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View Full Version : DC voltage on output of SB2



Craig
2005-07-30, 03:16
I recently changed my main squeezebox in my hifi to a SB2 and started noticing a thump when changing the input selector of my preamp (Audiolab 8000C) to the squeezebox. This didn't occur with the SB1.

A bit of testing has revealed 2 things - When the output of the SB2 is left unterminated, a DC potential slowly appears on the O/P of about 0.6V after an hour and 5V overnight!!!

My preamp does not terminate unselected inputs, they go straight to the selector switch and only get a termination if selected.

So what's happening is, if I listen to the CD for awhile then the DC voltage builds on the output of the SB2 then when I switch to the SB I get an unwelcome thump.

So the cure is pretty obvious - I need to put 1 meg resistors across the outputs of the SB2 but is it a fault or a design problem?

Craig

Patrick Dixon
2005-07-30, 07:01
It's a feature of the design.

The output stage runs between 9V and 0V and is AC coupled (via an electrolytic cap) to the connector. There's no DC path to ground, so it relies on that being path of the input stage of the amp - which it usually is.

Craig
2005-07-30, 07:53
Thanks Patrick,

Well if that's the case then I'm gonna have to terminate the output with resistors, I'd figured that it was probably capacitor leakage.
I'd be very suprised if the Audiolab is the only preamp that doesn't terminate all it's inputs though

Craig

Craig
2005-08-02, 13:18
Well I soldered 1meg resistors to the underside of the phono connectors in the SB2 and now switching between inputs is silent.

I'll be surprised if this doesn't crop up again

Craig