by Janne Isotalo - published 2021-02-06

CALIBRATION

An article about how to calibrate your PROGUE synthesizer

Like many vintage-style analog synthesizers, Progue has trimmers that need to be set in order to achieve the proper "1V/OCT" -tuning. The first section of this article has a Get-It-Over-With -section for those who are eager just to get the synth in tune. The latter part of the article will do A-Deeper-Dive with explanations about the key concepts of the 1V/OCT calibration procedures.

Get-It-Over-With

All of the nine trimmers (VR1-VR9 on the PCB) can be accessed from the panel holes with a small-sized flat head screwdriver. The adjustment screw on the SMT trimmer is tiny, so if your screwdriver doesn't fit the hole in the panel it won't fit the trimmer either. The only other tool needed is a tuner that is connected to the synth's output. You can also use an digital oscilloscope or even only your ears if you have a reference tone (A=440Hz) available. The procedure is very similar in many analog synth.

Start by carefully adjusting the panel settings to match the settings in the drawing. Connect a midi keyboard to the PROGUE midi input and play Low-A. The proper octave might vary depending on your midi controller. With the Low-A key pressed, the frequency you will hear should be somewhere around 50-60Hz.

The first step is to calibrate OSC1. Adjust the following:

Play "LOW-A" and adjust VR2 to 55Hz.
Play "2-octaves higher A" and adjust VR3 to 220Hz.
Repeat steps 1 and 2 until the tuning is correct.

The second step is the octave switch calibration. Adjust the following:

Switch the octave to 8", play "Low-A", and adjust VR1 to 220Hz.
Switch the octave back to 32", Play "2-octaves higher A", and you should have the same identical pitch.
Re-adjust VR1 until frequencies for steps 1 and 2 are identical.

The third step is the Hi-End calibration. Adjust the following:

Switch the octave to 8", play "2-octaves higher A", and adjust VR6 to 880Hz.
Switch the octave back to 32", Play "2-octaves higher A", and you should have the same identical pitch.
Re-adjust VR1 until frequencies for steps 1 and 2 are identical.

Repeat the first and the third step for OSC2. You can also use the OSC1 for reference. The most important thing is the "beating consistency" between OSC1 and OSC2 in all octaves.

The VCA offset trimmer VR8, adjust the following:

Turn OSC1, OSC2, and NOISE fully off, and put Gate-mode to "Auto".
Boost up the volume and adjust the VR8 to minimum "thump".

The filter emphasis trimmer VR9 (single-turn) can be used to limit the maximum Emphasis (resonance) level when the Emphasis potentiometer is at maximum (CW). Adjust according to taste.

That's it, all done!

A-Deeper-Dive

..will be continued soon..