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

['LIVEWIRE?']

The attached photos should give some idea how to connect an 'aux-in' lead to Radios in the Motorola 112/114/122/124 series(pictures are of a 114)
and the Motorola 515T/616T/717T/828T, 525/626/727/828series(equivalent to Radiomobile 970/980, etc.) In this case pictures are of a Motorola 828.

In all cases, the principle is the same. Break the connection between the detector o/p and the volume control 'hot' side, then connect one core of a two-core screened lead to the volume control, and the other to the detector o/p, with the screens going to the common return(V/C 'cold' side)
In the Motorola 114 series, simply remove a wire link between det. o/p & v/c
whilst in the older 727/828, etc., desolder the v/c 'hot' tag from the printed circuit, and CAREFULLY bend it clear thereof. To be certain the two points remain isolated from each other the track from the detector o/p can be cut near where the v/c tag was soldered.

The screened lead can be routed out of the radio's via(in the 114 series) the hole through which the battery & speaker leads are already passed, and in the 515/616/727/828, etc., by carefully enlarging a slot in the heatsink, the lead can exit this way. The usual connector for iPods & similar devices is a 3.5mm stereo jack, and there are various ways to accommodate this. Most recently I have used pcb mount 3.5mm stereo switched jack sockets, wired for mono use. This allows for radio reception
by removing the plug. As far as I know switched LINE sockets are not available, so an alternative might be to use an unswitched line socket.
If radio reception is still required, a DPDT switch can be fitted, allowing radio or aux source selection.
Apologies in advance if some of these pictures aren't too clear, but I hope they will be helpful.

(Note to Mods. Perhaps this post could go in the 'sticky' section)

['LIVEWIRE?']

As per my note at the bottom of the above post-would it not be a good idea to put this in the 'sticky' section for future reference.

[gfiandy]

Just though I would add my experience modifying a much later unit and try and collate the information.
I bought a Radiomobile K200 new old stock for £16.
The plan is to modify it for a iPod and then replace the DIN mount unit.

Modifying it took ages as it needed quite allot of reverse engineering to work out the combined on/off tone and volume control, especially as the tone control feeds into the volume control carbon track. Very clever but confusing. Practical upshot was the iPod needs to be feed through the same input resistance as the radio section for the tone control to work. The control had three rows of pins, 3 pins (Tone) 4 pins (Vol) and 2 Pins (on off). I went through with a multimeter to identify what each set of pins did by changing the controls and identifying which control affected which reading. I also worked through the circuit and made drawing of what was going on.

Once I had identified what the circuit was I made a jack plug up with two 100R resistors to mix the signal to mono then a 33K resistor to feed into the volume control. This worked but cause the radio to pick up quite allot of noise from the iPod lead. So I introduced a micro-switch which is activated by tuning to the far side of the dial to switch between the iPod and radio into the volume control circuit. Problem is now solved, I also updated the lead I had used to a properly screened one.

Next problem was I did not have a radio plate to mount the twin spindle radio. Fortunately another forum came to the rescue and provided a drawing of the original item so I manufactured a simplified version in a bit of aluminium plate. It has no recess in it but this doesn't seem to be needed as there is plenty of space between it and the gear stick.

Currently the radio plate is just in the aluminium finish, I have ordered some sticky backed leatherette vinyl to cover it but decided to dry fit it to check it is strong enough and fits properly.

I have the reverse engineered circuit, I can't guarantee it is correct however it was good enough to do the modification, if anyone is interested it is attached.

Some photos of the modifications and the installation.

['LIVEWIRE?']

I've just realized that nowhere in my original post did I mention the isolating/matching resistors, which are desirable in all cases where a stereo signal is being fed into a mono amplifier.

['LIVEWIRE?']

I have found that breakthrough from the internal radio(or cassette)audio is a problem with some radios & stereos. Fitting a 4-pole c/o switch for 'Radio/Aux' with the two 'spare' poles being used to short to ground the unwanted signal is a simple cure for this problem

[Don_Zalmrol]

Here are my two cents for a Becker Europa 2 Stereo radio with 5 pin DIN aux for normally a cassette deck.

Here is the original topic (where even some of you have commented on)
https://www.vintage-radio.net/forum/...ad.php?t=41176

In the enclosed schematic you can add double poled switch to choose between the radio input and the iPhone/ iPod/ … input.

You can even go further and charge your device with pins 2 (-) and 7 (+), but be carefull that your radio can deliver a decent current to it.

I use it to switch an audio relay via a switch, because I had a noise problem with the switch…

[sparticate]

Hi Guys

I have read this thread with interest as I would like to do something like this with a car radio of mine.
I am also wondering if it is possible to install a USB port instead of the 3.5mm jack?

The other option open to me lies with a modern car radio with usb input which is only 80mm deep. The problem is that is a 4 channel stereo radio. The console I have only has space for a single 5.25" speaker at best. Would it be possible to bridge the 2 front speaker connections, and thus have mono output?

Rylan

[bobbyball]

Not to be recommended as you are likely to destroy the output amplifiers on your radio...

['LIVEWIRE?']

AFAIK, there would be no problem with fitting a USB port instead of a Jack. However I, for one, do not know what the connections to a USB port are. To my knowledge there are at least three different USB ports, the connections to each of which may be different. Perhaps there's a Data Sheet 'out there' for them?

[julie_m]

You could unsolder a USB connector from an old computer motherboard and add a 5 volt regulator such as a 7805, to allow charging of USB devices.

Obviously it won't be able to do any more than that, as the old radio won't have the microprocessor needed to read data from a USB mass storage device, decompress the data and convert it to analogue audio.

[sparticate]

Thanks for the input everyone.

I did think that bridging a car radio would be a bad idea!

