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Tuesday, November 25, 2014

Beogram 4002: Signal Path between DIN5 Plug and Cartridge, Plug Replacement

I finally wanted to try out the Beogram 4002 that I am getting ready for the 21st century. While everything seems to work now, the DIN 5 plug looked really bad. Rusty and bent...so I decided to replace it with a modern quality plug (Neutrik AG Rean NYS 322G) with gold plated pins to ensure lasting contact at my Beomaster 6000 Aux input. Here is a pic of the old plug...pretty ugly! Not sure what the previous owner was up to...:























Before I soldered the new plug on, I noted the signal path down to ensure that I would make the right connections after cutting off the old plug. Here is a schematic of my measurements (note that the cartridge connectors are shown on a mirror that I held below the arm):

















It is interesting to note that the cartridge is essentially directly connected to the amplifier with the recommended 'star arrangement' ground (all ground connections come together at one central point and loops are avoided). The Beogram has its ground connected to the chassis, which could cause a ground loop if it were connected to the phono preamp ground and there were a conductive connection between the Beogram chassis and earth (usually the Beogram chassis floats due to the isolating feet and the absence of a earth connector at the standard two-prong power entry). The shield of the cable, however, is connected to the chassis, and will make a direct connection to the amplifier chassis, i.e. in the end the Beogram ground is connected to the amplifier ground. But this should be o.k due to the star-arrangement, even if there is a potential difference between the two units. And indeed, I was not able to discern any hum from the speakers after hooking the Beogram up.
Another interesting detail is that the back channel connections are fed to the plug, even in a 2-channel Beogram 4002 or 4004. I guess, when these decks were new, the CD4 upgrade was available for an easy plug-in at the Bang & Olufsen dealerships. Sometimes, I wish I had a time machine!...;-)

Here are a few pics from the plug replacement procedure. This was actually not trivial due to the heavy duty double shielded cable, which required a few sweat producing manipulations of the 22 gauge leads that carry the signal, while soldering on the heavy duty shield and signal GND connection:























And here the final result: 























Just hooked the Beogram to my Beomaster 6000, and it sounds beautiful! Andrew Hill: Dance with Death on an original 1970s Blue Note pressing. Fantastic!

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