Moog Rogue: adding a Filter CV input

The Rogue in its original form includes keyboard CV and Gate inputs and outputs. It’s a slightly odd arrangement of TRS (stereo) jacks – one for the CV, with the input on one terminal and the output on another, plus signal ground, while the Gate connector has an even more awkward arrangement of short-to-ground on one terminal and positive trigger on another, either of which can act as input or output. It’s not great. But it does work, providing you have the right cables.

Rather than split these into separate jacks, which would be a handy mod, I just use custom made cables for my interconnects between CV devices. However, the Rogue lacks a CV input for the filter, which I thought might make a useful addition. It’s a simple enough job.

I decided to use a 3.5mm minijack for the sake of convenience. Pick a spot on the rear panel and drill a suitable hole:

photo showing a newly drilled hole for the Moog Rogue filter CV input modification

Freshly drilled hole for the Filter CV input jack

 

photo showing a newly drilled hole for the Moog Rogue filter CV input modification (inner)

Inner shot of the Filter CV input jack hole

I had a switched 3.5mm mono socket to hand, so used that:

photo showing the Moog Rogue Filter CV input jack (inner)

New Filter CV input jack (inner)

 

photo showing the Moog Rogue Filter CV input jack (outer)

The new Filter CV input jack from outside

Solder a ground wire from the appropriate jack terminal to the Rogue’s jack PCB. Its large solder plane is suitable and easy to work with:

photo showing the ground wire of the new Moog Rogue Filter CV input jack

Grounding the Filter CV input jack

The filter CV input requires a 45k3 resistor to give the same scaling as the keyboard. As presented here, there is no onboard scaling, so if you want to run the input as anything other than 100% follow, use an external amplifier/attentuator. It would also be possible to build such a circuit into the Rogue, but I chose not to for simplicity.

photo showing a resistor soldered to the Moog Rogue Filter CV input jack

Solder a 45k3 resistor to the Filter CV input jack

The other end of that blue wire goes to the filter CV node on the main PCB. Rather than outline it on the schematic, I’ll just show you where that is on the board. This is the point where various filter CV inputs are summed. It’s an easy job to solder a wire at the top of this area:

photo showing the Moog Rogue Filter CV summing node

Filter CV summing node

Here’s a wider shot. Note the longer black wire is a previous bodge and not related to these mods and repairs:

photo showing the Moog Rogue Filter CV summing node and input mod wiring

Filter CV summing node and input jack wiring

I used a Dymo labeller to add the finishing touch to the back panel:

photo showing Moog Rogue Filter CV input jack mod

Filter CV input jack mod, finished!

Hey presto! A filter CV input scaled at the same degree as the keyboard. I use a Kenton MIDI-CV interface, which has an auxiliary output for filter CVs, amongst other things, so this little mod should come in quite handy.

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2 responses to “Moog Rogue: adding a Filter CV input”

  1. Ron says :

    Hello,
    Thank you for making such a great set of instructions. I plan on doing this to my Taurus ii which is the same thing as the rogue. I already have a cv midi interface which allows me to play a full 5 octaves, I’m a little confused by what you mean when you say scaling of the filter. I know the cv voltages are respectively scaled to the keyboard, but what exactly is scaled for the filter? Doesn’t it articulate the same for each note? Also you mentioned you used a switched jack, but wouldn’t that shirt t to ground when a connector was not inserted into it? Would an open jack work as when a cable is not present the filter controls would resume normal operation? I would appreciate any help. Thank you.

    • synthnerd says :

      Hi. OK, so when you play a note on the keyboard, a corresponding CV is generated that governs note pitch, on a scale of 1 volt per octave. Filter tracking is when the filter cutoff also changes depending on which note you play (making higher notes brighter, usually). Many synths have a front panel control which allows you to vary the amount by which this happens – in other words, they allow you to scale the note CV that goes to the filter, which means not 1V/oct but maybe .5V/oct or 2V/oct, etc. LFO and envelope articulation is not affected by this control, nor is note pitch itself.

      The Rogue/Taurus 2 has a Keyboard Tracking knob for this on the panel, and this governs the amount of CV going to the filter from both the keyboard and any incoming pitch CV on the existing input jack. The scaling I refer to for the above mod is only for the mod. If your MIDI-CV interface has an ‘aux’ output CV for something like velocity or aftertouch, you could route that to this new input, for example. Basically, if you want this new input to follow your applied CV as-is, use the resistor value in the write-up; if you want to be able to vary that sensitivity, vary the resistor value.

      Regarding the switched jack, no, it doesn’t short to ground when disconnected. The signal ground is not connected to either signal connection at any time. To use a switched jack, simply don’t wire anything to the break connection, and take your signal insertion point to be the tag on the jack which connects to the jack tip when it’s plugged in.

      You could indeed just use a non-switching jack, with only ground and signal connections. Any incoming CV here is just summed with the other internal CVs that control the filter, so plugging nothing in only means that you’re not adding anything else into the mix.

      Hope that helps!

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