Leak Troughline stereo tuner and LM4500 decoder

HI. I have this lm4500 decoder and wish to install it in my troughline stereo.

Would anybody have any images and or clear diagrams for its connection. The ones i have are not very clear and i dont want to do any guess work with it to mess things up.

I have some capacitors and resistors. It would also be good to hear which parts you recommend for connection.

I enclose an image of the decoder.


  • IMG_20230715_223443.jpg
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Would anybody have any images and or clear diagrams for its connection.
It's not as simple as that. First of all, is there an existing decoder? Second, is this a Troughline Stereo? III? II?

You will need:

1. A voltage-doubling DC supply taken from the adjacent heater wiring point. This adds two diodes and a 2200uF/25V axial capacitor to what you show in the picture.
2. A ground connection.
3. A connection to the appropriate signal take-off point in the tuner. This varies with model and with how much extra work you're prepared to do. Some tuner modification may be required, depending on the model.
4. 120K of series resistance in that connection to bring the signal down to an acceptable level for the decoder, working as a voltage divider in conjunction with the LM4500's 50k input impedance. 47pF across this 120k could be useful to increase the channel separation, but you will easily get -30dB from this decoder, and that's plenty.
5. Connections from L and R outputs to the output leads or output RCA sockets if you have them, without introducing a ground loop.
6. You will need to rig all this up outside the tuner first so you can access the trimpots and do the required adjustments.
7. Then fit the decoder. It will fit in the same space as the existing one if any, i.e. at the rear of the right side of the chassis.