Two-channel 100 W amp with diode clipping, 1982 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 Marshall JCM800 2210 (100 W split channel).

The 2205’s preamp on four EL34s. A clean channel and a lead channel switched by transistors, sharing one input stage. The lead channel runs two more gain stages with a diode clipper between them, then the treble-middle-bass stack. The channels meet at the master, then a reverb mix and one more triode drive the phase inverter.

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. V1a feeds both channels. The clean channel has its own bass and treble network right after V1a, then two triodes with unbypassed cathodes, so it stays clean to a high volume. The lead channel goes through V1b, whose cathode sits on a diode, so it’s biased hot and gains a lot. The Gain pot’s second gang sends it into a clipper made from a bridge rectifier and one more diode, about three diode drops each way. V3a amplifies the clipped signal again and drives the tone stack from its plate. At the master, a 470 kΩ and a 10 kΩ drop the level a long way for the effects send, and V4a brings it back up for the phase inverter. Probe the clipper node, then V3a’s plate, to see where the lead channel clips.

Download.

Parts and what they do

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

R58, 10 kΩ
Dropping resistor, 10 kΩ 1 W, from node X (the phase inverter’s node) to node A, which feeds every preamp plate.
C44, 50 µF electrolytic
Filter cap on node A.
C1, 47 nF
Input coupling cap, .047 µF.
R1, 1 MΩ
Grid leak.
V1a, 12AX7 / ECC83 / 7025
Input stage, shared by both channels.
R4, 100 kΩ
Plate load.
R2, 2.7 kΩ
Cathode resistor.
C2, 470 nF
Cathode bypass, 0.47 µF against 2.7 kΩ. The stage has full gain above about 125 Hz.
Cb, 22 nF
Feeds the top of the clean channel’s bass pot.
Normal bass, 1 MΩ pot, audio taper
The clean channel’s bass, 1 MΩ log. Turning it up passes more of the signal through the .022 µF cap to its wiper, and that cap passes the bass.
R2b, 100 kΩ
Below the bass pot.
C3, 5 nF
Feeds the bass pot’s wiper directly. At .005 µF it passes the mids and treble at any bass setting.
R5, 100 kΩ
Series resistor to the treble pot’s wiper.
Normal treble, 1 MΩ pot, audio taper
The clean channel’s treble, 1 MΩ log. Toward the top, more treble passes through C5 around R6. Toward the bottom, C23 shunts treble to ground.
C23, 2 nF
From the bottom of the treble pot to ground.
C5, 10 nF
Treble path from the top of the treble pot to the volume pot.
R6, 330 kΩ
Main path from the tone network to the volume pot.
Normal volume, 1 MΩ pot, audio taper
Normal volume, 1 MΩ log. Its wiper feeds V2a.
C4, 100 pF
Bright cap, 100 pF across the top of the volume pot. It does the most with the volume low.
C40, 220 nF
Mutes the clean channel. In the amp a transistor in IC1 grounds this cap while the lead channel plays. On the bench it’s grounded while the Lead channel switch is on.
V2a, 12AX7 / ECC83 / 7025
Clean channel’s first gain stage. The 10 kΩ unbypassed cathode resistor holds its gain to about 10.
R14, 150 kΩ
Plate load.
R13, 10 kΩ
Cathode resistor, unbypassed. It biases the stage cold and adds a lot of feedback.
C13, 22 nF
Coupling cap.
R15, 470 kΩ
Grid leak.
V2b, 12AX7 / ECC83 / 7025
Clean channel’s second gain stage, unbypassed.
R17, 100 kΩ
Plate load.
R16, 1.5 kΩ
Cathode resistor, unbypassed.
C14, 22 nF
Coupling cap.
R18, 150 kΩ
With R19, a divider that drops the clean channel to about 40 %.
R19, 100 kΩ
Bottom of the divider.
C15, 470 pF
Treble cut at the divider, above about 5 kHz.
R21, 470 kΩ
Mixes the clean channel into the master node.
C7, 2 nF
Lead channel coupling cap, .002 µF. With the 1.1 MΩ behind it, it cuts below about 70 Hz, so the bass doesn’t muddy up the gain stages.
R11, 100 kΩ
Series resistor to the gain pot.
Lead gain, 1 MΩ pot, audio taper
Lead gain, first gang, 1 MΩ log.
C39, 47 nF
Coupling cap from the gain pot to V1b.
R12, 220 kΩ
Grid leak.
V1b, 12AX7 / ECC83 / 7025
Lead channel’s second gain stage. With a 470 kΩ plate load and its cathode held near one diode drop, it gains about 60.
R7, 470 kΩ
Plate load, 470 kΩ.
R3, 10 kΩ
Cathode resistor. On its own it would bias the stage very cold. D1 across it sets the bias.
D1, 1N4001
1N4007 across the cathode resistor. It holds the cathode near half a volt and acts as a low-impedance bypass, so the stage runs hot with full gain.
