Re: [Elecraft] K2: connecting a condenser mic

2010-01-30 Thread David Woolley (E.L) 
If it really is a simple condenser microphone, it will not work with 
only 5, or even 12 volts of bias.

It is almost certainly an electret microphone, which is a composite 
device, consisting of an electret transducer and a MOSFET pre-amplifier. 
  The element is biased by the permanent charge on the electret, and the 
power supply is actually for the pre-amplifier.
-
400k is too low for the element itself and too high for the FET, in a 
two wire configuration.  I suspect a two wire configuration and that the 
reading is being distorted by reverse polarity or too low a measurement 
voltage.
-
Most, if not all, amateur use electret microphones are two wire devices, 
even though those for PC sounds use stereo plugs; the ring and tip are 
actually connected together, and the plug is just a trick to ensure that 
the bias is not applied to a dynamic microphone, which will use a mono plug.

Applying 5 volts DC to one of these without either a resistor or AF 
choke, will create an AC short on the output, and, depending on how good 
the power supply bypassing is, you may get no output at all!
---
A two wire electret will not behave like a resistor.  It will have the 
approximately square law characteristic of an FET drain, so you cannot 
use simple potential divider calculations.
---
The risk of a short would be due to a cable fault

Non-interleaved top posting by list policy, not desire.   
indicate where to interleave.

Brian Machesney wrote:
> I have a condenser mic that is not on the list of "known" mics in the docs
> or on the Elecraft web site. I'm trying to decide whether to simply short
> the +5V to the AF when connecting my condenser mic to the KSB2, or to place
-
> 
> A DMM shows the DC resistance of the element to be 400 Kohms! Not really
> surprising, I guess, since a condenser mic is electrically similar to a
> capacitor.
-
> The manufacturer specs the mic element at 4.5Kohms and 1.5V to 9.0V bias.
> Applying the KSB2's +5V directly to the mic element's 4.5K ohms should
> produce 1mA drain, no sweat for the KSB2, and right in the middle of the
> manufacturer's applied DC voltage spec.
-
> resistor would apply nearly 11V to the mic, if the mic element and the
> series act as a pure voltage divider. The 2.2K ohm resistor would produce 8V
> at the mic.

> 
> The KSB2 schematic shows a 2.2uF electrolytic cap between the MIC AF and the
> rest of the KSB2, so I wouldn't think there's any risk of a short.
> 


-- 
David Woolley
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encourage postings on a wide range of amateur radio related topics"
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Re: [Elecraft] K2: connecting a condenser mic

2010-01-29 Thread Jim Brown 
On Fri, 29 Jan 2010 08:49:43 -0500, Brian Machesney wrote:

>I have a condenser mic 

If it's like most 2-wire mics, you want a series resistor between V+ 
and the "hot" terminal of the mic. It serves as the load resistor 
for the output stage of the mic, and also limits current to that 
output stage to a safe value. If I knew nothing about the mic, a 
value on the order of 4.7K - 5.6K would be a good starting point. 
The mfr is giving you lower values. If you use NO resistor, the V+ 
shorts out the audio. 

73,

Jim K9YC



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Re: [Elecraft] K2: connecting a condenser mic

2010-01-29 Thread Don Wilhelm 
Brian,

You *could* put the resistor in the mic plug, but I would think it 
easier to add the resistor in the K2 to the back of the microphone jack 
between pin 1 and pin 6 as is normally done.  In the K3, you simply turn 
Bias on in the menu.

If you choose to put the resistor in the mic plug, run the K3 without 
Bias selected, it will pick up the voltage from pin 6

