Beocenter 3500, Beomaster 3000 bias setting

3 replies
BE
beovoxnewbie
Bronze
32 posts
Posted November 23, 2020 at 10:44 GMT
#2147720

Hi all,

I have noticed that the Beocenter 3500 service manual calls for 100mA bias current through the test points/connectors. This was easy to set after replacing trimmers with multi turns.

After setting at these points l then checked through my usual method by measuring voltage across ONE emitter resistor, which measured at around 12mV.

In my mind this is much too high for this type of amplifier as the emitter resistors are only 0.15 ohms. I am much more comfortable with voltage across one emitter resistor in the 4.5-5.0mV range and have set it as such. This is around 30-35mA.

Could there be an error in the service manual? I assume this also applies to the Beomaster 3000.

 

Cheers.

DI
Dillen
BronzeModeratorFounder
12777 posts
Posted November 23, 2020 at 13:32 GMT
#2147721

The servicemanual is correct.
And 12mV over 0,15 Ohms is no problem at all. It will get much higher when playing and still be no problem.

A slightly too low idle current can be more dangerous than a slightly too high.
If you set the idle current too low, you will get crossover distortion, that may overload (and even kill) the tweeters in your speakers due to a very high content of harmonics.
I suggest you set it right.

Martin

BE
beovoxnewbie
Bronze
32 posts
Posted November 23, 2020 at 22:09 GMT
#2147722

Hi Martin,

Thank you for your quick reply, very much appreciated. No worries, l will set it as per the manual then, it was just that the heat sink is warmer at idle than other Beomasters l have worked on, also other B&O models have that sort of figure or slightly higher across two emitters. I do understand about crossover distortion and the crucial effect bias has on this.

Cheers.

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