On the USB front I have come across one on ebay I think it may be suitable. At the moment I am hoping to win a Motorola 124 on ebay, it will need a service though! Hopefully I can work out how to connect it etc.

Rylan

['LIVEWIRE?']

I've noticed that commercially made adaptors tend to use a lead terminated with a stereo 3.5mm jack plug for the input lead, which is fair enough, since Ipods, MP3 players, etc. have a 3.5mm socket as the output. However I prefer to use a 3.5mm socket, preferably a headphone type with the extra contacts, so that the two matching resistors can easily be fitted, and, more importantly perhaps, the changeover from radio to aux & vice-versa is achieived simply by inserting or removing the external connection. A ready-made lead having two 3.5mm stereo jack plugs can be used to connect the Ipod, etc. to the radio.

['LIVEWIRE?']

Originally Posted by 'LIVEWIRE?'

I have found that breakthrough from the internal radio(or cassette)audio is a problem with some radios & stereos. Fitting a 4-pole c/o switch for 'Radio/Aux' with the two 'spare' poles being used to short to ground the unwanted signal is a simple cure for this problem

Further to the above, I am currently (10 May 2014) in the process of fitting an 'aux-in' jack to a Radiomobile 1085X, and have used an earphone socket salvaged from a scrap stereo for this purpose. With a 10k resistor in series with each channel, this set-up works well, but there is breakthrough, admittedly quite a few dB below the external signal level. Any suggestions as to how to eliminate this without adding an additional switch would be welcome.

[PaulR]

Oddly I have had no problem with breakthrough at all with this model, just with valve sets. I use a rotary switch in a small box with stereo jack sockets for the radio side and the input from the CD player or whatever. If there is space this can be mounted on the dashboard to make an easy switchover from radio to "Aux". A spare pole on the switch can be used to short out the radio when on the Aux setting if necessary.

The only problem I have with them is trying to stop interference from the petrol pump!

Paul

['LIVEWIRE?']

A recent (May 2015) post in the 'Vintage Audio' section of this forum has highlighted a problem which arises when attempting to recharge the internal batteries of a connected device via the cigarette lighter socket of a negative earth vehicle whilst the Ipod, etc., is plugged into the 'aux-in' connector fitted to radios in the Motorola 717/828/727/828/737/838 series, and their Radiomobile equivalents (900/920/970/980/1070/1080, etc.) In these sets the volume control 'cold' side, and hence the screen of the 'aux-in' cable is connected to AF positive regardless of the radio's (or vehicle's) polarity. Thus, in a Negative Earth) vehicle, a short circuit will exsist betwen the 'aux-in' lead's screen and the radio Positive Line whilst the IPod or other external device is plugged in, due to the fact that in probably all audio devices the signal return path is common with the negative line of the IPod. Ideally any adaptor should incorporate a 1:1 audio isolating transformer when used with the above range of radios, and possible a few other Radiomobile & Motorola models made between 1964 & 1974. AFAIK, later models, and all other makes of which I know have their Volume control common side connected to AF Negative, and the above fault will not arise.

Coincidentally, I have just fitted a bluetooth receiver to my bike radio so I can listen to plays from my iPod, works a treat, it cost less than a tenner (http://www.ebay.co.uk/itm/2614335454...%3AMEBIDX%3AIT) and no earth loops. This one doesn't have a 'pair' button so no need to press anything when turning on. I did remove the battery so when I turn on the radio it starts to connect at once. Seamless!

['LIVEWIRE?']

As a follow-up to my earlier posts, here are some pictures of an 'aux-in' adapter I made up to add to a Radiomobile 108SR. This player is stereo, but the principle is the same as for the mono radios mentioned earlier, except that there is no need to combine the stereo outputs into one channel as is the case with mono radios. Shunt resistors, to provide a charging path for any capacitor(s) in the I-pod or other device, series resistors, and shunt capacitors, to assist in RFI suppression, are, at the suggestion of M. Hennesey, included. In this case I used 4 x 820R, and 2 x 390pf ceramic caps., simply because I had them to hand. Picture #1 is actually the PCB Layout of a 108SR with my notes as to where to break into the circuit in order to add 'aux-in' adapters. Pictures 2 & 3 show the internal connections between the 3.5mm stereo jack socket and the Radio/Aux c/o switch, but with 3k3 series resistors in pic.2, which I later reduced to 820 ohm as shown in pic.3 to improve the sensitivity of the aux. i/p. I'll try and post a diagram later.

['LIVEWIRE?']

A further photo, this time showing the adapter box from the outside. It is connected to the radio or stereo via about 1.5m 4-core screened cable. Fitting a 4-pole c/o switch allows for two things, (1) the I-pod, etc., can be left plugged in, using the switch to select sources. (2) the 'spare' poles are used to ground the unwanted input to prevent unwanted signal breakthrough.
A similar device could be made using a switched stereo jack, omitting the switch altogether, or using a double pole c/o switch instead of a 4-pole one.

['LIVEWIRE?']

This is the circuit I use when building 'aux-in' adapters for use with vintage car radios & stereos. The values of R3 & R4 may need changing, and, if the adapter is for use with a mono radio, the two channels should be commoned (joined together) at the connections to the Volume control
(P.S. Apologies for my poor handwriting!)

[Newshound68]

Originally Posted by merlinmaxwell

Coincidentally, I have just fitted a bluetooth receiver to my bike radio so I can listen to plays from my iPod, works a treat, it cost less than a tenner

Having fixed my Motorola 114 and with the kind help of the Forum folk added an iPod lead, I've also now attached one of these Bluetooth devices which are cheap and brilliant.

One question: as it runs out of battery in two hours and needs to be recharged, how do I wire it up directly to the 114 so it can be powered by the radio?
Am a newbie so please keep it simple as possible.
Thanks in advance