How can I externally amplify Blaupunkt Mannheim radio?

[Dennism]

Hello to all,

I am new to the forum and have just bought a 1971 Blaupunkt Mannheim.

My convertible car has four, 4 ohm speakers in it and with the radio outputting about 5 watts, I look for some amplification because there is wind noise with roof down!

I think my options are to get an external amplifier with "speaker inputs" which means I can put the mono output into the amplifier, OR perhaps I can get some preamp output through the DIN connector on the back of the radio.

I would be really grateful if there is anyone with experience who can advise me on these two options.

Thanks

Dennis
Vancouver

[Mike. Watterson]

You'd need to make sure your speakers are suitable for the new amplifier(s). Note the power rating stamped on speakers is often very optimistic. The inputs can be connected direct to the existing radio, though I'd put 33 Ohm 0.5W resistors as dummy loads on the existing outputs. You don't need an amp with "speaker inputs".

[Dennism]

Thanks Mike.
I have 4 four ohm speakers and if I have two set of speakers in series (8 ohms) and I then parallel them with another two, the amp will see four ohms resistance which is what the blaupunkt puts out (It has one mono channel)
I am new to radio technology and don't quite understand what you have written. I thought that amplifiers that I would buy either need the radio preamp output or some amplifiers can accept speaker inputs from the radio.

[Herald1360]

Not that likely by '71, but if it's a classic convertible beware it isn't positive earth.......

[Mike. Watterson]

ANY amp can easily take the speaker output connections as inputs.

[Refugee]

I once bought a cheap bridge amp and opened it up.
It had a potential divider to reduce the speaker output to suit the chips within.
It was something like 47 ohms and 10 ohms to reduce the signal down from 10 volts peak to peak to about 1 or 2 volts.

[cheerfulcharlie]

...
Have a look for C56 and see if the track goes to the din socket possibly pin 1-
this should be the output of the tuner to the amp?

pins 3 and 5 of the socket should be earths?

Pins 1 and 2 have a bridge which you can break to stop the internal amp interfering with your new amp connected to pin 1.

All if I am thinking of the right model

['LIVEWIRE?']

If the Mannheim has a 5 or 6 pin DIN socket fitted with a blanking plug, then cheerfulcharlie is right. Pin 3 is the signal ground, whilst pin 5 is the DC Supply (normally negative) earth. This output can drive an added amplifier, but, because the Mannheim is a mono radio it will be necessary to divide the signal between the two channels of any added amplifier, which will almost certainly be stereo. A resistor of (say) between 3 & 10k in series with each channel's input, joined together at the radio end, should suffice. Referring to Mike. Watterson's comment in post'5, with respect, that is not strictly true. When I worked for a B;aupunkt main dealer back in those days, their 'Booster' amplifiers as they were then called, usually had dedicated Speaker Level inputs, which had a low-value - 10 ohms or so - load resistor across their inputs, plus an attenuator/matching network to reduce the 5 watts or so max. o/p from the radio's internal amplifier to maybe 200mv in order to match it to the Booster's input. Somewhere I still have circuit diagrams which explain this perhaps better than I have.

[cheerfulcharlie]

Thanks Livewire for confirming which Earth is which.
.does pin 4 carry the 12v+ rail ?
from which one could connect a relay (don't rely on the ancient circuit to carry enough current) to switch on the new booster with the radio knob

['LIVEWIRE?']

Yes, Charlie, pin 4 on those 5 or 6pin DIN sockets is a switched +12v* line intended to operate the relay or electronic switch in Booster amplifiers. It should only be 'live' i.e. have the 12v. on it, when the radio is switched on. Generally speaking, the switched +12v 'automatic aerial' supply can also be used to turn an added amplifier or tape player/recorder on and off. (all Blaupunkt and some other makes of car radio were factory fitted with the automatic aerial supply) *If the radio is, as I'm sure the Mannheim is Negative Earth

[Dennism]

Thank you all so much for the replies. I am very grateful for your help and have some questions

1) Regarding "Speaker Input" to an Amplifier versus Input from from DIN pin 1.

