Classic car radio. MP3 and iPhone connectivity?

[Tiggers]

Hello all,

I'm looking forward to benefiting from the obviously very knowledgeable people on this forum.

I know next to nothing of radio design, construction or operation, but I am a keen classic car owner. In one of our cars is fitted the Smiths Radiomobile 980 (positive earth car) and very good it is too, but a shame there are so few MW / LW stations worth listening to. I would like to ask a question and the background is as follows:

Possible solutions so far identified is fit an auxiliary lead with a 3.5MM jack to take DAB radio, mp3 iphone etc. however an engineer I consulted advised against this on this model as follows:

“I wouldn't recommend fitting an mp3 lead, the amplifier in this set uses germanium transistors which are prone to failure, an mp3 player would place extra load on the amplifier and there's a good chance you'd blow it up.”

I could fit one of the very expensive converted radios or one of a range of new stereos for classic cars, but a digital panel is not really in keeping, and both require conversion to negative earth which I am averse to doing for reasons I will not bore you with.

An interesting option is a device that ‘taps’ into the aerial lead and ‘broadcasts’ the output from an external device directly into the radio. Of two versions of this I have seen on the market, the one with the track record (made in the US) broadcasts at 1000Mhz. The printed tuning range on the Radiomobile is 1100 – 2000mhz, although the indicator and tuning knob can go further than this. I note on American classic car radios the 1000mhz (or 10) position is in the centre of the range.

Questions
Is there a way of identifying the true range?

I might have at one time tried to tune in GEM am 999 or 945 but they are no more, and below 1100 on the radio is silent at my location (Chester / Wirral).

Is there a way of altering the range?

I look forward to reading your comments,

John.

[Edward Huggins]

As regards to the advice you have been given as to the use of your (usually well built) Radiomobile for MP3 output, that's a complete nonsense. Yes, germanium transisitors can fail like any other device, but all this about "blowing up" is nonsense. This make me despair of so-called experts. Yes, I think you can use a small local transmitter to generate an RF signal that can be received at an AM frequency on your radio. Of course you wiill only hear the signal in Mono. This will mean you don't need tamper with the radio at all other than to find a very quite place on the tuning range and tune your transmitted output to this. There are other Members, far better informed than me on this topic and hopefully they will place a Post for you. Edward

[ms660]

Originally Posted by Tiggers

An interesting option is a device that ‘taps’ into the aerial lead and ‘broadcasts’ the output from an external device directly into the radio. Of two versions of this I have seen on the market, the one with the track record (made in the US) broadcasts at 1000Mhz. The printed tuning range on the Radiomobile is 1100 – 2000mhz, although the indicator and tuning knob can go further than this. I note on American classic car radios the 1000mhz (or 10) position is in the centre of the range.

You won't get anywhere with the frequency range figures you've quoted, according to a picture of that radio I'm looking at the tuning scale is marked in metres, converting that to Khz (Long Wave) and Mhz (Medium Wave) gives:

LW (Long Wave)...150Khz to 272Khz.

MW (Medium Wave)...0.545Mhz to 1.5Mhz.

Lawrence.

One of these https://www.vintage-radio.net/forum/...d.php?p=839656 will work very well.

[Herald1360]

Returning to the American device, it's clearly going to be transmitting on 1000KHz not 1000MHz, and this frequency is slap bang in the middle of the medium waveband on your Radiomobile where it will be scaled as 300 metres. It should work just fine. America never used long waves, roughly 1000-2000 metres or 300-150KHz for AM broadcasting so a device operating in that band would be unlikely!

The incompatibility of germanium is as already said nonsense, but there is a possible problem with the positive earth aspect if your ipod or whatever is not operating on its own internal battery since the ipod will be a negative earth device. If it's being run from the car electrics then the +/- earth crossover could release the infamous Joe Lucas magic smoke

[Tiggers]

Thank you all. The metres / khz / mhz explanation is really useful, as is the caution if using a negative earth device. At least I am familiar with the smoke system and I will have a good read of the Minimods thread.

All the best,

John.