73,
Don W3FPR

Brian Machesney wrote:
> Thanks, Don.
>
> Not knowing any better, I simply shorted the AF and MICBIAS when I connected
> the mic to the K3. From what I can see in the K3 schematics, the only
> bypassing on the MICBIAS line is 1uF (rev B, sheet 5 of 7, "Front Panel -
> Miscellaneous"). Can I build the same resistor into the mic plug and use it
> that way for both the K2 and K3?
>
> Brian K1LI
>
> On Fri, Jan 29, 2010 at 9:34 AM, Don Wilhelm  wrote:
>
>   
>> Brian,
>>
>> Is that a 3 terminal mic element?  If so, then you can follow the
>> manufacturer's instructions and apply the 5 volts to the voltage terminal on
>> the element.
>> OTOH, most of these elements are 2 terminal, and the voltage should be
>> applied to the AF pin through a resistor - try 5.6k like the Elecraft MH2
>> uses as a first trial, it will likely work because the resistance is not
>> critical.
>> If you try to connect the 5 volts directly to the AF terminal, you will
>> effectively bypass all the audio to ground.  For AC signals, a power rail is
>> jst the same as ground because there are large bypass capacitors on the
>> voltage rail.
>>
>> 73,
>> Don W3FPR
>>
>>
>> Brian Machesney wrote:
>>
>> 
>>> I have a condenser mic that is not on the list of "known" mics in the docs
>>> or on the Elecraft web site. I'm trying to decide whether to simply short
>>> the +5V to the AF when connecting my condenser mic to the KSB2, or to
>>> place
>>> a resistor in between. I am more concerned about potential long-term
>>> adverse
>>> effects on the mic element by operating it out-of-spec than I am concerned
>>> with damaging the K2.
>>>
>>> A DMM shows the DC resistance of the element to be 400 Kohms! Not really
>>> surprising, I guess, since a condenser mic is electrically similar to a
>>> capacitor.
>>>
>>> The manufacturer specs the mic element at 4.5Kohms and 1.5V to 9.0V bias.
>>> Applying the KSB2's +5V directly to the mic element's 4.5K ohms should
>>> produce 1mA drain, no sweat for the KSB2, and right in the middle of the
>>> manufacturer's applied DC voltage spec.
>>>
>>> The manufacturer's tech sent me a wiring diagram that shows a +12V supply
>>> with a series resistor between 470 and 2.2K ohms to the mic. The 470 ohm
>>> resistor would apply nearly 11V to the mic, if the mic element and the
>>> series act as a pure voltage divider. The 2.2K ohm resistor would produce
>>> 8V
>>> at the mic.
>>>
>>> The KSB2 schematic shows a 2.2uF electrolytic cap between the MIC AF and
>>> the
>>> rest of the KSB2, so I wouldn't think there's any risk of a short.
>>>
>>> Help from those in the know, please?
>>>
>>>   
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Re: [Elecraft] K2: connecting a condenser mic

2010-01-29 Thread Brian Machesney 
Thanks, Don.

Not knowing any better, I simply shorted the AF and MICBIAS when I connected
the mic to the K3. From what I can see in the K3 schematics, the only
bypassing on the MICBIAS line is 1uF (rev B, sheet 5 of 7, "Front Panel -
Miscellaneous"). Can I build the same resistor into the mic plug and use it
that way for both the K2 and K3?

Brian K1LI

On Fri, Jan 29, 2010 at 9:34 AM, Don Wilhelm  wrote:

> Brian,
>
> Is that a 3 terminal mic element?  If so, then you can follow the
> manufacturer's instructions and apply the 5 volts to the voltage terminal on
> the element.
> OTOH, most of these elements are 2 terminal, and the voltage should be
> applied to the AF pin through a resistor - try 5.6k like the Elecraft MH2
> uses as a first trial, it will likely work because the resistance is not
> critical.
> If you try to connect the 5 volts directly to the AF terminal, you will
> effectively bypass all the audio to ground.  For AC signals, a power rail is
> jst the same as ground because there are large bypass capacitors on the
> voltage rail.
>
> 73,
> Don W3FPR
>
>
> Brian Machesney wrote:
>
>> I have a condenser mic that is not on the list of "known" mics in the docs
>> or on the Elecraft web site. I'm trying to decide whether to simply short
>> the +5V to the AF when connecting my condenser mic to the KSB2, or to
>> place
>> a resistor in between. I am more concerned about potential long-term
>> adverse
>> effects on the mic element by operating it out-of-spec than I am concerned
>> with damaging the K2.
>>
>> A DMM shows the DC resistance of the element to be 400 Kohms! Not really
>> surprising, I guess, since a condenser mic is electrically similar to a
>> capacitor.
>>
>> The manufacturer specs the mic element at 4.5Kohms and 1.5V to 9.0V bias.
>> Applying the KSB2's +5V directly to the mic element's 4.5K ohms should
>> produce 1mA drain, no sweat for the KSB2, and right in the middle of the
>> manufacturer's applied DC voltage spec.
>>
>> The manufacturer's tech sent me a wiring diagram that shows a +12V supply
>> with a series resistor between 470 and 2.2K ohms to the mic. The 470 ohm
>> resistor would apply nearly 11V to the mic, if the mic element and the
>> series act as a pure voltage divider. The 2.2K ohm resistor would produce
>> 8V
>> at the mic.
>>
>> The KSB2 schematic shows a 2.2uF electrolytic cap between the MIC AF and
>> the
>> rest of the KSB2, so I wouldn't think there's any risk of a short.
>>
>> Help from those in the know, please?
>>
>
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Re: [Elecraft] K2: connecting a condenser mic