C8, 22 nF
Coupling cap.
Lead gain, 1 MΩ pot, audio taper
Lead gain, second gang, 1 MΩ log. It turns with the first.
R20, 27 kΩ
Series resistor into the clipper. It sets how hard the stage can push current into the diodes.
C16, 2 nF
Across R20, so the treble passes it above about 3 kHz.
DR1, D6, 3 × 1N4001, one each way
A W005 bridge rectifier with a 1N4007 across its DC side, from the clipper node to ground. Either way the current passes two bridge diodes and D6, so it clips evenly at about three diode drops.
Lead volume, 1 MΩ pot, audio taper
Lead volume, 1 MΩ log, after the clipper and before V3a.
C48, 47 pF
From V3a’s grid to its cathode. With the cathode bypassed, it works as a small cap to ground.
V3a, 12AX7 / ECC83 / 7025
Lead channel’s third gain stage. Its plate drives the tone stack.
R27, 100 kΩ
Plate load.
C22, 2 nF
From the plate to the supply, which is ground for the signal. It cuts the fizz from the clipper, above about 2 kHz.
R24, 1.5 kΩ
Cathode resistor.
C18, 22 µF electrolytic
Cathode bypass, full gain down through the bass.
R28, 10 kΩ
Series resistor from V3a’s plate to the tone stack.
C17, 470 pF
Treble cap.
Lead treble, 220 kΩ pot, linear taper
The lead channel’s treble, 220 kΩ linear. Its wiper is the stack’s output.
R23, 56 kΩ
Slope resistor.
C19, 22 nF
Bass cap, to the bottom of the treble pot.
C21, 22 nF
Mid cap, on its own branch to the mid pot.
Lead middle, 100 kΩ pot, audio taper
The lead channel’s middle, 100 kΩ log, a variable resistor from the mid cap to ground. Turned down, it shunts the mids from the slope node.
R33, 4.7 kΩ
In series with the bass pot.
Lead bass, 1 MΩ pot, audio taper
The lead channel’s bass, 1 MΩ log, a variable resistor. Turned up, it lifts the bottom of the treble pot further from ground, so more bass gets through.
C20, 2 nF
From the bottom of the treble pot to ground. It holds the bottom of the treble pot down for high frequencies at any bass setting.
R22, 100 kΩ
From the treble wiper to the master node.
Master, 1 MΩ pot, audio taper
Master, 1 MΩ log, a variable resistor from the master node to ground. It sets the level of both channels.
R35, 220 kΩ
Feed to the reverb driver.
C27, 10 nF
Coupling cap to the reverb driver.
R36, 1 MΩ
V3b’s grid leak. V3b and the reverb tank aren’t modeled, so this network stands for the load the reverb driver puts on the master node.
R32, 470 kΩ
Dry path to the effects send. With R29 it drops the level by about 34 dB.
C24, 100 pF
Across R32, so more treble gets through.
R29, 10 kΩ
Bottom of the send divider.
R31, 56 kΩ
From the reverb pot to the send node.
Reverb, 100 kΩ pot, audio taper
Reverb, 100 kΩ log. The tank isn’t modeled, so on the bench it only changes the load on the send node slightly.
R42, 10 kΩ
From the recovery stage to the reverb pot’s wiper.
C29, 10 nF
Coupling cap from the recovery stage.
V4b, 12AX7 / ECC83 / 7025
Reverb recovery stage. With no tank, its grid sits on the tank’s output coil, so all it adds is the load at its plate.
R38, 100 kΩ
Plate load.
R39, 1.5 kΩ
Cathode resistor, unbypassed.
Tank out, 200 Ω
The reverb tank’s output coil, as a resistor. Typical, not measured.
C26, 220 nF
Coupling cap from the effects return (normalled to the send) to V4a.
R34, 1 MΩ
Grid leak.
V4a, 12AX7 / ECC83 / 7025
Return stage. It makes up the level lost at the send and drives the phase inverter.
R30, 100 kΩ
Plate load.
R25, 1.5 kΩ
Cathode resistor, unbypassed.
C25, 22 nF
Coupling cap into the phase inverter, on the second sheet.
V5a, 12AX7 / ECC83 / 7025
12AX7, the driven half of the long-tail pair phase inverter. Its plate swings opposite the input and drives tube A. Its grid is fed through the preamp’s coupling cap, so there’s no second one here.
V5b, 12AX7 / ECC83 / 7025
The other half of the inverter. Its grid sits at the feedback point for signal, so it’s driven through the shared cathodes, and its plate swings with the input. It drives tube B.
330k, 330 kΩ
Grid resistor for the driven half, returned to the bias point above the tail, not to ground.
120k, 120 kΩ
Grid resistor for the other half.
470, 470 Ω
Bias resistor for both halves. The cathodes sit this far above the grids’ return, a volt or so.
22k, 22 kΩ
The tail resistor. It’s large, so the pair shares a nearly fixed current. When one half conducts more, the other conducts less, which splits the phase.
