Re: BC780 Audio Mod, The short version

Posted by J.T. Makatura on January 13, 2001 at 13:49:38:

In Reply to: Re: BC780 Audio Mod, The short version posted by Bill on January 13, 2001 at 13:01:10:

I aree with most of this Bill. The TDA1905 is a four ohm output chip that can also be run at 8 or 16 ohms. As you know, you can always go higher, to a point, but I too am puzzled as to why they chose to put the 18 ohm resistor in there. Thermal protection was not a concern since the radio is silent more than 50% of the time. I tested this with an open squelch at a moderate volume for about an hour last week and the chip showed no signs of any abnormal heating. The resistor placed across the speaker terminals was purely for the amplifier to see a 4 ohm load and not necessarily for the listener as noted.

Finally, the phase reversal of the speaker has a great effect as to where your ear thinks the sound is coming from and whether the speaker fires to the front or to the rear. Like another poster said it is harder to notice the effect with only one speaker but it still exists. If the peaks and valleys of the audio wave remain relatively in phase and otherwise intact from point of origin to your speaker, it will make a noticeable difference.

Joe

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