I'm investigating building a modular analogue synthesizer, and learning electronics along the way.

I want to get a firm understanding of the supply voltage, inputs and outputs specification that is generally adopted, between each of the modules.

For example I'm aware a 15V power supply seems common; and 1V/Octave for the VCO. Is this correct? Is a +15v, -15v supply used? Also what is the output spec for the audio VCO?

Could anyone recommend further reading for these generally specifications and ratings?

I'm very new to this, and I'm starting with looking into the fundemental principles of a VCO, but want to build my experiments with the common specifications in mind - to drive to a useful goal. I don't want to just build a project thats out there, but learn the principles, design and build - I might not end up with the most stable modules.

No doubt pioneers such as Moog set initial standards, but keen to learn what the standard electrical spec for analogue synthesizers are, and how these expand out into the music studio.

Hope someone can help further.

Thanks in advance, Alex


1 Answer 1


For a VCO, 1 volt per octave is common practice but when it comes to power supplies, it's completely down to what the designer feels are most appropriate to do the job. For instance, it makes sense for the VCO to work from a range of supplies maybe as low as +/-9 volts to +/-15 volts (without noticeable loss of performance or error).

Having said that, I'm very aware that to get the best and most accurate 1v/octave performance you'd probably want very stable +/- supplies - the human ear will easily pick-up up tuning problems if the 1 volt/ octave changes slightly and you have to think about this when you have three VCOs working in tandem - you don't want the relative pitch ratios changing as you ramp up the control voltage or it'll sound a complete mess (been there, bought the T shirt etc..)

+/- supplies tend to be used (rather than a single + supply) because that means the 0V midpoint can be used as the reference for analogue signals and the reference point for control voltages such as what is used for the VCO and VCF.

Voltage controlled filters won't suffer the same issue as non-linearity in the 1V/octave that VCOs can suffer from - they are just filters and not the basic sound generator so a bit of non-linearity won't suddenly sound like a mess as it would with tandem/parallel VCOs.

  • \$\begingroup\$ My somewhat delayed response to your reply! Thanks for your insight. One further question - what would be the output waveform voltage be, as a rule? For example VCO output's a saw tooth waveform of pitch Middle C, and I'm using a + - 15V supply - what would be the signal output voltage peak-to-peak? and should the waveform cycle positive through negative? Finally are there any standards in input / output Impedance? Thanks Alex \$\endgroup\$
    – Alex2134
    Jan 9, 2016 at 21:00
  • 1
    \$\begingroup\$ For audio input impedance can be very high and output impedance can be very low. They don't need to be matched. I'd look up a few audio amp specs to get a spread but if I were to choose numbers I'd say 600 ohms for output and greater than 10k for inputs. Voltage levels dictated by what you are wishing to drive into. \$\endgroup\$
    – Andy aka
    Jan 9, 2016 at 22:12

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