How to isolate a noisy transformer?

Posted by: peteS on 21 August 2001

I have a line doubler which I use to give me great TV pictures, but the bad news is that this takes its power from a dc transformer. I feed the L/R channels of my AV stuff into my 82/250, which means I have to have the hifi on when I'm watching TV. However, whenever I'm watching TV there's an annoying buzz from the L/R speakers, which is being generated by this transformer. Anyone got any ideas how I can isolate this noise?

Posted on: 22 August 2001 by Derek Wright

Do you have to use the TV as the source - can you use a VCR, Sky box or other digital box to provide the sound signal direct to the pre amp.

Derek

Posted on: 22 August 2001 by bam

PeteS,
Would you provide more detail of the configuartion? Do you know whether this is conducted or airborne interference?

Posted on: 22 August 2001 by Martin Payne

I wonder if you have an earth loop?

Does the hum go away if you disconnect all other sources than the TV?

cheers, Martin

Posted on: 27 August 2001 by peteS

Hi All. So, some more details. The audio side of the setup is .....
I take the audio output from the cable box as line-level inputs into a Sony AV 5.1 amp, which I have on a "virtual surround" mode to create a 5.1 signal from a stereo input. I then take the left and right pre-outs from this amp and feed them into the VCR input of the 82. I do it this way so that I can use a single set of left and right speakers and have a clean path for audio playback when I'm listening to CD's (CDX) or vinyl (LP12).

The "noisy" box is the transformer for a "line doubler", which turns the normal interlaced TV image into a progressive scan image. When it's off - no hum - when it's connected - nasty noise. I'm gonna try changing its transformer for a different one, but assuming it's still noisy I'm trying to find ways to isolate it. The interference it creates is on the mains - it has no audio connections at all.

thx