Simple boom cable system

[dcsimon]

It has definitely been done before. But I wanted to see if I could do it for less. I sourced all my parts from markertek, lowes and the local frys. For about $30-$40 dollars it's not a bad package at the end of the day.

It obviously draws a lot of ideas from the BoomBox v1. Integrating talk back from the boom op is the next step, but it achieves the goal of having one cable for the boom to wrangle.

For more detailed pictures you can read my brief writeup here: http://www.danacsimmons.com/content/boom-buddy-integrated-boom-cable-system

[Jeff Wexler]

It has definitely been done before. But I wanted to see if I could do it for less. I sourced all my parts from markertek, lowes and the local frys. For about $30-$40 dollars it's not a bad package at the end of the day.

It obviously draws a lot of ideas from the BoomBox v1. Integrating talk back from the boom op is the next step, but it achieves the goal of having one cable for the boom to wrangle.

Nice job... that's a good Do It Yourself project (if you're able to do it). Did you use the same multi-pin connector that Trew Audio uses for their boom systems? I have used duplex cables for the boom operator for so long, originally actually 2 cables tied together and later multi-pair cable in the same jacket, but have often considered a single cable approach. Maybe I will re-consider and make up a single cable duplex with quick release connector.

[Nicole Hankerson]

Very cool Dana. I need to come over and check it out. Make another one for me. I can buy it today or tomorrow. I could use one for sure man. I wish I had this knowledge but thats what you're for. My cable guy. Dana is great at cable work.

Thanks

Nicole

[dcsimon]

Nice job... that's a good Do It Yourself project (if you're able to do it). Did you use the same multi-pin connector that Trew Audio uses for their boom systems? I have used duplex cables for the boom operator for so long, originally actually 2 cables tied together and later multi-pair cable in the same jacket, but have often considered a single cable approach. Maybe I will re-consider and make up a single cable duplex with quick release connector.

It uses the same connectors that the remote audio systems use and the same pinout, so you can plug in one of their cables and get straight to work.

[John Blankenship]

Nice work.

I built all my breakaway cables using the 8-pin Neutrik connectors at each end, but decided to make my duplex boom cables using 6-pin XLRs. They're easier to wire up and/or repair, and work as well for that application. I also have pigtails that allow me to reverse either type cable for its opposite use (mixer to camera, or mics to mixer, etc.).

[dcsimon]

Nice work.

I built all my breakaway cables using the 8-pin Neutrik connectors at each end, but decided to make my duplex boom cables using 6-pin XLRs. They're easier to wire up and/or repair, and work as well for that application. I also have pigtails that allow me to reverse either type cable for its opposite use (mixer to camera, or mics to mixer, etc.).

Yea, in the long run 6 pin XLRS may be more cost effective. I already had a great deal of cable terminated in neutricon so chose to go that way. The three pairs of cable also allows for adding boom talk back in the future. But as you mentioned it's very simple to customize this idea to fit whatever connector system is needed.

[Philip Perkins]

Yea, in the long run 6 pin XLRS may be more cost effective. I already had a great deal of cable terminated in neutricon so chose to go that way. The three pairs of cable also allows for adding boom talk back in the future. But as you mentioned it's very simple to customize this idea to fit whatever connector system is needed.

Good job. I've made several boom boxes over the years to suit the wishes of the boom ops I've worked with, esp back before there were commercial system avail (back then all sound people made their own). The hardest part was always figuring out how it would clip onto the boom ops belt, or if it would have its own belt etc., as well as various talkback schemes.

phil p

[Nikolozj]

Hi guys, I'm beginner boom operator and at the same time I do some electric wiring/soldering stuff.

I recently finished similar boom box project and now I'm through the movie project, where just in the beginning of shootings I found out that the box doesn't work properly. The problem is that I wired the box input with 5 pin XLR connector: 3 pins of connector go to the boom input through the box and 2 other pins together with ground signal go to the headphone output of the box.

If I'm explaining it clearly then you probably notice that I simply used one ground signal for both: microphone and headphone signal.

We use sound device mixer and recorder. Both signals, for mic and headphones, come from mixer.

As a result, on a first try I thought I got a clear sound. Then we noticed that the gain was little bit low and the main thing which was most terrible, is that, it was getting unusual fuzzy noise when you would turn up the gain.

After some experiments and tests I came to conclusion that the main problem in my wiring is shared ground signal of mic and headphone that conflict. I thought that mixer had one main ground signal for all input/output signals and I guess it's not this way??? Does it have separated ground signals for every input/output?

here's the picture of my box

[studiomprd]

" getting unusual fuzzy noise when you would turn up the gain "

gain would require an active amplifying circuit.

