Grumman AA5 pilot experiences a puff of smoke from the glare shield during approach and apparent radio failure. An emergency is declared in the blind and a green light is received from Tower for landing and taxi.

Narrative

Per Tower request; I reported three miles from the airport. I was instructed to enter downwind for Runway XX. I then had a puff of smoke come up from my glare shield above the instrument panel. I attempted to contact Tower with no joy as I started going through my emergency procedure for electrical fire. Smoke dissipated but I was unsure if there was an actual electrical fire. I squawked 7700 and made a call in the blind on guard 121.5 declaring an emergency and that I was continuing approach to land runway XX. I received a green light to land from Tower on base to final. I continued to receive light signal guidance from Tower to parking. I contacted Tower by cell phone from parking. I gave details of what had occurred. I had an A&P/IA look at the plane that afternoon. It was discovered a capacitor had shorted out in my audio com selector panel. He determined that the panel would still select the proper com and transmit; it would not however receive through the headsets. The radios were functional and transmissions could be received over the aircraft speaker system. He released the plane for flight. I returned home the next day. The flight was uneventful. The audio com panel is being removed and sent out for repair.