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Dumb mic battery question

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Anonymous
June 5, 2005 8:44:58 PM

Archived from groups: rec.audio.pro (More info?)

As I recall, the manual for the original Radio Shack PZM microphone
suggested using two 6V photo batteries in place of a single AA cell to
achieve higher output and lower self noise. Is this possible or even
desirable with other mics, specifically the Audio Technica AT822?
Anonymous
June 5, 2005 11:32:58 PM

Archived from groups: rec.audio.pro (More info?)

Robert Ehrhardt wrote:
> As I recall, the manual for the original Radio Shack PZM microphone
> suggested using two 6V photo batteries in place of a single AA cell to
> achieve higher output and lower self noise. Is this possible or even
> desirable with other mics, specifically the Audio Technica AT822?

The usual FET common source or source follower circuit
(which I am pretty sure is what was/is in that mic) will
allow one rail to go higher with more voltage but since the
bias point doesn't change and the load resistor doesn't
change, the other rail will be the same as it was and
nothing will be gained. It is possible with a voltage
divider using huge resistors to make the bias point track in
a simple way but they are physically large and expensive and
not used in inexpensive circuits that typically rely on self
biasing of the FET which is supply independant.

I can also see no reason why with such a circuit (or most
any other) the self noise would be affected by higher supply
voltage.

Are you sure the manual said that?


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein
June 5, 2005 11:58:19 PM

Archived from groups: rec.audio.pro (More info?)

I think this is a pretty good damn question. I'd like to know as well.

On Sun, 05 Jun 2005 16:44:58 GMT, Robert Ehrhardt
<r_ehrh@bellsouth.net> wrote:

>As I recall, the manual for the original Radio Shack PZM microphone
>suggested using two 6V photo batteries in place of a single AA cell to
>achieve higher output and lower self noise. Is this possible or even
>desirable with other mics, specifically the Audio Technica AT822?
Related resources
Anonymous
June 6, 2005 8:33:35 PM

Archived from groups: rec.audio.pro (More info?)

Bob Cain wrote:
>
>
> Robert Ehrhardt wrote:
>
>> As I recall, the manual for the original Radio Shack PZM microphone
>> suggested using two 6V photo batteries in place of a single AA cell to
>> achieve higher output and lower self noise. Is this possible or even
>> desirable with other mics, specifically the Audio Technica AT822?
>
[snip]
> I can also see no reason why with such a circuit (or most any other) the
> self noise would be affected by higher supply voltage.
>
> Are you sure the manual said that?
>
>
> Bob

Yes, though I no longer have the manuals, I still have two of these
microphones and have been using them with two 6v photo batteries for
more than fifteen years. There is a marked improvement in the noise
level and a slight increase in output.

Robert
Anonymous
June 6, 2005 8:33:36 PM

Archived from groups: rec.audio.pro (More info?)

Robert Ehrhardt wrote:
> Bob Cain wrote:
>>
>>
>> Robert Ehrhardt wrote:
>>
>>> As I recall, the manual for the original Radio Shack PZM microphone
>>> suggested using two 6V photo batteries in place of a single AA cell
>>> to achieve higher output and lower self noise. Is this possible or
>>> even desirable with other mics, specifically the Audio Technica
>>> AT822?
>>
> [snip]
>> I can also see no reason why with such a circuit (or most any other)
>> the self noise would be affected by higher supply voltage.
>>
>> Are you sure the manual said that?
>>
>>
>> Bob
>
> Yes, though I no longer have the manuals, I still have two of these
> microphones and have been using them with two 6v photo batteries for
> more than fifteen years. There is a marked improvement in the noise
> level and a slight increase in output.

I wonder if you could measure the output level increase. I used to own an
EV PL-76, which would 'work' on a AA, but sounded much better with a photo
battery...I could just never find them.

Headroom was much increased, as well as output. I believe the lowered noise
level to be the result of the increased output, although in sound
reinforcement--where I used it--noise wasn't really an issue.. The noise
doesn't actually go 'down' per se, it's just the ratio between the noise
floor (which stays the same) and max undistorted output (which rises
considerably).

jak
>
> Robert
June 6, 2005 8:57:12 PM

Archived from groups: rec.audio.pro (More info?)

