VRG - Versatile Ramp Generator

Construction difficulty: Easy

The Oakley Versatile Ramp Generator (VRG) is a single width 5U high module that can function as a voltage controlled variable symmetry oscillator, a traditional attack-decay envelope generator, a one shot transient generator with patch programmed repeat, a voltage controlled slew generator, a gate delay and an audio filter. The output slope can be either linear or exponential.

The output signal will rise at a rate determined by the UP control and the up control voltage input. The output signal will fall at a rate determined by the DOWN control and the down control voltage input.

An additional output is available called NEG OUT. This output is a gate style signal that is 0V when off and +5V when activated. It will be activated when the main output falls below 600mV. This can be used as an 'end-of-cycle' output when the VRG is in one-shot mode.

A bi-colour LED gives visual indication of the module's main output signal level.

The various operating modes of the instrument are determined by the three way mode switch and use of the SLEW IN jack socket.

1. Slew generator

Inserting a jack into the SLEW IN socket activates the slew generator. The output of the module now attempts to follow the input signal. However, the rise and fall times are determined by the module's controls and CV inputs. Fast moving inputs are thus slewed at rates controlled by the VRG. You can use this mode for portamento effects, basic filtering and creating attack-release envelope shapes.

2. Variable symmetry low frequency oscillator

With no jack inserted into the slew in socket and the switch set to LFO, the VRG behaves as an oscillator. The waveshape and frequency are controlled by the up and down controls and their CV inputs.

Maximum frequency: 600Hz - linear, 300Hz - exponential

Minimum frequency: 0.009Hz (one cycle per two minutes) – linear, 0.003Hz (one cycle per 5 minutes) – exponential.

Output level: +5V to -5V.

3. Traditional attack-decay envelope generator

The gate input allows the VRG to be triggered as you would an ordinary envelope generator. This makes it ideal for generating plucked sounds. A falling gate signal while the attack phase is ongoing will cause the output to fall back to zero at a rate determined by the decay controls.

Attack time: 0.5ms to 30s (linear), 0.75ms to 50s (exponential)

Decay time: 0.5ms to 30s (linear), 2.2ms to 3 minutes (exponential)

Output level: 0V to +5V.

4. One shot transient generator

The gate input starts an attack-decay curve much like a traditional attack-decay envelope generator. However, the attack phase will always complete even if the gate is removed before it gets to the top of the cycle. This can create long lasting output signals that can be triggered from just momentary gates.

Attack time: 0.5ms to 30s (linear), 0.75ms to 50s (exponential)

Decay time: 0.5ms to 30s (linear), 2.2ms to 3 minutes (exponential)

Output level: 0V to +5V.

The one shot can be triggered to cycle endlessly up and down by connecting a patch lead from the NEG OUT socket to the GATE socket.

The NEG OUT can be also used as a gate delay in the one shot mode.

The issue 2 Oakley VRG behind a natural finish Scheaffer panel. Note the use of the Sock6 board to keep the socket wiring nice and tidy.

The module accommodates either our standard Oakley/MOTM power header or a Synthesizers.com power header. The current consumption is +44mA and -37mA.

The board size is 109mm (deep) x 124mm (high). As with all Oakley projects both PCBs are double sided with through plated holes, have tough solder mask both sides, and have bold component legending for ease of construction.


Click here for how to order.

VRG issue 2 PCB ......................................................... 20GBP
Sock6 issue 1 PCB ........................................................ 6GBP

VRG pot bracket kit ........................................................ 0.75GBP
1K +3000ppm/K temp co resistors (pack of two) ....... 3GBP

The optional Pot Bracket Kit contains the three 16mm Alpha pot brackets required to complete one module.

All other parts can be purchased from you usual electronic component supplier.

All prices include VAT at UK rates. Shipping and postage is additional to these prices. See also the FAQ page.

VRG ready made modules may be available from Krisp1.com.

Project Downloads

VRG User Manual

VRG issue 2 Builder's Guide

Construction Guide Our handy guide to building Oakley DIY projects

Parts Guide Our handy guide to buying parts for Oakley DIY projects.

Links to schematics are available to purchasers of the PCB or module and will be sent via e-mail when the board(s) are shipped.

Front Panel database

A Schaeffer front panel can be made for this module. The databases can be found by downloading the following links:

5U format 1U wide VRG module in traditional black

5U format 1U wide VRG module in natural finish

To read these files you will need a copy of 'Frontplatten designer' from Schaeffer. The program also features on-line ordering, so it's easy to buy your panels from Scheaffer.

The company are based in Berlin in Germany and will send out panels to anywhere in the world. Delivery to the UK normally takes around ten days. For North American users you can also order your Schaeffer panels from Front Panel Express.

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Copyright: Tony Allgood.
Last revised: October 12, 2016.