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

[Scott Gravenhorst]

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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>>-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
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>>
>
>
>
>
>_________________________________________________________________
>MSN Photos is the easiest way to share and print your photos: 
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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
-- NonFatMan: home1.GTE.NET/res0658s/electronics/index.html