On Mon, 06 Jun 2005 16:33:35 GMT, Robert Ehrhardt
<r_ehrh@bellsouth.net> wrote:

>Yes, though I no longer have the manuals, I still have two of these
>microphones and have been using them with two 6v photo batteries for
>more than fifteen years. There is a marked improvement in the noise
>level and a slight increase in output.
>
>Robert

I rarely use mine, but my experience has been the same for probably
the same number of years.
Anonymous
June 6, 2005 8:57:13 PM

Archived from groups: rec.audio.pro (More info?)

Greg Taylor <gtaylor@umd.umich.edu> wrote:
>
>I have a Crown Sound Grabber mic which I believe was very similar, if
>not the same, as the Radio Shack flavor. Reckon I can get the same
>result with this dual battery arrangement?

Yes, but it really doesn't fix any of the major problems. Look for the
Phil Rastoczny modifications, which do.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous
June 7, 2005 12:46:35 AM

Archived from groups: rec.audio.pro (More info?)

jakdedert wrote:

> I wonder if you could measure the output level increase. I used to own an
> EV PL-76, which would 'work' on a AA, but sounded much better with a photo
> battery...I could just never find them.
>
I use 2 Duracell P28L in place of one AA cell. Get mine at Walmart in
the Camera Dept.

Robert
Anonymous
June 7, 2005 6:19:15 AM

Archived from groups: rec.audio.pro (More info?)

Bob Cain wrote:

>
>
> Robert Ehrhardt wrote:
>
>> As I recall, the manual for the original Radio Shack PZM microphone
>> suggested using two 6V photo batteries in place of a single AA cell to
>> achieve higher output and lower self noise. Is this possible or even
>> desirable with other mics, specifically the Audio Technica AT822?
>
>
> The usual FET common source or source follower circuit (which I am
> pretty sure is what was/is in that mic) will allow one rail to go higher
> with more voltage but since the bias point doesn't change and the load
> resistor doesn't change, the other rail will be the same as it was and
> nothing will be gained. It is possible with a voltage divider using
> huge resistors to make the bias point track in a simple way but they are
> physically large and expensive and not used in inexpensive circuits that
> typically rely on self biasing of the FET which is supply independant.
>
> I can also see no reason why with such a circuit (or most any other) the
> self noise would be affected by higher supply voltage.
>
> Are you sure the manual said that?
>
>
> Bob

I know this to be true of other battery powered condensers. No
clue what the circuit is.

--
Les Cargill
Anonymous
June 7, 2005 6:19:16 AM

Archived from groups: rec.audio.pro (More info?)

Les Cargill wrote:

> I know this to be true of other battery powered condensers.

I sure wish somebody could explain why that might be. I'd
really like to know. It flies full in the face of all the
microphone circuits that I've seen and those include most
all the major players for which internal circuit diagrams
can be found.


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein
Anonymous
June 7, 2005 6:19:17 AM

Archived from groups: rec.audio.pro (More info?)

Bob Cain wrote:
> Les Cargill wrote:
>
>> I know this to be true of other battery powered condensers.
>
> I sure wish somebody could explain why that might be. I'd
> really like to know. It flies full in the face of all the
> microphone circuits that I've seen and those include most
> all the major players for which internal circuit diagrams
> can be found.
>
Perhaps some enlightenment would come from this link:
http://sound.westhost.com/project93.htm

jak
>
> Bob
Anonymous
June 7, 2005 12:24:00 PM

Archived from groups: rec.audio.pro (More info?)

Bob Cain <arcane@arcanemethods.com> wrote:
>Les Cargill wrote:
>
>> I know this to be true of other battery powered condensers.
>
>I sure wish somebody could explain why that might be. I'd
>really like to know. It flies full in the face of all the
>microphone circuits that I've seen and those include most
>all the major players for which internal circuit diagrams
>can be found.

I would bet a lot of it has to do with the front end FET being
horribly nonlinear.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous
June 7, 2005 3:52:27 PM

Archived from groups: rec.audio.pro (More info?)

