Power for Transistor Base

[peterg]

Why are some circuits designed so that the power for the transistor base is direct from source i.e. EHX LPB and some circuits base power is connected to the collector's power and collector i.e. ZVEX SHO?

[Mike Burgundy]

I think you're referring to different biasing methods. Read everything you can find on BJT (Bipolar Junction Transistor) bias methods. This type of transistor is in an LPB1.
The SHO uses a different kind of transistor (MOSfet) which needs different bias schemes. finally the other common one is a "regular" FET. All 3 kinds come in 2 flavours, NPN/PNP for BJT, N-and P-channel for FET/MOSFET, which also has a very definitive influence on the hows and whys of biasing it. Biasing a transistor of any kind is necessary for it to work as an amplifier (or buffer, or switch). Different ways of achieving that bias have different pro's/cons like low parts count, reliability, accuracy, headroom, simplicity, low noise, ability to use different transistors, ability to use unselected/unmatched transistors, etc. One chooses the best way for a specific set of wishes. Well, in fairness, usually "good enough with least amount of effort" will do just fine.

[peterg]

Thanks Mike. The SHO may not have been the best example. There are many circuits using a FET, like the Electra, that have the base power resistor connected to the collector.

[Thecomedian]

http://www.allaboutcircuits.com/vol_3/chpt_4/7.html
http://www.allaboutcircuits.com/vol_3/chpt_4/6.html
http://www.allaboutcircuits.com/vol_3/chpt_4/5.html
http://www.allaboutcircuits.com/vol_3/chpt_4/10.html

EHX LPB is a common emitter amplifier circuit in the voltage divider bias form. it's probably the most stable and easiest type of design to apply.

Collector feedback bias occurs when there is a path through the resistor on the collector, to a resistor which goes to the base, so that the resistor for the base is "behind" the collector resistor which is between it and the battery.

[peterg]

http://www.allaboutcircuits.com/vol_3/chpt_4/7.html
http://www.allaboutcircuits.com/vol_3/chpt_4/6.html
http://www.allaboutcircuits.com/vol_3/chpt_4/5.html
http://www.allaboutcircuits.com/vol_3/chpt_4/10.html

EHX LPB is a common emitter amplifier circuit in the voltage divider bias form. it's probably the most stable and easiest type of design to apply.

Collector feedback bias occurs when there is a path through the resistor on the collector, to a resistor which goes to the base, so that the resistor for the base is "behind" the collector resistor which is between it and the battery.

Thanks. Looks like I have lots to learn!