signal level adjust circuit

PHOBoS

hmm it's a bit dusty here,..
I haven't been building a lot lately and when I do it's mostly for video as is this circuit. It's easy to adapt for something else though.

What this circuit was designed for is to make it possible to use my modular synth to control my video synth (technically also a modular synth).
The latter uses levels of only 0 .. +1V (LZX standard) which is a lot lower than your average modular level so I needed a circuit to convert the signals.
I also wanted a bit more control over the signal so I added an input range switch, attenuverter and offset control.

stage 1: INPUT RANGE
this first stage provides the option to select between input levels of 0 ..+5V / -5V .. +5V / 0 .. +10V
If the correct input range is selected than the output range of this stage is -5V .. +5V (inverted) which makes it useful for the next stage

stage 2: ATTENUVERT
this stage let's you attenuate and/or invert the signal
the gain is -/+1x so the output range stays at -5V .. +5V

stage 3: OFFSET + LIMITER
this stage lets you add a DC offset to the signal (also useful to just create a DC voltage without an input signal)
the gain is -1.5x (inverted) to give the offset and the previous (attenuverter) stage a wider range
zener diodes are used to keep the signal between -5V/+5V (you could leave this out if that's not important)

stage 4: ATTENUATION + OFFSET FOR VIDEO
this is the stage that actually adjusts the -5V .. +5V range to 0 .. +1V that I need for video.
if you leave out the 100K biasing resistor to -5v and change the gain to -1x the output range will be -5V .. +5V
you could also do something similar as the first stage and use the circuit to convert between different ranges.

there is another zener diode on the output for extra protection in case anything were to go wrong with the circuit.
this will keep the voltage below +3.3V (and above -0.6V) but doesn't really affect the signal otherwise.
Of course you could leave this one out as well.

it's nothing spectacular or original for that matter but it might be useful for someone.

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