Question for audio guys

[srtga]

I jumped off the internal speaker in my scanner and added an 1/8 jack for an external speaker.

It's running through an amplified CB speaker.

When I'm listening to any extended TX I get a brief "cut" at a pretty predictable rate. It reminds me of when you get 2 speaker wires shorted on a stereo and it "cuts" as you increase the volume.

I've traced everything and can't find a short but something is up with it.

Anyone think that the amp is screwing with the audio on the scanner?

[MOPARado]

Is it possible there's an impedance mis match between the scanner speaker output and the CB amp's input? Did you use a cut-out jack or a parallel output jack?

What type of input does the CB speaker amp require? Does it have a volume control?

Are you overdriving the CB amp input by cranking up the scanner's volume which could indeed cause cut outs?

Since it seems to basically work most of the time, that tells me the wiring is probably OK barring any intermittent opens or shorts.
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[srtga]

Impedence is the same, no volume on the amp.

I'm thinking that I pay have the speaker polarity wrong and the amp circuit is grounding or something...

[MOPARado]

Impedence is the same, no volume on the amp.

I'm thinking that I pay have the speaker polarity wrong and the amp circuit is grounding or something...

Offhand, if that was the case, then you would get no sound at all.
You did say it does work but cuts out now and then?

Keep in mind if you crank up the volume on the scanner to the point it overdrives the speaker amps input, it would turn a class A amplifier into a class D amp, which could cause the intermittent cutouts.

If you have an ordinary non-amped speaker available, try driving it 'in free air' with the scanner output wires as an experiment and see what happens. Do not ground the speaker-hold it in free air-just connect the scanner wires to it.
This would possibly provide a clue to any wiring issues, spooky amp or grounding issues.
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[srtga]

I'll check it out. I get a sort of:
"blah, blah, bla,... bla, blah, <click> blah, blah, bla,..., bla, bla, <click> repeat..."

It's at a very predictable interval and didn't start until I added the jack from the speaker wire. Now it's driving the internal scanner speaker and the amplified speaker.

It wasn't loud enough coming off the headphone jack. Now the volume is great but I have this "cut" problem.

[MOPARado]

Now it's driving the internal scanner speaker and the amplified speaker.

There's a chance the speaker amps's input common is grounded to the battery's Neg.-the car's chassis. There's also a possibility one of the terminals on the scanner's internal speaker is also grounded.
Its also possible the speaker amps input and/or the scanner's speaker is isolated from ground via a transformer but it would have to be rung out with an ohmmeter or schematic to verify. If one is grounded and the other is not, depending on the circuit design could result in unpredictable feedback.

It sounds like you wired the jack such that both the scanners speaker and the speaker amp are in parallel. Which might result in some spooky feedback situation depending exactly how the scanners speaker is being driven.

If i were doing this, i would of first off identified any grounds on both the scanner's speaker and the speaker amp's input.

Secondly, i would of definitely used a cut-out jack which is a little more tricky to wire up. The scanner speaker circuitry would only drive the internal speaker OR the speaker amp-NOT both.
Driving both the internal speaker and the speaker-amp at the same time depending on the circuit designs of each could be a recipe for a feedback loop which its starting to look like.

Another thing you might try if you have a battery operated transistor radio with an external speaker/earphone jack is driving the speaker amp with the radio's external speaker jack.

Barring any cold solder joints, wiring shorts, bad speaker amp, etc. try those experiments to pin down whats going on. You might have to end up installing a cut-out jack.
There also a possibility depending on whats going on, that you could damage the scanner. I personally would not operate the speaker amp with this setup until the problem is identified and fixed.

Is the scanner a hand held battery operated? Or is it designed for mobile use?
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[bradthemad]

It's at a very predictable interval

Could this be the result of the scanner operating in some form of priority mode? I'm not sure of the RS equivalents' names, but on my Uniden, if I enable priority scanning of a particular frequency, close call (Signal Stalker?), or weather alerts, every two seconds the audio cuts out as it checks whichever of those things is enabled. It sounds like annoyingly poor reception dropping below squelch, but it's always every two seconds.