Fitting 'Aux-in' connector to a Stereo Radio

[Old Sparky]

The 108 was disconnected from the supply when I did my resistance checks, and the 'aux-in' connection is, as I always do them, connected via the 'radio/aux' switch directly to the top of the v/c, so, unless there was a mod. made to the 108 I have that makes it differ from the published circuit, not unknown of course, then I'm at a loss to know why I don't measure a DC resistance to chassis at this point. I'll try and post a higher resolution drawing at some point, but I did get a 'file size is too large' message when I first attempted to post that circuit diagram. Incidentally, with regard to your earlier suggestions, Mark, I've never put shunt resistors on 'aux inputs, since the radio's volume control forms a DC load.
Admittedly this can be anything from 5k to 100 or 220k in different radios, so perhaps a low value resitor is desirable.

[Old Sparky]

I've now modified my 'aux-in' adapter to include the components you suggested, Mark, and will bear those in mind for future adapters. Purely because I had them to hand, I used 820 ohm resistors in both the series & shunt positions, and 390pf ceramic caps. for the RFI filters. This seems to work well with the 108SR, using a cassette player as the 'aux' source, after testing with an audio Signal Generator (I don't possess either an I-pod or MP3 player.) (BTW I don't see a way to add pictures to this reply)

[Terry]

Did you use the 'Quick reply' option by any chance?

If you choose 'Reply to this topic' instead, you should see the attachment upload dialogue - under 'Attachments' - at the bottom of the screen.

It also appears if you preview a 'Quick reply' (in case you change you mind, possibly?)

[Old Sparky]

As you say, Terry 'Read the Instructions!'
The photos are of an adapter I made up for use with a 108SR, and incorporating the components recommended by Mark.  The 3rd & 4th. pictures are essentially the same, except that I reduced the value of the series resistors from 3k3 to 820 ohms to improve the sensitivity of the aux. input.

[Old Sparky]

This is the circuit, incorporating the components suggested by Mark Hennessey, which i use when building 'aux-in' adapters for use with vintage car radios & stereos.  The values of R3 & R4, in particular, may need changing.  In one version I fitted a couple of 10k pre-set pots., adjusting them as required.  IF desired, the 'radio/aux' switch could be omitted and a switched 3.5mm jack socket used instead.  Alternatively, if grounding the 'unwanted' inputs isn't required, a double pole switch could be used instead of the 4 pole one.
(P.S. Apologies for my poor handwriting!!)