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  #1  
Old 12-23-2013, 01:18 AM
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How Do I Wire Four Speakers In 1965 W111 220S With Mono Radio?

I have been tinkering with my roommate's 1965 W111 220S. He wanted to replace the aged and damaged original mono speaker in the dashboard with four speakers.


He bought a pair of 4" Boss 200W 4 ohm speakers for the front. They didn't exactly fit because they are wider than the original speaker, but I used a rotary tool and cut a section off of the sides of the speakers.


I also had to bend in the tabs to get the clearance I needed.


Once the speakers fit into the opening, I cut out a brace from a thick piece of steel, then drilled and threaded some holes.


The speakers fit nice and snug with the brace in place. I wedged a cloth in where the speakers contacted the body, and used it to keep dust off of the speakers. Since it can be seen through the speaker grille, I made sure it was black.
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1967 W110 Universal Wagon, Euro, Turbo Diesel, Tail Fins, 4 Speed Manual Column Shift, A/C
1980 W116 300SD Turbo Diesel, DB479 Walnut Brown, Sunroof, Highly Optioned, 347,000+ Miles
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  #2  
Old 12-23-2013, 01:50 AM
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There was enough clearance for the speaker grille to fit in place.


In the rear (behind the headrests), he installed a large pair of Acoustic Audio 200W 8 ohm speakers. At some point, we may replace them for something more tasteful.


This is what his Grundig mono radio looks like:


He did not want to install a modern radio as he wanted the original look. However, an MP3 player or other device can be attached to the original auxiliary input in back with the proper 6-pin DIN cable, so he will be able to enjoy his music.


First question: I am not exactly sure how to wire the radio for power.
I am assuming there was originally a special plug that plugged into the two connections at the bottom right of the rear of the unit. I am assuming the large prong is positive, and the small prong is negative, but I don't like assuming things. Off to the side of the two prongs is marked 12+. I know that there is a prong for ground on the left side of the unit.

Second question: I am not exactly sure if it is safe to wire four speakers to this radio without damaging it. This radio has only two speaker wires; a positive and negative to power one speaker only. I still have the speaker wire plug that fits into the speaker holes just to the left of the power prongs.

Please understand that I have spent several hours today researching wiring a mono radio to four speakers, but I am just not finding the information that I need, and I think that asking for help will save time.

I have read that wiring the speakers in series would lessen the chance of frying the radio, but at the cost of volume, and that there is still a chance of frying the radio. I think that connecting a modern amplifier to the radio will sufficiently power the four speakers without straining the radio, but I am not sure. I'd hate to find out after cranking up the volume that the radio is dead. Is there any danger of frying the radio if I use a modern amplifier?

There are two 4 ohm speakers in front, and two 8 ohm speakers in rear. I am assuming the radio was only built to power one 4 ohm speaker in front. I thought that in electricity, the lower the number of ohms, the less resistance is in a circuit, but it seems that the reverse is desirable with speakers? I don't get it.

I appreciate the help. Once again, I am diving into something that I don't quite understand.
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1980 W116 300SD Turbo Diesel, DB479 Walnut Brown, Sunroof, Highly Optioned, 347,000+ Miles
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  #3  
Old 12-23-2013, 02:39 AM
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Do you know the radio drives a 4-ohm or 8-ohm speaker? This is what you can do.

Run the front 2 4-ohm speakers in series which gives you 8 ohm. Run the back 2 more in series which gives you 16 ohms. Hook both sets up in parallel. That should give you about 5 ohm load to your radio. I think it should be OK. Ideally you need to get a speaker configuration to match the radio load. If the back ones were 4-ohm speakers then it would match perfectly.

Disclaimer: Mono radio is dying species so I have not done it myself. Others can chime in.
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  #4  
Old 12-25-2013, 12:48 AM
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Thanks for the reply. I don't know for sure what the ohm rating of the original speaker is, or what load the radio can handle.

