Elecraft

CM-500

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Ira J Saber DMD

CM-500

GA Everyone

I hope this has not been answered before, but I could not
find my answer in the archives, so here goes.

Can anyone tell me how much bias the microphone is able to
tolerate? Since the battery pack supplies 3v
dc, I am sure that 4-5 volts probable won't hurt. But how
about 10-12v DC?

I use my headset with my K2, but would like to try it with
another rig that supplies 10v. To get my other rig voltage
down to the 3-4v region require about 12 meg ohms in series
with the 10volts supplied.

All of you guys and gals are a great source for info
regardless of topic and I wish to thank all and any of you
who choose to answer my "novice" question. I have learned
something in my years on this earth, that if you don't ask
you do not get any answers.

Thanks again in advance.

73

Ira N2IS
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Josh Fiden

Re: CM-500

I used the CM-500 extensively with a 756 which provides 8V bias (IIRC).
Worked great.

73,
Josh W6XU

On 3/14/2013 11:45 AM, Dr Ira J Saber wrote:

> GA Everyone
>
> I hope this has not been answered before, but I could not find my
> answer in the archives, so here goes.
>
> Can anyone tell me how much bias the microphone is able to tolerate?
> Since the battery pack supplies 3v
> dc, I am sure that 4-5 volts probable won't hurt. But how about
> 10-12v DC?
>
> I use my headset with my K2, but would like to try it with another rig
> that supplies 10v. To get my other rig voltage down to the 3-4v
> region require about 12 meg ohms in series with the 10volts supplied.
>
> All of you guys and gals are a great source for info regardless of
> topic and I wish to thank all and any of you who choose to answer my
> "novice" question. I have learned something in my years on this
> earth, that if you don't ask you do not get any answers.
>
> Thanks again in advance.
>
> 73
>
> Ira N2IS
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

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Joe Subich, W4TV-4

Re: CM-500

In reply to this post by Ira J Saber DMD

> I use my headset with my K2, but would like to try it with another
> rig that supplies 10v. To get my other rig voltage down to the 3-4v
> region require about 12 meg ohms in series with the 10volts
> supplied.

An electret does not draw current in the classic sense. 5.6K seems
to be a good value of resistor for almost anything from 5 to 8V but
12K might be safer for your 10-12V.

The "big name" aviation headsets use 33 - 48K resistors for the typical
48V aircraft system. They tend to not work well with the 3-5V ham and
computer supplies but if they are opened and the resistor removed (or
replaced with a 2K2 depending on whether the equipment already contains
a resistor), they work perfectly well at the lower voltage.

I've always used a rule of thumb of 1K/V for electret mics.

73,

... Joe, W4TV

On 3/14/2013 2:45 PM, Dr Ira J Saber wrote:

> GA Everyone
>
> I hope this has not been answered before, but I could not find my answer
> in the archives, so here goes.
>
> Can anyone tell me how much bias the microphone is able to tolerate?
> Since the battery pack supplies 3v
> dc, I am sure that 4-5 volts probable won't hurt. But how about 10-12v DC?
>
> I use my headset with my K2, but would like to try it with another rig
> that supplies 10v. To get my other rig voltage down to the 3-4v region
> require about 12 meg ohms in series with the 10volts supplied.
>
> All of you guys and gals are a great source for info regardless of topic
> and I wish to thank all and any of you who choose to answer my "novice"
> question. I have learned something in my years on this earth, that if
> you don't ask you do not get any answers.
>
> Thanks again in advance.
>
> 73
>
> Ira N2IS
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

Fred Townsend-2

Re: CM-500

In reply to this post by Ira J Saber DMD

Ira:
Your comments concern me a bit. It is important to remember the electrolet
microphone requires a bias voltage but does not consume any electrical
power; i.e. you are not powering the microphone. Rather the microphone is
modulating the bias voltage. However there may be a current flow within the
microphone circuit depending on how the microphone is terminated and coupled
to the microphone input circuit. The bottom line is the bias voltage is not
important. As long as the voltage rating of any electrolytic capacitors in
the network is not exceeded it is not critical. What is important is the
quality of the powering circuit. It must be extremely well filtered. One
good way of filtering is to use a RC filter in conjunction with a voltage
divider. However if you leave out the voltage divider and apply only the RC
you will be applying the filter to the mic input rather than to the power
source.