It is probably a good idea to use separate grounds for input and output lines, and actually a dual audio cord with separate shields, as you are running a mic level and a line level iin opposite directions through the same "cable"...(you do not specify, but Canare makes a popular dual audio cable for these duplex applications, as do other wire+cable companies. BTW, many of of these boxes are wired with only a single channel (aka mono) return audio, to keep them simple..

I have built (successfully) boxes like this with an attenuator to reduce the volume by adjustment at the box.

[Nikolozj]

" getting unusual fuzzy noise when you would turn up the gain "

gain would require an active amplifying circuit.

It is probably a good idea to use separate grounds for input and output lines, and actually a dual audio cord with separate shields, as you are running a mic level and a line level iin opposite directions through the same "cable"...(you do not specify, but Canare makes a popular dual audio cable for these duplex applications, as do other wire+cable companies. BTW, many of of these boxes are wired with only a single channel (aka mono) return audio, to keep them simple..

I have built (successfully) boxes like this with an attenuator to reduce the volume by adjustment at the box.

well, I must specify that in "gain" I meant the main gain of the mic channel on sound device mixer. I guess you thought I had a potentiometer in my box, but I don't. It (the box) only has one 5 pin male xlr, one 3 pin female xlr and headphone jack. And clip of course ))

So the way I thought it would work is this: I'm getting stereo cable with 5 pin XLR connectors on one end and splitting another end to mini jack connector and 3 pin XLR (for mixer headphone output and mic input). On the other end of cable I have one 5 pin XLR that goes into box and inside of box I solder 3 pins of mic input signal, coming from mixer, to 3 pin female xlr of box (to connect the boom). After this, I'm left with only 2 free pins of my stereo cable, that I can use for headphone output, but it also needs shield. So I wire up together microphone and headphone ground signals.

And as a result.. I get what you already read above... Low gain and very bad and unusual noise, when you turn up the gain on mixer.

[studiomprd]

" Low gain and very bad and unusual noise, "

yes, by using terms incorrectly, I was confused...

you are still not getting any "gain" (low or high) in the cable/box. you may have a low level signal, signal loss, and even crosstalk at work here.

try separating the grounds, and mono-ing the return signal (connecting the 2-channels together to tip, or even to tip+ring)

Although |I am reading reports of sub-atomic particals traveling faster than the speed of light, I suspect you will not be able to break any of the laws of physics ...

[Nikolozj]

" Low gain and very bad and unusual noise, "

yes, by using terms incorrectly, I was confused...

you are still not getting any "gain" (low or high) in the cable/box. you may have a low level signal, signal loss, and even crosstalk at work here.

try separating the grounds, and mono-ing the return signal (connecting the 2-channels together to tip, or even to tip+ring)

Although |I am reading reports of sub-atomic particals traveling faster than the speed of light, I suspect you will not be able to break any of the laws of physics ...

Sorry for confusing, I'm not native English speaker.

I tried all possible configurations for return signal, I think and none of them worked properly. Either there was no return signal in headphones or there was mono signal in one ear. I'll go through it once again carefully once I finish this project that I'm through right now. I'm using two taped cables now.

I just wanted to know if there's anyone here who knows Sound Device mixers's ground signal functioning principle. All I could find out by myself is that it may have separated ground signals for headphones and for input mics, which is weird, because to me, theoretically, ground signal is one signal in circuit for all components.

[studiomprd]

" theoretically, ground signal is one signal in circuit for all components. "

theoretically, ground signal is one signal in circuit for all components.

[Nikolozj]

" theoretically, ground signal is one signal in circuit for all components. "

theoretically, ground signal is one signal in circuit for all components.

so, do you have any practical knowledge about sound device mixer ground signal system?

[Jeff Wexler]

No, he doesn't. Just theories.

[studiomprd]

" sound device mixer ground signal system? "

actually, yes, I do.

"ground Loops" happen, and so careful; attention to detail is important. Also, many devices have separate earth-ground (power ground, chassis ground, etc) and signal ground points and connections (circuits) (JW: Cooper mixers come to mind).

One time when I described something as "a piece of cake", I was reminded: one can choke on a piece of cake, too.

[LarryF]

I believe, he was pointing out, with an underline, that a ground is rarely a real ground. More specifically, ground is a theoretical concept, an ideal state rarely achieved in practice. Therefore, it is generally good practice to keep grounds isolated until you are forced, kicking and screaming, to tie them together, such as by the mixer manufacturer at the mixer input (or whatever).

Cheers,

LarryF

No, he doesn't. Just theories.

[studiomprd]

Thanks, Larry...

