Transformer noise - question

[Daniel75]

Hiya,

My dual mono power amp's transformer "hums" quietly - which is, Im assuming, perfectly normal. However its noise level increases a lot when, for example, Im turning on floor lamp (it does have a dimmer) connected to completely different power socked on the other side of the room.

googling gave me this;


it is often caused by the presence of DC on the line. Usually this comes from some appliance using current asymmetrically, such as a lamp dimmer. The hum comes usually from toroidal transformers, which saturate easily with DC, and when they recover, they draw an extra pulse of current, causing the noise.

So how do I deal with it? Searching gave me the whole spectrum of answers - from "ignore" to "get power conditioner".. Please advise:)


Thank you

[StanleyB]

Transformers are designed to operate efficiently within a narrow raneg of frequencies. In the case of a linear mains transformer that would be in the mains frequency range, which is in the 50 Hz region.
The dimmer relies on switching On and OFF at specific points in the mains cycle when the mains cycle voltage is at about 0V. This is normally done by a thyristor. But thyristors can cause big spikes on the mains, especially if it is a faulty or poorly designed dimmer circuit, and those spikes have a far higher frequency than the regular mains cycle. If not properly filtered by the dimmer circuit, these spikes can be anything up to the maximum mains voltage of 240V. The linear transformers in your power amp is not designed to cope with such large spikes outside their own operating frequency. So they are going to choke when those spikes hit them. So now you know why they call some coil designs a choke:).

[The Black Adder]

Is it a valve amp or transistor?

[Daniel75]

Thank you for clarifying it. Would I benefit from upgrading from Belkin AV Isolator to something more sophisticated? (and getting rid of dimmer lights:)?

D

[Daniel75]

Is it a valve amp or transistor?

Transistor - Morgan Audio Deva power amp.

[StanleyB]

Thank you for clarifying it. Would I benefit from upgrading from Belkin AV Isolator to something more sophisticated? (and getting rid of dimmer lights:)?
Keep the dimmer off when listening to music. I only have my incandescent lamps on a normal on/off switch when listening to music on a serious basis. The LED lights are on dimmers, and they stay off when I am playing music. I won't go into why since I don't want to create a new market in discussions on which dimmers are more musical than others :rolleyes:. I just follow my own experience.

[Rare Bird]

Is it a valve amp or transistor?

Ive had Humming/buzzing transformer on both a Quad '405' & A Radford 'STA25'

[Daniel75]

Keep the dimmer off when listening to music. I only have my incandescent lamps on a normal on/off switch when listening to music on a serious basis. The LED lights are on dimmers, and they stay off when I am playing music. I won't go into why since I don't want to create a new market in discussions on which dimmers are more musical than others :rolleyes:. I just follow my own experience.

haha yeah :) Lets keep dimmers out of audio voodoo. Anyway - switching dimmer lights off when listening to music is a very sensible approach and Im not sure why it wasnt my first thought - and why I was immediately contemplating upgrading to power conditioners or sth. Too much time spent on audio forums me thinks:)