When you ask if 10-12v is OK I wonder as to the quality of that power
source. If the 12 volts is shared it may well be dirty and unsuitable for a
mic circuit.

If you are using a 12meg resistor I suspect you may be forming a voltage
divider with the leakage resistance of a electrolytic cap. This could damage
the cap and not solve your problem. There are plenty of published circuits
on how to setup the bias. I would stick with one of them.
73
Fred, AE6QL

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Dr Ira J Saber
Sent: Thursday, March 14, 2013 11:46 AM
To: [hidden email]
Subject: [Elecraft] CM-500

GA Everyone

I hope this has not been answered before, but I could not find my answer in
the archives, so here goes.

Can anyone tell me how much bias the microphone is able to tolerate? Since
the battery pack supplies 3v dc, I am sure that 4-5 volts probable won't
hurt. But how about 10-12v DC?

I use my headset with my K2, but would like to try it with another rig that
supplies 10v. To get my other rig voltage down to the 3-4v region require
about 12 meg ohms in series with the 10volts supplied.

All of you guys and gals are a great source for info regardless of topic and
I wish to thank all and any of you who choose to answer my "novice"
question. I have learned something in my years on this earth, that if you
don't ask you do not get any answers.

Thanks again in advance.

73

Ira N2IS
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

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Mark Goldberg

Re: CM-500

In reply to this post by Joe Subich, W4TV-4

A standard aviation microphone approved to TSO C58 is supposed to meet
DO-214 "Audio Systems Characteristics And Minimum Operational Performance
Standards For Aircraft Audio Systems And Equipment" although not all do.
Unless you belong to the RTCA, it will cost money to see that document. The
standard is bias excitation is 8 to 16V with a 470 ohm current limiting
resistor, providing about 10 ma to what usually is an amplifier circuit in
the mic. The ac output level is supposed to be between .02 and .08 V/Pa,
where 1 Pa is 94 dB SPL referenced to 20 uPa. Normal close speech is in
the range of about 1 to 10 Pa, so this is pretty high compared to a lot of
other mics, up to .8 V. I have not tried connecting one up, but I would
think if you had a resistor that provides about 10 ma it should work, if
the rig can stand that high an input and if the bias can supply 10 ma.
Active Noise Cancelling headsets have other power options, maybe running
off 28V. I am not aware of 48V systems in Commercial aviation, but I don't
know everything that is out there. Carbon mics were different but not
common any more.

One issue is to keep the load mic preamp from disturbing the bias. I had to
filter the bias end of the series resistor on one rig with a big cap. Also,
connections vary.

Mark
On Mar 14, 2013 12:27 PM, "Joe Subich, W4TV" <[hidden email]> wrote:

>
> I use my headset with my K2, but would like to try it with another
>> rig that supplies 10v. To get my other rig voltage down to the 3-4v
>> region require about 12 meg ohms in series with the 10volts
>> supplied.
>>
>
> An electret does not draw current in the classic sense. 5.6K seems
> to be a good value of resistor for almost anything from 5 to 8V but
> 12K might be safer for your 10-12V.
>
> The "big name" aviation headsets use 33 - 48K resistors for the typical
> 48V aircraft system. They tend to not work well with the 3-5V ham and
> computer supplies but if they are opened and the resistor removed (or
> replaced with a 2K2 depending on whether the equipment already contains
> a resistor), they work perfectly well at the lower voltage.
>
> I've always used a rule of thumb of 1K/V for electret mics.
>
> 73,
>
> ... Joe, W4TV
>
>
> On 3/14/2013 2:45 PM, Dr Ira J Saber wrote:
>
>> GA Everyone
>>
>> I hope this has not been answered before, but I could not find my answer
>> in the archives, so here goes.
>>
>> Can anyone tell me how much bias the microphone is able to tolerate?
>> Since the battery pack supplies 3v
>> dc, I am sure that 4-5 volts probable won't hurt. But how about 10-12v
>> DC?
>>
>> I use my headset with my K2, but would like to try it with another rig
>> that supplies 10v. To get my other rig voltage down to the 3-4v region
>> require about 12 meg ohms in series with the 10volts supplied.
>>
>> All of you guys and gals are a great source for info regardless of topic
>> and I wish to thank all and any of you who choose to answer my "novice"
>> question. I have learned something in my years on this earth, that if
>> you don't ask you do not get any answers.
>>
>> Thanks again in advance.
>>
>> 73
>>
>> Ira N2IS
>> ______________________________**______________________________**__
>> Elecraft mailing list
>> Home: http://mailman.qth.net/**mailman/listinfo/elecraft<http://mailman.qth.net/mailman/listinfo/elecraft>
>> Help: http://mailman.qth.net/mmfaq.**htm<http://mailman.qth.net/mmfaq.htm>
>> Post: mailto:[hidden email].**net <[hidden email]>
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>>
>> ______________________________**______________________________**__
> Elecraft mailing list
> Home: http://mailman.qth.net/**mailman/listinfo/elecraft<http://mailman.qth.net/mailman/listinfo/elecraft>
> Help: http://mailman.qth.net/mmfaq.**htm<http://mailman.qth.net/mmfaq.htm>
> Post: mailto:[hidden email].**net <[hidden email]>
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

