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Loud thump when I power on or off

I have some NHT VT3's hooked up to a fairly nice system. The amp is the Mc6850. These speakers have the built in power amps and come with a preamp of they're own. The thumping noise never happened on my last several pairs of speakers with my current Amp. It also seems to of gotten quite a bit worse since I hooked up a turntable a few weeks ago. It is worse when the volume is turned up more.
I don't mean to sound like an idiot but my first few ideas are as follows: Buy a line conditioner, hmm, not sure what else. Do I have a ground issue? Does anyone have any ideas. Thanks,
128x128rilands
reubent
6,939 posts
 
Rilands,

Sounds like the typical thump when using a subwoofer amplifier that has an auto-on circuit. When the amp senses a signal, it turns the amp on. I've heard this thump in many setups that have an amp that uses an auto-on circuit.

I would guess that the built-in amp in your NHTs has an auto-on circuit and you are hearing the amp turn on and "thump" the woofer.

TIC
hiend2's avatar
hiend2
376 posts
 
Another way of thinking about it is , try Floating a ground or 2. A turn off thump can be leaking caps on the amplifiers also
mechans
3,048 posts
 
Hiend2: What is the point of floating a ground? Either it should be grounded or not exist at all because if it's floating around you might hurt some one!
hiend2's avatar
hiend2
376 posts
 
I said try to float the ground you may learn more about the systems grounding. To me turn on/off thunps are leaking DC to some extent, I have repair bills to prove it can be the case
hifi57audio
15 posts
 
Hiend2 is close. The turn on/off thumps are caused by a rapidly climbing or decaying DC signal component being coupled to your speakers. This occures as the ciruit RC constants are charged/discharged. Most equipment is designed as to not allow this, by circuit design, or relays. Turn on your powered speakers last, if that does't work, they are likely defective.
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