Is it as simple as I have read, a couple of dioodes in the feedback loop on an opamp or am I missing something here?
Well, NEARLY so.
A single pair of diodes will not give a very nice waveform. A good way of doing it is to use multiple diodes and a "piecewise linear approximation" of a smooth waveform.
This may help:
Hybrid amplifiers and soft-clipping circuit
In an Op-Amp NFB loop using zener diodes and series resistors would do the equivalent.
Let's take an Op-Amp with +/-18V Supply and +/-16V Output into our load and we want to implement a limiter that starts soft clipping at +20dBu (+/-11V) with a soft compression of peaks to less than 16V.
We take a pair of back to back 15V zener diodes and connect across the feedback resistor. This is the "hard limit, at 15.65V Peak with ~ 5mA flowing in the diodes.
We use a pair of 12V zener diodes as the start of the limiting and (say) 14V diodes for the midpoint.
Add a suitable series resistor and you got your smoothed out rounded waveform.
While I appreciate all the schemes with sidechains and VCA's and the like, I feel that the simple diode based system is superior.
It has essentially no attack and release time.
It is largely not frequency dependent.
It behaves more like tape or transformer saturation, with H3 being dominant and symmetric waveform. If we make the zener diode voltages unequal we can generate asymmetrical, H2 dominant distortion.
Thor