Joe Subich, W4TV-4

Re: CM-500

> Active Noise Cancelling headsets have other power options, maybe
> running off 28V. I am not aware of 48V systems in Commercial
> aviation, but I don't know everything that is out there. Carbon mics
> were different but not common any more.

Maybe it was 28 instead of 48 volts ... it has been a while since I
ran into the problem of making the aviation headsets run in an "AV"
environment. I do know that the headsets in question were spec'd as
"carbon mic" equivalent and required a high voltage bias until the
resistors were reduced by a factor of about 20.

73,

... Joe, W4TV

On 3/14/2013 4:27 PM, Mark Goldberg wrote:

> A standard aviation microphone approved to TSO C58 is supposed to meet
> DO-214 "Audio Systems Characteristics And Minimum Operational Performance
> Standards For Aircraft Audio Systems And Equipment" although not all do.
> Unless you belong to the RTCA, it will cost money to see that document. The
> standard is bias excitation is 8 to 16V with a 470 ohm current limiting
> resistor, providing about 10 ma to what usually is an amplifier circuit in
> the mic. The ac output level is supposed to be between .02 and .08 V/Pa,
> where 1 Pa is 94 dB SPL referenced to 20 uPa. Normal close speech is in
> the range of about 1 to 10 Pa, so this is pretty high compared to a lot of
> other mics, up to .8 V. I have not tried connecting one up, but I would
> think if you had a resistor that provides about 10 ma it should work, if
> the rig can stand that high an input and if the bias can supply 10 ma.
> Active Noise Cancelling headsets have other power options, maybe running
> off 28V. I am not aware of 48V systems in Commercial aviation, but I don't
> know everything that is out there. Carbon mics were different but not
> common any more.
>
> One issue is to keep the load mic preamp from disturbing the bias. I had to
> filter the bias end of the series resistor on one rig with a big cap. Also,
> connections vary.
>
> Mark
> On Mar 14, 2013 12:27 PM, "Joe Subich, W4TV" <[hidden email]> wrote:
>
>>
>> I use my headset with my K2, but would like to try it with another
>>> rig that supplies 10v. To get my other rig voltage down to the 3-4v
>>> region require about 12 meg ohms in series with the 10volts
>>> supplied.
>>>
>>
>> An electret does not draw current in the classic sense. 5.6K seems
>> to be a good value of resistor for almost anything from 5 to 8V but
>> 12K might be safer for your 10-12V.
>>
>> The "big name" aviation headsets use 33 - 48K resistors for the typical
>> 48V aircraft system. They tend to not work well with the 3-5V ham and
>> computer supplies but if they are opened and the resistor removed (or
>> replaced with a 2K2 depending on whether the equipment already contains
>> a resistor), they work perfectly well at the lower voltage.
>>
>> I've always used a rule of thumb of 1K/V for electret mics.
>>
>> 73,
>>
>> ... Joe, W4TV
>>
>>
>> On 3/14/2013 2:45 PM, Dr Ira J Saber wrote:
>>
>>> GA Everyone
>>>
>>> I hope this has not been answered before, but I could not find my answer
>>> in the archives, so here goes.
>>>
>>> Can anyone tell me how much bias the microphone is able to tolerate?
>>> Since the battery pack supplies 3v
>>> dc, I am sure that 4-5 volts probable won't hurt. But how about 10-12v
>>> DC?
>>>
>>> I use my headset with my K2, but would like to try it with another rig
>>> that supplies 10v. To get my other rig voltage down to the 3-4v region
>>> require about 12 meg ohms in series with the 10volts supplied.
>>>
>>> All of you guys and gals are a great source for info regardless of topic
>>> and I wish to thank all and any of you who choose to answer my "novice"
>>> question. I have learned something in my years on this earth, that if
>>> you don't ask you do not get any answers.
>>>
>>> Thanks again in advance.
>>>
>>> 73
>>>
>>> Ira N2IS
>>> ______________________________**______________________________**__
>>> Elecraft mailing list
>>> Home: http://mailman.qth.net/**mailman/listinfo/elecraft<http://mailman.qth.net/mailman/listinfo/elecraft>
>>> Help: http://mailman.qth.net/mmfaq.**htm<http://mailman.qth.net/mmfaq.htm>
>>> Post: mailto:[hidden email].**net <[hidden email]>
>>>
>>> This list hosted by: http://www.qsl.net
>>> Please help support this email list: http://www.qsl.net/donate.html
>>>
>>> ______________________________**______________________________**__
>> Elecraft mailing list
>> Home: http://mailman.qth.net/**mailman/listinfo/elecraft<http://mailman.qth.net/mailman/listinfo/elecraft>
>> Help: http://mailman.qth.net/mmfaq.**htm<http://mailman.qth.net/mmfaq.htm>
>> Post: mailto:[hidden email].**net <[hidden email]>
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>>
>

