P-300 Pulse Interface

Music today has become more eclectic, sophisticated, and multi-element influenced. Groups are expanding into areas of musical expression that have never been explored. All of this puts heavy demands on synthesizers and nowhere is the demand greater than with rhythm systems. Because of programming limitations, voicing problems, or any number of other problems, most professional studios employ different brands of rhythm machines. Each manufacturer has it’s own approach and there are not a lot of interface facilities are provided.

p300 pulse interface

The P-300 pulse interface is a very versatile device for it can process both analog and digital signals. As we can see, the P-300 accepts an analog input and a MIDI input. Both analog and digital outputs are also provided. A needle pulse and a step pulse are available at the analog output. You can select which of a ten-pulse sequence will serve as a sync pulse for either analog or digital output.

Analog and digital inputs are mixed to produce a composite MIDI output that can drive two rhythm generators or any other device with a MIDI input. The possibilities are endless and much experimentation will open up new complex patterns.

The MIDI input will accept an output from any MIDI device, synthesizer, rhythm machine, sequencer, etc. The signal is then processed through an optoisolator and then a 555 timer. This enables you to omit a variable number of pulses set by a 1 meg potentiometer connected to pins 6 and 7 of the 555 timer.

An internal MIDI pulse generator can be activated that can produce a one of ten-stage sequence output. This output rate can be set by a front panel control that is monitored by an LED. The step pulse duration lasts until the next pulse while the pulse output is available as an analog output and a MIDI output.

p300 circuit diagram

Phone jack J2 will accommodate a remote switch that will trigger at a rate set by a 100K potentiometer and a 1 MFD capacitor. This control will always reset to trigger when the control button is pressed.


Banana jack J4 and phone jack J6 will accept an analog pulse from external generators. All of these pulse sources can be mixed to provide a composite MIDI output available at DIN jacks J7 and J8.

output board

Output Board

Pulse generator

The internal pulse generator consists of a unijunction transistor that is controlled by a remote switch. The pulse feeds a 4001- IC that in turn feeds a step generator that will allow you to choose which one of a ten stage sequence out put will be added to the composite MIDI output.

The pulse is only available when the remote switch is not pressed and it starts in sync with the pressing of the button.

No on off switch has been provided for it may be operated from a power strip that activates a few units that are used in your studio. If you require a switch for the circuit, you may select a rate control potentiometer with a switch built in.


Flow Chart

Below is a flow chart to represent the patching possibilities. Two analog pulse inputs can be used simultaneously. A MIDI input DIN jack accommodates an input from any digital machine.

flow chart

A MIDI rate control allows the user to set the output response from every pulse to one of every 10 pulses. An internally generated pulse produces a pulse, step, and MIDI output. The frequency is adjustable and selectable stage (1 to 10) output is available as analog and MIDI output. This internally generated pulse is turned on by the sync remote control switch and always starts when the sync button is pressed. Outputs can control two drum machines or other MIDI devices and two analog outputs. Light emitting diodes provide a visual monitor for the internal pulse generator pulse and step outs as well as the MIDI output.



Power for the unit can take a variety of forms. Below is an example of a wall power supply unit. Make sure that the unit produces a DC output. An alternative is to build the power supply inside the unit.

Single regulator

Below is an illustration of a circuit board for a two-regulator power supply and a one-regulator power unit. Notice the large screw hole in the board that secures the board to the ground. A terminal strip will suffice for the mounting of the single regulator.

regulator pcb


Very elaborate rhythms can be generated with the many features. With a basic rhythm input, three other pulse sources can be added to the mix.