Diagnosing Beogram 4004 hum

[heavytunes]

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). Audio sample here if you’re curious.

My setup is Beogram 4004 with MMC20EN cartridge => DIN-7 to RCA w/ Ground => Phono Solutions PS1 => Sonos Amp

Funny enough when I swap the PS1 with a $30 Pyle P444 it doesn’t sound as good (as I’d expect), but the hum is gone and it’s dead silent (i.e., I can crank my Sonos to the 90s and only hear the faintest of background noise vs. audible hum when in the 30s-40s with the PS1).

Things I’ve tried:

• Using different turntable (Music Hall MMF-1.5) with the PS1 (no hum! sounds great in fact)
• Different RCA cables from preamp => amp (still hums)
• Using the same outlets (still hums)
• Using different outlets (still hums)
• Using a power bar vs directly plugged into wall (still hums)
• Jiggling the power cord (still hums — no change)
• Jiggling the DIN-7/RCA cord (still hums — but it does tend to change a bit)
• Moving the turntable / preamp super far away from everything else (still hums)
• Triple checking the grounds (still hums)

I suspect it’s maybe the cable or the DIN/RCA adapter … but what totally confuses me is why the cheap Pyle preamp has no hum. Any ideas or things to try!?

Thanks in advance!

• This topic was modified 5 hours, 12 minutes ago by heavytunes.

[Nebojsa Jankovic]

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…”

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Location: Eindhoven, NL
Favourite Product: Beogram 4002/04, Beocenter 7007, Beosound 6000/02

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