2010-01-29 Thread Don Wilhelm 
Brian,

Is that a 3 terminal mic element?  If so, then you can follow the 
manufacturer's instructions and apply the 5 volts to the voltage 
terminal on the element.
OTOH, most of these elements are 2 terminal, and the voltage should be 
applied to the AF pin through a resistor - try 5.6k like the Elecraft 
MH2 uses as a first trial, it will likely work because the resistance is 
not critical.
If you try to connect the 5 volts directly to the AF terminal, you will 
effectively bypass all the audio to ground.  For AC signals, a power 
rail is jst the same as ground because there are large bypass capacitors 
on the voltage rail.

73,
Don W3FPR

Brian Machesney wrote:
> I have a condenser mic that is not on the list of "known" mics in the docs
> or on the Elecraft web site. I'm trying to decide whether to simply short
> the +5V to the AF when connecting my condenser mic to the KSB2, or to place
> a resistor in between. I am more concerned about potential long-term adverse
> effects on the mic element by operating it out-of-spec than I am concerned
> with damaging the K2.
>
> A DMM shows the DC resistance of the element to be 400 Kohms! Not really
> surprising, I guess, since a condenser mic is electrically similar to a
> capacitor.
>
> The manufacturer specs the mic element at 4.5Kohms and 1.5V to 9.0V bias.
> Applying the KSB2's +5V directly to the mic element's 4.5K ohms should
> produce 1mA drain, no sweat for the KSB2, and right in the middle of the
> manufacturer's applied DC voltage spec.
>
> The manufacturer's tech sent me a wiring diagram that shows a +12V supply
> with a series resistor between 470 and 2.2K ohms to the mic. The 470 ohm
> resistor would apply nearly 11V to the mic, if the mic element and the
> series act as a pure voltage divider. The 2.2K ohm resistor would produce 8V
> at the mic.
>
> The KSB2 schematic shows a 2.2uF electrolytic cap between the MIC AF and the
> rest of the KSB2, so I wouldn't think there's any risk of a short.
>
> Help from those in the know, please?
>   
>
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[Elecraft] K2: connecting a condenser mic

2010-01-29 Thread Brian Machesney 
I have a condenser mic that is not on the list of "known" mics in the docs
or on the Elecraft web site. I'm trying to decide whether to simply short
the +5V to the AF when connecting my condenser mic to the KSB2, or to place
a resistor in between. I am more concerned about potential long-term adverse
effects on the mic element by operating it out-of-spec than I am concerned
with damaging the K2.

A DMM shows the DC resistance of the element to be 400 Kohms! Not really
surprising, I guess, since a condenser mic is electrically similar to a
capacitor.

The manufacturer specs the mic element at 4.5Kohms and 1.5V to 9.0V bias.
Applying the KSB2's +5V directly to the mic element's 4.5K ohms should
produce 1mA drain, no sweat for the KSB2, and right in the middle of the
manufacturer's applied DC voltage spec.

The manufacturer's tech sent me a wiring diagram that shows a +12V supply
with a series resistor between 470 and 2.2K ohms to the mic. The 470 ohm
resistor would apply nearly 11V to the mic, if the mic element and the
series act as a pure voltage divider. The 2.2K ohm resistor would produce 8V
at the mic.

The KSB2 schematic shows a 2.2uF electrolytic cap between the MIC AF and the
rest of the KSB2, so I wouldn't think there's any risk of a short.

Help from those in the know, please?

-- 
73 -- Brian -- K1LI
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