SB Midi Cable

Description: The Sound Blaster MIDI port utilizes two pins from a 15-pin joystick port, which typically serve as redundant +5 volt and ground lines. In the context of the Sound Blaster, these pins are designated as MIDI TXD (Transmit eXternal Data) and MIDI RXD (Receive eXternal Data). The signals exchanged with the Sound Blaster are TTL logic signals. MIDI employs a current loop interface, necessitating an interface box to convert between TTL level signals and the MIDI current loop. For simultaneous use of the MIDI interface and the Sound Blaster joystick interface, a simple adapter can be constructed by connecting one male and two female 15-pin connectors via a short length of ribbon cable. The file SBMIDI1.PCX contains a PCX format graphic of the schematic diagram for the MIDI connector circuitry, which can be viewed and printed using Windows Paintbrush. For clarity, the schematics depict the MIDI input and output circuits separately, although they share the +5 volt and ground lines (pins 8 and 5 on the Sound Blaster). The interface utilizes a 4-wire shielded cable to connect the computer to the interface box, along with two 2-wire shielded cables for connecting the interface box to the input and output ports of the MIDI instrument. The MIDI input port connects to a single instrument, while the MIDI output from the computer can connect to up to five MIDI instruments. The schematic illustrates one complete MIDI output line, with the capacity to add up to four additional MIDI outputs by integrating a 220-ohm resistor (from the buffer output to pin 5 of the MIDI plug) for each output and a 220pF capacitor between each additional MIDI line and ground. The construction process begins with a dual 20-pin IC board, utilizing the first six pins for the optocoupler and the last fourteen pins for the hex buffer. Certain copper traces on the circuit board must be removed using an X-Acto knife, following the schematic guidelines. The installation of components requires meticulous attention, ensuring that the ringed end of diode D1 connects to pin 1 of the optocoupler, and ground connections are properly established. The assembly process includes connecting shielded cables to designated pins and ensuring proper grounding and shielding for signal integrity.

The Sound Blaster MIDI port is designed to facilitate MIDI communication by converting TTL signals into a format compatible with MIDI devices. The use of the 15-pin joystick port allows for dual functionality, enabling both joystick and MIDI operations through a shared interface. The MIDI TXD and RXD pins are critical for transmitting and receiving data, respectively, while the interface box serves as the intermediary that ensures proper signal conversion.

For the construction of the interface box, it is essential to utilize high-quality components, including the optocoupler and hex buffer, to maintain signal integrity and prevent data loss. The choice of a 4-wire shielded cable is crucial, as it minimizes electromagnetic interference, which can adversely affect MIDI signal quality. The additional MIDI outputs can be achieved by adhering to the specified resistor and capacitor configuration, allowing for multiple instruments to be connected without signal degradation.

During the assembly, careful attention must be paid to the soldering process, ensuring that no solder bridges occur between connections, which could lead to malfunction. The installation of the diode and proper grounding connections are vital for the functionality of the circuit. The final assembly should include adequate shielding to protect against external interference, ensuring reliable MIDI communication.

In summary, the Sound Blaster MIDI interface serves as a versatile solution for integrating MIDI capabilities into computer systems, enabling musicians and audio engineers to connect multiple MIDI instruments seamlessly. The detailed schematic and assembly instructions provide a clear pathway for constructing a reliable MIDI interface tailored for Sound Blaster systems.The Sound Blaster MIDI port uses two pins from the 15 pin joystick port. These normally would be redundant +5 volt and ground lines. In the Sound Blaster, there are called MIDI TXD (Transmit eXternal Data) and MIDI RXD (Receive eXternal Data). The signals to and from the Sound Blaster are TTL logic signals. MIDI uses a current loop interface, so t he job of the interface box is to convert between TTL level signals and the MIDI current loop. If you want to use the MIDI interface and the Sound Blaster joystick interface simultaneously, you can make a simple adapter by connecting one male and 2 female 15 pin connectors to a short length of ribbon cable. SBMIDI1. PCX is a PCX format graphic file of the schematic diagram of the MIDI connector circuitry. You can use Windows Paintbrush to view and print the schematic. For simplicity, the schematics show the MIDI input and output circuits separately, but they share the +5 volt and ground lines.

(Pins 8 and 5 on the Sound Blaster). The interface uses 4 wire shielded cable to connect the computer to the interface box and two 2 wire shielded cables to connect the interface box to the input and output ports on the MIDI instrument. The MIDI input port only can connect to one instrument, but the MIDI Out from the computer could go to up to 5 MIDI instruments.

The schematic diagram only shows one complete MIDI output line. You can connect up to 4 additional MIDI outputs by adding a 220 resistor (from the buffer output to pin 5 of the MIDI plug) for each output. You should also add a 220pf capacitor between each additional MIDI line and ground. Start with using half of a dual 20 pin IC board, using the first six pins for the optocoupler and the last fourteen pins for the hex buffer.

Then remove portions of some of the copper lines on the circuit board with an X-Acto knife, as is shown in the schematic below. Cut each trace on both ends first, then remove the copper between the cuts. Looking at the diagram, I now believe the links from IC2 pin 2 to IC1 pin 3, and IC2 pin 2 to pin 4, to be incorrect.

The links IC2 pin 5 to pin 9 and IC2 pin 9 to pin 11 are only required if you intend to use the corresponding outputs - pins 6 and 8. This also explains the additional track cutting Now on to component installation! Be sure to use rosin core solder and a low wattage soldering iron. Solder the 20 pin socket to the center of the board, being careful not to bridge solder between connections.

Then install the other components in the locations shown in the above schematic. Note that the ringed end of diode D1 needs to connect to pin1 of the optocoupler. Be sure to run hookup wires from the ground pin on the optocoupler (Pin 4) to the ground pin of the hex buffer (Pin 7) and between pins 11 and 12 on the hex buffer. The remaining hookup wires are optional for additional MIDI outputs. Notice that both a resistor and a capacitor must be connected in the same hole for each MIDI Out. Then connect the 4 conductor shielded cable to pins 5, 8, 12 and 15 of the 15 pin plug. Connect the shield to the metal case of the plug. Connect the other end of the 4 wire cable to the corresponding locations shown in the above schematic.

Tie the cable shield to the large mounting hole in the circuit card and connect one end of each of the two connector shielded cables to pins 4 and 5 of the MIDI plugs. Connect the shield in the MIDI plugs to pin 2. Mark one cable "MIDI IN" and the other cable "MIDI OUT". Connect the other end of the cables tot he corresponding locations on the circuit card. Tie the shields to mounting holes in the circuit card and connect all three shields together with a hookup wire.

Check the card and cables to ensure that all connections are correct, file small notches in the cover of the aluminum box for the cables, and wrap a piece of heavy paper around the circuit card to prevent shorting. Your next step is to plug the 15 pin connector into