Hum from a Beogram 1700

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paul_f Posted: Sat, Apr 28 2018 8:06 PM

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I have a Beogram 1700 connected to a Beomaster that has an awful amount of hum through the dpeakers.  I can hear a hum from the  Beogam transformer when it is plugged in, but only if I put my ear to the case.

I have replaced the signal cable as it had been modified.  It is connected as per the service manual and the chassis ground is definitely connected to the Beomaster ground.

Could the capacitors need replacing?  Or is there anything else that it could be?

Thanks

Paul

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Dillen replied on Sat, Apr 28 2018 9:25 PM

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It's a grounding problem.
In the Beogram, in the cable or in the Beomaster.
There are no electronics (or capacitors) in the signal path in the Beogram.

Which Beomaster are you using?

Martin

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paul_f replied on Sat, Apr 28 2018 9:27 PM

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Hi Martin

Thanks for your help.

It is a Beogram 1700 and a Beomaster 2300 that I recapped.

If I plug the Beogram in to the tape input I still have the hum (but very low as is the volume).

I tried connecting the screws on the rear of both units with no change. Also connected an earth to the Beomaster chassis with no change

Regards

Paul

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paul_f replied on Sat, Apr 28 2018 9:30 PM

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IMG_20180410_210159_crop_830x691.jpg

Here is a picture as to how it was originally wired, however the pins of the DIN were incorrect and it was very short.

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paul_f replied on Sat, Apr 28 2018 9:32 PM

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The replacement csble came from Steve at Sounds Heavenly, and was slightly different as the signal ground was its own separate wire, and then the outer braid I connected to the terminal with the black wire leading to the chassis

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Dillen replied on Sat, Apr 28 2018 9:49 PM

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Has the small grounding leaf spring broken off the cartridge socket?
It goes into the small hole at the lower part of the MMC cartridge.
Do you have continuity from the MMC cartridge house to the DIN metal shield?

The signal ground (from the two cartridge coils) goes to the center pin in the DIN.
The chassis ground (from the tonearm and the rest of the Beogram metal parts) goes to the DIN metal shield.
Both grounds will have to go through and they must be kept separate.

Martin

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paul_f replied on Sat, Apr 28 2018 10:06 PM

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The small grounding leaf is there, but is connected to the centre pin of the DIN not the shield.  I assume that is incorrect and it should be to the metal shield

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paul_f replied on Sat, Apr 28 2018 10:37 PM

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Thanks Martin!

I had connected the shield and the ground the wrong way round

Sounds nice now