I've taken on a project to get my father-in-law's well-cared-for Beogram 4004 up and I'm running into an annoying hum that only seems to show up with my nicer phono preamp. I'm already expecting this to be potentially expensive and futile but hey might as well try!
It's not a super loud bass-y ground loop hum ... a bit more faint but still noticeable. It shows up as long as the turntable is powered on (i.e., even when not playing).
I had the same problem with my 4004 earlier this year and fixed it mid-June. See attached photos for reference, specifically the 1st one (I am showing a DIN7 plug, but only pins 2, 3, 5 and shield are required for functionality), while the 2nd one really shows that the system ground and signal ground must be one and the same! This is specific to the Beogram 4004 version only!
Back to your DIN plug coming out of the 4004, need to open it, make sure that the black wire is disconnected (desolder it and tuck away) from the plug housing, than take the shield wire, connected to pin 2, split it in half, and solder part of it to the shield of the plug (in place of the black wire)! This way, system GND and signal GND (L/R low) of BG4004 will be at the same potential, so should become independent on the RIAA types/models and how they have GND implemented internally…
Courtesy of Rudy, aka Beolover, he confirmed this for me as well:
“It is my experience that connecting shield and system ground usually takes care of humming. In later 4004s they actually implemented this as factory standard on the output board. It only took them ~5 years to figure it out back then…”
Location: Eindhoven, NL
Thanks for the help! I'll see if I can spend some time this weekend taking a look.
To clarify, the second image is showing the desired end result / wiring where the plug housing (black wire) is tied to Pin 2 (shield wire)?
And a potentially dumb question, but am I disassembling the DIN cable itself, or just looking at the wires inside of the Beogram where the various wires from the cable connect to the board?
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