Please help fix an Adcom hum?

AdamRagland · February 2008

i kind of skimmed through posts but so forgive if this has already been mentioned but have you tried just using diffrent interconnects? maybe you have a bad cable?

Mike Reeter · February 2008

Funny,I just moved our 2-channel rig into a different room...hooked everything up and now I have a hum coming from a Parasound amp.

Never had it before,same i/c's,power cords,everything the same as before...I have not had the time to do all the trouble shooting you and Danger have,but I hope I can track it down...annoying to say the least.

BottomFeeder · February 2008

Look, just blame me!

It's a curse!

danger boy · February 2008

maybe it's RF interference... there are a number of tall radio station antennas not to far from where he lives..

BottomFeeder · February 2008

Hi there,

Sitting down to begin trying some of the options that have been suggested here.
1st off, trying to hook a strand of speaker wire between the two amps...hooked one end to the NAD, but don't have whatever kind of screw driver needed for the Adcom! Arg! So, don't know if this would work, but I'm holding the other end of the wire to the frame of the Adcom. Still a hum.

I'm hoping that DangerBoy has the proper screw driver to loan me.

Still trying!

Thanks again for your advice.

BottomFeeder · February 2008

Tried moving everything to another room...didn't work.

Bigger hum.

danger boy · February 2008

anyone know what kind of screws might be on his Adcom amp? they should be some kind of standard ones right, unless someone replaced them somewhere along the way.

BottomFeeder · February 2008

DarqueKnight wrote: »

Sounds like you may have a ground loop problem. Which is a ground voltage difference between two components. This can induce hum.

The Adcom GFA-5500 is a non-common ground amp, meaning the grounds of the right and left channel are not electrically tied together.

I am not familiar with the NAD C320Bee, but if it has common ground outputs it may be the source of a ground loop when it is connected to the GFA-5500. Sometimes, connecting a common grounded preamp to a non-common grounded amp can cause hum.

Turn off and disconnect everything, then connect the two negative speaker output terminals together with a piece of wire. You won't hurt the amp by doing this. Reconnect everything and see if that gets rid of the hum. If this reduces the hum but does not completely get rid of it, you may need to connect a grounding wire between the chassis of the NAD to the chassis of the Adcom. Just connect a wire from one of the chassis screws on the Nad to one of the chassis screws on the Adcom.

If the grounding wire test works, make permanent grounding wires of the same or larger gauge as your speaker cables.

Ok. Tried connecting the negative speaker cables together. Maybe slightly reduced the hum. So connected wire to the chassis of both components & the hum was there.

Any other idea???

Thanks for your help!

DarqueKnight · February 2008

You said you moved everything to another room and the hum increased.

You have also said there was no dimmer switch in the room.

Are there any florescent lights in the room?

Can you identify what other electrical devices are on the same circuit as the amp in the current room and in the room where the hum increased?

BottomFeeder · February 2008

Thanks again, DarqueKnight.

In the main room, there IS a dimmer switch, though it's across the room.

There are no florescent lights in either room.

In the main room, there are a couple of lamps & the dimmer switch across the room (chandelier over dinning room table).

In the room where the hum increased, there is a computer and a tv (w/cable)

Again, I am grateful for your help!

ben62670 · February 2008

Cable TV can cause serious issues. Completely unplug your cable TV. It by law has to be tied into ground. If your neutral is even slightly loose it can cause major noise through your whole house via the ground. If you ground sucks the neutral can pick up this noise, and a cheater plug will not alleviate this problem whether associated to the CATV, or not. We had this same problem in our shop, and it took a while to chase it down to loose panel connections.

DarqueKnight · February 2008

The dining room lights and dimmer switch and the main room electrical outlets may be on the same circuit.

If the hum disappears when the dining room light is off you have found your culprit. Also, vary the dimmer up and down and listen for the hum increasing and decreasing with the dimmer switch position.

Mike Reeter · February 2008

DarqueKnight wrote: »

The dining room lights and dimmer switch and the main room electrical outlets may be on the same circuit.

If the hum disappears when the dining room light is off you have found your culprit. Also, vary the dimmer up and down and listen for the hum increasing and decreasing with the dimmer switch position.

Not to hi-jack...we have a ceiling fan in my listening room...this was the culprit.

Fan is switched on the wall...the switch was turned off,but the speed switch (located on fan) was turned on low...Turned fan on,increased speed to medium,hum gets louder.