[Phil G4SPZ]

John,

I would also recommend a MiniMod. Having built a couple myself I can confirm that they work extremely well.

Other MW modulators were once or are still commercially available, subject to legal disclaimers, and you might find one second-hand. Search for "AM03", "Gizmo", "Spitfire" and "SSTRAN". I've used an AM03 and a Spitfire, but still suggest the MiniMod gives best value and quality of sound.

[Nuvistor]

Using a MiniMod at the moment, the quality of the audio puts the other "professional " MW stations to shame.
Frank

Edit, just don't overdrive the audio, it does not require much audio to sound excellent.

[Tiggers]

Dear Phil & Frank,

I have a number of contacts in the Classic Car world, so I have managed to arrange for an evaluation RediRad to be sent over to me, and in return I have agreed to report on installation and findings to the Classic Car clubs I'm in and the magazines they produce. Should be with me in around a week, and will copy report here hopefully within a fortnight. Would you suggest a new thread, or just add as a comment to this one?

Cheers,

John.

[JoshWard]

I have fitted MP3 inputs to many Radiomobiles with germanium transistors and never had a problem. It's usually cheaper than any AM transmitter I have seen although an AM transmitter does mean the radio is kept all original and undisturbed.

If using in a positive earth car I have had success with ground loop isolators in the audio line. Also worth using if you want to charge your device from the cigarette lighter whilst listening to it through the radio.

[Tiggers]

If using in a positive earth car I have had success with ground loop isolators in the audio line. Also worth using if you want to charge your device from the cigarette lighter whilst listening to it through the radio.

Forgive my ignorance, but would you be willing to explain a little more please? Charging via cigar light is an attractive option, but I presumed a positive earth DC input would fry most of today's gadgets.

Thanks,

John.

['LIVEWIRE?']

A Ground Loop Isolator does exactly what it says 'on the tin'- i.e. it isolates the earth of one device, e.g a radio or amplifier, from that of another, such as your car. It's essentially a transformer.

[JoshWard]

Yes, they use a small isolating transformer in each audio channel. Saying that the earth of the volume control (which is where an MP3 input lead would connect) in a typical Radiomobile with Ge transistors is not true earth and is in fact at 12v anyway. To overcome that some isolating capacitors in the signal path are a good idea and essential in a negative earth car in case the live jack plug contacts any part of the bodywork.

Most ground loop isolators come with RCA connectors but these are easily snipped off and a jack plug/socket arrangement can be used to fit them in line with an MP3 lead.

[Phil G4SPZ]

Originally Posted by Tiggers

Would you suggest a new thread, or just add as a comment to this one?

Both, probably, John. RediRad is a new one to me, and it would be interesting to hear how their modulators perform. Perhaps if you were to start a new thread about your review in the "General Vintage Technology Discussions" or "Components and Circuits" section, then post a link to it in this thread, it would get most attention.

It's perhaps a pity that they have designed their units for 6 or 12 volts power input, rather than running off a self-contained battery. Also, from the pictures on their website it appears that their units have a Motorola car radio aerial plug and socket on flying leads, for permanent connection in-line with the aerial feed to the car radio. Whilst these factors make for more sales, it does mean that the unit is basically stuck in one car and not portable. They say they're going to launch a model for home use though.

[cheerfulcharlie]

How about something like these?

http://www.ebay.co.uk/itm/New-Car-LE...UAAOSwvgdW3-5f
http://www.ebay.co.uk/itm/DC-12V-TDA...IAAOSwv9hW4niq

you could put them in an isolated plastic box and use your imagination to hide them in the car.

[Tiggers]

Pretty fab things aren't they?

The RediRad has been shipped so I will give it a try, and an attractive feature is the lack of modification and ease of removal / return to original spec. If it works okay, might replace / recone the speaker, as I'm sure after 50 years in the car it will have lost something.

Thanks to 'LIVEWIRE?', Phil G4SPZ and Cheerful Charlie for explanation and forum advice.
Hopefully should have review in a week or so and will start a new thread to post it.

