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Old 4th Aug 2016, 9:45 am   #41
'LIVEWIRE?'
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Default Re: Wiring 'Aux-in' (iPod) connectors to Car radios

The 'Redirad' and similar devices sound (pun intended!) like a very good idea, allowing the connection of all sorts of external devices withouth the need to remove the radio for internal modification. Years ago a similar technique was employed to allow an AM radio to receive FM stations, admittedly only in mono, and converted to AM. With the 'Redirad' it would appear that the same principle is used, presumably by Amplitude Modulating an internally generated 1000kHz signal with AF from an Ipod or other device. Again, the resultant audio is only going to be mono and with a max. frequency response of no more than 5kHZ, at least in the AM version.
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Old 4th Aug 2016, 3:11 pm   #42
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Default Re: Wiring 'Aux-in' (iPod) connectors to Car radios

The fixed 1 MHz output frequency could potentially be a problem with some sets, since it isn't a "real" station frequency. (All real station frequencies in the MW and LW bands are multiples of 9 kHz. Interestingly, made-up radio stations in films and TV often use non-multiples; I am not sure whether this is deliberate, and if so to what end, or just simple ignorance on the part of the writers.)

There were some digitally-tuned, but still MW/LW only, radios fitted to Fords in the 1980s, and these can only be tuned to multiples of nine.
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Old 4th Aug 2016, 7:20 pm   #43
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Default Re: Wiring 'Aux-in' (iPod) connectors to Car radios

This problem, which occurs because the 'Redirad' is an American market device, and there the AM (MW)channels are 10kHz apart, so 1Mhz (1000kHz) is a designated broadcast channel. The nearest equivalent channel in the British & European system is 999kHz, which isn't used in the UK, AFAIK, so there may not be any real problems with digitally tuned MW Radios. Of course the older mechanically tuned sets can be tuned to exactly 1Mhz, so no problems there!
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Old 6th Aug 2016, 1:02 pm   #44
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Default Re: Wiring 'Aux-in' (iPod) connectors to Car radios

Quote:
Originally Posted by julie_m View Post
The fixed 1 MHz output frequency could potentially be a problem with some sets, since it isn't a "real" station frequency.
I fitted a RediRad to my 1960’s car with original Smiths Radiomobile (LW/MW) and it works great. (There is also an FM version for those cars with FM radios.) Good sound, and no problem on the tuning. I was so impressed I now import them from the US manufacturer and offer them at an all-inclusive discounted cost to members of classic car clubs. More information on the website. I don’t want to get in trouble with the mods, but if you want to know more there is a bit of a website; just search for RediRad UK.
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Old 29th Mar 2018, 9:00 am   #45
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Default Re: Wiring 'Aux-in' (iPod) connectors to Car radios

As a follow-up to all the foregoing, and, in response to numerous questions about connecting modern stereo devices such as I-pods, MP3 Players, etc., to vintage mono domestic radios, a similar principle to that covered in this thread could be used, the basis of which is two resistors, one from each channel, to combine the LH &RH channels, plus a blocking capacitor in series with the input to the vintage radio. where no 'aux' (i.e. 'Gram') i/p is present, the same approach as used with mono car radios -i.e. disconnecting the lead between the detector and volume control, wiring in the additional components as described. Please be aware, though, that many vintage radios use a Live Chassis technique, and necessary safety precautions must be taken when connecting external sources to these. If in doubt do not attempt this without consulting an experienced engineer.
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Old 29th Mar 2018, 1:01 pm   #46
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Default Re: Wiring 'Aux-in' (iPod) connectors to Car radios

Anyone care to submit a sketch showing the basic two resistor and capacitor arrangement?
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Old 29th Mar 2018, 1:59 pm   #47
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Default Re: Wiring 'Aux-in' (iPod) connectors to Car radios

One thing that needs to be considered here, as I mentioned on another post, if it is a live chassis scenario an isolating audio transformer is required.

While some isolation can be afforded by capacitive coupling for the combined L & R signal and the common connection from the ipod (say with a two resistor two capacitor combo) this is NOT satisfactory from the safety perspective for a live chassis set. The required value of the capacitors to have a satisfactory audio bass response could pass too much current at 50Hz if the chassis went live and represent a shock hazard and the voltage ratings of them would be high too.

The only way to safely couple audio to a live chassis set would be with a split bobbin (double insulated style) iron cored transformer to eliminate the risk of electrocution. Ideally it would be wound for the task, though it may be possible to use a mains plugpack transformer in reverse. In general, I would not attempt it due to the hazards and as I suggested, use a Pantry transmitter to get the ipod signal into the radio instead.

Obviously coupling into battery powered radios is fine.
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Old 29th Mar 2018, 3:03 pm   #48
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Default Re: Wiring 'Aux-in' (iPod) connectors to Car radios

Not the only way, though probably the easiest....., though an off the shelf RF mini transmitter would come close.

Otherwise, isolation amps and optical come to mind.
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Old 29th Mar 2018, 3:13 pm   #49
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Default Re: Wiring 'Aux-in' (iPod) connectors to Car radios

Ok, the only "passive component way" the optical method & mini transmitter etc required powered active circuits and are much more involved.
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Old 29th Mar 2018, 7:33 pm   #50
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OK here is how I would wire to the gram socket on a vintage radio.
The resistor values R1a & b can be found by experimentation, but I would start off with 2.2k for each, if the volume is too much then increase to 4.7k or 10k.
R2a & b are optional if the signal is still too loud at normal volume setting on the radio. but you could try 4.7k for both.

Or you could substitute a 10k trimmer for the R2 resistors.
You will probably ideally want the iPod volume to be set to normal for earphones.
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Last edited by Station X; 29th Mar 2018 at 8:41 pm. Reason: Posts merged.
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