Film-Tech Forum ARCHIVE: Component Engineering MS-55 Booth Monitor Question

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Posted by Mitchell Dvoskin (Member # 751) on 06-05-2007, 09:42 AM:

I have aquired an old Component Engineering MS-55 Booth Monitor. When I hook up the power amp outputs to it, I get a loud hum on only those channels that are connected, along with low volume. As I don't have the owners manual, am I doing something wrong, or is the unit defective.

The inputs from the Dolby processor are not being used.

Posted by Robert Minichino (Member # 3495) on 06-05-2007, 12:11 PM:

You might want to try reversing the polarity of the power amp output connections on the monitor side. (I assume you're talking about the connection between the amp outputs and the inputs for the same on the monitor)

If you want I can stop over and have a look some time [Smile]

Posted by Chris Slycord (Member # 4239) on 06-05-2007, 02:52 PM:

http://www.componentengineering.com/contact.html

If you email them I'm sure they've got a manual they could send you.

Posted by Gordon McLeod (Member # 33) on 06-05-2007, 03:45 PM:

If the amps have a ground refereneced speaker output then you will probably find that one wants to run only a hot lead to the monitor and at most one with a ground
often monitors are a source of ground loops

Posted by Steve Guttag (Member # 268) on 06-05-2007, 10:01 PM:

Stop right there!...you have not ground referenced the whole monitor! The Power amp inputs do not have their returns (grounds) connected internally to avoid idiots from connecting either a bridged (balanced) power amp or to avoid those amps that will set up a ground loop if the low side is grounded.

Therefore...connect any "E" terminal from your cinema processor to the MS-55 (on the processor side) to provide it with a ground reference...you will most likely solve both your hum and low level issues.

Steve

Posted by Gordon McLeod (Member # 33) on 06-05-2007, 10:21 PM:

I have several CE monitors that have been aquired used that there is an internal ground connection maybe not factory original so as always with anything used open it up

Posted by Steve Guttag (Member # 268) on 06-06-2007, 01:56 AM:

Since the MS-55 used genuine lamp cord (2-wire) thre is no ground reference. The chassis can't be used as a reference for the signal for that would mean that you have to ensure that somehow it picked up the ground reference (at low resistance) through the paint of the chassis, the rack rails, which may be movable so they would need to conduct through their paint/powdercoat, though the possibly washered screw. And while star washers can improve that...it is still a very poor way to provide a ground reference...a wire connected for the purpose of grounding is a very good way to provide that reference.