Seeking help- something caused HUGE noise

I was turning on my adcom gfa-2 when it put out INSANELY LOUD NOISE through my newly restored speakers. I am still determining if it damaged the speakers themselves, possible tweeter destruction, but the thing is I have no idea why it did this.

I have never had a problem from my preamp or the source, the adcom has not been serviced as far as I know but it never did that before. There was something like 20 or 25mv DC offset per channel so it didn't sound unreasonably unhealthy. I have since used it on the speakers and it produced high end noise, making the tweeters make sound even when supplied nothing. What do you guys think did this? The RCA connectors on the back of the adcom seem to be a little loose, the outer connector to the ground inside sometimes lose contact it seems if I wiggle it and it is my completely unprofessional inkling that this might have had something to do with it.

Assistance would be greatly appreciated! Thank you.
 
Re: Re: Seeking help- something caused HUGE noise

Netlist said:


Definitely something to check. A cheap test speaker wouldn't hurt either. :)

Welcome, Billy.

/Hugo
thanks Hugo.
I was just looking at the unit and yes the ground connection comes in and out. I used a multimeter, so I knew it lost when the sound broke. Could a non-existent ground cause such a loud constant sound? It must have been on for a few seconds, pure noise, it was thunderously loud. Thank you.
 
Duo said:
sounds like a reasonable proposition. Some amplifiers of high gain will do a good job amplifying that ungrounded input noise to excess. I've had the same sort of thing happen from a lost ground.
Duo,
just to make sure I am explaining this correctly,

The female socket on the adcom where the outer ring of an rca cable is supposed to make contact is wiggly- inside, there is simply a piece of bend metal holding that connection to the ground wire. Both of the rca inputs share this ground wire, so when the connections work, if I put my multimeter to the outer of the left rca input and the outer of the right rca input they do indeed contact eachother.

Does that situation make sense to you, or anybody? Does this mean that the outer rings are shorting, or does it mean that they are supposed to be doing that and if they aren't then there is a problem?

Thanks
 

jnb

Member
2006-12-30 11:55 pm
This assumes that the amp is not connected to ground in it's own right (from the wall).

Conversely, if the amp is grounded and the source isn't, it wouldn't so much be the loss of ground but the gross difference of the source signal wire from ground
 
The RCA connectors on the back of the adcom seem to be a little loose, the outer connector to the ground inside sometimes lose contact it seems if I wiggle it and it is my completely unprofessional inkling that this might have had something to do with it.

You are correct...this is the cause of your noise. You are very lucky if the amplifier hasn't been damaged. Repair the connectors fire the amp up without speakers and check DC offset and AC voltage on output. If everything is ok shut the amp down reconnect the RCA jacks and speakers and power it up again.
 
I don't know what I'm talking about lol- I am simply wondering if that loose contact could have been the culprit for that giant noise. The noise lasted a good few seconds before I could shut it off. Could a lose contact there, or incomplete contact, cause it? I may have my terms confused, but that is what i am trying to ask. Thanks!
 
burnedfingers said:


You are correct...this is the cause of your noise. You are very lucky if the amplifier hasn't been damaged. Repair the connectors fire the amp up without speakers and check DC offset and AC voltage on output. If everything is ok shut the amp down reconnect the RCA jacks and speakers and power it up again.

I can measure the DC offset easily, ac voltage is simply doing the same thing but changing measurement to ac on multimeter correct?
 

jnb

Member
2006-12-30 11:55 pm
billybudapest said:
I am simply wondering if that loose contact could have been the culprit for that giant noise.
Yes, it could.

ac voltage is simply doing the same thing but changing measurement to ac on multimeter correct?

Yes, but I think you'd get more workable results with a cheap speaker plugged in. If you have them, why don't you plug in a different source with a different cable, and turn the volume down low (but not right down). Keep one finger on the amp power button and use the other to move the plug.