s DC feedback.
R107, 36 kΩ
Other half of the DC feedback.
C108, 1 µF electrolytic
Grounds the middle of R106 and R107 for audio, so they set only the DC.
C110, 1 µF electrolytic
Feeds the compressor’s output to its rectifier and gain cell.
R105, 10 kΩ
Feeds the repeats into the compressor’s summing node, beside the input.
VR105 Feedback, 20 kΩ pot, linear taper
Feedback trim, 20 kΩ as a variable resistor in series with R105. It sets how much the Repeat knob can send back, so where the repeats run away. At 0.35, assumed, full Repeat runs away slowly near 1 kHz, as most analog delays are set. At half the repeats die about 1 dB a pass even at full.
C109, 1 µF electrolytic
Couples the Repeat wiper back into the compressor.
R108, 10 kΩ
First of three 10 kΩ resistors in the filter ahead of the bucket brigade.
C111, 6 nF
Filter cap to Q101’s emitter, which follows the output, so it lifts the filter’s corner into a sharp knee.
R109, 10 kΩ
Second filter resistor.
C112, 6 nF
Second cap to Q101’s emitter.
R110, 10 kΩ
Third filter resistor.
C113, 3.3 nF
Filter cap to ground. With the other two, a three-pole low-pass that cuts above about 3 kHz so nothing near the clock gets into the chip.
Q101, 2SC1815
Emitter follower closing the filter. 2SC536 on the drawing, 2SC1815 values.
R111, 10 kΩ
Q101’s emitter load.
C114, 1 µF
Non-polar coupling cap into the bucket brigade’s bias.
R113, 4.7 kΩ
Top of the Bias trim.
VR103 Bias, 10 kΩ pot, linear taper
Bias trim. Sets the DC on the bucket brigade’s input. At half, as a factory-trimmed unit, 6.0 V, the middle of the chip’s swing, so the wave clips evenly top and bottom.
R114, 4.7 kΩ
Bottom of the Bias trim.
C115, 1 µF electrolytic
Keeps the signal off the Bias trim’s wiper.
R112, 100 kΩ
Carries the bias to the chip’s input.
R115, 4.7 kΩ
In series with the chip’s input (pin 7).
IC103, MN3005
MN3005 bucket brigade, 4096 stages. Each clock cycle moves the samples one stage on, so the delay is 2048 clock periods. Its two outputs are drawn as one pin. Swing set to 2.2 V for the 12 V supply, assumed. Clock feedthrough isn’t modeled. The sheet’s parts list says MN3007, the drawing MN3005.
R119, 130 kΩ
Load on output 1 (pin 3).
R120, 130 kΩ
Load on output 2 (pin 4).
VR102 Balance, 20 kΩ pot, linear taper
Balance trim, across the two outputs. It balances them so the clock cancels. Here both ends are on the one output pin, so at half it’s 5 kΩ in series. The clock it cancels isn’t modeled.
VR104 Level, 50 kΩ pot, linear taper
Level trim. Sets how loud the delayed signal is going into the output filters. At 0.8, assumed, the first repeat of a 440 Hz note comes back about 3 dB under the dry (1 dB at 1 kHz). Even at the top of the trim it stays about 2 dB under.
R121, 100 kΩ
Under the Level trim.
R122, 10 kΩ
First resistor of the first filter after the chip.
C118, 3.3 nF
Filter cap to Q102’s emitter.
R123, 10 kΩ
Second filter resistor.
C119, 3.3 nF
Second cap to Q102’s emitter.
R124, 10 kΩ
Third filter resistor.
C120, 1.8 nF
Filter cap to ground.
Q102, 2SC1815
Emitter follower closing the first output filter. 2SC1815 values.
R125, 10 kΩ
Q102’s emitter load.
R126, 10 kΩ
First resistor of the second output filter.
C121, 2.2 nF
Filter cap to Q103’s emitter.
R127, 10 kΩ
Second filter resistor.
C122, 2.2 nF
Second cap to Q103’s emitter.
R128, 10 kΩ
Third filter resistor.
C123, 1.2 nF
Filter cap to ground. The two filters together cut the clock and its images steeply above about 4 kHz.
