Tascam dr70D with GH4 both powered from power bank causes strange noise

Ted Ramasola

Ted Ramasola

Veteran
I got an XTpower/anker 10000 mAH power bank which has both USB and 9v out to power simultaneously my GH4 and Tascam DR70D. They both work fine.

BUT when I connect the line out of the tascam to the GH4 a warbling/pulsating sound like an out of phase device can be heard from the headphones. This can be heard from either gh4 or tascam headphone out.

The distorted pulsating sound disappears when either of the gh4 or tascam is disconnected from the power bank.

The sound is also not present if I connect the GH4 and Tascam to different powerbanks.

The sound is present only when they are connected to one power bank, but only if the line out from tascam is connected to mic in on the gh4.

Anyone has an idea whats going on?

Thanks in advance.
 
ground loop. While the sound is not what would lead one in that direction the connections you describe and when it happen and when not describes exactly that condition.

You can probably stop it by running the camera to recorder connection through a "hum stopper" or other isolation transformer.

BTW your picture looks like a Galago (Bush Baby), or is it a bat?
 
A sample of the audio would be required if you want something better than wild shots in the dark.

Ground loops are generally found when gear is connected together when the source and destination are powered from different mains power circuits, etc.
I wouldn't expect to hear a ground loop problem from a battery-operated configuration.

My first guess was that maybe you are hearing a hetrodyne between the switch-mode power-supply (SMPS) frequencies of two of the devices.

Or there could be several other causes. But impossible to even make a wild guess without hearing a sample of the audio.

Also, we are assuming that there is NOTHING else connected here.
 
I think it is ground loop too, I could be wrong, you guys probably are more informed about this than I am.

Heres a clip of what the interference sound like.

*first part is me recording with cable not yet plugged into gh4,-sound is built in mic.

*cable is plugged in while record is ongoing- sound from tascam comes in, no interference.

*recording is stopped, - the interference is heard on my headphone.

*recording is initiated with cable in -interference can be heard on the clip.

https://www.youtube.com/watch?v=DR3d9kmAkzM

@Noiz2, my pic is of a tarsier,-found on my home island back in the Phil.
 
Richard Crowley said:
Ground loops are generally found when gear is connected together when the source and destination are powered from different mains power circuits, etc.
I wouldn't expect to hear a ground loop problem from a battery-operated configuration.
Click to expand...

Actually the loop is in the ground and that (in a non isolated (normal building) situation) means the grounds are connected in the power lines. All that it takes to create a ground loop is to form a way for the grounds to form a loop. Since battery powered devices are all DC there is generally not a big issue with having the signal ground tied to the power ground. Except of course if you power both devices from a common source.

Usually what you hear with ground loops is a buzzing or hum because most of the time you are using AC power and the biggest RF around is the 60 (50) Hz power line. But the core of the issue with a ground loop is that the loop instead of acting to shunt errant RF to ground is now acting as an antenna. With out a strong AC RF field it's going to pick up other RF sources so it's hard to tell what it would sound like.

Interesting point on switching power supplies. Since they are both battery operated there shouldn't really be any switching power supplies, though there may be some DC to DC converters (which are kind of the same thing). If that were traveling on the power or audio line though one would expect it to be present when that connection was made even if the other was not. Since this issue seems to require both power and audio connections to occur this seems unlikely. On the other hand IF they are generating enough RF the ground loop could pick that up and then you might get a beat frequency.
 
Wow that is loud. Does this only happen when you are not recording? Is it only in the headsets?

It definitely could be a ground loop picking up RF from the computers (both devices are essentially specialized computers).

I'm unclear though as to if this is making it onto recordings, or if you were recording your earphones and it happens when not in record.

If it goes away in record then I'm a bit stumped.

Interesting creatures. They seem related in a lot of ways. I couldn't find a reference to yours but the "bush baby" gets it's name from it's call. It sounds VERY much like a baby crying. Very reclusive and nocturnal. I needed some recordings of one for a film, near imposable to get decent ones.
 
Just tried a ground loop isolator between the tascam line out and mic in to GH4, -it's gone! You were right! Thanks a lot!
 
Glad to help. The trick is being around long enough and making lots of mistakes. After awhile most problems that come up are kind of like some you already found a solution for.

Kind of like the title of a recent book "Failure: Why science is so successful".

Haven't read it but there was a great interview with the author on NPR.
 
Speaking of recording animal sounds, I was once hired by a production company from zoological society of new zealand doing a project for nat geo on tarsiers. They wanted me to document the tarsier while giving birth! LOL! We were waiting on 3 specimens waiting to go into labor. They were waiting on my island way beyond production time, they couldn't wait anymore and got me to wait for them while they fly back to NZ. End of story, I ended up not able to capture it since, one miscarried due to welding noises, one escaped, I forgot what happened to the other. Haha!
 
I worked on a film once where they needed the sounds of Geese hatching. They filmed it but never thought to record decent sound, as in folks talking over the shots. So we are in post and guess what, geese only lay eggs once a year and we are a good six months from laying time!

Needles to say some very "accurate" sounds in features are complete fakes.
 
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