Please enter at least two complete channels with numeric voltage and resistor values.
Formulas & Mathematical Logic
For each channel: Rp = parallel resistance of all other active channel resistors.
Channel contribution: Vo = V × Rp / (R + Rp).
Vout Sum = Vo1 + Vo2 + Vo3 + Vo4 + Vo5 + Vo6 + Vo7 + Vo8.
Practical meaning: each input is attenuated by its own resistor and the parallel loading from the other channels.
Step-by-Step Example
Example: V1 = 3 V, V2 = 6 V, V3 = 9 V and all resistors are 10 kΩ.
With equal resistors in a three-channel passive average, the output becomes close to the average.
Vout = (3 + 6 + 9) / 3 = 6 V for the equal-resistor case.
Practical meaning: equal resistors create a simple passive averager, while unequal resistors create a weighted voltage summer.
About This Calculator
Combine multiple voltages through resistors and estimate the passive summer output.
This CalcBoy calculator helps analyze passive voltage summing, resistor averaging and simple multi-channel analog mixing circuits.
A passive voltage summer uses resistors to connect multiple voltage sources to one common output node. Each input contributes part of its voltage to the output, but the contribution depends on its resistor and the loading created by the other channel resistors. When all resistors are equal, the circuit behaves like a passive averager. When resistor values are different, it becomes a weighted voltage summer.
Best UsePassive audio mixing, analog averaging, sensor combining and voltage summing networks.
Key InputsUp to 8 channel voltages and their series resistor values.
Design BenefitQuickly compare equal-resistor averaging and weighted summing behavior.
Practical ReminderA passive summer should usually feed a high-impedance buffer or amplifier input.
This calculator is useful for early circuit design, test benches, resistor network experiments and analog signal combining. It can help you understand how each channel resistor affects the final output. Smaller resistors give stronger influence, while larger resistors reduce that channel’s contribution.
Quick tip: do not drive a heavy load directly from a passive summer. A low load resistance will pull the output down and change the expected result.
Real circuits can deviate because source impedance, resistor tolerance, output load, op-amp input bias current and signal bandwidth all affect the final node voltage. For accurate work, use precision resistors and a buffer stage after the summing node.
Frequently Asked Questions
What is a voltage summer circuit?
It is a circuit that combines multiple input voltages into one output using resistors or an active summing amplifier.
What is a passive averager?
A passive averager is a resistor network where equal resistor values combine input voltages into an average output.
Can I use different resistor values?
Yes. Different resistor values create a weighted voltage summer where some channels have more influence than others.
Why should I use a buffer after the output?
A buffer prevents the next circuit stage from loading the passive summing node and changing the calculated voltage.
Can this work for audio signals?
Yes, for passive audio mixing, but signal loss and impedance matching should be checked.
Does this replace an op-amp summing amplifier?
No. A passive summer is simple but lossy. An op-amp summer gives better isolation and gain control.