Fred Townsend-2

Re: CM-500

In reply to this post by Mark Goldberg

Gentlemen:
I think you muddy the waters when you refer to preamps and electrolet
headsets such as the CM500 in the same context. There is no appreciable
current flow in the CM-500. That's why you can run the bias for years with a
pair of AAA batteries. Let's take discussions of preamps with 10 ma circuits
and legacy items like carbon mics to another thread.
73
Fred, AE6QL

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Mark Goldberg
Sent: Thursday, March 14, 2013 1:28 PM
To: Joe Subich, W4TV
Cc: Elecraft Mailing List
Subject: Re: [Elecraft] CM-500

A standard aviation microphone approved to TSO C58 is supposed to meet
DO-214 "Audio Systems Characteristics And Minimum Operational Performance
Standards For Aircraft Audio Systems And Equipment" although not all do.
Unless you belong to the RTCA, it will cost money to see that document. The
standard is bias excitation is 8 to 16V with a 470 ohm current limiting
resistor, providing about 10 ma to what usually is an amplifier circuit in
the mic. The ac output level is supposed to be between .02 and .08 V/Pa,
where 1 Pa is 94 dB SPL referenced to 20 uPa. Normal close speech is in the
range of about 1 to 10 Pa, so this is pretty high compared to a lot of other
mics, up to .8 V. I have not tried connecting one up, but I would think if
you had a resistor that provides about 10 ma it should work, if the rig can
stand that high an input and if the bias can supply 10 ma.
Active Noise Cancelling headsets have other power options, maybe running off
28V. I am not aware of 48V systems in Commercial aviation, but I don't know
everything that is out there. Carbon mics were different but not common any
more.

One issue is to keep the load mic preamp from disturbing the bias. I had to
filter the bias end of the series resistor on one rig with a big cap. Also,
connections vary.

Mark
On Mar 14, 2013 12:27 PM, "Joe Subich, W4TV" <[hidden email]> wrote:

http://mailman.qth.net/**mailman/listinfo/elecraft<http://mailman.qth.net/ma
ilman/listinfo/elecraft>
>> Help:
http://mailman.qth.net/mmfaq.**htm<http://mailman.qth.net/mmfaq.htm>
>> Post: mailto:[hidden email].**net <[hidden email]>
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>>
>> ______________________________**______________________________**__
> Elecraft mailing list
> Home:
http://mailman.qth.net/**mailman/listinfo/elecraft<http://mailman.qth.net/ma
ilman/listinfo/elecraft>
> Help: http://mailman.qth.net/mmfaq.**htm<http://mailman.qth.net/mmfaq.htm>
> Post: mailto:[hidden email].**net <[hidden email]>
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
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