Wiring 'Aux-in' (iPod) connectors to Car radios

['LIVEWIRE?']

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.

[julie_m]

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.

['LIVEWIRE?']

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!

[Tiggers]

Originally Posted by julie_m

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.

['LIVEWIRE?']

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.

[Station X]

Anyone care to submit a sketch showing the basic two resistor and capacitor arrangement?

[Argus25]

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.

[Herald1360]

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.

[Argus25]

Ok, the only "passive component way" the optical method & mini transmitter etc required powered active circuits and are much more involved.

[crackle]

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.

[Hampus]

I am trying to add an auxiliary input to a 1980's Clarion stereo, I have made some conclusions but would appreciate some feedback about it.

It is a thirty year old unit and quite advanced for it's age including frequency presets, LED display, cassette player with Dolby and chrome/metal ability.

I have attached the service manual for a similar model, the circuits are the same except my stereo do not have the jack for connecting of an equalizer. The 'short plug' in the diagram is alway plugged in so to say.

Most IC's have no other markings than Clarion's own codes so it is not easy to find information about them.

ICx2 is something related to Dolby. The radio signal also passes through this.
ICx3 is a preamplifer of sorts, the bass and treble control is connected to it.
TP-L and TP-R is voltmeter test points for when making adjustments as mentioned in the manual.

I have tried injecting signals at these test points and the sound will make it to the speakers. I first tried directly at the volume control but that of course bypassed the tone controls so that was no good.

I am thinking of fitting a switched jack breaks the internal circuit when a plug is plugged in. When no plug is present the internal signal just travels to the jack and back.

Do I need capacitors to connect to ICx3? Is there a need for DC blocking? And what is the point of the 3,3k resistors?

['LIVEWIRE?']

The usual point in such circuits is at the point where the 8-pin socket is connected, i.e. between the preamplifier(s) and power amps. (TA7240 & 7241), so the connections should be cut at the points where the signals would pass through the socket. If radio & Cassette audio is still required then either a changeover switch or switched socket is needed, if not then the 'aux' input can be wired to the 'output' side of these points directly. (i.e.) the 'aux-in' signals should go to where pins 1 & 4 of the 8-pin socket are shown connected in the service manual, whilst the 'Radio-aux' changeover switch, if fitted, should be wired between pins 1 &3, and between pins 2 & 4. A screened lead should be used, with the screens taken to Audio ground-i.e. pin 2 on the cocket.

[Hampus]

Thank you Livewire for your answer. Problem is that if I connect the input to the output amplifiers, the bass and treble controls will be non-functional, this bugs me a bit as I prefer to turn up the treble in the noisy environment a car is.

I earlier called ICx3 a preamplifier, but in fact I am not sure if it is an amplifer or not. In any case it is where tone correction is done. Since it is a custom part I have not found any useful information about it.

Do you think it is ok to connect the input to this IC instead of the output amplifier? I did try it earlier but maybe it can have some ill effects?

[Hampus]

I guess no one wish to comment on a circuit which consists of unknown parts Fully understandable. I took the risk and all seems to work well.

Anyway, I did cut the PCB traces before ICx3 and soldered a female DIN lead here and two capacitors for blocking DC. I fitted a male DIN lead to a audio jack that I installed in the car's dashpanel. I could have skipped the DIN connector and wired the jack directly to the radio, but this way it is easier to unplug the radio if I have to take it out for some reason.




The jack is switched so if no plug is inserted the signal passes from the radio/cassette circuit, to the jack and back in again, to the amplifier stage. When a plug is inserted the internal signal is disconnected and the auxillary signal is routed to the amplifier stage.



I had a concern that the disconnected signal would crosstalk to the other wires in the cable since they are not individually shielded, but that was not the case.

['LIVEWIRE?']

That's a nice neat job, Hampus. Somewhere among my rather large collection of Clarion Service manuals I have quite a few for sets of that series, if not that 'SAAB' badged version, but, if the way you have wired your 'aux-in' cable assembly works well, then I'd be inclined to leave it that way.

[YKrishna]

I recently got a classic car and I am having radio Radiomobile K200, can you please help me to upgrade this?

[Station X]

See post #3 in this thread.