SSL Top Octave Gen Utility PCB

Synthetic Sound Labs TOG-1 top octave generator is a small PC board containing a microprocessor that produces thirteen equal tempered notes, along with a 16 MHz crystal and other support components.

In the late 1960s and 1970s, many polyphonic electronic instruments used Top Octave Generator (TOG) ICs. These TOGs took an input frequency that was typically derived from a 2 MHz crystal oscillator circuit and provided twelve or thirteen square waves by dividing this input frequency by factors from 239 to 478 (between 4434 Hz and 8368 Hz) to produce the highest practical notes of the equal tempered scale. Unfortunately, these older top octave generator ICs are no longer made.  

Our modern TOG-1 uses a microprocessor and a built-in 16 MHz crystal clock that is enabled by connecting pins XTL and CLK.  For more flexibility, it is also possible to apply an external high frequency clock to the CLK pin.  TOG-1 notes are very close approximations to the pitches of the musical scale.  Lower frequencies may be generated by dividing each output by consecutive powers of 2 using counter ICs, thus providing octave relationships.

Specifications

Typical Applications

Power

Connect a clean regulated positive 3.3 to 5 VDC power source to pin #1, and negative ground to pin #2.  TOG-1 has an internal reverse power protection diode and is NOT internally regulated, so DO NOT exceed rated VCC power voltages.  Doing so may cause permanent damage.

Internal crystal oscillator

The TOG-1 has a bult-in 16MHz crystal oscillator.  To use it, simply connect pin 4 (XTL) and pin 5 (CLK) together.  The internal crystal should provide fairly accurate tempered scale tunings, but fine tuning is not available.

External User Supplied Oscillator

If you want to adjust tuning or add pitch bends / vibratos, you can also use your choice of external high frequency oscillators to drive the TOG-1.  Examples might include the VCO section from a 74HC4046 (or similar), or a specialty IC such as the LTC1799 VCO chip (https://www.analog.com/en/products/ltc1799.html).  Simply connect your chosen VCO’s square wave output to pin 5 of the TOG-1, leaving pin 4 open (unconnected). Be sure that the VCO’s square wave is in the 0V to VCC range!

Top Octave Outputs

Thirteen top octave outputs are available on pin 6 thru pin 18, in descending equal tempered pitches.  For your convenience, both C9 and C8 notes are provided.  The outputs are roughly 50% duty cycle square waves that transition from ground to VCC.  Although the outputs are rated to drive upwards of 15ma current, it is highly recommended to keep the current draw to less than 5ma per pin.  These outputs will typically be used to drive a high impedance CMOS divider chip such as a CD4040, CD4024, or similar, so current draw should not be a problem.

Notes:

Specifications may be subject to change without notice.