Weird hum problem

JLNorthGA

Active Member
We are doing a musical (Spitfire Grill). We haven't been plugging our Yamaha Clavinova into the sound system for rehearsal as it had been in a rehearsal room rather than in the orchestra pit. We moved it into the pit when we started get ready for the performances.

We hooked the Clavinova into the sound system by hooking up a 1/4 TRS cable from the L/L+R 1/4" jack into a DI box. The DI box was then hooked into our sound system via a XLR microphone cable.

Initially there was no problem. However, after about a hour or so, there was an annoying hum.
I swapped out the cables and the DI box. It worked fine - for a few minutes. Then the hum started again.

The Clavinova does not have a grounded plug. The noise only occurs when the instrument is plugged into the sound system via the DI box. I suppose we could run 1/4" TS cable to the Clavinova.

Thoughts?

We have had grounding issues (annoying hums) from time to time.
 
Interesting, I've had problems with Clavinovas before, but usually based on them being beaten up from trying to transport them. Never had a bad hum from one.

If you come out of the same output from the clavinova into another device (amp?) is the hum still present?
If you come out of the R output (instead of L/L+R) do you still have a hum?
If you lift the ground with the DI (assuming it has a lift) does the hum go away?
Is the DI already Ground lifted (that'll do it)?

Try changing out the cables and the DI, a bad cable or a bad DI could be a culprit.

Really the DI should make it LESS noisy, not more. But sometimes DIs are not so good, or have gone bad.

What kind of DI are you using?

Also I just have to ask, how old is the venue (what is the electrical like)?
 
Is the DI transformerless or does it use a transformer? Most passive DIs use a transformer and can pick up magnetic fields from nearby transformers and other electronic equipment. Pick up the DI box and rotate it. If the hum changes depending on position, then that is the problem.
 
Interesting, I've had problems with Clavinovas before, but usually based on them being beaten up from trying to transport them. Never had a bad hum from one.

If you come out of the same output from the clavinova into another device (amp?) is the hum still present?
If you come out of the R output (instead of L/L+R) do you still have a hum?
If you lift the ground with the DI (assuming it has a lift) does the hum go away?
Is the DI already Ground lifted (that'll do it)?

Try changing out the cables and the DI, a bad cable or a bad DI could be a culprit.

Really the DI should make it LESS noisy, not more. But sometimes DIs are not so good, or have gone bad.

What kind of DI are you using?

Also I just have to ask, how old is the venue (what is the electrical like)?

Didn't try it in another amp - just to our snake.
Same hum out of R as well as L/L+R.
Lifted ground, didn't do anything.
Was in Ground mode.

Swapped out cables, swapped out DI - to no avail.

DI is a Behringer DI20 Ultra DI box.

Venue dates from the 1980s. IMO, the grounding leaves a bit to be desired. When we had the lighting electrical redone, it REALLY improved the lighting situation.

There is a single female plug, looks to be 1/4" possible TRS hanging out the back. I will try that next.


I did "park" the DI box on top of the Clavinova - which may also cause a problem.
 
Didn't try it in another amp - just to our snake.
Same hum out of R as well as L/L+R.
Lifted ground, didn't do anything.
Was in Ground mode.

Swapped out cables, swapped out DI - to no avail.

DI is a Behringer DI20 Ultra DI box.

Venue dates from the 1980s. IMO, the grounding leaves a bit to be desired. When we had the lighting electrical redone, it REALLY improved the lighting situation.

There is a single female plug, looks to be 1/4" possible TRS hanging out the back. I will try that next.


I did "park" the DI box on top of the Clavinova - which may also cause a problem.

Yeah I would not park the DI on the keyboard, always off of it IMO. First so it does not fall, second interference (more a problem with passive DIs), etc.
1980s buildings SHOULD be okay for grounding etc, but may not be ideal (then again there is always the lowest bidder problem).

I've never really cared for the Behringer DIs myself.

"There is a single female plug, looks to be 1/4" possible TRS hanging out the back. I will try that next." - What is this hanging out of?
Generally the only things plugged into the Clavinova should be Power, Pedal & Outputs (L/M & R).

I'd try running a 1/4" cable out from the Clavinova to something like a keyboard amp, if there is a hum than the problem is in the Clavinova. If you try pushing down your snake without a DI I doubt you'll have any improvement.
 
Yeah I would not park the DI on the keyboard, always off of it IMO. First so it does not fall, second interference (more a problem with passive DIs), etc.


"There is a single female plug, looks to be 1/4" possible TRS hanging out the back. I will try that next." - What is this hanging out of?
Generally the only things plugged into the Clavinova should be Power, Pedal & Outputs (L/M & R).

Will try putting the DI on the floor. As for getting rid of the Behringer's - maybe one day - when we can afford it.

There is this cable w/ a female 1/4" plug on the end. That's about all I know. There are three pedals on this Clavinova, so it definitely isn't a pedal hook-up.
 
Will try putting the DI on the floor. As for getting rid of the Behringer's - maybe one day - when we can afford it.

There is this cable w/ a female 1/4" plug on the end. That's about all I know. There are three pedals on this Clavinova, so it definitely isn't a pedal hook-up.

Ive seen my share of Clavinovas, don't think I've seen one with a 1/4" female "hanging out of it", it is possible this piano has been modified by someone? (Perhaps there is your problem right there?). Do you know the model of Clavinova?

If moving the DI does nothing, I well suspect that the issue is the piano itself and it will need to be repaired or replaced.
 
I plugged it into the female hanging out the back. Success - no hum. I also moved the DI box down to the floor afterwards.
 
You need a better DI to avoid these headaches. On the budget side, the ProCo DB1 always seems to get the job done. One of the best is the Countryman 85.
 
I plugged it into the female hanging out the back. Success - no hum. I also moved the DI box down to the floor afterwards.

Okay that cord sounds like a modification to bypass a bad output! That really wierds me out. I wonder who "fixed" it.

I also of course have to agree that the Countryman 85 is a ROCK SOLID DI that will give GREAT sound and last nearly FOR ALL TIME. I've seen one run over with the truck and not even blink. There are of course other DIs that are recommended, pretty much all the Behringer DIs are last resorts.
Then again as you said, low budget, so the Behringer DIs Im sure will serve you well-enough.
 
You need a better DI to avoid these headaches. On the budget side, the ProCo DB1 always seems to get the job done. One of the best is the Countryman 85.
Countryman 85 is way out of budget range. Will put new boxes on the list.
 
The plot thickens - at some time in the past, someone drilled a hole through the case and put in the 1/4" female.

The reason why? The 1/4" L/L+R and R plugs were acting up. Rather than send the Clavinova out for service, they added the 1/4" female. So it already was causing hum.

Now why didn't anyone write it down??
 

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