Mono Audio Schematic - Turn it up
Read through the instructions carefully before attempting this how to. Also read the disclaimer.
This schematic is for mono audio sources only and is useful for Atari and NES portables when you are using a screen that doesn't have a built in amp like the AEIComp LCD screens.
It is based off the popular LM386 which is a low voltage audio amplifier. There are plenty of basic schematics on the web that so how to use one of these so why post another? I found most designs lacked some basic features that portables would need.
[The mono audio schematic.]
[Headphone jack pinout.]
For my schematic you will need the following parts.
- 1 LM386
- 1 Headphone Jack
- 1 10K Audio Taper Potentiometer
- 1 Speaker (1 Watt 8ohm)
- 2 100uF Polarized Capacitors
- 1 .1uF Ceramic Capacitor
- 1 10ohm Resistor
- 1 6.8kohm Resistor
- 1 4.7kohm Resistor
- 1 1.2kohm Resistor
Other schematics on the web don't include a 100uF filter cap on the +5V to +12V input. This is important for battery operated devices so that the screen doesn't flicker or dim when a loud noise is being played. Some may or may not need it but it is better to put it in now then take your device apart later to add it.
Some notes about the extra resisters R1, R2, and R3. These are here to balance the volume of the amp. R1 and R2 cap the maximum range of the volume to about 60-65%. I did this because any higher and the volume became distorted and way to loud. R3 lowers the Headphone volume. Since headphones are smaller and rated at a lower wattage they will be much louder then the on board speaker. These 3 resistors could be removed from the circuit if you find that it is to quiet but I found that it is to loud without them. You may want to add potentiometers instead of the 3 resistors and adjust them till you find a comfortable range.
If you need to change R1 and R2 make sure to follow this formula.
(1/(1/10k+1/R2))+R1=10k
That is the equivalent resistance of the 10k potentiometer and R2 in parrallel plus the value of R1 equals 10kohms.