.1µ, 100 nF
Ties the second grid to the feedback point for signal, so the feedback acts across the pair.
82k, 82 kΩ
Plate resistor for the driven half. It’s smaller than the other so the two outputs come out about even.
100k, 100 kΩ
Plate resistor for the other half.
100p, 100 pF
A small cap from plate to plate. It rolls off the far top end the inverter passes on, which keeps the feedback loop steady.
100k, 100 kΩ
The feedback resistor from the speaker. With the 4.7k Ω below it, it sends about 4 % of the speaker voltage back to the inverter, which lowers the gain, flattens the response and tightens the bass.
4.7k, 4.7 kΩ
The bottom of the feedback loop, 4.7k Ω to ground. The fed-back speaker voltage arrives here and moves the tail.
.1µ, 100 nF
The presence cap, in series with the pot across the leg. With the pot it sets where the lift starts.
Presence, 22 kΩ pot, linear taper
Presence, a 22k linear pot as a variable resistor, its resistance falling as it’s turned up, in series with the cap across the leg. Turned up, the cap shunts more of the leg’s treble, so less treble is fed back and the top end rises.
.022µ, 22 nF
Coupling cap to tube A’s grid.
.022µ, 22 nF
Coupling cap to tube B’s grid.
2.8k, 2.8 kΩ
Grid stopper for tube A. It keeps the tube from oscillating and softens grid current. Each of the two tubes has its own 5.6k. The resistors are drawn as one part, the two in parallel.
2.8k, 2.8 kΩ
Grid stopper for tube B. Each of the two tubes has its own 5.6k. The resistors are drawn as one part, the two in parallel.
V6, V8, EL34 / 6CA7
EL34, tube A of the push-pull pair, cathode grounded, biased from the fixed bias supply. Two tubes in parallel, drawn as one.
V7, V9, EL34 / 6CA7
EL34, tube B of the pair. Two tubes in parallel, drawn as one.
220k, 220 kΩ
Grid leak for tube A, returned to the bias supply. Driven into grid current, the coupling cap charges through it and the bias goes colder for a moment. That’s blocking distortion.
220k, 220 kΩ
Grid leak for tube B.
500, 500 Ω
Screen resistor for tube A. It limits the screen current when the tube is driven hard. Each of the two tubes has its own 1k. The resistors are drawn as one part, the two in parallel.
500, 500 Ω
Screen resistor for tube B. Each of the two tubes has its own 1k. The resistors are drawn as one part, the two in parallel.
12 H, 12 H
A choke from B+ to the screen supply, as in the amp this style is based on. It passes DC with little drop, so the screens sit close to B+. With the cap after it, it would filter ripple, but ripple isn’t modeled here. Typical of the part, not measured.
107, 107 Ω
The choke’s winding resistance, typical, not measured. It’s all the DC drop the screens see from B+.
50µ, 50 µF electrolytic
Filter cap on the screen supply.
50µ, 50 µF electrolytic
Second filter cap on the screen supply, beside the first.
10k, 10 kΩ
Dropping resistor from the screen supply node to the node for the inverter and the preamp, as on the Marshall JCM800 2210 drawing. The current drawn past it drops the voltage, so each stage down the chain runs lower than the one before, and a hard note that pulls B+ down pulls these down too. The preamp runs off this node instead of its own HT supply.
50µ, 50 µF electrolytic
Filter cap at the node for the inverter and the preamp. With the dropping resistor it filters the supply and keeps the stages on this node from coupling to each other through it.
OT, 1.61 kΩ to 4 Ω, 20 H primary, 5 mH leakage
The output transformer, 1.61 kΩ plate to plate into 4 Ω, center tap on B+. Tap any piece of it to change its figures. The core saturates as the flux nears its knee. Every figure is typical of the part, not measured.
PT, 360 V ac, 60 Hz
The power transformer’s high-voltage winding, 360 V ac end to end, into a bridge of four silicon diodes with the center tap unused. It’s drawn as two sources of 360 V ac a half cycle apart into two diodes, which charges the reservoir the same way at one diode drop (under a volt) higher. The value is typical of the part, not measured.
PT, 360 V ac, 60 Hz
The same winding on the other half cycle. It runs opposite the first source, so the bridge charges the reservoir on every half cycle.
PT R, 40 Ω
Resistance of the whole winding, plus the primary’s share. In a bridge every charging pulse runs through the whole winding. With the diodes’ drop it sets how far B+ sags on a hard note. Typical of the part, not measured.