Yes, I was pointing out the qualifying word: theoretically!!

...it's a tough room, here.

[LarryF]

But that makes it more fun.

LarryF

...it's a tough room, here.

[David Levine]

so, do you have any practical knowledge about sound device mixer ground signal system?

I have a little practical experience with SD ground systems. I adapted a two-channel snake to connect my MM-1 and 552. I originally built it as a camera snake with 2 outs and a return, using 2-channel canare starquad and 7-pin XLRs. Not ideal for 3 channel cable, but no problems so far. All three channels (or two with an mm-1) share share the same ground, and I have never heard any bleed between the signals. Correct me if I'm wrong, but isn't the purpose of ground to provide a drain for excess signal as well as a reference for the receiving mixer? That being the case, as long as everything is functioning properly, there shouldn't be any bleed.

If someone who understands electronics better than I do wanted to explain how a ground REALLY worked, that would be great!

David L

[LarryF]

Hi David,

Balanced systems theoretically (that word again) don't drive currents into the ground (shield). The ground just acts as a shield against stray fields, RF and AC, from inducing currents in the twisted pairs. If the pairs had no separation, even that wouldn't be a problem but they are at least some distance apart due to insulation. The twist helps balance the induced currents out so there is cancellation. Problems crop up when large signals and low level signals share the same cable and even worse when they share the same ground. Balanced systems are never perfectly balanced and when line level signals at +20 dBm are in the same cable as mic signals at -60 dBm the 80 dB difference begins to overcome the goodness of a balanced system. Common grounds make it worse. If one of the signals or both are unbalanced, then the situation is 30 to 60 dB worse. The length of the cable also proportionally affects the cross talk.

If you are running signals that are similar in level and if you are running balanced lines from and into well balanced inputs, then you can get away with common grounds. You can also be helped if the signals are related. That is, if the return signal is large it is because the mic signal is large and the high level of one is covered by the high level of the other. If you sent a 20dBm reference tone down the return and listened to a voice mic signal, you might very well hear a faint tone. It is a good way to test the setup.

You just have to be aware of the choices you are making and be aware of what problems crop up if circumstances make you use the cable for less forgiving signals. Your cable setup works well for your setup and the phase of the moon is not going to suddenly cause you to have problems. If your setup changes and cross talk or a ground loop rears its head, the ground configuration would be one element to at least look at.

Best Regards,

Larry Fisher

Lectrosonics

I have a little practical experience with SD ground systems. I adapted a two-channel snake to connect my MM-1 and 552. I originally built it as a camera snake with 2 outs and a return, using 2-channel canare starquad and 7-pin XLRs. Not ideal for 3 channel cable, but no problems so far. All three channels (or two with an mm-1) share share the same ground, and I have never heard any bleed between the signals. Correct me if I'm wrong, but isn't the purpose of ground to provide a drain for excess signal as well as a reference for the receiving mixer? That being the case, as long as everything is functioning properly, there shouldn't be any bleed.

If someone who understands electronics better than I do wanted to explain how a ground REALLY worked, that would be great!

David L

[studiomprd]

IOW: simple is not always as simple as expected....

[David Levine]

Hi David,

Balanced systems theoretically (that word again) don't drive currents into the ground (shield). The ground just acts as a shield against stray fields, RF and AC, from inducing currents in the twisted pairs. If the pairs had no separation, even that wouldn't be a problem but they are at least some distance apart due to insulation. The twist helps balance the induced currents out so there is cancellation. Problems crop up when large signals and low level signals share the same cable and even worse when they share the same ground. Balanced systems are never perfectly balanced and when line level signals at +20 dBm are in the same cable as mic signals at -60 dBm the 80 dB difference begins to overcome the goodness of a balanced system. Common grounds make it worse. If one of the signals or both are unbalanced, then the situation is 30 to 60 dB worse. The length of the cable also proportionally affects the cross talk.

If you are running signals that are similar in level and if you are running balanced lines from and into well balanced inputs, then you can get away with common grounds. You can also be helped if the signals are related. That is, if the return signal is large it is because the mic signal is large and the high level of one is covered by the high level of the other. If you sent a 20dBm reference tone down the return and listened to a voice mic signal, you might very well hear a faint tone. It is a good way to test the setup.

You just have to be aware of the choices you are making and be aware of what problems crop up if circumstances make you use the cable for less forgiving signals. Your cable setup works well for your setup and the phase of the moon is not going to suddenly cause you to have problems. If your setup changes and cross talk or a ground loop rears its head, the ground configuration would be one element to at least look at.

Best Regards,

Larry Fisher

Lectrosonics

Thanks Larry!