[sdiy] (Semi-OT) cap polarity in microphone

[Happy Harry]

How different depends on the meter.. The 8060a is a
pretty NICE meter, and a lot of people have much less...

We wish the voltmeter was infinite in impedance... but
it is not. Even a 10 meg load is a lot in some cases. The
impedance of the microphone side will depend a lot on the
pullup resistor value.

I guess its preference... I'd rather make that measurement to
ground.

H^) harry


>From: Scott Gravenhorst <music.maker at gte.net>
>Reply-To: music.maker at gte.net
>To: synth-diy at dropmix.xs4all.nl
>Subject: Re: [sdiy] (Semi-OT) cap polarity in microphone
>Date: Mon, 18 Mar 2002 14:08:51
>
>But I wonder by how much the measurement would be different.
>Aren't voltmeter circuits designed to be very high impedance
>specifically so that the meter's load is negligable in most
>cases?
>
>I just looked at the specs for the meter I own, a Fluke 8060a,
>not that it's typical, but the manual says that for DC voltage
>measurement on the 200mv and 2v ranges, the input impedance
>is greater than 1,000 megohms, typically being 10,000 megohms.
>For the other ranges, they state a nominal input impedance of
>10 megohms.  Even 10 megohms doesn't seem like much of a load.
>
>harrybissell at prodigy.net wrote:
> >I suppose it would, but it would also put the meter
> >impedance across the capacitor as leakage. Measuring
> >both sides to ground would eliminate that possibility.
> >
> >H^) harry
> >
> >
> >>From: Scott Gravenhorst <music.maker at gte.net>
> >>Reply-To: music.maker at gte.net
> >>To: synth-diy at dropmix.xs4all.nl
> >>Subject: Re: [sdiy] (Semi-OT) cap polarity in microphone
> >>Date: Mon, 18 Mar 2002 09:45:27
> >>
> >>I'm curious, why wouldn't measuring the DC across
> >>the cap terminals tell you?
> >>
> >>harrybissell at prodigy.net wrote:
> >> >If the bias on the preamp side of the cap is higher than
> >> >the mic bias voltage... its correct.
> >> >
> >> >If not it is an assembly error. Measure the DC on both sides
> >> >with respect to ground, and decide...
> >> >
> >> >H^) harry
> >> >
> >> >
> >> >>From: Ingo Debus <debus at cityweb.de>
> >> >>To: synth-diy at dropmix.xs4all.nl
> >> >>Subject: [sdiy] (Semi-OT) cap polarity in microphone
> >> >>Date: Mon, 18 Mar 2002 11:02:21 +0100
> >> >>
> >> >>Hi,
> >> >>
> >> >>out of curiousity I had a look into my cheap (about $50) stereo 
>electret
> >> >>condensor mic. Not much in there, two capsules with two wires each,
> >> >>powered via 6.8k resistors from a 1.5V battery, and two 10uF 25V
> >> >>electrolytic caps in the signal paths. But the funny thing is, minus 
>of
> >> >>the caps is connected to the capsule side, where the plus of the 
>power
> >> >>supply is connected (through the 6.8k resistor). That's backwards,
> >> >>correct? Is there a specific reason for that, or is this an assembly
> >>error?
> >> >>
> >> >>Ingo
> >> >>
> >> >
> >> >
> >> >
> >> >
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> >
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>- Government: The other religion.
>- The media's credibility should always be questioned.
>- Lambs who lie down with lions are lunch.
>
>-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
>-- Linux Rex         | RedWebMail by RedStarWare
>-- FatMan: home1.GTE.NET/res0658s/FatMan/index.html
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