Basic components functions in buffer circuits?

[carboncomp]

Hello!

Just have a couple of real basic question about the components functions in these buffer circuits. 



Q1: What is the function of R1 and R2?



Q2: Are C1 & R3 just there as a low pass filter (and if so dose it mater if the resister is before or after the capacitor in a LPF?)?
Q3: Are C3 & R4 working as a high pass filter (and, C3 blocking DC too)?
Q4: Whats R5 function? (assume if it was going to ground it would attenuate the output, but what dose it do in series?)

[R.G.]

Q1: What is the function of R1 and R2?

R1 forces the gate of the JFET to be biased properly in spite of the (small) leakages inside the JFET. R2 generates the output voltage by exercising its Ohm's Law rights when the JFET allows a current through. It also applies that voltage as a feedback signal for both AC and DC to the Vgs difference that allows/changes the current through the JFET.

Q2: Are C1 & R3 just there as a low pass filter (and if so dose it mater if the resister is before or after the capacitor in a LPF?)?

It matters. C1 is there to FORCE the bias voltage to be quiet, as any AC on the bias voltage would also be fed to the input. R3 is there to add some input resistance to allow the signal input to drive the opamp input without also having to drive the loading of the voltage divider and C1.

Q3: Are C3 & R4 working as a high pass filter (and, C3 blocking DC too)?

C3 is there to block the DC voltage that the opamp output has to have. It does this by being a high pass filter with R4. DC is blocked. At some higher frequency, signal passes.

Q4: Whats R5 function? (assume if it was going to ground it would attenuate the output, but what dose it do in series?)

It is there so when your bass player shorts the output wires or connects them to a hot dog to see what happens, the opamp is preotected from large currents being drawn. Also, when your bass player plugs the output wires into an AC power socket, the resistor limits current - somewhat...    It's a protection device against output conditions. For some opamps, the capacitance of a long cable can make them unstable. It also stabilizes the opamp against this eventuality.

[bluebunny]

Thanks for asking the questions, carboncomp.  And thanks for providing the answers, R.G.  Clarity, insight and good humour as always.

But go easy on us bass players!   

[Kipper4]

Here here.
I love those questions and Definitely thanks to RG.
The only thing more nuts than a bass player is a drummer.
Take solice BlueBunny

[Thecomedian]

The smaller the cap on the input, and the larger the biasing resistors connected to Gate or Base of the transistor in the buffer circuit, the higher the impedance, meaning the higher the bridging effect, which is how to achieve maximum signal transfer, or how to reduce losses from a high impedance output source.

In simplistic terms, Impedance between two circuits behaves much like a simple voltage divider. The lower Z1 is compared to Z2, the load, or usually, the input of your buffer circuit, the less Z1 is loaded. Maximum Voltage and minimum current goes across Z2.

http://en.wikipedia.org/wiki/Electrical_load

Im wondering if those resistors are so high because of needing to make the variable resistance (impedance) of the small cap so insignificant compared to the resistor (voltage divider rules again), in order to keep lows from being substantially lost.

- I went ahead and used LTspice, and the size of that gate resistor does matter for protecting lows, but anything above 100k works just fine. Lower resistor size also reduces gain, since the gate will be more negative, as Negative voltage applied to the gate is what reduces the gain. The size of the resistor also increases the input impedance of the circuit, which is what maximizes voltage from the output of the other circuit.

[bluebunny]

Here here.
I love those questions and Definitely thanks to RG.

Yeah, me too.  +1 +1 +1  If given the choice, I'd be more than happy to have the p!ss taken than miss out on R.G.'s wisdom.  Even the stuff about cactus recipes.