amplifier hum and dimmer switches

[gcmarshall]

i was wondering if anyone can offer advice on something. i am considering a separate power amp, possibly a rotel RMB-1095. rotel tells me there are reports of a "hum" being amplified by the system when the unit is installed on a circuit that has a dimmer switch on the same circuit.

my question is - is the dimmer able to cause the hum when light the dimmer is controlling is turned off? or, must the light that the dimmer controls be "on" for the dimmer to possibly induce a hum into the system?

[Sim reality]

I believe the dimmer must be on to induce any hum...

It will depend on the type of dimmer switch you are using as well. The really old dimmer use a variable resistor to dim the lights which should not induce any hum on the circuit but the current ones which use digital switching will.

How much you have to worry about it will depend on your listening environment:

The "audible" hum is usually cause by a ground-loop problem between the audio components because they are not grounded in the same spot which allows a alternating current to flow between the components. This is very noticeable.

The dimmer switch causes "dirty power" at a regular frequency which might filter into the background noise of the amp. This should not be really noticable if you even have even the slightest ambiant sound in the room you are listening in. Personally I have my doubts if this could be present at all given the 1st thing the input power encounters is a step down transformer and the 3rd thing it encounters is a really big capacitor which should filter out all the smaller power "blips" (before I get flamed, I am not saying that the power supply can filter out everything thrown at it by the power company, but a dimmer switch is not going add that much "dirtyness" to the power circuit and a decent power supply should have been designed for the amp to filter that out)

[gcmarshall]

thanks. the dimmer in question is a rotating (circle) dimmer that is (or was?) traditionally used in dining rooms to dim the lights. you push it in to turn the light on/off and you turn it like a dial in order to dim or brighten the lights.

[Sim reality]

My bet is you have a newer types ("new" is a relative term... It's been out for 25 or so years)...

You can't really tell unless you take it apart or have an oscillascope.

[Azeke]

I use Lutron dimmers and haven't experienced any issues.

Peace and blessings,

Azeke

[George Bellefontaine]

I have one of those older dimmer switches in my dining room and when it is on it does cause a hum on my radio, but only on the fm band for some strange reason. It has no affect whatever on my HT which is likely on another circuit.

[ToddAnisman]

i was wondering if anyone can offer advice on something. i am considering a separate power amp, possibly a rotel RMB-1095. rotel tells me there are reports of a "hum" being amplified by the system when the unit is installed on a circuit that has a dimmer switch on the same circuit.

my question is - is the dimmer able to cause the hum when light the dimmer is controlling is turned off? or, must the light that the dimmer controls be "on" for the dimmer to possibly induce a hum into the system?

what you need is a variac dimmer. they are basically a transformer isolation dimmer that will eliminate that type of Hum/noise.

http://www.variac.com/

They can be had for about $70/ea. worth It IMO.

-Todd A.

[Armand]

i was wondering if anyone can offer advice on something. i am considering a separate power amp, possibly a rotel RMB-1095. rotel tells me there are reports of a "hum" being amplified by the system when the unit is installed on a circuit that has a dimmer switch on the same circuit.

my question is - is the dimmer able to cause the hum when light the dimmer is controlling is turned off? or, must the light that the dimmer controls be "on" for the dimmer to possibly induce a hum into the system?

The dimmer has to be on. Electronic dimming using triacs or thyristors which switches on the device at a certain point after the AC cycle has crossed the zero axis. It's the on/off switching of the dimmer that generates the noise. I had a serious problem until I installed a dedicated 20 amp circuit. You could install a large inductor across the dimmer to smooth it out but as Azeke said, try Lutron dimmers. Check out their faq:

http://www.lutron.com/product_technical/FAQ.asp#OLE_LINK16