Transformer Hum...

[Per Hansson]

Hi, I bought a new receiver a few months ago because the 30 year old Sony was starting to show it's age...

I did not need anything fancy so I went with the cheapest with the most features I could find... It's only driving 2x speakers of unknown wattage...

Anyway, it's a "Centrum Titan 500" also known as "Eltax AVR-800" I'm using both Optical input and analog from my computer... With both of them I can hear a humming sound best decribed as the sound you hear standing outside a really big stepdown transformer station... Anyway could this be filtered somehow? Some magic gizmo to put on the transformers cables perhaps?

EDIT; The receiver is on a true sine wave UPS that delivers 230.0v 24/7/365, the hum is coming from the speakers, it disapperars if I tune the volume down to 0, but is as audiable at sound level 1 as on 15...

[Tom41]

Re: Transformer Hum...

EDIT; The receiver is on a true sine wave UPS that delivers 230.0v 24/7/365, the hum is coming from the speakers, it disapperars if I tune the volume down to 0, but is as audiable at sound level 1 as on 15...

Sounds like turning the volume down to 0 actually cuts power to the amplifier. Some amps (mainly those with digital volume controls) are like this, others just mute the sound going into the amp (typically with analog volume controls).
If the amp were still on, you'd hear the hum.

Since the hum is audible both at minimum volume and at maximum volume, I'd say the problem lies within the amplifier circuitry itself. It may not even be a mains hum, it could well be interference caused by the transformer coils being too close to signal wires. Does the hum still occur if you disconnect your computer from the input? Have you tried another input device? (guitar, microphone, tape deck etc.)

[willawake]

Re: Transformer Hum...

I'm using both Optical input and analog from my computer

this is the key, if you get the hum with only optical connected then it is internal

[arneson]

Re: Transformer Hum...

Is the power plug a two wire or grounded three wire.
In other words, can you reverse the power cord?

[kc8adu]

Re: Transformer Hum...

disconnect all inputs and test.
if it still hums its an amp problem.if not it could be a ground loop.
maybe it simply forgot the words.

[Per Hansson]

Re: Transformer Hum...

Ok, I disconnected the Optical and Analog cable and then there was no hum at all, but the hum is the same with either the analog or the optical cable only connected... The analog goes to my computer and the optical to my satellite receiver...

The equipment is properly gounded, however the only equipment in this discussion that actually is grounded is the the computer, because all the other gadgets come with only the usual two lead wires... No ground...

There was no difference heard by reversing the power cable to the receiver...

There is also no hum if I switch to the inputs not in use, like Coaxial or Optical-2

[arneson]

Re: Transformer Hum...

My AV receiver was doing this also and I found that the inputs were on a small daughter board plugged into the main board.
When I pulled the board and reseated it the hum was fixed, still works perfect now.

[stretch0069]

Re: Transformer Hum...

had this problem with an old McIntosh amp. If I remember correctly, my roomie ran a 12ga wire from the amp chassis to the ground inside the the wall outlet. No more hum.

[arneson]

Re: Transformer Hum...

I've recently found that sat receivers are often the cause of ground loop problem.
Had two units out of three with AC on the cables. They were wipeing out boards on the tracking device.

[kc8adu]

Re: Transformer Hum...

if the amp mutes on loss of input that may complicate things.
time to go poking around inside with a scope.
btw is it 60 or 120 hz hum?
60=something on amp input.
120=bad filter caps.since every one i have seen used a full wave bridge in the psu.

[brbpab94]

Re: Transformer Hum...

can't you sheild it.between the transformer and the signal wires.