Hum in the incoming signal

[audioguru2]

If the generator is grounded to exactly the same point as the mains, and used the same wires to your equipment, then the problem of hum shouldn't exist.

 

[walid1]

If the generator is grounded to exactly the same point as the mains, and used the same wires to your equipment, then the problem of hum shouldn't exist.

exactly it is grounded to exactly the same point as the mains, and used the same wires to the equipments.
we notice the following:
if we disconnect the main circuit breaker of the digital studio either it is oprating or not, the hum is reduced to 90% or more
note also we have two other analog studios and hese not contribute to the broblem.
this problem appears only the last 3 monthes and at that time we had the same conditions we have now, only we as i told you enhance the grounding abnd the problem remain.
thanks very much.

 

[ante1]

Hi walid,

The hum; can you establish if it is the mains frequency 50 or 60 Hz whichever you got?
What kind of alternator do you have, I am especially interested in the exciter circuit! :

 

[SM2GXN]

Hi walid and all the others!

All hum you got in your studio is caused by groundloops or induced mains field into signal carrying cables, to fix this in a big studio could be a real big pain.
The only cure is to break the groundloops wherever they are and be sure that power cables (especially those carrying high current) not are running in parallel with signal cables audio/video and rf.
I don't think a scope is of any help, the generator probably produce a fine sine wave  and proper voltages.
audioguru it doesn't matter if grounds are connected to same spot the thing is that signal cables between all gears usually create a loop which causes hum on audio and video.
Starground in a amplifier will save lots of trouble but the difference here is that grounds of all the stages (stages=equippments) is also connected through the cable shield, right?
If a volume pot is connected through a Shielded cable usually only one end is grounded because otherwise it will create a loop created by a current flowing in the metal chassie itself to starground and finally back to the other ground connection of the cable shield, hopefully you see my point  ;D
I wouldn't recommend breaking the safety ground as some people suggest you could in no time be prepared to buy a one way ticket to the graveyard  :'(
Walid As I understand your studio is a big one and therefore it might be to much to ask you to make a  simple drawing on all connections  :
Hm...not much but lots of text  ;D

 

[audioguru2]

Hi 4-1000A,
I thought if the generator used exactly the same wires as the mains, then there wouldn't be a problem since the mains works well with no coupling and no ground loop.

Maybe the generator is grounded at its location, far from the mains ground.

Inside a grounded metel cabinet, I always ground a shield only at the receiving device to avoid a ground loop. ;D

 

[SM2GXN]

Maybe the generator is grounded at its location, far from the mains ground.

Could be like that, I don't know what would happen if the ground at the generator isn't as good as the one comming from the power company or vice verse.
One question walid, from your generator is there 4 or 5 conductors. Please make a drawing how you run these cables from the generator, breakers etc and how the system is grounded.

I think we covered these earlier on.  Walid got it narrowed down to generator induced as it does not show up when running on regular power.  That would indicate posssible miswiring of the generator or improper ground connections or incompatible output configuration.  Worse case he should get a power monitor unit to capture the generator power configuration: phase voltages, phase currents, ground current and have it evaluated for proper impedance loading and grounding.

tnk2k you are right that's a good way to check that everything is ok from the generator.
Sorry for repeating myself haven't read the posts for a while, I should have updated my memory which become shorter and shorter, got to replace it with a new one with higher speed and size  ;D

 

[audioguru2]

I should have updated my memory which become shorter and shorter, got to replace it with a new one with higher speed and size.

Hee, hee. ;D ;D Maybe you could cram some memory modules for cameras into your head. But 1st you'll need to add a low-dropout 3.3V regulator for them, 'cause your existing brain probably operates at the obsolete 5V. Maybe you could also fit some little hard drives from MP3 players in there somewhere. ;D ;D

 

[SM2GXN]

Good idea!!
I got plenty of space, I'm going to the dentist on monday I'll ask him to make som space for the backup battery but for the hard drive I will use external  battery with beltclip  ;D

 

[ante1]

It would be interesting to know if the “smooth over” UPS cut out when the big one is up and running or does it stay on to supply the exiter circuit. Sometimes the exiter circuit runs of the diesel starter batterys but the first alternative is also possible. The reason for these questions is that the exiter circuit can cause harmonics in the phases if something is wrong with it or it has a bad quality supply. The wires for the supply (DCV) might run near the AC output wires and pickup the magnetic field that then amplifies. To make a rough comparison you could say that the exiter is like the base of a transistor, what you put in here will come out amplified on the phases. Even the diesels alternator (for starter system) can in some cases disturb the exiter if it’s faulty. I have seen strange things happening with these things. 8)

 

[SM2GXN]

Hi Ante!

That's another thought but since the hum produces hum bars synchronized with the vertical frequency of the television set it has to be 50 or 60hz.. but wait, don't remember if the humbars was on the computer monitors  : as well.

 

[ante1]

I think it’s solved by now. 8)