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November 1st 03, 08:31 PM

Mark Rehorst wrote:
On 01 Nov 2003 03:35:10 GMT, r (Mike Knudsen)
wrote:

But why would the SX-190 suddenly develop this problem, unless it's something
else? --Mike K.

It didn't develop the problem suddenly. It has buzzed since the day I
got it a couple years ago. Now that much bigger problems are solved,
I am looking at the more minor problems, such as buzzing audio. The
literature (magazine reviews, etc.) on the radio has some vague
references to audio hum or buzz, so I think this behavior is normal
for the radio. Why they didn't just fix the problem before releasing
it onto the market I can't say.

The audio amp buzzes at all times, and it is steady. It even buzzes
when the radio is switched to standby. I believe there is some noise
in the power supply lines and that the audio amp stage has poor power
supply rejection, so the buzz gets to the speaker.

I will check the supply line and the audio output with a scope and see
if the noise looks the same. Then I need to figure out how to kill
the noise.

A brute force solution would be to use a modern IC audio amp that has
a reasonable amount of power supply rejection. But I would rather try
to quiet the source of the noise than to make such a severe
modification to the radio. The noise may have some effect on RF
performance as well as the audio, so it would be best to kill it.

Thanks for all the input so far...

MR

Could you elaborate a bit more on what it sounds like? Is it an AC buzz
or an AC hum? Is it 60 cycles?
Is the power supply a plain-jane bridge or is it a switching type?

-Bill

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