The Transistor Superladder Variable Slope VCF

PCBs for this module are now discontinued

This is the 1U wide 'Filter Core' version of the Transistor Superladder. One would use this module in conjunction with external mixers for maximum control.

The Transistor Superladder or TSL is a voltage controlled transistor ladder filter. Cut-off frequency and resonance are both voltage controllable.

The Superladder VCF module has a variable shape output. It incorporates a feature first seen on the Oakley Orbital prototypes. A single pot allows you to vary the output from one pole low pass to four pole low pass via band pass in the middle.

The Superladder's output is what I call 'Q compensated'. This means that the output volume will not drop significantly when you turn up the resonance pot. This design uses two inbuilt VCAs to achieve voltage controlled resonance without the hassle. At high levels of resonance the Superladder will self-oscillate across most of the audio band and thus can be used as a sinewave voltage controlled oscillator.

The module design uses a discrete transistor core which means it does not clip the signal abruptly but saturates smoothly. This allows the Superladder to sound very different depending on the input signal level. When used with signals below 1.5V peak the Superladder will sound clean and bright. However, take your signal levels above 1.5V peak and it will start to take on a more strident tone particularly at higher levels of resonance. Coupled with the variable slope control, this sensitivity to input level means the Superladder can produce a wonderful array of different tones.

The voltage controlled filter, or VCF, may be built as a 1U filter core or as a complete 3U filter system. The 1U 'Filter Core' format is my way of handling filter modules. Although the 1U module can be used as a filter module on its own, it is expected that users will make use of external mixers to control CV and audio levels going into the filter. In this way, you will be able to have a collection of space saving 1U filter cores that can be used with any generic mixer module. The Oakley Multimix is an ideal choice for a handy mixer module.

Power (+/-15V) is provided to the board either by our standard Oakley 4-way header or header. Current consumption is approximately 40mA per rail.

Also available from Oakley Sound is the Diode Superladder. This is similar in function to the Transistor Superladder but uses diodes instead of transistors in the filter core, and sounds considerably different.

This is the 3U version of the Superladder. This is a fully featured filter module that includes inbuilt CV and audio mixer sections.

Sound Samples

Simple sequence with two Oakley VCOs at one octave spread on sawtooth outputs. The filter is manually being swept via the 'shape', 'freq', 'resonance' pots and altering ADSR sweep depth.

A different simple sequence being played using an Oakley VC-LFO as the single audio source. Again the filter is being altered by manually controlling the front panel pots. Some reverb and echo is being used to add ambience.

The above photo shows the older issue 3 TSL PCB fitted to the 1U wide MOTM compatible panel in Scheaffer's natural finish. Note also the use of the optional Sock4 socket board to help keep the wiring to the sockets neat and tidy.

The PCB is 102 mm (deep) x 143 mm (height). The frequency, resonance, resonance CV depth and shape pots can be board mounted for easier construction.

Project Downloads

TSL-3 Builder's Guide

TSL-3 User Manual

Construction Guide Our handy guide to building Oakley DIY projects

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

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

Front Panel database

A Schaeffer front panel can be made for either of the two variants of the new SuperLadder module. The 1U version is also available in natural aluminium finish. The databases can be found by downloading the following links:

3U format in traditional black

1U 'filter core' in black

1U 'filter core' in natural silver

To read these files you will need a copy of 'Frontplatten designer' from Schaeffer. The program also features on-line ordering, so its now even easier 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: December 04, 2023.