Beepre2 hum

[Doc B.]

That is not smooth 60Hz hum from a transformers magnetic field. That is classic buzzy 120Hz hum from either a bad ground connection somewhere or a ground loop. Probably time to inspect ground connections and reflow some stuff.

[Alby0521]

Hello.

I reflowed the 2 ground tabs (see pictures circled in red) and all the IEC connection. Is there anything I'm missing. What other solder point would be involved?

[Paul Birkeland]

Everywhere there's a black wire or the banded end of any capacitor other than the ones on the PC board.

[Alby0521]

Ok I'll re solder all the points with those characteristics this afternoon and report back.

Thanks for the help so far.

Best

AB

[Doc B.]

You probably want to check the connections around the little double diode, cap and resistor filter thingamajig between terminals 32 and 36.

[Alby0521]

Hi

I solder again all the black wires, all the banded caps, removed the strip on 31 32 33 and re built that with new solder. Also I re solder all the 3 strips in that corner including 36, 35 and 34.

Nothing changed. Still the same hum.

Also I connected the beepre to another amp in another room. Still same hum.

I’m out of ideas.

Any ideas?

Thanks

AB

[Paul Birkeland]

Are the outlets in your house earthed?

[Alby0521]

Yes l, I plug all the equipment into a power bank. And that it’s plugged into a earthed outlet.

[debk]

I would unplug (not just turn off) all the sources from AC and see if hum is still there.  I once had an issue with hum and it turned out it was the cable box causing the ground loop.  I ended up getting a power-strip with coax in and out and connected all the equipment to it,  and this broke the ground loop

[Alby0521]

Ok I unplugged everything but the Kaiju and beepre. Still hum. So I plugged the Kaiju alone in the power bank and run an extension cord to the garage to plug the beepre on another breaker. Still hum.

Any other idea?

[johnsonad]

While it's on, if you touch to metal of the chassis plate, does that change the sound?

[Paul Birkeland]

This could also be something as simple as a loose filter capacitor that isn't sucking down the power supply noise like it should. 

I had a SEX amp in for repair last year that made a similar noise to this.  I went through and repaired a bunch of other operational issues with the amp and was ultimately left with an amp that functioned fine but had that kind of dirty 120Hz buzzy noise at the output.  It took me forever to track down that what had happened was the builder put a lock washer from one of the binding posts on the ground screw between the chassis plate and the #8 ground lug.  This is very unlikely to be what's going on with your BeePre, but it may help to illustrate the kinds of things that can cause that noise that you're having.

[Alby0521]

Should I re solder the black banded caps on the board? I already re soldered all the 3 brown. Anything else to look at while I’m on the board?

[Paul Birkeland]

You could pop the screws off the board and show a photo of the bottom of it. 

[Alby0521]

While it's on, if you touch to metal of the chassis plate, does that change the sound?

No it doesn’t change. I also run a wire from the bell to the chassis and no change.