advanced audio production
a modular pld-based electronic organ
This is a design of an electronic organ making use of DDS-based tone generation with programmable logical devices (PLDs). It is a modification of the smaller version, I created before, see PLD-ORGAN.

It can now be configured for up to 6 octaves with the current oscillator design.

The strategy is again to generate all required 12 fundamental frequencies with only one unit and then derive the sub harmonics by simple switching the digital vector. Compared to the former version, this concept was changed in that way, that octave switching can be done with simply mounting the cable in between the modules in a different way. Doing this the sound generation modules can be easily configured without reprogramming the PLD. They can also be stacked and overlaid for the same tone bank more than once to create overlay sounds.

Also filtering has been improved. Next to the individual adjustment of the basic sound wave by distorting the R2R-ladder, a filter feedback is available for a more living sound. (not shown in the design).

The final mixing is done by a 12ch-summation amplifier which also contains the switches for the keyboard.

2001 2003
Clock Frequency 15 MHz 25 MHz
Master Tones 12 12
Octaves 5 6
Tones 60 72
Keyboard 61 72
Tuning balanced balanced / pure
Wave Forms 3 4
Phase Res 7 Bits 8 Bits
Amplitude Res 6 Bits 8 Bits
AD - Conversion real R2R real R2R
DAC OUT 10 Bits 12 Bits
Octaves 5 6
Registers 2 3
Modules 10 18

The design has been done for Xilinx PLDs/FPGAs of the XC4000 type. They are relatively huge today (around 50 times larger than the 3020 type, I once started).

A nice step would be to integrate my universal distortion sound module but unfortunately the PLDs do not offer enough calculation power yet.

In the future, it might be possible to fully do this the digital way.

Analog Organ with programable devices
12 channel sound generation
6 frequency levels including 5 SUBs
Digital 6 Bit Tone Generation Module
R2R- Digital-to-Analog Conversion

base frequencies for electronic organ
frequency setup table

For more information, see the former approach

PLD-based Sound Generation for DIY organ


© 2003 Jürgen Schuhmacher