[sdiy] Giga-Ohm Resistors--Where?

[Theo]

>That resistor charges the diaphragm. The capacitance of the diaphragm is
>very low, so you have to use fairly high values to get a decent low
>corner frequency.
>
>Cheers,
>  René

I see, makes sense.
However when looking at the Gyraf G7 schematic there is also a 1G resistor
used for grit bias.
Makes me wonder, isn't the internal "grit to other electrodes" resistance of
the tube in the order of a mere 200M to 500M?
The Neumann schematics just below the G7 show (in a slightly different
approach) much lower resistance values for the grit resistor.


Theo


From: Craig Critchley <craigc at nwlink.com>

> 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
> >
>