help! Dc cone movement while volume adjust.

[mikee12345]

hi i just plugedd my small amp into my audio out of my tv,for a movie,running an 8inch sub.
it works.a nice improvement on crappy tv speakers..

the problem is..

when i adjust the volume knob,the cone moves,with DC !

when i turn it up,the cone moves out,then goes to resting position, and the inverse when i turn it down,

whats going on!

is it safe!!!! is it doing DC all the tiem from the tv, a fault? but i dont know?

if so oh well :-S

my amp doesnt do this when running of my stereo ..

thanks
_mike

[MadMax]

Is the cone moving fast and making noise or just stroking like when you turn some amps on.
Mark
Hay what part of NZ are you in?

[mikee12345]

(im in Dunedin)


the cone moves in a slow manner,sorry,not DC i didnt describe so well,its not instant,it sorta moves out over,say 3/4 of a second or slightly longer, then moves back at the same rate,to where it was(hopefully at 0)

i dont like it doing strange things LOL

its pretty much silent as it moves.

i called it Dc cos it only moved out,or In, oops..

it is similar to when u switch on and off,but i noticed it is MUCH more worser when switching on and off,while connected to this tv!! where as connected to my stereo it doesnt move nearly as much,thump i mean.

[MadMax]

If its moving slowly then I dont think it will harm anything. It could be a diffrance in earthing sort of causing an offset problem, the tv probley has no earth conection. Iam not expert so hopefully others will jump in with more info, the other thing to keep an eye on is that the amp isn't running hotter than normal. Its good to talk with a local Im just down the road in Balclutha. Hope this helps. Mark

[mikee12345]

oh awesome! not many DIYers around down here lol...

yeh its nice to know whats going on inside things....

heres my site..

http://homepages.paradise.net.nz/quadroph

and have u got msn ?

i think my diyaudio email function works anyway..

[subwo1]

It could also be that your TV has a DC bias on its outputs which is entering your amp through a faulty capacitor. You may want to install a 1uF blocking capacitor in the signal path between the TV and the amp if you do not wish to try to replace a possibly bad capacitor in the amp, possibly near the jack.

[MadMax]

That sounds like a couple of good ideas, the cap should stop it. I dont use msn, your email dosnt seem to be on, checked your site
what are you going to do when you finish tech. Iam a sparky. Ill turn my email on.
Mark.

[EC8010]

When you say you plugged into the audio out of your telly, was it a phono, a SCART, or a headphone jack?

Subwo1 is on the money saying that there's DC leaving your telly.

[mikee12345]

it is RCA mono out:P



yep it makes sense,,dc across the volume pot.

[EC8010]

Assuming that your amplifier doesn't do the same thing on other sources, the fault is in the telly, and is a leaky coupling capacitor (porbably 10uF 10V, or so).

The trouble is, domestic tellys are downright dangerous to poke inside. You are probably better off adding a 22k (ish) resistor to ground (at your pre-amplifier) from the output of the telly. then another 10uF capacitor in series with the signal.