[Edward Huggins]

Why do you think you need to re-cone the speaker - is it still working? If so, leave well alone. If you still feel obsessive about it, take the speaker out and check over the cone, if it does not "grate" when moved, it be OK. Re-coning is not easy especially for such a small car speaker as this. A modern 4 ohm replacement with soft-cone suspension and whizzer cone will of course sound good, but do remember your Radiomobile is AM only. Edward

[Tiggers]

Thanks Edward, just thinking out loud really, and I appreciate your experienced advice.

[Tiggers]

Apologies for the delay in posting a write up of the 'Redirad' gadget, the package has been stuck in UK customs since 24th May.

[Tiggers]

Unit finally arrived, and then I have had nearly a month of 12 hours a day, 7 days a week work, but managed a free day yesterday, so fitted the unit. I review as follows:

An attractive feature in my 1966 Jag is the original Smiths Radiomobile radio fitted by Henlys when new, and the appearance and sound quality is very good despite being a LW / MW only unit. Unfortunately, there are nowadays nearly no radio stations worth listening to still broadcasting on MW/LW. I did not want to go down the route of converting to negative earth and fitting a modern stereo, and wanted to retain the original unit and sound quality. The solution is what is known as a ‘wired modulator’ and there are a few variants available in the marketplace, but the one I have settled on is the Redirad, designed and manufactured in the US. What this does is connect iphone, mp3 player, smartphone, CD player, whatever makes sound and has a 3.5mm output socket, directly to the original radio via the antenna lead. The unit is small (a little larger than a pack of playing cards) light, and easy to connect. The case seems sturdy, and the wires, particularly the antenna male & female leads are of a very good quality. Instructions are clear, and adapters to allow connection to existing fused power supply are included. The power and earth wires around 5 feet long, the 3.5mm jack lead is around 6 feet long, although the antenna connectors are short, it is designed to be located near where the antenna leads enters the radio itself. I did find also a short series of videos on youtube showing one of these being fitted to a 1980’s BMW (FM version). The only difficulty if there is one, and this will vary from car to car, is the routing of wires etc. The unit is designed for the very widely used ‘Motorola’ type aerial lead connectors, but adaptors are widely available online for around £5 if your car or radio is fitted with a different set up.

Unplug radio antenna from radio.
Plug RediRad into Radio antenna socket.
Plug Antenna lead into RediRad.
Electrical connection is one to an ignition controlled power supply, and to earth.

That’s it, and you are left with a lead (with a 3.5mm jack) to plug into whatever you would like to play. I have placed the unit in my car behind the facia just on top of the radio itself, secured with cable ties (again included in the pack). Connect up the player, and tune in on the radio to 1000KHz (the ‘10’ position on some radios, or 300 metres.) I have tried an mp3 player, Nokia smartphone and an iphone, and all work fine.

Available for positive & negative earth cars, 6 or 12v, and there is an FM version for cars fitted with FM radio. The sound quality is as good as the radio amp & speaker, adn I like the tone of modern music on my cars single 6” speaker. Not just for music; plug in your smartphone and you have effectively got a hands free installation, (and in my car the unused ashtray is the perfect cradle for a phone) with the inbound call being heard through the radio speaker(s), as you would with a modern hands free system, and if you want to use the satnav on a phone, again, it will play through the radio.

On ebay, they can be bought for around $100.00, but shipping and import charges (including VAT) mean the total price paid in the UK is around £120.00 - £130.00, plus hanging around in customs etc. I have seen cheaper variants from China (although western ‘branded’) but these don’t have the track record of the Redirad, which the manufacturer tells me is used by thousands in the US, and around 100 a year are sold to UK customers. An online search reveals favourable reviews, as is this.

I am very pleased with the Redirad, and I didn’t know this old radio in my car could sound as good as it now does. As to transferring from car – car, well if I had more than one car that I used regularly that did not have FM or CD player I would probably install a unit in each, and would consider it an added feature when it came to sell the car.

I am so impressed I have arranged with the manufacturer, to offer units to members of classic car clubs at a discounted fully inclusive cost, and they will be sent from my UK address, so no hanging around for customs etc.

I hope this covers all the bases, but I will attempt to answer any questions if there are any.