Turned off speed switch,no more hum.

Thanks soo much for your imput.

DarqueKnight · February 2008

No hi-jack at all. You make a very good point. That is why I asked him to identify all electrical devices on the same circuit as the amp.

BottomFeeder · February 2008

DarqueKnight wrote: »

The dining room lights and dimmer switch and the main room electrical outlets may be on the same circuit.

If the hum disappears when the dining room light is off you have found your culprit. Also, vary the dimmer up and down and listen for the hum increasing and decreasing with the dimmer switch position.

No difference w/the light w/dimmer switch on or off and no difference when I increase or decrease w/the switch.

Perhaps interesting...when I connected the two negative speaker posts on the amp w/speaker wire, the hum diminishes, but not completely. However, the hum is louder when I connect both chassis to each other w/the same wire.

More ideas?

tom t · February 2008

dude, there might always be a low level hum coming from the woofers. is it low enough now not to be a factor when playing music??. you might never get rid of the hum completely. you said the hum diminishes. by 50%??. how much did it do down by.

adam2434 · February 2008

Building on Ben's comment...

Did you try disconnecting the cable TV at the main splitter, so no cable signal is present anywhere in your house?

If cable is the problem, something like this Holland CISP isolator can help a lot (did in my case). I have it in-line with the main cable feed, and it allows HD TV, analog TV, and internet to pass through without issues.

http://www.cencom94.com/gpage.html8.html

heiney9 · February 2008

Since you've tried isolating the problem with other devices on the same circuit it might be time to chalk it up to low line voltage coming into your residence. Like I stated earlier my 545 used to hum at my old place (transformer hum), took it into for service at the time and no issue. When I moved the hum never returned. If the line voltage is just a tad low it can cause transformer hums.

H9

DarqueKnight · February 2008

H9 is right. BottomFeeder, do you have a voltage meter you can use to test the outlet voltage in the main room and in the room where the hum increased?

Adam's suggestion of disconnecting the main cable feed is also worth a try.

tom t · February 2008

i say re-wire the whole house. that should to do it!!! just kidding brent. come'on jet the thing fixed already.

jakelm · February 2008

Would bad PS caps cause this problem?

heiney9 · February 2008

Really, if you can't hear it over normal conversation or music I wouldn't worry about it. I know we all want things perfect, but if it is low line voltage there is nothing you can do short of buying an expensive AC conditioner or AC regenerator.

If you can take it to another person's house, friend, relative, co-worker and plug it in there and see if it still hums. Take it to work if you can and plug it in there for the day and see what happens.

H9

heiney9 · February 2008

jakelm wrote: »

Would bad PS caps cause this problem?

Not a transformer hum, possible I suppose, but highly unlikely. It's the cycle of the electricity that it's being fed that cause some vibration in the transformer. It's harmless but annoying if that's what it turns out to be.

H9

heiney9 · February 2008

Here's a nice article that might help you.

http://www.psaudio.com/articles/hum.asp

Keep in mind while reading that they sell products to reduce/eliminate hum so they come off a bit biased, but the core info is good.

H9

tom t · February 2008

come on brent, how are we making out with that hum???????. should be fixed by now.

danger boy · February 2008

last I heard from Brent.. was that the hum was still a problem.. i'll call him today and see if any progress has been made.

tom t · February 2008

he said when he ran a wire between the negative post the hum went down a little. i really think the problem is somewhere in the house,not with the amp. i told him to take it out of the house and try it somewhere else.

danger boy · February 2008

tom t wrote: »

he said when he ran a wire between the negative post the hum went down a little. i really think the problem is somewhere in the house,not with the amp. i told him to take it out of the house and try it somewhere else.

that is a half good idea.. because once the amp is back in his house it's gonna have the hum back. at least we'd know it was in his house wiring or some thing like that.

I'll see if he wants to haul it over to my house. I've never had a problem with hum from an amp before. so maybe that will narrow it down some.

tom t · February 2008

danger boy, how far are you from him. it wouldent hurt if you took the map home with you to hook it up to see if the hum goes away. then we would know if there is a problem with the amp or not

tom t · February 2008

i ment amp, not map. im just trying to avoid having him send it back to me if its not the amp itself. im paying the shipping both ways.so its going to cost me $80 for nothing if i get the amp back and it works ok here.

Please help fix an Adcom hum?

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