Using old german head unit as a 'remote'?
Posted
#1251503
(In Topic #149978)
Old Timer
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
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Old Timer
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Old Timer
Last edit: by r_chez_08
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Moderator
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Old Timer
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Old Timer
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!
Posted
Settling In
If you want an updated retro radio buy one from a company.
Posted
Old Timer
Is there no way of taking the pre amplified signal of the radio and taking it to a car amp?
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Settling In
Jon
Posted
Old Timer
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.
Posted
Settling In
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
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Moderator
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Moderator
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Old Timer
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!!!
Last edit: by r_chez_08
Posted
Settling In
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
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Old Timer
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Settling In
Jon
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Old Timer
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Moderator
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Old Timer
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