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Old 15th Jan 2020, 10:24 pm   #1
DJDUNKY
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Default Blaupunkt Frankfurt UK radio circa 1965

Hi all,

I have a 1965 Blaupunkt Frankfurt with FM which I believe is a fairly rare UK unit.

I want to put this in my 1965 VW splitscreen but the output would not be high enough for the noise!

The radio is mono and has 3 x jacks for banana type plugs for either one speaker or two (parallel) connection.

I was thinking about using a line converter to change the speaker inputs to an amp to RCA.

Is there a better way to do this to have 4 x speakers connected?

Thanks in advance.

Duncan
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Old 16th Jan 2020, 6:19 am   #2
'LIVEWIRE?'
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Default Re: Blaupunkt Frankfurt UK radio circa 1965

Hi, Duncan. Radios similar tp yours used to be fitted in split-screen VWs, and many other cars of the day, but, to answer the question, the easiest way to get more volume, or, more correctly, better sound distribution, is to fit two speakers. I'm not sure if it is wise to connect 4 speakers to a mid-sixties Frankfurt, but, at one time, Booster Amplifiers were available from Blaupunkt and others, which could raise the output to around 20 watts, though most were stereo. Blaupunkt radios also used to have a 5 or 6 pin DIN socket to allow for the connection of an in-car tape player, though this may not have been until later. If this is present, the signal from there could be used to feed a higher power amplifier. Can you post pictures of your Radio, showing the connections on the back, please. It will help to identify what is possible to connect to it, though I have to say that in those days a maximum output of 6 or 7 watts was all that was available from any car radio. Booster amplifiers didn't appear until the early 70s, IIRC. You're right that any FM car radio of that era is rare in the UK, as all the available stations back then were on MW & LW, so few thought the added expense of a FM set necessary. Incidentally I don't think any Blaupunkt radio ver used banana jacks - they all used DIN speaker sockets.
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Old 16th Jan 2020, 1:04 pm   #3
Leon Crampin
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Default Re: Blaupunkt Frankfurt UK radio circa 1965

The early Frankfurts (circa series V) had 4mm sockets for the speaker(s). They were arranged in a trapezoidal form, such that the centre pair was used for a single speaker and the two outer pairs for twin speakers. The output transformer was tapped accordingly.

It might be helpful to know the series letter on the paper label of your set. In general, running on a 12V supply, these sets have plenty of audio output if the bias is correctly set (but change the selenium bias diode in the output stage and reset the quiescent bias current before you start). The bias diodes have a habit of failing open circuit and cooking the output stage.

Using efficient speakers of the correct impedance (I think 5 ohms - but check) I would be surprised if there was insufficient output - unless your car is insanely noisy, in which case a radio might not help anyway....

Leon.

Last edited by Leon Crampin; 16th Jan 2020 at 1:14 pm.
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Old 16th Jan 2020, 2:34 pm   #4
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Default Re: Blaupunkt Frankfurt UK radio circa 1965

Leon, of course you're right that BP used 4mm speaker sockets until c.1970-71. I should know, I've repaired enough of their radios & stereos in my time, particularly between late 71 & mid 95. AS to speaker impedance, IIRC, like almost all car radios, this was nominally 4 ohms.
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Old 16th Jan 2020, 8:05 pm   #5
DJDUNKY
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Default Re: Blaupunkt Frankfurt UK radio circa 1965

Thanks for your replies.

The reason for the amplifier was to have 4 channel output.

I have tried to put some photos up but not sure they will appear. Here goes...

https://ibb.co/CVzSzm3
https://ibb.co/60mzyBZ
https://ibb.co/yYxNNSQ
https://ibb.co/RvS1vpf
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Old 16th Jan 2020, 10:40 pm   #6
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Default Re: Blaupunkt Frankfurt UK radio circa 1965

Because your Frankfurt is Mono, it would be difficult to connect it to a four-channel amplifier, since the output would need to be divided into four parts, whilst maintaining the correct loading (nominally 4 ohms) on the radio's output. You cannot simply connect the output of your radio to four inputs in parallel, besides which, as I previously mentioned, what is called a Booster Amp. - i.e. one that can accept speaker-level inputs - would be needed. I'm not sure if anyone makes such a thing any more. One way this sort of thing used to be done was to connect a fader control between the output of the radio and the inputs to amplifiers, but these were only made to connect a radio to a 2-channel amplifier (as far as I recall),, though some 2-channel amplifiers could drive four speakers. When your radio was made nobody thought of adding amplifiers to them.
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Old 16th Jan 2020, 11:55 pm   #7
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Default Re: Blaupunkt Frankfurt UK radio circa 1965

I have purchased a small Pioneer amplifier which has 4 outputs but can accept to or 4 inputs.
I also have seen line converters that can turn the hi level speaker inputs into RCA low level. However this doesn’t seem to make much difference.

I can get sound but even on the minimum volume it is very loud and the ‘noise’ is very scratchy.
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Old 17th Jan 2020, 10:02 am   #8
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Default Re: Blaupunkt Frankfurt UK radio circa 1965

I don't have an easy answer to that problem, Duncan. A speaker level tp line level converter should in theory be OK, but bear in mind that you are connecting a mono radio's output to a stereo amplifier, so the output from the radio needs to be split between two inputs via resistors. Have you also taken note of the points raised by Leon Crampin in post #3 above i.e. that the radio may have an internal fault. As Leon says, the Frankfurts of that era have plenty of audio output to produce more than adequate volume and drive efficient 4 ohm speakers. If using two speakers, connect them in parallel to the RH pair of speaker sockets as viewed from the rear of the radio. With four speakers a fader control is, as I said, needed. Maybe it's a generational thing, but, to me, you are trying to find a 21st. Century to a solution, which, in the mid 20th. century, didn't exist. Radios of that type were fitted in all the makes & models of cars then available, using only the output facilities provide by the makers, and worked adequately that way.
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