Adding aux input to an old boombox

[archeo...@gmail.com]

I picked up a boombox from a thrift store the other week that looks like it's been sitting in a garage for a couple of years. The drive belt on the cassette player basically melted into goo, so it's no good anymore. I want to rewire the box so that there's an input jack for an mp3 player instead of a tape head. I've read a couple of tutorials online, but if someone has actually done, I'd like to hear how you did it. 

Additionally, the box has an external mic for recording. I want to cannibalize that too, so it's the input for a VU meter. I know you need amps and caps to properly get input from a mic, and I know I could get a mic with all that already set up, but I'll bet there's already a circuit built in. So I guess I'm wondering if anyone would know how to trace it out to see what's there.

I plan to add LEDs and control the meter with an Arduino or a Trinket, and power it with the power meant for the drive motor, which I'd also remove. The motor runs at 8V, so I don't think it'll be difficult. I can come by today or tomorrow, or possibly Sunday if anyone is willing to look over it in person. Or just post replies; those are good too.

-Joanna

[Mark]

If I were doing that, I'd open up the box, and find the amplifyining device, possibly it will be what;s called an STK pack.

I'd then look up the schematic to find the input pins. 

With the unit plugged in, I'd carefully touch a wire to the input, the other end on my finger to get some interference noise.

Once you've got the right pin identified, I'd temporarily connect the ground and your aux signal onto the input pin you've identified.

Then test with a real aux signal, and check the effect the aux voulme and the ghetto blaster volume have. 

If the volume ranges work for you (no distortion, yet louad enough), make that a permanent connection, and cut the signal in trace so the signal no longer comes from the board.

Warning, you could fairly easily destroy the thing, but there are hundreds more blasters around town.





Mark

--
You received this message because you are subscribed to the Google Groups "makerspaceca" group.
To unsubscribe from this group and stop receiving emails from it, send an email to makerspaceca...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

-- 
ma...@mediawizard.ca

[Mark]

Forgot to add there will be a right and left input, or 2 STKs.  You'll need to do both inputs.

[archeo...@gmail.com]

I didn't see any parts that looked like that. I only found an IC that was covered by a heat sink. 

According to the datasheet I found, that's probably what I'm looking for. But, i have no idea what the chip is, because the heat sink is soldered to the pins and I can't pull it off to see.

[Mark]

Hm, not too sure where to go with this unit.  That looks pretty small for an amp to me.  That aluminum case is likely to stop noise, not heat sinking.

Maybe there's something else hidden somewhere?

What is the make and model of the unit?

-- 
ma...@mediawizard.ca

[Matt Richardson]

Might be an LM1818, or the like hiding under that faraday coffin.

[archeo...@gmail.com]

I have found a clue! There are 2 ICs on the main board that aren't related to the tuner labeled M51164AL (IC701) and TA7769P (IC702). The schematics of these two ICs, according to the repair manual, are here:

I also uploaded wiring diagram and the circuit schematic for the main board. However, the wiring diagram has all the parts laid out backwards to how they are in the stereo itself. I have a feeling this manual might be for a slightly different model of stereo. But other than that, everything seems correct.

[Mark]

The photo from your first email shows the opposite side of the circuit board included in this email.  It looks like the same board to me.

That said, the power output from the amp TA7769P appears to be 1 watt per channel; total 2 watts.  That's a very low powered blaster.  Are you sure you don't want to just find a more powerful unit that already has aux inputs?

--
You received this message because you are subscribed to the Google Groups "makerspaceca" group.
To unsubscribe from this group and stop receiving emails from it, send an email to makerspaceca...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

-- 
ma...@mediawizard.ca