MS wrote:

You can see real quick that small electrolytics pretty much suck, they
have a pile of ESR. And though you don't see this in the tables, that
ESR isn't linear, it reduces as frequency increases but on a curve
particular to that device. The larger caps do the same thing, but if
you have .95 ohm nominal ESR and scale down to point-0-something ohm
over frequency, it's alot different than starting at 1K or so and
scaling down... I ESR sized the blocking caps of an INA103 based pre
and it sounded great.

I'm not calling this untrue, but I think it's an odd way to think about
it. Of COURSE the ESR at 120Hz is higher in a smaller-value capacitor.
That's what capacitance does! "equivalent series resistance" at a
given frequencyis simply the net impedance (resistance plus capacitive
and inductive reactances) at that frequency. We already know that
capacitors block low frequencies, and that's the same as calling it an
increased (frequency-dependent) equivalent series resistance. So what
you're really saying is "use bigger capacitors" than what the arbitrary
LF cutoff might ought to be (which a lot of people ass-ume should be
20Hz or so). It's no big secret that picking a LF cut-off point a
decade or two below that (by using a cap 10 or 100 times as big) will
improve a bunch of things like LF phase response.


I used standard Belden 24ga tin clad copper/teflon and 4% silver solder
for the entire signal path to the JFET. All I can say is "you got to
be freaking kidding me that wire insulation can make that kind of
difference" after hearing the results (it's actually a great mic
now)... Of course if it ever will, it's going to be in this
application, there's just not very many electrons carrying the signal
from the capsule to the JFET...

This makes a lot of sense. Teflon is used as a dielectric in very
high-precision capacitors because it is so stable and makes a capacitor
that performs very well, but it also has a very low dielectric constant
which means teflon caps don't have very much capacitance for a given
physical size. If you consider the insulation on your wire to be a
capacitor of fixed size, then using teflon insulation will result in a
lower-value (and higher-quality) capacitor than other common insulator
materials. In ordinary circuits this capacitance would be negligible
in any case, but in a 10,000Mohm circuit this tiny capacitor becomes
meaningful. So, was it the decreased parasitic capacitance that
improved your mike or was it the improved qualities of said
capacitance? In what way did the sound improve? Simply increased
high-end or some kind of improved clarity or lower distortion? Hmm?

ulysses