Humm Humm

[Steve1812]

Hi,

 

Putting on a rock and roll show starring kids from the school with a staff backing band for the solo singers - no karaoke here!

 

A studiomaster px 10 I think, is fine for a bit of vocal foldback from the mixing desk. It has a line in and a link which I presume is a way of sending the signal in to another power amp. And indeed this is what happens. Question, why when a second amp is connected do both amps pick up the same humm and it sound "mainsy" to me :)

I appreciate any replies now, as tomorrow I thought I would try the Art Audio Isolation unit in case its the old earth hum thingy - brilliant bit of kit for getting rid of hum when the power supply is connected to a lap top.

 

Thanks in advance,

 

Steve

[Andrew C]

Earth loop. Try swapping cables around, and amps to see if you can tie down what combination causes your problem. You may be looking at some balanced and some unbalanced cables or kit.

[KevinE]

Yep Andrew I agree. If the 'slave' amp has a switch called 'earth lift' or 'ground lift' then flip it to the ungrounded position. If not then a ground-loop isolator (available from maplin etc) is a cheap solution at a fiver. A DI box will do as well but for a £90 powered monitor speaker may seem a little overkill!

 

I've looked at the PX10 and its line sockets are described as 'TRS balanced-compatible' whatever that means..I suspect they work with balanced inputs/outputs but arent actually connected to a balanced input circuit.

[johndenim]

I presume the "hum" only appears when the second amp is connected?

 

plug in a pair of headphones or a passive speaker to the link out.

If you still hear the hum the problem lies with the wedge.

if not, then check all of your cables and the second amp for a ground connection.

 

 

John Denim.

[Steve1812]

Thanks Chaps. Today I did connect a cheap and cheerful Behringer version of an Audio Isolation transformer and the humm went completely.

Tomorrow I will try the head phone trick and will let you know.

 

Thanks for the "tips"

 

Steve 1812

 

ps just plugging in an lead to the px 10 does not produce the hum, its adding the extra active amp what ever it is - foldback or guitar amp etc.

[Steve1812]

Tried putting headphones in to the link/ line out and there was no noise on the head phones or the main speaker.

 

Took a balanced line mic cable, added some xly to stereo jack conertors to make it balanced line using stereo jacks and connected this "link" to another power amp - the hummm all but disappeared.

 

I dont understand why but thanks for all the input/ideas.

 

We enthusiastic amateurs welocome this kind of constructive help - not the slagging off found lately on RATS.

 

Steve 1812