Film-Tech Forum ARCHIVE: Proper Monitor Input Wiring

This is topic Proper Monitor Input Wiring in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=004556

Posted by Tom Wienholt (Member # 1510) on 02-15-2003, 01:50 PM:

When wiring a monitor to the power amplifier outputs, what is the proper method? The monitor i am using has one terminal and a groung for each channel. So, i assume that the + output from the amp should be connected to each channels input on the monitor. But, what should be connected to the ground for each channel on the monitor?

Posted by Gordon McLeod (Member # 33) on 02-15-2003, 02:52 PM:

That depends on the amplifier you are using. If the output is ground referenced (not bridge mono) then only one ground needs to be connected

Posted by Darryl Spicer (Member # 711) on 02-15-2003, 02:53 PM:

the way I have seen it done is you have the outputs of the amps going to a strip or tied together with the speaker wiring. Usually red and black wires to indicate + and -. Then you have a black and red wire tied in with those lines that go to the monitor. Red for + on the terminal and black for - or ground on the terminal for each channel

Posted by Tom Wienholt (Member # 1510) on 02-15-2003, 03:05 PM:

So the + amp output should go to each channels input on the monitor and the - amp output should go to the ground for each channel. What about the shield? Should the shield be connected at the monitor end only to the ground or is that not necessary?

Posted by Darryl Spicer (Member # 711) on 02-15-2003, 03:24 PM:

I think you will be fine with just connecting the + and - to the monitor imputs. On our rack systems they had a ground that went from a strip that connected the speaker wiring to the outputs of the amps all the way to the monitor ground point for each channel. We cut the ground and just tied the speaker wires together. If your amp outputs are going to a terminal strip were the speaker wires are connected you may need to use the shield. not a hundred percent sure about that though. the problems we were having was groundloop issues with our subs causing them to overload. So we eliminated all the terminals on the rack tieing them in direct and cutting the grounds at those points.

Posted by Kenneth Wuepper (Member # 1174) on 02-16-2003, 07:23 AM:

Tom,

Regarding the connection of shields within cables for unbalanced (ground, +) systems:

The black wire may be ground for the signal, the red wire the + or hot wire for the signal but the shield should be connected at the input end only. (On the monitor amplifier)

In this unbalanced situation the shield acts as a "Static Shield". The shield intercepts high frequency interference and keeps it away from the unbalanced leads inside the cable. Many installations can have reduced Xenon ignition interference by using this static shielding technique on the unbalanced power amplifier inputs. This technique is also effective where the output of the CD player to the non-sync input is causing noise on lamp ignition. The two wires inside the cable are used for the signal and the shield functions as a static shield when connected at one end only.

Many new systems are using transformer balanced circuitry and integrated circuit amplifiers (the signal is not referenced to ground) to reduce the effect of induced noise and these balanced cables can be shielded with the shields connected at both ends of the cable. Basically you do not want the shield to be part of the signal path to the equipment.

KEN

[ 02-17-2003, 06:29 AM: Message edited by: Kenneth Wuepper ]

Posted by Gordon McLeod (Member # 33) on 02-16-2003, 01:00 PM:

If you connect the - outputs to the e (ground terminals) of each of the inputs on the monitor you do run the risk of a ground loop

Posted by Steve Guttag (Member # 268) on 02-16-2003, 01:16 PM:

Ken touched on some good points...

In order to properly answer your question, one must know several things. Is the monitor balanced or unbalanced? Are you amplifier outputs balanced or unbalanced (most common). If if your amplifier outputs are unbalanced, if you "bridged" your amplifier then the output is now balanced.

If your monitor is of the balanced type, then you will need to run a separate pair of wires to each amplifier output to the + and - terminals on the monitor. Don't just use one amp's "-" for all...that would be very poor practice that can breed oscillations.

If your monitor is unbalanced...only connect the high-side of the amp's output and make sure the monitor has a good ground reference...connecting all of the amp's "-" terminals to a commong "E" buss is also very bad practice and practically defines ground loop. Many unbalanced monitors dont even connect, internally, the "E" terminals.

BTW...one error Ken made in his statement is that balanced connections are "not ground referenced". Unless they are isolated with a transformer, they are indeed ground referenced and often exactly in the middle of + and - voltage swing (henced balanced).

To shield or not to shield...certainly, shielding doesn't hurt. The amp side of the monitor is almost always a high-impedance input (often over 100K) so noise is easily impressed onto the lines...if you have a multi conductor shielded cable tie the shield to the monitor's "E" terminal and verify it is grounded or it won't do much. Most monitor manufacturers simply dont "get" grounding but then again, neither do most techs.

If you have rather long monitor lines, you will need to go to runing individually shielded lines if you don't want such horrible crosstalk that you might as well have bought a mono monitor.

Steve

Posted by Tom Wienholt (Member # 1510) on 02-16-2003, 03:37 PM:

The amplifiers I am using have a + and a Ground output for each channel. The monitor I am using has a one input and a ground for each channel. I am confused with the answers I am getting. I assume that each + amp output should connect to the corresponding monitor input, but what about the Ground amp output for each channel. Should this be connected to the monitor ground inputs. Or should i only connect the amps + output to the monitors inputs and the sheild to the monitor ground only at the monitor side?(nothing connected betwwen the amp Ground and monitor Ground) Any help would be great.

Posted by Gordon McLeod (Member # 33) on 02-16-2003, 05:16 PM:

If you have the common stereo style amp I use a piece of belden 9251 two conductor shielded cable for each amp
connecting Red of the cable to channel 1 out hot and black to channel 2 output hot and the shield to the ground (either one)
At the monitor input the red goes to the + in for the channel in question the black to the + in for its channel and the shield on one only connects to the E terminal (ground
The other amps I connect the shield only at the amp end

Posted by Dave Macaulay (Member # 813) on 02-17-2003, 01:29 PM:

If only connecting the + inputs to each amp's + terminal works, this is the way I would go. The monitors I've used lately don't have "-" terminals for each channel. This avoids the destructive effects of miswiring a bridged amp, I presume.
If everything is in a metal rack and you have used a toothed lockwasher in one of the screws attaching each component the grounding will be consistent. If you want to use shielded wire connect the shield at one end only, we use the convention that the end at an input is grounded, in this case at the monitor. Modern cinema transistor amps are (as far as I know universally) connected with the "-" terminal at chassis ground. Connecting all of them to the monitor gets you into potential ground loop problems. Possibly this monitor expects or will accomodate transformer coupled tube or transistor amps with a floating output? Assuming it has a "mix" setting I expect ignoring all or at least all but one "-" will work file. It's possible to have a 2-pole selector switch and keep all inputs isolated but I've not seen that done. I think the old Altec monitors could be wired that way by clipping some wires on the switch.