Sample/Slew Generator

PCBs for this module are now discontinued

This compact single width module features a powerful sample and hold module with controllable correlation, a slew generator, a wide range clock oscillator and a dual output noise generator. It can be used to generate random and pseudo random control voltages, staircase waveforms, deliberate aliasing of audio signals and many other uses.

The Oakley sample/slew module has two modes of operation selected by a switch on the front panel.

The first is the 'hold' mode. This mode is the traditional sample and hold (S/H). It has a signal input, a signal output and a clock input. The module's job is to memorise the input voltage and present that to the output socket on command of the rising edge of a clock signal. The clock signal is any signal input you like, but it is traditional to use a gate type pulse. If a signal is inserted into the clock input, when the signal rises over 1V or so, the command is given to hold. The hold output will then remain fixed no matter what the input signal is now doing. That is until the command to hold is given again whereby it attains a new output value.

The second mode is 'track'. This functions like the so-called 'sample and hold' module on the Korg MS-20. With a clock input above 1V then the output of the module will follow in the input signal. When the clock input falls below 1V the output will then be held and not change again until the clock input rises again above 1V.

The restriction pot affects the way the hold output changes with respect to the current input level and previously held output level. With the pot fully off the unit behaves just like any other S/H, but at full, the output is restricted to move by only a small amount after each new sample. The output will still have the same range as the input, but will need more hold commands to get there

In reality the hold function is not perfect in either mode. The module uses an analogue memory module and as such the stored voltage will slowly change over time. We typically call this change' droop' because the voltage tends to be drawn down to zero. The droop is relatively small and for most synthesiser patches it is not a problem.

The module features an inbuilt clock generator. This essentially is a wide range VCO (from about one cycle per minute to over 2kHz) which can be used to directly control the S/H module when no jack is inserted into the clock in socket. The output of the oscillator is available as a +/-5V square wave at the clock out socket.

The slew generator can be accessed separately from the S/H section, but its input is normalised to the output of the S/H when there is no jack plug inserted into the slew input socket. The slew generator smooths any sudden changes in the input signal. Thus a square wave becomes more like a triangle, and keyboard CVs start sliding between notes.

A noise source is available from the noise out socket. The noise could be described as white with a gentle roll off above 6kHz. This analogue random voltage source can used in conjunction with the S/H to produce the classic sample/hold patterns heard in numerous recordings. The clipped out socket is an alternative noise source. This features the same white noise signal but soft clipped to +/-5V. This signal is less random as the noise signal swings between defined levels, but it is ideal when used with the S/H as it creates a more predictable output.

The CLK LED lights when the clock input is above 1V.

The 1U MOTM version behind a natural finish Scheaffer panel. Note the use of the optional Sock-8 board to make wiring the socket field much easier.

The module accommodates either our standard Oakley/MOTM power header or a power header. The current consumption is +44mA and -34mA.

The board size is 112mm (deep) x 104mm (high). As with all Oakley projects the PCB is double sided with through plated holes, has tough solder mask both sides, and has bold component legending for ease of construction.

Project Downloads

Sample/Slew issue 5 User Manual

Sample/Slew issue 5 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.

Schematics are only available to purchasers of the PCBs and will only 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 Sample/Slew issue 5 module in traditional black

5U format 1U wide Sample/Slew issue 5 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.

Schematics and Projects: Projects

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Copyright: Tony Allgood.
Last revised: November 23, 2023.