CurtPalme.com Home Theater Forum

[brenwaterys]

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Ok, I am asking for some help here, may not be the best forum but I know the electronics know-how is here to solve my problem. I have been asked by a guy in my office to help debug his 1980's boom-box. For some reason the line-in on the box has quit working so he asked me to either fix that or find another way to integrate one of these bluetooth devices (http://www.parts-express.com/pe/showdetl.cfm?Partnumber=320-352) so he can use his ipod wirelessly. In my initial attempt I wired the input into the recording circuit of the tape deck on the downstream side of a cut-off switch but apparently the impedence of the circuit is too low because the audio wires from the bluetooth device are heating up during use. It seem to work fine except for this behavior, this includes the audio levels being at an expected level. Any suggestions on either a better place to insert a line-in or maybe a way to up the impedance of this input. As soon as my co-worker brings back in the box I will pull the part number and add it to the thread.

[macgyver655]

Are you sure it's not just the input selector?

[brenwaterys]

Admittedly it has been over a month since I actually worked on this so I may be mis-remembing something but hooked up as it is now has the same behavior as before the true line-in quit working. It requires the input selector set to tape and the recording button has to be pushed. The boom-box doesn't have a dedicated aux input on the selector.

[macgyver655]

[brenwaterys]

Ok - I have it back in front of me. It is a Sanyo M 9975. I will get it pulled apart again and see what I can find.

[AE_Stereo]

Belated reply, but seen this only today. I am new to the Forum. Hello to everyone.

Copied from my posting elsewhere.

Here is a way to connect line input to any radio/stereo - learned from my childhood friend Benny (I learn that he is sadly no more now). It will even work with a pocket radio, as long as it has a manual volume control, whose legs you can access.

Find out the earthing and input pin (normally the center pin) of the Volume control pot of your radio or stereo.
Connect the Line-out terminal from any external device to these two points. The radio will play the input as long as it is on. It doesn't matter whether it is Radio, Tape or Line in/Phono is in on position. Only thing is that the input will get mixed with what is playing within the stereo. Hence use either Phono or tune to no signal area with radio. Don't use the tape, as the motor will be always running, wearing out.

Earth terminal is common throughout the chasis/pcb. Hence it could be connected to almost any earth point near to the pot. You can find the input terminal by trial and error. If you connect to the output, radio will play at full volume, that's all.

Being a stereo, you will have to connect to the Left & Right side potentiometers separately.

If you can find out a schematic for your stereo, you can even trace out the PCB path to the potentiometer legs and connect the inputs on the PCB itself.


I have successfully done this with my Sony MHC-1200 mini deck and I am using it as the amp for my HT rear channels. It is having only Phono input. What I did was, I isolated the Phono input RCA socket pins from the system circuit by cutting off the PCB (make a groove on the PCB with a sharp blade!) and then used jump wires from the +ve RCA socket legs to a point on the PCB leading to the L/R pots. Thus I am able to use the same Phono sockets for Line-In now.

For a Boombox, another point you can check to input the Lin-in will be the Radio/Tape/Aux-in selector switch. This switch must be connecting the different source signals after the Pre-Amp to the Volume control. Try inputting the source signal with a probe (similar to the Multimeter probes) at the probable pins of the switch.

Happy Line-in Listening. The best way to transmit analog audio losslessly.