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How do I make a simple, portable P.A. system using a boom box and a microphone?

I have a boom box with dual cassette, AM/FM radio and line-in input.  It also has a microphone input.  I have tried plugging a mic in but it seems to work only when I have a cassette in it and it is on record. What do I need to do or to add to make a simple public address system without running the cassette record?

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If you're lucky, there's a mechanical switch in the box that simply engages the mic when the record head moves into position. If that's the case, all you have to do is find the switch, cut the wires going into it and twist them together. If not, maybe the easiest thing to do would be to get a cassette and remove all the tape, then just push Record and let the box think you're recording.
Or maybe it would be easier to just build one of the amplifier circuits on this site to convert the mic output to line level and use the line-in. Any idea if the box will play line-in signals without having to push Record?
> If not, maybe the easiest thing to do would be to get a cassette and remove all the tape, then just push Record and let the box think you're recording.
.  Excellent idea! ... as long as auto-shutoff is not triggered by a stopped supply reel.
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.  Line-in is looking for a 1Vp-p signal, while, IIRC, mic in is looking for a mV signal. That would require a preamp to use a mic on line-in. A simple op-amp circuit would probably work.
You think having two empty reels would trigger the auto-shutoff? I've never tried it, but I was thinking that having no tape at all would circumvent the auto-off. Of course, it's been approximately a gazillion years since I last hacked a cassette recorder, so I may be missing something....
.  Same here - haven't touched a cassette or deck in ages. My memory could be faulty, but I think a stopped supply reel is what signals end-of-tape for many decks.
.  I've had decks that sensed the clear/translucent leader.
I vaguely recall leader-sensing cassette decks (also leader-sensing reel-to-reels - very handy doing sound cues for shows in the days before mp3).
In any case, I think it's worth testing. Not like it would cost much. You can get a cassette of Donny Osmond's Disco Train for a dime at every rummage sale I've ever been to. And no big loss removing the tape on that one, either.
.  Well it took some digging in the back of closets but I finally found an auto-stop tape deck. It took a lot more digging to find a cassette with a broken tape.
.  On the deck I just tried it is the takeup reel that controls auto-shutoff. The deck would shutoff at the end of a normal tape but would not shutoff with the broken tape.
Cool. I'm impressed that you found a cassette deck, and even more impressed that it still works. Good to know that the theory is sound, at least for some decks.
blodefood (author)  RavingMadStudios7 years ago
I have used an MP3 player and a CD player using the line-in.  I don't know what you call the connectors that go into the back of the machine, but there are two (stereo) that look like older stereo speaker connectors, a sort of cup with a smooth peg in the centre.
They're called RCA connectors. If you want to use the mic with the line-in, just get an adapter cable that goes from whatever you mic plug is (1/8" phono plug?) to RCA stereo. You probably won't get much out of it without some kind of amp between the two, though.