Q103, 2SC1815
Emitter follower closing the second output filter. 2SC1815 values.
R129, 10 kΩ
Q103’s emitter load.
C124, 2.2 µF electrolytic
Couples the filtered delay into the expander.
IC102 (9 to 16), NE570 (one half)
NE570 half wired as an expander. The rectifier and gain cell take the delayed signal, and pins 10 and 11 are joined. Every 1 dB at its input is about 2 dB at its output, which undoes the compressor and pushes the delay line’s hiss down when the signal is quiet.
C125, 470 nF electrolytic
The expander’s rectifier cap, the same as the compressor’s so the two track.
R130, 10 kΩ
From the expander’s summing node to ground. With the chip’s own resistors it sets the output’s DC near 6.6 V.
C127, 1 µF electrolytic
Output coupling cap of the expander.
Repeat, 10 kΩ pot, reverse audio taper
How much of the delayed signal goes back into the compressor, so how many repeats. 10KC on the drawing, a reverse audio taper: most of the change comes early in the turn.
R131, 1.8 kΩ
Feeds the delayed signal to Blend’s DRY end.
C129, 47 µF electrolytic
Couples the dry signal from IC101a to Blend.
R133, 1.8 kΩ
Feeds the dry signal to Blend’s DELAY end.
Blend, 50 kΩ pot, linear taper
Blend, 50 kΩ linear, its wiper grounded. Turned toward DELAY it shorts the dry signal and leaves the delay. Toward DRY it shorts the delay. At half each side has 25 kΩ to ground and both come through.
R132, 7.5 kΩ
Mixing resistor for the delayed side.
R134, 7.5 kΩ
Mixing resistor for the dry side.
C128, 4.7 µF electrolytic
Couples the mix into IC101b. On the pedal Q105, the effect-on FET switch, sits between. Here it’s a wire.
IC101b, TL022
Output stage, inverting, with de-emphasis: gain about 1 for the lows, cutting toward −21 dB in the treble, which undoes IC101a’s lift on both the dry and the delay. TL022 values.
R142, 10 kΩ
Holds IC101b’s + input on the 6 V line.
R141, 10 kΩ
IC101b’s feedback resistor.
C133, 47 pF
Small cap across R141.
R140, 1 kΩ
De-emphasis: with C134 it lowers the gain in the treble, the mirror of R104 and C104.
C134, 15 nF
De-emphasis cap.
R143, 470 Ω
In series with the output.
C135, 10 µF electrolytic
Output coupling cap.
R144, 10 kΩ
Holds the output at 0 V so the jack doesn’t pop.
IC104, MN3101
MN3101 clock chip. Its timing cap is C116, 120 pF (this part’s cx). The current out of pin 6 through R117 and the Clock trim and through R118 and Delay Time sets the clock. kf 3.0 and a 15 k series term are the DM-2’s fit for the same chip. R116 22 k (pin 7) is left out.
R117, 390 kΩ
In series with the Clock trim.
VR1C1 Clock, 1 MΩ pot, linear taper
Clock trim, wired as a variable resistor. It sets the slowest clock, with Delay Time full up. At 0.8, assumed, the longest delay is about 273 ms. The trim reaches 173 to 284 ms.
R118, 5.1 kΩ
In series with Delay Time. With the knob at 0 it sets the fastest clock.
Delay Time, 500 kΩ pot, audio taper
Delay time, 500 kΩ audio taper as a variable resistor beside the Clock trim. Turned up, its resistance rises and the clock slows, so the delay gets longer: about 15 ms at 0, 24 ms at a quarter, 50 ms at half, 119 ms at three quarters and 273 ms full up. Most of the change comes in the top half of the turn.

About this version

As drawn
Negative ground, on a 12 V regulated supply. The op-amps work around a 6 V line from R156 and R157.

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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