LPB1 bypass capacitor

[Kipper4]

Any reason I shouldnt put a 22uf emitter bypass cap in the lpb1.
Just trying to up the gain a bit.

[Gus]

The input resistance is reduced.

[Kipper4]

Thanks Gus.
I'll breadboard it. Maybe try a few tricks like putting a 500k ( trial and error) pot in series with the bypass cap as a kinda gain control.
If it messes too much with the input resistance I'll whop a voltage follower in front and see how it works out.

[midwayfair]

a 500k ( trial and error) pot in series with the bypass cap as a kinda gain control.

A cap is a short for frequencies above a certain amount. If you put resistance in series with it, it'll impede those resistances. Gain goes up as the emitter resistance decreases.

It's not a good idea to just pick a random number for a potentiometer. Think about what it's going to do. Let's look at the schematic:

http://www.muzique.com/images/lpb1.gif

There will be two paths for the emitter to go through: one with 390 Ohm resistance and a cap with up to 500,000 Ohms of resistance. At halfway, it's 250,000. At 1/500th, it's 1,000.

Imagine you're an electron. Which path looks more appealing to you? Where will you have to set the pot to make the path through the capacitor more appealing than the 390 Ohms already there?

With that in mind, you might want to pick a different value of potentiometer to experiment with.

[Kipper4]

Good point Jon.
Thanks for the food for thought.

[Kipper4]

Maybe I should make the bypass cap with a switch and have a 500k-1M resistor to ground on the cathode of the cap so it can drain when not in use.
Will this cause noise or popping when the cap charges up when switched in?

[Kipper4]

Just to say this is all just fluff for a circuit I'm already happy with.
But in the intrest of science. 

[Groovenut]

The input impedance for that circuit is already pretty low (~33K if my math is right using 300 as the gain), I dont think there's any reason not to try the cap with the 500k pot in series (though as Jon says, a 1k-5k should be plenty). You never know what happy accidents you may encounter. It certainly wont harm the circuit any. The resistance in series with the cap actually changes the angle of the slope after the knee in my experience. The knee should be set by the RC combo of the 390R and the 22uF (in this scenario) cap, ie 18Hz.

Of course I could be all wet about this, YMMV

Im sure those more knowledgeable will let me know of my err