This board is for a TRS-80 Model 100/102/200 sound card that uses the ubiquitous Yamaha YM3812 and plugs directly into the LPT port on the Model T. It requires an external +5V “clean” power supply, a mini-USB port or header pins are provided for this purpose. Use of a good quality supply is recommended as any power supply noise will impact the audio quality. The audio jack is intended to allow the use of headphones or an external speaker. The max gain on the board is limited due to a single +5v supply rail. The trimpots can be used to set the:

*‘Volume’ (the range is limited due to the power supply) for optimum performance with the external speaker.

*‘Bass Boost’ (if installed) can be used to enhance the lower frequencies.

*‘Gain’ (if installed) is used to alter the gain of the Audio amp.

Link 1 and Link 2 can be used to configure the board for use with other parallel port devices. On the Model T link 1 should be shorted and Link 2 can be left open. The reset button is used to reset the device.

All the parts are readily available and through hole to make assembly relatively easy. A simple BASIC driver is required to convert the LPT port into a parallel port to drive the unit.

Materials

All the ICs should be socketed make it easier to debug in case of any issues.

DigiKey Parts

Digikey Parts list Digikey is used to list some parts however other suppliers might have lower prices.

eBay Parts

U3 YM3812

U4 YM3014B

Jameco Parts

*C10, C15- deleted.

Resistors

All the resistors are generic 1/8W through hole parts and can be sourced any where.

Note: The parts lists in some cases includes more than is required for one board this is due to the lower overall price for a larger quantity.