Using old german head unit as a 'remote'?

Hi, 
I want to get a nice old early 70's blaupunkt or grundig head unit,  one with twisty knobs and no screen/cassette. 
If I am correct, then they are mono. My original plan was to use this,  maybe through an amp, but I would much prefer stereo sound, and my speakers are designed to run off a modern head unit,  and don't need to be amped. 

I was thining- would it be possible to get a old non working hu, and use this to control a modern head unit, hidden out of view (under seat, under dash or glove box)? 
Basically, I would want the on/off, volume and radio knobs to control the modern unit,  and one of the buttons at the bottom to select between ipod and radio. It would be great if I could get the radio dial on the front to show the actual frequency too. 
Am I asking too much? I am pretty sure I have seen something similar for sale, but big money.  Oh and no retro sound units please,  I personally think that they look terrible! 
Cheers
Rob

serious electronic work there complete rebuild,

you can get remotes for a modern head unit, mount it in the glove box or summit, just have the old one on show

Thanks. Do you not think the dials in the old hu could be wired into the remote? Or even a new stereo amp wired in? Or maybe there is a way of taking the pre amplified radio signal and sending it straight to a small external amp, and wiring up the volume control to this? Just thinking aloud. 

As JB says even that sounds like massive ball-ache for very little gain. Why not have something hidden completely as mentioned already ?

Do you think it would be possible to find the pre amped radio out and wire it directly to an amp? Then use the volume control to control the amp? I could have a remote, but that's still on view. I just really like the idea of using an old head unit,  they are also fairly simple to use whilst driving (yeah true,  a remote is too!) 

its a right can of worms

there's a company out there that put new insides into old units, i found it years ago, think it was german but were mega money

or just google retro car radios and found these

http://www.classiccarstereo.co.uk/classic-car-audio.html

but to do what you want to do at home, makes my bits tingle with pain!

Agree with JB, even with extensive experience in electronics it is very hard to do. I did build one once for myself, never again! Not used Classic Car Radios personally, I worked with older cars and had a company that rebuild valve radios to latest spec radios, but they were MUCH more expensive.
If you want an updated retro radio buy one from a company.

Aw you guys are no fun  Ok fair enough, point taken.
Is there no way of taking the pre amplified signal of the radio and taking it to a car amp? 

Yeah, but again it requires specialist knowledge of the particular radio, unless you want to damage the radio and/or the amp. It's possible to find the right points with an oscilloscope and then run leads from there, oh yeah, you might need to fit either a pre-amp or buffer depending on voltage levels and impedences, did I mention it is not as easy as it souinds?

Jon

Hmmm…  Sounds tricky,  but I love a bit of a challenge, and I feel it may help and reinforce the physics a level I am taking.

I expect if I was to ask nicely enough, I could use an oscilloscope at school. What would I be looking for? Then would you just measure voltage levels with an ac multimeter, or the oscilloscope? What about impedance?
If it proves too difficult I could always leave it and go the other route, or sell the hu on.
 
Oh and a question that has been bugging me- from where is the radio mono? Right from where it receives the signal, or later down the road? 

A little googling shows that a 1976 model blaupunkt frankfurt is a stereo unit. If I got hold of one, could I simply use one of those signal reducer things, and connect it to a small amp? 

Sorry for all the annoying questions,  just electronics is one thing that I would like to get my head around. 

OK, you asked for it, here it comes both barrels, but I'll be kind and go through it one bit at a time:

The easiest way to find a suitable output point for an external amplifier without a diagram:

Power up with the casing open, tuned to a stereo station and follow the speaker output to the power transistors, normally screwed to the casing to help dissipate heat. Put one channel of an oscilloscope on the speaker output, carefully probe the connections around the power transistors with the second channel (I'm assuming that you can lay your hands on a 2 channel scope) until you find a point the wave form matches that of the speaker waveform and is between 200mv to 1 volt peak to peak (the input signal may be the inverse of the speaker wave form). Do the same for the other channel. If you've got it right, pipe this into an amp and you are now boosting the audio output. Normally at the pre-amp point in a radio there is very little distortion created by the receiver and decoder.

Using a scope will give a visual conformation that you have the right signals.

If you can find a pre-amp output impedance is not too much of a problem.

Depending on the internal construction your volume and tone controls may or may not affect the signal output.

For understanding the way stereo radio is transmitted and receiver try reading this, read the paragraph headed stereo FM it's a bit wording and the equations at the beginning of the article are not necessary to understand the basic operation of a stereo receiver.

It is possible to use the speaker output to power an amp, but you would need to build a buffer unit to match the original output impedance of the radio (speaker impedance) 4,8,16 ohms or whatever of the right power rating, or else the output will be distorted and you can damage the output transistors of the radio.

For a basic understanding on how to build an impedance matching Pi resistive network read this. In fact, if you want to learn electronic you might want to read all the tutorials on this site.

Jon

Fabulous post there Jon. My brain hurts just reading it    

Gotta say Rob,, if you undertake this one your definatly up for a challenge!!  

Ah Jon, thanks so much! I am going to need a while for my brain to digest that, but I will try and read through some of those articles.
I am going to ask my physics teacher about the oscilloscope if I get a chance!
Would it be possible to get an MP3 feed in there somewhere too so that can be controlled with the volume knob?
Yup, I am difficult, but I would really like this 'right'. It is one thing that I am being really picky on. Just l really think it would be awesome getting 'modern' sound through a period radio.

Should the volume control not work, (and even if it did, I would assume it would be mono, and therefore my MP3 signal would be mono too, which defeats the point of this!) would it not be easy enough to install a new one in the form of a potentiometer, either before the input to the amp, or wired from the amp?

Once again, thanks for the help!
Rob

Edit: Gordonthegolfer : If it doesn't work, I may loose out on some time, and possibly damage an old head unit (which could still be used for display.) I would however gain some knowledge, which is always good. If it does work however, I would have a period HU with half decent sound, and decent power (50w or so, instead of 4w), and I will have gained a lot more knowledge. I need to get a head unit first, come on Germans, stop outbidding me!!!

Rob, the short answer is yes but, there's always a but, depending on the construction of the radio you may be able to use the same point as you would use for the output, if the volume is contoled in the pre-amp, which is the normal way then you would need to find the audio signal(s) after the decoder and before the pre-amp.
A brief description of how the decoder works is in the Wiki article chapter Stereo FM.
The output would be in stereo.
To beating the Germans at their bidding is the same as beating them to the sunbeds on holiday,.

To the rest of you reading these posts, I am not trying to hurt brains, just trying to explain that whilst it might be posible to get lucky, to do something like this requires a good electronics knowledge, either professionally or by hobby. To someone who repairs TV and radios all day this is easy meat, but would you want them to do a head gasket for you!, unless of course their hobby was classic cars.

Jon

Thanks. Found a couple of radios that look like they have potential on ebay de. They are both quite scruffy which will hopefully put people off. Then a rattle can and some silver paint pen, and they should be looking nice. Both end in 5 days . Hopefully I will win one of them! They both have vw stickers on the side which is pretty cool too. Probably too early for my car, beetle, camper or ghia era, but I am no purist. 

Just remembered a cheap and easy trick for mp3 player etc.. Buy a period radio cassette player, must be one WITHOUT auto-reverse. Buy one of these (they can be found cheaper else where) plug anything that has a headphone socket in it .

Jon

Thanks. Thought of this, but I don't like cassette players for some reason! 

Oh its certainly not a criticism dude, just complimenting your determination  

Haha yeah I know silly  just saying that I don't have a lot to loose.