Is there a reason I should use DIN pin 1 as input to an external Amplifier as opposed to simply taking the radio's mono output and feeding it into the amplifier (as I think this is what "Speaker Input" means). Excuse my ignorance on this!

2) Mono signal output and dividing it.
Can I not simply feed the mono input into a one channel amplifier and then drive four, 4 ohm speakers that consist of two speakers in series, then paralleled with another two (which means the amplifier sees 4 ohm resistance)?

3) Might anyone have an internal wiring diagram of the 1971 Blaupunkt Frankfurt
And while I am asking about this, is there anything I can do internally in the Franfurt to optimize the quality of the radio output signal?

4) Anyone have the pinout key for the DIN socket?

Many thanks

Dennis

[Dennism]

OOPS. I meant model Mannheim in my last reply. Not Frankfurt!!

['LIVEWIRE?']

I may have a circuit diagram for a '71 Mannheim somewhere, Dennism. If you can quote the part Number which begins 763xxxxxxxm from a label which should either be on the back or one side of the radio, along with it's serial no., which is prefixed by a letter. This info. isn;t essential, but will help as I have a large no. of Blaupunkt service manuals & diagrams, and, over the yr=ears BP used the same model name on a variety of differing sets. I'm not sure what you mean by 'optimisingthe quality of the radio output signal' In my experience, based on 23 years of servicing Blaupunkt and other makes of car radio & stereo, their radios always produced decent quality audio. Obviously the strength of the received signal affects the quality of reproduction, and, in turn, the type and state of the aerial and aerial cable used affects the sensitivity of the radio AS far as which output to use is concerned, the signal at pin 1 of the DIN socket is at so-called 'line level', whilst that at the speaker sockets is high level, low impedance, so is better suited to a booster amp with speaker level inputs. If a suitable mono amplifier is available then you could do as suggested in your point 2, as long as the correct impedance load, usually 4 ohms, sometimes 2 ohms(intended to drive 2 x 4 ohm speakers in parallel) is presented to the amplifier, which, in your example it would be. AFAIK, the speakers fitted in buses & coaches were often wired that way for that reason. Whether a mono car booster amplifier is available now, I wouldn't know. Even years ago most were either stereo or 4-channel.

[Dennism]

Many thanks!
The serial number is 7631 330 000
Dennis

[cheerfulcharlie]

Doh! I had forgot all about the volume control, as you would need to tap a new power amp into that, and the Din plug maybe confusing....

So probably connecting straight onto the speaker output with a 'booster' amp is the way to go.. a good booster will have presets so that you can adjust the action of the volume control so that it fades up and down normally without any sudden loudspots . You can then measure which pin on the din has the 12+ rail
to switch it on with. The one down turn is that if there are any faults in the senile internal amp they will of course be magnified by the booster.

['LIVEWIRE?']

Dennis, I haven't forgotten that you're looking for a circuit diagram for your Mannheim, just haven't had time to look for one yet. Regarding Charlie's comments about the volume control, the connections at pins 1 & 2 of the DIN socket, are, IIRC, taken from the control in any case. The switched +12v is, again, IIRC, on pin 5 of the DIN socket, as well as on the automatic aerial connection.

['LIVEWIRE?']

Apologies for not getting back to you, Dennis, but I haven't yet found my Mannheim Circuit Diagrams-I probably have 100 or more Blaupunkt car radio Service manuals & diagrams, some of which are in BP binders, but quite a lot are loose copies in a Filing Cabinet drawer in no particular order, and mixed in with manuals for other makes & models of radios, etc. (I really must sort that cabinet out sometime!!)

[Dennism]

I do appreciate you having had a look!
Dennis

['LIVEWIRE?']

I have found a circuit diagram for a Blaupunkt Mannheim, but it's for the earlier 7639300000 series, dating from around 1968-69. That model has no 5-pin DIN socket, is dual polarity, and uses germanium transistors (AF121 & 126) in it's RF/IF stages, so differs considerably. from the 7631330000 model. Dennis, I can e-mail you a copy if it will help, but I may have the 7631 diagram somewhere.