Hello,

I did a quick search on the forum for this but couldn't find a solution.

I have discovered over the past few years that the liquid pro bob has a low level hum on the auido outputs. This seems to happen on all the BOBs I have regardless of the computer etc.

In my main edit suite I have the inputs and outputs of the box connected to a balanced to unbalanced converter so that I can interface it with a pro sound desk. I can then tell that there is hum there as it is even visable on the metres of the desk.

Does anyone know the true audio output level of the BOB? I'm guessing as it is a consumer device it would run at -10 dBu? Also has anyone had experience of this problem before? It doesn't bother me to much as I rarely need to export back to an analogue device but it would be nice to try and get it fixed.

Thanks

Nick

The output level is -10 db. I have never heard hum out of my BOB and I have used it to create broadcast programming and if there had been hum, it would have been detected by the QC process that all the tapes went through.

I've never noticed a hum from the BOB. For a sanity check, try a set of cables directly from the BOB to a set of amplified speakers and turn up the volume on the speakers. See of the hum shows up without the converter. If it does, then try a different set of cables (if you've not already done that).

Thanks for the replies. I will try that and see what happens. Is it a bad idea to boost the -10 level up to broadcast 0 or should that be ok?

 

If you are feeding something like a beta deck, you should bring the gain up to zero with plus three peaks on the meters on the beta deck. What output media are you delivering on??

Usually we output to DV so there is no problem but we need to be able to output back to Beta SP so I have been doing exactly that and bringing the level up using a pro converter. I just wanted to make sure that was the proper way.

Why do you need a converter? You just need cables that go from RCA out of the BOB to XL male into the deck and you adjust the audio level on the deck. Comprehensive makes the appropriate cables. I got mine from B&H. The less stuff in the audio chain the better.

 

Well the converter is supposed to take unblanaced audio and interface it with balanced audio and the other way round. It also has audio trims on it. I think you are right though, it would be exactly the same result without it. I think the hum on the box has something to do with a voltage on the audio outputs. Would that make sense?

I don't think that makes sense. I have no discernible hum on my BOB. Get rid of that interface and see if that helps.

Ok I will try some experiments and let you know.

Thanks

Nick

Hum at line frequency or a line frequency harmonic on analog audio interconnects is often caused by a ground loop. Not always easy to fix, but some of the long standing fixes to try include using isolation transformers in the audio lines, ensuring all involved electronics are on the same ground (e.g., the same power strip), and if the power cords are not polarized, reversing a plug.

That's interesting. When I put an active D.I. box in the loop it solves the problem. Everything is being fed off the same power source but it's possible that a plug is reversed as you say. Will need to check that one out!

Yep, sounds like you have a ground loop.