Re: Blues Blaster Mic - Capacitor

[Bruce Steinberg <bruces@xxxxxxx>]

re:

                                <...>
        
            Pretty close. Had I seen the original post, I would have responded.
        Actually there are only a couple of thing that need clarification:
        
        :The cap is there as a filter.  A cap appears as an open circuit to low
        :frequency signals and a closed (or short) circuit to high frequencies.
         Actually a capacitor blocks DC and passes AC which is essentially what you
        said. Depending on any given resistance that is coupled with the capacitance
        will determine what if any frequencies are passed.
        
        :Not a whole lot of complex filtering you can do with one capacitor...
        :either pass treble or lose treble. 
        To an extent this is also true but in reality all one capacitor can do is
        pass ALL AC. It takes resistence to create a filter and that filter can
        either be a high pass, low pass or band pass. In other words it can filter
        out the highs, leaving lows and mids, filter out the lows, leaving highs
        and mids or filter out the lows and highs, leaving mids(band pass). Most
        mics end up with the cap and a volume pot wired as a band pass circuit. The
        
                                <...>

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Actually, while Rs and Cs can be used to make simple high- or
low-pass filters with specific frequency responses, a C by itself
~can~ be used to create basic high- or low-pass filtering in the
widest sense (e.g., audio vs. radio frequencies).

In its most basic terms, what we call "impedance" of a given
circuit is the vector sum of its DC "resistance," plus something
called "reactance" (think of it as frequency-specific "AC
resistance") provided independently by any C (or inductance, L)
in the circuit.  Both resistance and reactance are expressed and
measured in ohms (although they are always out of phase to some
degree, which is another discussion :).

In the case of capacitors, capacitive reactance is inverse to
frequency (1/2[pi]fC), so a given C has an infinite reactance to
DC, decreasing as the frequency increases, all the way up to
effectively a dead short for very high frequencies -- even with
with no appreciable R in the circuit at all.

Therefore, capacitors don't "pass all AC";  in fact, they are
~lousy~ conductors at very low frequencies, but get "better" as
the frequency impressed across them goes up.

So it's possible for a simple C by itself to be used as the
simplest and grossest possible low- or high-pass filter, either
in parallel or in series as required.  Adding resistance can
only help to shape a more specific frequency response (as in
"db/octave").

BTW, you need an *L* and a C to make a tuned *band*-pass filter,
at least out of strictly passive components (i.e., no active amp
to provide balancing phase shift at the "tuned" frequency).  Rs
and Cs can only be combined passively (even in complex
configurations) to provide high- and low-pass responses.  

Hope this helps (even if it still doesn't explain what the heck
that cap is really doing in the JT-30 :).  B*