Elimination of rather nasty hum?

Probably semantics

In the setup for taking two unbalanced lines stereo and summing them to mono and then connecting them to an balanced input and not connecting the input to pin 1 at all but simply leaving the shield only connected at the mixer end, you have the situation where on the unbalanced stereo side you do have a "ground" which serves as ground reference for the signal and also for the shield and on the balanced side, you don't really have a ground, since the input circuit is expecting a balanced signal, with an independant shield. By using the shunt resistor, you are creating a floating ground for the Stereo unbalanced side of the circuit, but still allowing it to "float" on the input side of the balanced mixer input, and use the shield for the cable run.

Probably a poor use of terminology, personally I still like to simply use a transformer.

Sharyn
 
Thankyou all for you amazing help!

With the help on here, I have made the situation much better (hum still audible :neutral: ).

However...*drum roll*...I took them to task and told them exactly what I think of their system :grin: and seeing as they don't want to lose me :grin: they're going to use the spare VGA lead we have and run the video for the projector up to the Booth and so we'll have a computer in the booth and a direct RCA stereo sound input into our mixer!
 
Months actually :) I don't intend on heading into school too soon!

However...slightly worried about needing amplification for the video signal on a long run.
 
Thanks for that Sharon.

Not likely I'll be buying that particular model though because it is in the US!

But it is what I need.

Um...15 pin HD connector? I didn't think the normal SVGA connector (you know what I mean) was called that or had that many pins?!
 
All vga computer connections are 15 pin three rows of 5 pins.

There is also the DVI connector, which has the digital connection, and the analog connection imbeded it it.
Sometimes it is cheaper to get stuff in the US and ship it down to you, but you know your local situation.
As you go up in resolution you need a good quality vga line driver to get long distances. If you do decide on another option make sure it will support the resolution you are likely to use, a lot of solutions look ok at 640x480 but really look awful at 1024x768 and above, the higher resolutions are higher frequency signals, and the cable length acts as a capacitor and starts to roll off the signal
Sharyn
 
For what it is worth, the HD15 connector is so called because the HD refers to High Density ie. it has 3 rows of pins not 2.

How long a cable run are we talking? It may be that amplification is not actually needed. Start with a good quality cable and minimise the number of connections in the line. Are you making your own cable or using a pre made one (or ones)? If you want recommendations on cable etc. let us know and I'll see what I can dig up, as well as some tips on soldering them from what I have been told.

Just think, it is only about 37 days until you go back to school... :p

Afterthought: I tend to think that DVI and other digital signals will have shorter maximum cable lengths - take USB compared to say RS232 - 5 metres or about 30... Anyone have any information on this?
 
Last edited:
In general with VGA at the higher resolutions you are lucky to get 25 feet. DVI and HDMI in theory can run longer, at the higher resolutions mainly because they are not attempting to run at a very high frequency, but again you will have problems (sparkle).

Part of the issue is that consumer cables use 28awg cable, pro ones use 24 awg and of course if you could move up to 22 or larger would help.
If you really are running long runs over 100 feet, I suggest you look at VGA over Cat 5, Extron and Gefen make units for this

Sharyn
 
My brain doesn't work in feet! :lol:

The height of the building is about 9m, so the run would be a bit over twice that.

I've been told VGA is fine up to about 30M?

Maybe this should be split into another topic...
 
I have a feeling that the cable run to the projector at church is about 25 metres. And the signal suffers very little noticable degredation. I think it is something along the lines of what was being discussed elsewhere, that using a good quality cable makes all the difference...

My boss is not willing to consider a projector of good quality unless it has 5 BNCs on the back for the RGBHV (Red, Green, Blue, Horizontal sync, Vertical sync) input... He also is of the opinion that the use of Cat5 Baluns etc. causes significant signal degradation, on what this opinion is based I do not know.

And Phantom, whilst it pains me to admit it, my mind does not suffer too much trouble working in feet... just remember than in rough numbers, a foot is 30cm and 10 feet is 3 metres (which I find to be in general the more useful number). When are the states going to get around to converting to the metric system? (Next you will be expecting me to spell colour without a "u"...):rolleyes:
 
Cable length and awg is a major factor.

Bnc connections if they run all the way from the source to the projector,gives you the advantage of running coax all the way, simply having the split out to bnc on the crt may give you the feeling that things are better but in fact it is a throw back to the older days when infact this was the high end connection. Simple baluns will probably degrade the signal, active cat5 is a total different matter. Sounds like your boss is living back in the days when ethernet ran over "golden rod" or coax. The advances in technology over twisted pair has made massive improvements, just look at Gigabit ethernet.

Sharyn
 
Sharyn, that all makes sense. All goes to prove that nothing is ever simple is it?
 
You must log in or register to reply here.

Similar threads

cjparsons74
Mixers/Consoles Wiring Mixer Aux-Send to Stage via XLR snake
Replies
11
Views
12K
TimmyP1955
TimmyP1955

Users who are viewing this thread

Total: 1 (members: 0, guests: 1)
Back