QUAD 303 why does signal trace move on scope

[Chrisr3521]

I've had a few Quad 303's and they all seem to do this

When first switched on the signal viewed on my Rigol scope moves down, off the screen before settling after a few minutes ( pressing the auto function corrects the view of the signal) why does it do this?

 

[jwilhelm]

Sounds like the amp has DC offset on startup. Try setting the scope ground to AC

 

[Logic800]

Are you testing the output when it is loaded?

 

[Chrisr3521]

The amp isn't loaded and the 303 is a cap coupled amp if this matters?

 

[as_audio]

yes, what you see is due to the output coupling cap charging up.

 

[Chrisr3521]

Ah, ok! So the larger the cap the longer the charge up / settling time, makes sense.