I was hoping that since people love the original radios, and it is common to now use MP3 players with them, that there would be others here that had upgraded the speakers in their vintage Mercedes.
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1967 W110 Universal Wagon, Euro, Turbo Diesel, Tail Fins, 4 Speed Manual Column Shift, A/C
1980 W116 300SD Turbo Diesel, DB479 Walnut Brown, Sunroof, Highly Optioned, 347,000+ Miles
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  #5  
Old 12-25-2013, 02:08 AM
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I did the math on your recommendation, and I actually got 6 ohms instead of 5, but I am new to this. Still, I think it would be acceptable. Doing some research, the original mono speaker seems to be rated at 4 ohms. So, as long as there are 4 ohms or a higher number of total impedance, then it should be safe for the radio. 6 ohms is very close, so it should be acceptable.

So, at this point, this is what I will try. Any disagreements? I believe wiring the fronts together in series, wiring the rears together in series, and then wiring front and rear sets together in parallel will give me a safe number of 6 ohms of impedance.

So, this will be safe for the radio, and the only downside I can see is that the speakers may not put out enough volume, but this can be determined once the speakers are wired.

If the volume is not acceptable, then I would need to use an amp, but I would need to make sure that the amp will not fry the radio.
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1967 W110 Universal Wagon, Euro, Turbo Diesel, Tail Fins, 4 Speed Manual Column Shift, A/C
1980 W116 300SD Turbo Diesel, DB479 Walnut Brown, Sunroof, Highly Optioned, 347,000+ Miles
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  #6  
Old 12-25-2013, 02:31 AM
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The impedance of the final configuration should be R below, 1/R = 1/8 + 1/16 as it is in parallel. R should be 5.333 ohm. I round it up to be 5 ohm. Do you have the original speaker? It should tell you what ohm value you need.

The volume will depend on the efficiency of the speakers. I believe it would be OK. Wiring an amplifier should be OK as the input impedance of an amp is very high. You would never fry the radio. You just need to match the speaker configuration to the output of the amp.
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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

2 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.
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  #7  
Old 12-25-2013, 03:00 AM
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I looked up the output of the radio, and it is 5W, 4 ohm. So 4 ohms or higher total impedance should be safe.

I am also assuming that if the input impedance of the amp is 4 ohms or higher, it should be safe.
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1967 W110 Universal Wagon, Euro, Turbo Diesel, Tail Fins, 4 Speed Manual Column Shift, A/C
1980 W116 300SD Turbo Diesel, DB479 Walnut Brown, Sunroof, Highly Optioned, 347,000+ Miles
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  #8  
Old 01-01-2014, 03:00 AM
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I wired the radio. It powers on, but absolutely no sound is coming from the speakers. The speaker connections on the refurbished radio are dead.

I touched a 9-volt battery to the banana connectors on the speaker wires and could hear a crackle and pop, so sound is getting from the connectors to the speakers.

Something must be shorted out inside the radio. How disappointing.
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1967 W110 Universal Wagon, Euro, Turbo Diesel, Tail Fins, 4 Speed Manual Column Shift, A/C
1980 W116 300SD Turbo Diesel, DB479 Walnut Brown, Sunroof, Highly Optioned, 347,000+ Miles
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  #9  
Old 01-02-2014, 01:51 AM
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I chatted with the seller of the radio, and he thinks that the banana plugs I used were too long, which fried the internal amplifier. So, now the radio has to be repaired.
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DON'T MESS WITH MY MERCEDES!


1967 W110 Universal Wagon, Euro, Turbo Diesel, Tail Fins, 4 Speed Manual Column Shift, A/C
1980 W116 300SD Turbo Diesel, DB479 Walnut Brown, Sunroof, Highly Optioned, 347,000+ Miles
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  #10  
Old 03-12-2014, 02:47 PM
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The radio was repaired locally. There were burnt traces and it appears something internal may have been wired incorrectly. Wiring the speakers in series-parallel worked great! There is ample volume and great sound. The MP3 player plugs into the back, as well.

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1967 W110 Universal Wagon, Euro, Turbo Diesel, Tail Fins, 4 Speed Manual Column Shift, A/C
1980 W116 300SD Turbo Diesel, DB479 Walnut Brown, Sunroof, Highly Optioned, 347,000+ Miles
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