Silicon Chip Online - The PortaPAL Public Address System

This portable PA amplifier can be powered from the 240VAC mains or its inbuilt 12V SLA battery. It delivers up to 70 watts and pulls a number of tricks to keep battery current low while still maintaining very high performance.

Back in March 2002 we published the "Mighty Midget", a 70-watt class-H audio amplifier module based on the Philips TDA1562Q power IC.

This ground-breaking IC uses special techniques to deliver up to 70 watts from a 12V battery and does away with the need for a DC-DC inverter.

At the time, we said the "Mighty Midget" was ideal for use in a portable PA system and now we have followed up with the PortaPAL: a complete system, including mixing for two 600Ω balanced or unbalanced microphones, guitar input and line inputs for a CD player or a cassette deck.

This new circuit makes use of the TDA1562Q's muting feature, to further reduce battery drain and keep hum and noise very low.

We've also taken advantage of the inbuilt 12V SLA (sealed lead acid) battery to eliminate a heavy transformer and large and expensive electrolytic filter capacitors from the power supply - leading to a considerable cost saving.

Features

Portable, 12V battery-powered unit with safe plugpack charger
High power output
Inbuilt 200mm (8") loudspeaker with tweeter
2 combined XLR/ 6.35mm microphone inputs plus 6.35mm guitar or aux input
Stereo RCA line inputs with stereo to mono mixer
2 line outputs with stereo RCA and 6.35mm jack outlets
Level control for each input
Bass and Treble controls
Automatic power-down to extend battery charge with power-down indication
Charger on and charging indication
Storage space for spare leads
Box includes carry handle, speaker stand socket and corner protectors

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