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Courtesy/Thanks to: Oakley Sound Systems

Description: This is a reworked version of the infamous TB-303 bassline. In essence it is just another clone of the analogue circuit of the bassline. However, I have added a few things to make it rather more interesting. I have listened to many peoples ideas on what a TB clone should or should not do, it is clear that some people feel very strongly about this machine. This in the end is therefore a mixture of many peoples ideas, but as the man said: You cannot please all of the people all of the time. So I have produced a design that is very flexible. Firstly, it can be just a TB clone without the sequencer. When the PCB is designed, it will fit in a 1U half rack mount unit. The pots are designed to be board mounted, but they don't have to be, you could make it into a table top thing. However, the TB3030 in its entirety is designed to be mounted in a 2U high rack. This could give possibilities to two TB3030s being in one 2U rack, or just one with patch points being brought out onto the front of the rack. This is not really a beginners project, although, I hope to have a comprehensive instruction set when the PCB becomes available.

New features include, a balanced output, an overdrive/distortion circuit, filter FM, a sub octave generator, VCA decay control and a accented decay control. Some of the pots now cover a wider range. The unit also incorporates a circuit that allows a velocity CV to control slide and accent. This means that computer sequencer users can simply control accent and slide by velocity values. MC-303 owners with a midi-CV convertor will be able to get complete control of the TB3030 by using the four velocity pads on the MC's front panel.

I have made the TB3030 fully compatible with traditional gate and CV. It does not have MIDI. You will need a midi-CV convertor to use a computer sequencer or modern keyboard controller. The VCO is 1V/octave and the gates are any positive voltage up to 15V. The velocity CV can be driven up to 15V but it will not respond to anything higher than 10V. The velocity CV control is split into four bands. Low values of velocity CV will give no accent or slide. With slightly higher values, accent only is triggered. Higher values still will produce slide only. And higher values still will produce slide and accent, should you need it. The sensitivity of the velocity CV input can be easily controlled by a trim pot on the board. When played with an ordinary midi keyboard, the results can be quite confusing at first. But you will soon learn how to get control of your sounds.

The circuit is on three pages. The format is rather different than the Roland schematic. Note that most of the signal path is very similar to the TB303. This included many little things that are really very quirky. I have not updated or improved most of the circuit, because that would possibly change the sound. However, I have used different semiconductors throughout, except for in the filter's feedback loop. The famed 2SC1583 is there, but only in the diff amp. I am sure any pair of reasonably matched NPNs would do. The other matched pairs have been replaced by a 3046 array in the filter, and a SSM2210/LM394 in the VCO.

The design is to be powered from a AC wall wart with an output of 12V at 200mA. The onboard power supply has been designed to able to run many other additional circuits if needed. However, if you are doing this make sure the wall wart can cope with the extra demand in current.

A PCB is now available! Please contact Tony Allgood for pricing and availability.

Email the author: Tony Allgood   


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   Schematics for the TB3030 1 of 3, VCO and Filter
   Schematics for the TB3030 2 of 3, VCA and Accent
   Schematics for the TB3030 3 of 3, Power
   Sound example of how the TB3030 sounds.
   Another sound example of the TB3030.
   Picture of the Oakley sound Systems TB3030
Oakley Sound Systems
   Synthesizer modules, repair and modification
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