Music and Synth DIY

Eurorack, Schematics, SMD, Synth DIY

Bipolar (+/-5v) to Unipolar (0-5v) converter (work in progress)

Eurorack standard for LFOs is 10v peak to peak, also described as +/-5v.

Sometimes, however, you’ll come across a module that expects 0-5v for its control voltage input – for example, 4ms’s Spectral Waveform Navigator, or the Bastl Grandpa expander, Spa.

And that’s where this simple 2hp utility module, with its four bipolar to unipolar converters, comes in.

Main board

This being Eurorack, these 0-5v inputs will most probably be clamped, and that being the case, you won’t do any harm plugging your standard Eurorack LFO into one – all that should happen is you lose the negative portion of the LFO wave, and it has no effect. However, if they’re not protected, the negative voltage has real potential to cause damage.

Jacks board

This module is effectively four copies of this simple circuit, based around the four op-amps in a single TL074 package.

D3 and D4 here are schottky diode clamps, limiting the input voltage to +/-5V.

R3 and R4 sum +5v and +/-5V together, and as they’re both the same value (10K), halve the result. So…

At the bottom of the range, a -5v input gives you (-5v+5v) / 2 = 0V.

If the input is 0v, you get (0v+5v) / 2 = 2.5v.

If the input is 5v, you get (5v+5v) / 2 = 5v.


And that’s about all that can be said about this one. Waiting for the boards to arrive to test, and then I’ll post the build files.