[sdiy] Giga-Ohm Resistors--Where?

[Craig Critchley]

In condenser microphones, you apprently want a high voltage across the
capsule, but you don't want the charge on the capsule to dissipate when its
capacitance changes in response to pressure. So you charge the condenser
slowly through a really high resistance. This results in varying potential
on the capsule which you sense as an audio signal. It's apparently a common
feature of vintage tube condenser microphones, at least judging by the
schematics at www.gyraf.dk.

gyraf has plans for a tube condenser mic, actually. Is that what the project
is? If so, where's the capsule coming from?

                        ...Craig

----- Original Message ----- 
From: "Theo" <t.hogers at home.nl>
To: "Magnus Danielson" <cfmd at swipnet.se>
Cc: <synth-diy at dropmix.xs4all.nl>; <mclilith at charter.net>
Sent: Sunday, September 07, 2003 1:47 PM
Subject: Re: [sdiy] Giga-Ohm Resistors--Where?


> Yes I already noticed these extreme value resistors exist.
> But even so other than circuits running in controlled conditions to rule
out
> the environment or high voltage applications,
> resistors of 1G or up doesn't seem a practical thing to use.
> In a synth diy context it seemed like a joke or a misprint to me.
>
> Wonder what function they fulfill in your Neumann.
> And no I don't take high-end audio designs too seriously, even from Alfred
> E. ;)
>
> Cheers,
> Theo
>
>
> From: Magnus Danielson <cfmd at swipnet.se>
>
>
> > From: "Theo" <t.hogers at home.nl>
> > Subject: Re: [sdiy] Giga-Ohm Resistors--Where?
> > Date: Sun, 7 Sep 2003 21:40:45 +0200
> >
> > Theo,
> >
> > > ROTFL
> >
> > You are? WHY????? Please let me know what the joke is...
> >
> > > Err, don't think the resistors are that hard to get,
> > > just cut some plastic tubing to match the resistance.
> > > But where do you get the 1000000V power supply to run the circuit?
> >
> > Ehum... we have a power line expert here... (I still expects him to give
> us a
> > insiders geek-tour of the big powerfailure earlier this year...)
> >
> > If you need DC I am sure we could dig up some extraordinary rectifiers
or
> you
> > need to settle with a Van de Graaf generator...
> >
> > But that is all beside the point.
> >
> > > BTW In April of what year where these schematics published? ;)
> >
> > BTW, My Neumann U87A contains 3 pieces of 1G Ohm resistors - and they
> really
> > sit there, I've checked! Did you know that the U87A isn't a 1st of April
> joke?
> >
> > I think another box I have have a bunch of Gigaohm range resistors...
> since it
> > goes all up to 10^15 Ohm in its resistance measurement capabilities...
> > This same box is used to ensure that satellites handles NASA
requirements,
> > hospital equipment like electrocardiogram machines don't fry you etc.
etc.
> > It is also used to check qualities of oil...
> > That box isn't nearly a joke...
> >
> > So I don't understand why you are rolling around the floor laughing your
> guts
> > out...
> >
> > Cheers,
> > Magnus - a bit of a joker, but not this time, except for the highvoltage
> stuff
>