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previous: Mark Hammer Re:Thanks Mark and All. -- 7/15/2000 4:15 PM View Thread

VR3: "BIAS" ?

7/25/2000 6:57 AM
Preben Hansen
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VR3: "BIAS" ?
I would like to clear up the purpose of (VR3) on the CE-2 schem.  
 
I have compared the CE-2 and the BF-2 schems, and found following main difference:  
CE-2: Uses 9 Volt devices for BBD, MN3007, and Clock, MN3101.  
BF-2: Uses 5 Volt devices for BBD, MN3207, and Clock, MN3201.  
 
Look on the CE-2 schem: There is NO dc-blocking cap in the signalpath between the emitter-follower and the input of the BBD. VR3 is used to set the Bias at the BBD input. (Voltage goes thru the resistors and ends at the emitter).  
 
Look on the BF-2 schem: There is a dc blocking cap between the emitter follower and the BBD input. There is a separate Bias trimpot, feed from the 5-volt regulator. The dc blocking cab is there, to separate the 9-volt dc part from the 5-volt dc part, BBD-Clock-LFO, of the circiut.  
 
I cant see any other purpose of the VR3 than Bias adjustment, on the CE-2.  
 
Now, let me guess:  
The BF-1 uses MN30xx/MN3101 series of chips  
The CE-3 uses MN32xx/MN3201 series of chips.  
Can anyone confirm that ?  
 
Regards Preben.