PT R, 40 Ω
The same winding’s resistance, on the other half cycle. Typical of the part, not measured.
D1, 1N4001
One of the silicon rectifier diodes. It drops under a volt, so B+ holds up better under load than with a tube rectifier.
D2, 1N4001
The other rectifier diode, on the other half cycle.
50µ, 50 µF electrolytic
The reservoir caps’ first. It feeds the output transformer’s center tap. It charges in short pulses at each peak of the mains and drains between them, so B+ carries ripple, and on a hard note it sags.
50µ, 50 µF electrolytic
Another reservoir cap, in parallel with the first.
Bias tap, 96 V ac, 60 Hz
The power transformer’s bias tap, 96 V ac, as a sine source at the mains frequency. Typical of the part, not measured.
27k, 27 kΩ
Series resistor into the bias rectifier, 27k Ω. It limits the charging current.
Bias diode, 1N4001
The bias rectifier, a silicon diode turned so the supply comes out negative.
10µ, 10 µF electrolytic
Filter cap on the bias supply, its plus side to ground.
15k, 15 kΩ
Second resistor of the bias supply, 15k Ω to the bias line. With the cap after it, it filters the ripple a second time.
10µ, 10 µF electrolytic
Second filter cap, on the bias line, its plus side to ground.
47k, 47 kΩ
From the bias line toward ground, 47k Ω, in series with the bias pot. These two and the 15k Ω above them divide the supply down to the bias.
Bias 22k, 22 kΩ pot, linear taper
Bias adjust, a 22k Ω trimmer used as a variable resistor, the bottom of the divider. More resistance puts more of the supply on the grids, so turned up the tubes idle cooler. Which way it turns isn’t marked on the drawing.
Coil R, 4.34 Ω
Voice coil resistance, the floor of the speaker’s impedance. The shape of a 1x12 open-back cab with an alnico 12 in, measured (a 93 Ω peak near 74 Hz on 8 Ω), scaled to the 4 Ω tap. One real cab, not every speaker. The Speaker menu by the play buttons is separate. It plays the note through a speaker and cab impulse response, with either load.
Coil L, 128 µH
Voice coil inductance. It makes the impedance rise through the treble. The feedback holds the output steadier against that than it would be without feedback.
Loss L, 232 µH
With Loss R across it, the treble rises and then levels off, like the losses in a real coil.
Loss R, 7.15 Ω
Limits what Loss L adds to the treble rise.
Loss L2, 1.06 mH
A second step in the treble rise, with Loss R2 across it: a real voice coil’s losses keep climbing from a few hundred hertz.
Loss R2, 1.09 Ω
Limits what Loss L2 adds.
Tank R, 41.9 Ω
Height of the bass resonance, about 46 Ω in all at its peak. The feedback holds the output steadier against that than it would be without feedback.
Tank L, 10.6 mH
With Tank C, sets the resonance: 74 Hz.
Tank C, 440 µF
With Tank L, sets the resonance. With Tank R, it sets how narrow the peak is.

About this version

ECC83 throughout
Four 12AX7s, the factory tubes. V3b, the reverb driver, isn’t drawn. The tube models are typical of the type, not measured. Real tubes spread 20 % or more.

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, not measured parts. Caps are ideal, and the battery or HT is a voltage behind a resistance.

Spot an error, or want a circuit added? Email info@swellamps.com. A schematic or a clear photo of one helps. Anything you send may be used to improve these models and our desktop app.

© 2026 Swell Amplification LLC. All rights reserved. The simulator, its circuit models, drawings, presets and text are the property of Swell Amplification LLC and may not be copied, reproduced, redistributed or used to build another product without written permission. The original circuits are historical designs documented in public sources, and no claim is made to them. Everything here is provided as is, without warranty of any kind, for study and personal use. Results are simulations of typical parts, not measurements of any real unit. Don’t rely on them for the safety of any build or repair. Tube amplifiers carry lethal voltages.

Product and company names are trademarks of their owners. They are used here only to identify the circuits these models are based on; this site is not affiliated with or endorsed by any of them.

From Swell Amplification, swellamps.com.