speaker cone expand and contract when power on SA-3

[ferringi]

dear all,

Recently found out that when i turn out my threshold SA3 power amp, the speaker cone will start to poping out and contracting for 3 to 4 times. Its pretty scarely seeing both my left and right speaker are expanding and contracting in different phase, the speaker cone is being pushed to the extreme as if the rubber seal as it is going to burst.

Would like to seek the advice/ explain what is the cause of this problem?

thanks in advance

[Nelson Pass]

That's a pretty serious turn-on thump. They shouldn't do
that, and the fact that both channels do it leads to the
possibility that your source is involved.

I would check to see that it does it with shorted inputs.

[Andrew Eckhardt]

That left/right opposite phase thing is really werid. What Are you using for a signal source?

[ferringi]

My heart sink when seeing my beloved speaker being torture like that.
BTW, the SA3 is pair with audio research SP9 preamp (still hunting for FET 10) and denon player.Nvr strike my mind that this involve the preamp.

will replace with other preamp and CD player this evening and update you guys

thanks..

[Zen Mod]

as Papa sez :

disconnect input cables from power amp ( while shut of)

short inputs on power amp , then power it up ;

do you still have thump in speakers ?