Need help getting a jack-output from an old radio/casette-player

[Nerocyne]

Hello. I recently bought this radio/cassette player: **broken link removed**

The problem is that I want to be able to connect Mp3-player/Cellphone via a male jack. Of course, it does not have audio-in capabillity. Would it be possible to use an RCA-Jack cable, like this one,
**broken link removed**
Cut of the RCA-ends, solder it onto the right part of the circuit, and get a male jack out?

Or more specifically what I'm wondering, I've figured that some of the cables that lead to the speakers are marked "+, R, -, L". Could I solder the red part of the former RCA-cable onto R, and the white part onto L?

Thankyou.

If it would help, I can provide pictures of the circuit-boards of the Stereo player.

 

[Reloadron]

Or more specifically what I'm wondering, I've figured that some of the cables that lead to the speakers are marked "+, R, -, L". Could I solder the red part of the former RCA-cable onto R, and the white part onto L?

My guess is no. The cell phone MP3 player out is designed to work into head phones (ear buds) and not drive speakers.

What you would need to do is find where either the radio or cassette player drive the amplifier stages and tap in at that point. For example if there is a switch for switching audio input to the amp from either radio or cassette.

Ron

 

[Nerocyne]

Oh, I did not mean to use the cellphone to drive it, I will use power either from batteries or cable, only use the cellphone/Mp3-player to provide the music.

Unfortunately, I am not the most skilled person in the world considering circuitboards, which is the reason I came here.

Thanks for the reply.

 

[Reloadron]

Oh, I did not mean to use the cellphone to drive it, I will use power either from batteries or cable, only use the cellphone/Mp3-player to provide the music.

Unfortunately, I am not the most skilled person in the world considering circuitboards, which is the reason I came here.

That is what I was getting at. The audio signal out of the cell phone (MP3 player) is a low level audio signal. It is designed to drive earphones of a high impedance, it is not designed to drive speakers with a very low impedance. Thus the problem. To hear the cell's MP3 player through speakers would require amplification.

A low level audio signal is fed from the radio section or the cassette player section to the units amplifier, much like the signal you have from the cell's MP3 player. The trick now becomes placing that low level audio signal at the input to the systems main amplifier. The little cell's MP3 output lacks the power (signal strength and amplitude) to drive speakers.

What you want to do is not impossible or all that difficult but does require some skills and a good working knowledge of how things actually work. For example if there is a switch to select Radio or Cassette the cassette option could be replaced with the signal from the cell's MP3 player. That point where switching happens is the key to making this work.

My reference to "drive it" was based on audio not main power. Drive as in audio power drive.

Ron

 

[Nerocyne]

This, which is the main circuitboard (There are two, this one and the radio one), shows the button from the frontside.
https://i51.tinypic.com/2yki5bp.jpg
Turned around, you can see the curcuits. https://i53.tinypic.com/122cfpe.jpg
The curcuits soldered to the button on the left side seems to lead to the radio. Any suggestions?

And again, thanks for your feedback.

(Since the images were huge, I only included links.)

 

[Reloadron]

Man it is really hard to tell. Before I forget, the images are really not that large at all as to file size and uploading to the forums. Anyway, the trick would be to try and trace out from the switch where numbers one through eight actually go. Six pins would make sense for audio input to the amp switching. The remaining two might be power for the cassette. Meaning when cassette is selected power is provided for the cassette drive motor. That is pure speculation on my part.

Ron

 

[carbonzit]

Unless I'm really missing something here, it shouldn't be that difficult.

You want to play your MP3 player through your new boom box, right?

Just find the volume control on the boom box. It'll be a stereo pot (potentiometer), each half of which has 3 connections.

Connect the high side of the inputs from the MP3 player to the high side connections of the pots. Connect the other side (ground) to the other side. Bingo!

If the output from the MP3 player is too high for the boom box (sound is distorted), you may need to add some resistors to attenuate the signal.

Does this make sense? Seems like it should be worth a try, anyhow.

 

[Nerocyne]

First of all, I want to connect an RCA-jack-cable to the boombox (The RCA-plugs cut off), to be able to switch what device I use to play music. I will most likely be using it with my phone.
Secondly, what did you mean by "high side"? Again, I'm not too well known within this subject
The volume-button has six different places I can connect the cable. Now connect what to the whatwhat?
Thanks

 

[carbonzit]

OK. There are six connections to the "volume button" (actually a variable resistor called a potentiometer).

These are divided into two groups of three. In each group, there are three connections:

• The "high side", which connects to an output stage of the boom box's amplifier;
• The "wiper", the middle contact that varies the resistance;
• The "bottom", or grounded side of the potentiometer.
  
  You can figure out which is which by their physical position. When the volume control is turned (or slid, if it's a linear pot) all the way down, the outside contact closest to the knob position (counterclockwise or left) is ground. The other outside one is the "high side", and the middle one is the wiper.
  
  You want to connect the "hot" input from your phone (the signal conductor, the center wire in the cable) to the "high side", and the other side to ground.
  
  Here, I drew you a picture:
  
  **broken link removed**
  
  This is looking down on the volume control (potentiometer), showing one half of it (the three dots are the three connections).
  
  To use the boom box with your phone, just turn it to "tape", "aux" (if it has that input, which it probably doesn't), or any other position besides the radio (AM or FM). Then the input from your phone will play through the boom box.
  
  By the way, you do mean you want an input to your old radio cassette player, not an output from, correct?

 

[Dean Huster]

This cassette recorder doesn't record or only records from off the air? If it's made for microphone input, there's you're starting point.

 

[carbonzit]

But that would be a terrible mismatch, wouldn't it? between a microphone-level input and a speaker/headphone-level output (from a cell phone). I suppose you could attenuate the signal with a pad or a potentiometer. My method requires a little hacking, true, but I think it would give better results.

 

[Dean Huster]

Of course it would be a terrible mismatch. As I said, it was a "starting point". Once you've found the mic input circuitry, there'll be a preamp stage and after that, you'd likely have line-level signals. Tap in there. Or, you could build a simple attenuator to knock the line-level signal down from your source to the mic level input of the recorder. Some of these low-end "boom boxes" used integral mics rather than external ones, so there'll be no jack and you will have to do some circuit tracing.

 

[carbonzit]

Well, I thought your idea was good until I realized that it's very unlikely that a boom box is going to have a tape monitor (i.e., PA) capability. More than likely the mike input will only be used for recording onto cassette, which won't do the O.P. much good here (at least not without a lot more hacking!). Finding the volume control (which is as close to line input as never mind) and tapping in there is the way to go.