Source: https://mokxi.com/op-amp-simulator Updated: 2026-09-27 Simulator # An op-amp simulator with a scope on the output Mokxi is a free op-amp simulator that runs in your browser, with nothing to install and no account needed. Wire an op-amp on a real breadboard, drive it from a signal generator and watch the output on a two-channel scope. Pick a 741, a TL072, an LM358 or a rail-to-rail part, and it has the gain-bandwidth, slew rate and output swing from its datasheet, so it clips and rolls off where the real one does. Sign up free or see every part - 192 parts on the bench - 25 boards running now - 1.00x real time, on every board Click to open it in the editor A 1 kHz sine into IN+, with Rf = 20 k and Rg = 10 k. Click it to open it in the editor and look at the Scope tab. ## What the running circuit above shows Gain from two resistors, and the supply that limits it. A signal generator puts a 1 kHz sine on IN+, 0.5 V either side of 0.8 V. The output goes back to IN- through a 20 k resistor, and IN- goes to ground through 10 k, so the gain is 1 + 20 k / 10 k = 3. On the scope the output is the same sine, the right way up, three times as tall: 0.9 V to 3.9 V. The engine gives 0.901 V and 3.899 V. Open it and turn the generator up to 1 V. Three times that asks the output for -0.6 V to 5.4 V, which a single 5 V supply cannot give, and the tops and bottoms of the trace are sliced flat. That is clipping, on the scope, the way it looks on a bench. ## Four op-amp models, from their datasheets Typical-column numbers. Every one can be overridden in the properties panel. Model Gain-bandwidth Slew rate Headroom, top / bottom Rail-to-rail (default) 10 MHz none 0 / 0 V 741 1 MHz 0.5 V/us 1.5 / 1.5 V TL072 3 MHz 13 V/us 1.5 / 1.5 V LM358 0.7 MHz 0.3 V/us 1.5 / 0.005 V The rail-to-rail part is an idealized op-amp with a 10 MHz gain-bandwidth and a 25 mA output limit, not a part number. The others behave like their datasheets: a 741 on a 5 V supply only swings from 1.5 V to 3.5 V, and an LM358 can reach ground but not the top rail. An input offset, in millivolts, is multiplied by the circuit’s gain along with the signal, and a negative-rail setting lets a textbook split-supply circuit swing below ground. ## Frequency response, sweeps and SPICE More than a scope: a Bode plot, a DC sweep and an ngspice deck. Analysis, in the editor’s more menu, draws a Bode plot of any circuit: gain in decibels and phase against a log frequency axis, with the -3 dB corner marked. An amplifier’s bandwidth is its gain-bandwidth product over its noise gain. A 741 in a non-inverting gain of 11 is 3 dB down at 90.85 kHz in the engine, against 90.91 kHz for 1 MHz / 11, and as a unity-gain buffer the same part is 3 dB down at 1.000 MHz. The same sheet sweeps any value you can set (a resistor, a supply, the generator’s offset) and plots a node against it, with a CSV of every point. And Save, then Download SPICE, writes the circuit as an ngspice deck, with each op-amp as a subcircuit carrying its model’s numbers. The non-inverting amplifier, on a scope The op-amp as a comparator SPICE netlists in the browser Mokxi and LTspice, compared ## What the model leaves out Said plainly, so a result is never taken for more than it is. The op-amp is a single-pole macromodel, not a transistor-level device. It has an open-loop gain with one dominant pole, a gain-bandwidth product, a slew rate, headroom short of each rail, an input offset, an output resistance and a current limit. It has no input bias current, no input resistance, no second pole (so no loss of phase margin) and no noise. The inputs draw no current at all. That is the right model for gain, clipping, active filters and comparators, which is most of what a class or a hobby project builds. For noise or stability margins, run the circuit as a SPICE deck; for a manufacturer’s full model of one chip, use LTspice or ngspice. ## Questions Is it free? Yes. Every op-amp model, the signal generator, the scope and the frequency response are on the free plan, with no card. Do I need an account? No. The circuit runs the moment the page does. An account is only for saving a project to the cloud and sharing it by link. Can I simulate a 741 op-amp? Yes. Pick the 741 model and it has the datasheet’s 1 MHz gain-bandwidth, 0.5 V/us slew rate and 1.5 V of headroom from each rail. Can I build an op-amp with a negative supply? Yes. Set the op-amp’s negative property to the negative rail in volts, and the output can swing that far below ground, the way a split-supply textbook circuit is drawn. Does it work on a Chromebook? Yes. It runs in Chrome with nothing to install. ## Build an amplifier and scope it Open the editor, drop a part on the breadboard and press Run. Nothing to install, and no account needed. Start building Open the editor