Linear amplification with the CD4069UBE.
Danger
Danger
The basic usage and pin mapping is explained in the datasheet [1]. It is not very common to use this chip for linear amplification, especially in our days where opamps are very cheap to get. But there is also an application note [2] that explains the basic usage. It will not go into too many details, we will have to figure out some details on our own.
Figure 1: The CD4069
For linear amplification only the unbuffered (UBE) chip can be used, the buffered chip will produce a binary output. Also, the chip should be powered by +5V/GND. With higher voltage, the heat dissipation will be too big and the chip will be damaged. the chip is powered on pins 7 and 14 with +5V and Ground. the other pins can be used as an amplifier.
The simplest circuit, to begin with, is a voltage follower or buffer. The buffer configuration looks similar to the opamp buffer. But there are some differences. The first important difference is that the feedback will also do the biasing of the input signal. when an ac signal is applied to the buffer the output will be a DC signal, as long as the chip is able to provide the needed biasing feedback. The gain can be calculated similarly to the opamp configuration. But there will be less gain as we would expect from the calculation.
Figure 2: Linear Amplification.
This is the first setup with the 4069 as a voltage follower. C1 and C2 are DC blocking capacitors. When we choose R1 and R2 as 100kOhm we would expect a gain of one.
Figure 3: Linear Buffer Analysis.
The blue line is the input signal (5V p2p) and the red is the output signal with 100kOhm resistors. The output is a little less than expected. For the other signals, the resistor R2 is replaced with 125kΩ, 150kΩ, 175kΩ and 200kΩ. With 150kΩ the gain is roughly one. We also see that the output is not symmetrical. The clipping occurs earlier for the negative part of the signal. With the higher gain, the signal is soft clipped.
The cmos inverter can also be used as a summing amplifier. In this example, two sinusoidal signals are added. The setup is the same as an Opamp summing amplifier. The gain can be adjusted with the feedback resistor.
Figure 4: Summing Amplifier.
A differential amplifier can not be configured like an Opamp amplifier. But when the inverse is added the result is a subtraction of the two signals. This is the same simulation but the second signal has a phase shift of 180°.
Figure 5: Summing Amplifier Analysis.
The grey line is the calculated result and the blue line is the simulated result. The actual result is close to the calculated one. here the feedback resistor has about half of the input resistors.
The Red Llama is actually a clone itself with some component changes. The original designer of the circuit is Craig Anderson. In an interview with Jeorge Tripps, creator of the way huge line, he said that he had bought this book called "Electronic Projects for Musicians" written by Craig Anderson. He also said that the first pedal he built was the Tube Sound Fuzz that was that book. Once I heard that this book existed, I quickly got it. In this book, Craig Anderson talks about the circuit. He explains how it works, why it works, and the reason it sounds so good.
The soft clipping, which is the special characteristic of valves, adds harmonics to the signal. Here we want to analyse what harmonics are added. therefore we add a second stage to out circuit. the first stage is a voltage follower with the gain of one (or less as saw). the second stage is a high gain stage. the simulation is done with different values for R4.
Figure 6: Way Huge Red LLama Schematic.
in the simulation R2 is unchanched. For R4 the simulation is done with 100kΩ, 500kΩ, 1MΩ and 10MΩ.
Figure 7: Way Huge Red LLama Analysis.
the simulation looks similar to the first one. we can see that the signal is transforming into a square wave, but always with the soft clipping. next we want to analyse the harmonics that are added to the signal.