input out put caps

[jimilee]

 So I'm trying to understand what I have been building. Is the input cap always the first cap and the output cap always the last? I have a small angel chorus that lacks bottom end for bass and was looking to maybe mod it a bit.

[midwayfair]

Colloquial terms for coupling caps, and yes, usually they are where you say, but it can also just be the input/output of a particular gain stage depending on context. These form low-pass filters, so often they can increase the bass in a circuit. Not always though. Many designers make input caps far larger than needed. (I tend to really go overboard ...)

[jimilee]

So should I just increase it in the chorus and see what happens?

[RobA]

I'm assuming that you are talking about the Little Angel Chorus. I've never built one, but I've had a look at the schematic(s) a couple of times. So, if that's the one you are working on and it is the version that has the inverting op amp input stage with the 470k resistor and the 0.1µF cap, then the input forms a high pass filter with a corner frequency given by the formula

F = 1/(2 * pi * 470E3 * 0.1E-6) = 3.4Hz

But, the actual start of the rolloff will be above that point. Still, it seems that it should be OK for bass.

On the output is another HP filter that is setup by the output cap and the 100k resistor. Assuming a high input impedance in whatever you have coming after, that filter has a frequency of about 16Hz. But, if the impedance of what follows is around the same as that 100k, it could be above 30Hz and that could get into the range of messing with your bass. You could look at changing the output cap to a higher value, but it might not work because that would be forcing the PT2399 to drive a higher capacitive load and it might not be good at it.

One thing you could try is to put a high input impedance buffer pedal after the chorus just to see if that helps (assuming that you don't already do this).  If it does, you might try increasing the output cap and resistor.

All of that of course depends on my having the right schematic. I could easily have an older version than what you are working with. Also, I don't think it is going to hurt to increase the input cap, so you might want to try that too.

[jimilee]

Thank you, plan b was to get a more chorusy chorus pedal..... maybe I'll do that. Mr black makes a double chorus pedal that looks and sounds pretty neat.