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INTRODUCTION

Here I detail some of the mods and changes I have made to this super little synth. Sure it's basic but like a chain saw it does what it does really well. While I own several other synthesizers, I have never had a Moog. I spotted a nice little Rogue synth on Ebay and took a chance. I feel when doing mods. it's important to try and keep the look of the instrument as original as possible. I therefore try and use original switches and knob caps if possible. Also check out my Prodigy page

These mods I have done are listed here for information only and I have no responsibility for any damage caused during work you may carry out.

 

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MIDI INSTALL

Many MIDI interfaces were either too expensive or had just too much functionality for what I needed. I just wanted to have a bass riff playing while I went on a knob twiddling rampage. I spotted a company called midi hardware.

They had a tiny circuit board called the miniCV that offered GATE and CV outputs plus a novel midi learn button. This enables commands to be sent to the miniCV such as which note to start up on, channel etc. It required a bit of work to install but was pretty straightforward.

The main issue I had was being able to split the midi signals away from the Rogue's keyboard input. I used a small ON/OFF 2 pole switch to switch in either the miniCVs converted midi signals or the Rogue's keyboard. It works well. Basically I cut the existing traces for CV and GATE going to the Rogue's voice architecture and inserted another 'path' i.e. the miniCV midi using a toggle switch. This is similar to the way Synhouse midi jack works although their design is more sophisticated and can switch in and out electronically.

 

I also added a midi signal indicator LED to the right side of the shoulder plastic. This gently pulses when a MIDI signal is present. Yes, I have too much time on my hands it seems.

 

midiLED

Midi signal LED

 

Here is the diminutive PCB ready for testing, prior to wire tidying

 

The midi learn button, socket and midi On/Off

 

POWER SUPPLY UPGRADE

Before I bought the Rogue I had read of a the horrors of the separate transformer that powers the Rogue. To be honest it is a bit naff but it is perfectly useable. The male power plug is not exactly a clever design. Plus the concept of a synth having a 'wall wart' just played havoc with my karma. So I decided to get a decent chassis mount transformer and fit this internally. Many other, better web pages detailing this exist but I include my experiences for completeness.

I used a quality 3 core main leads and drilled a hole for a rubber grommet to provide strain relief for the lead. I was going to use an IEC socket but I had already cut the Rogue up a bit and didn't want the hassle of making a rectangular hole. I fitted a fuse holder and 1A fuse. The Rogue appears to draw 6W so a 24VA tranny was ordered. I decided not to fit a mains switch before the internal transformer as I use a remote control mains switch and can use this to power the mains supply to the Rogue.

I ended up just using one of the taps as it put out 16v AC

mains wiring

Initial wiring, with soldering and heat sleeve to be fitted.

 

transformer fitted

 

24VA transformer installed internally. I covered over the gaps in the spade terminals with electrical tape. I blocked off the 24v AC input jack with a blank.

There is a 1K current limiting resistor soldered between pins one and two of U18, the 7812 positive voltage regulator. I replaced this with a 470Ω to ensure reliable ON/OFF switching with this new transformer.

Once PSU swap was completed, I did a calibration of the synth using the technical service manual. I used a mic and the excellent Windows Frequency tuner, to check the frequency. I managed to get within 3-5%

 

LFO RATE LED INDICATOR INSTALL

Let's be honest adding LED's to equipment can be fun but may not add anything worthwhile to the kit. The Rogue could really do with some means to visually gauge the LFO speed. This seemed an easy mod to do as I just needed to find the LFO output on the Rogue's PCB and use this to power a 3mm LED to earth. I used a 600Ω current limiting resistor. The LED was mounted on the left side plastic shoulder.

A short video showing operation. The solder points are shown at the end. (pin 1 of U5 and earth)

 

 

SLIDER CLEANING AND REFURB

All the slide potentiometers worked on my Rogue but some were stiff and made intermittent contact. There is a black gasket material which turns to a sticky crumbly goo. This can get inside the sliders and cause poor contact. This was all cleaned off the circuit board and tops of the controls. One can replace the sliders with new ones from various providers but his is expensive and may be unnecessary. After de-soldering. it's possible to dismantle the sliders and clean the internal tracks and contacts. There are little metal tabs holding the base of the slider to it's frame. Bend these back with a flat blade screwdriver to separate. Watch out that you don't stab your thumb.

 

This image shows the 2 tracks which should be cleaned. I also used a tiny bit of lithium grease on the top and sides of the inside of the slide case to smooth the operation. The result was far better contact and action. The rotary pots were fine so I didn't do anything with these.

 

PULSE WIDTH MOD (PWM)

This one involves replacing the existing fixed duty cycle resistor voltage divider with a 100k pot.

Square wave. First desolder resistors R87 & R88. Wire the centre wiper via a 10K resistor to the junction of where the 2 resistors met. Then wire the outer pins of the pot to the other holes were the resistors were.

The same can be done with R78 & R79 for the other oscillator.

PWM

 

FM TYPE MODULATION

I have already completed the FM mod on the Prodigy and though it would be fun to have a go on the Rogue. I did see a video on You Tube of someone who had an FM knob. So I just had to have one.

There's basically zilch on the web about this, so I post up my attempt as a starting point for those who want to try this out.

The basic idea is to overdrive the Rogue's filter from the output of one of the oscillators. It's quite effective although perhaps not the best way to achieve this. If anyone knows of a better solution, please get in contact and I can feature it here, with full credits of course.

Here's a image of the PCB during testing. Oscillator 1 drives the filter cutoff amount via a pot. I used a 10K with an integrated on/off switch as I didn't want the effect all the time. Pot is mounted in the shoulder plastic (going off my 'keep it original' mantra I know)

 

moog rogue FM

Some images from the mods

A pot yesterday driller killer

 

 

ADDING A TRIANGLEWAVEFORM

Yes that's right an attempt to add a third waveform to the Rogue. I will be honest, I got the idea from a mod on the MG-1 site SDIY.org. Full credit here. It has some excellent mods for the MG-1. As the Rogue is very similar, if a little less versatile, it was worth trying. I built two of these circuits, one for each oscillator.

The generator uses 3 741 Opamps (6 for both oscillators) to recify, centre and amplify the incomming signal. The trim pot is used to set offset to 0v. If I was a better circuit designer, all 3 could have been replaced by a triple input device such as LMH6738. As I had loads of old 741's around, I used these.

CIRCUIT

 

3rd oscillator

Connections:

+12, -12, earth

saw input from osc 1

saw input from osc 2

osc1 out to 3 way switch

osc2 out to 3 way switch

 

PCB

This is not the prettiest but it works, was fun to make and used up some of the crap in my spares box. It combines 2 copies of the above circuit.

I ran out of space

board rear

connection on mainboard

before 3 way switch fitted

I have ordered a 3 way OEM style switch to replace the 2 way waveform selector switch. With a little bit of board modification, i.e. drilling 2 holes, this should allow the third waveform to be switched in to the audio path. With the new waveform in the centre position. Of course one could split the oscillator paths into 2 and enable both oscillators to have a different waveform. This would require two 3 way switches.

Extra holes drilled. They just cleared the existing tracks. I checked with a continuity tester to be sure

 

The finished mods with extra knobs