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Author Topic: Practice oscillator problem  (Read 450 times)
WP4NXA
Member

Posts: 48




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« on: August 10, 2008, 06:11:33 PM »

I just build the project shown here http://www.af2cw.com/cw/CW%20With%20Your%20HT.pdf
but for some reason, the speaker now sounds very weird when I turn up the volume. (it sounds like scratchy noise or something.

The battery is fine. It was working before. Im not sure if there anything wrong with the solder joints. Anyone know what can cause the sound to go like that?

Thanks.
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KM5Z
Member

Posts: 24


WWW

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« Reply #1 on: August 11, 2008, 08:53:47 AM »

> I just build the project shown here http://www.af2cw.com/cw/CW%20With%20Your%20HT.pdf
> but for some reason, the speaker now sounds very weird
> when I turn up the volume. (it sounds like scratchy
> noise or something.
>
> The battery is fine. It was working before. Im not
> sure if there anything wrong with the solder joints.
> Anyone know what can cause the sound to go like that?

I think I built one of those a long time ago. Neat little project.

When the volume is turned up, the output of the little
555 IC is swamped by the speaker impedance (8 ohms), I
believe. Try some headphones (regular ear-cup models
are around 32 ohms), or some ear-buds (they vary from
320 ohms and UP...).

Or, if you can, just add an LM386 IC and provide some
additional output for the speaker.

Mike Yancey
KM5Z
Dallas, Texas
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WD4HXG
Member

Posts: 184




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« Reply #2 on: August 13, 2008, 12:19:45 PM »

Ditto on the tip of trying headphones.

Just as an aside, one of the problems with older Code Practice Oscillators which were built from discrete transistors, caps and resistors was the contact resistance of the key contacts. It would tend to cause a raspy grind in the tone.

Slip the side slide switch on your key into position like you would for tuning up the transmitter. Listen to the tone. Is it steady? Slip the slide switch back off.

If so then try holding down the key steady and listen to the tone. Does it now sound raspy? If you wriggle slightly from side to side does the raspiness increase during motion?

If so you can try cleaning the contacts and that may improve matters.

Hope this helps.

73

Chuck WD4HXG
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