On Sun, 05 Jun 2005 19:32:58 -0700, Bob Cain
<arcane@arcanemethods.com> wrote:

>> As I recall, the manual for the original Radio Shack PZM microphone
>> suggested using two 6V photo batteries in place of a single AA cell to
>> achieve higher output and lower self noise. Is this possible or even
>> desirable with other mics, specifically the Audio Technica AT822?
>
>The usual FET common source or source follower circuit
>(which I am pretty sure is what was/is in that mic) will
>allow one rail to go higher with more voltage but since the
>bias point doesn't change and the load resistor doesn't
>change, the other rail will be the same as it was and
>nothing will be gained. It is possible with a voltage
>divider using huge resistors to make the bias point track in
>a simple way but they are physically large and expensive and
>not used in inexpensive circuits that typically rely on self
>biasing of the FET which is supply independant.
>
>I can also see no reason why with such a circuit (or most
>any other) the self noise would be affected by higher supply
>voltage.
>
>Are you sure the manual said that?

Mine did. And it worked.
You could also convert these to balanced output with a simple mod.
Anonymous
June 7, 2005 4:41:30 PM

Archived from groups: rec.audio.pro (More info?)

Scott Dorsey wrote:
> Bob Cain <arcane@arcanemethods.com> wrote:
>
>>Les Cargill wrote:
>>
>>
>>>I know this to be true of other battery powered condensers.
>>
>>I sure wish somebody could explain why that might be. I'd
>>really like to know. It flies full in the face of all the
>>microphone circuits that I've seen and those include most
>>all the major players for which internal circuit diagrams
>>can be found.
>
>
> I would bet a lot of it has to do with the front end FET being
> horribly nonlinear.
> --scott

I was wrong about swing being independant of the supply if
the common source front end FET configuration is used. The
quiescent current Idss is independant of voltage but for
that configuration the point about which the signal swings,
the quiescent voltage, is Vcc-Idss*Rl so that increasing Vcc
does widen the rails.

OTOH if the source follower configuration is used, which is
a must if the distortion due to said non-linearities is to
be low enough to consider the thing of high quanlity, then
that quiescent voltage is just Idss*Rl and independant of
Vcc. Figure 8 of

http://sound.westhost.com/project93.htm

shows these two configurations, the first being the common
source and the second the source follower. The first
drawing must be completed by taking the drain through a
resistor Rl to Vcc and the singal from the drain. The
second must be completed by taking the drain directly to Vcc
and the signal is taken from the source.

As to noise, I just can't see how increasing voltage can do
anything to lower noise. If, in the signal path, there is
any increase of a DC current due to that then noise can only
increase. If I'm wrong about this I'd appreciate being set
straight. Where's Kevin when I need him. :-)


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein
Anonymous
June 7, 2005 11:30:39 PM

Archived from groups: rec.audio.pro (More info?)

Last time I bought them (those '0.5 of AA length' 6v batteries) for use in
my Radio Shack PZM's they gave no change in noise floor, but may well have
upped the available headroom...who can tell ? However, wouldn't soldering a
9 volt cell terminal snap-on connector to the AA terminals and taping a 9
volt cell outside the regular battery holder achieve similar results at
lower cost ?

Ray
----------------------------------------------------------------------------
----------------------
"jakdedert" <jdedert@bellsouth.net> wrote in message
news:w_8pe.100645$J25.32471@bignews6.bellsouth.net...
> Bob Cain wrote:
> > Les Cargill wrote:
> >
> >> I know this to be true of other battery powered condensers.
> >
> > I sure wish somebody could explain why that might be. I'd
> > really like to know. It flies full in the face of all the
> > microphone circuits that I've seen and those include most
> > all the major players for which internal circuit diagrams
> > can be found.
> >
> Perhaps some enlightenment would come from this link:
> http://sound.westhost.com/project93.htm
>
> jak
> >
> > Bob
>
>
>
Anonymous
June 8, 2005 2:12:01 AM

Archived from groups: rec.audio.pro (More info?)

Bob Cain wrote:

> As to noise, I just can't see how increasing voltage can do anything to
> lower noise.

I think buried in the article at the end of that link (up there
somewhere in the thread) was a mention that higher volgatge gives more
gain, hence larger signal output. So though noise level doesn't
increase, signal to noise ratio may do. But in the source follower
configuration you recommaned the gain can't go up much as it can only
tend to unity. So maybe you can have source follower for low
distortion, or common source for high gain and S/N... ?

--
Anahata
anahata@treewind.co.uk -+- http://www.treewind.co.uk
Home: 01638 720444 Mob: 07976 263827
Anonymous
June 8, 2005 2:16:28 AM

Archived from groups: rec.audio.pro (More info?)

anahata wrote:
> somewhere in the thread) was a mention that higher volgatge

Or voltage, even.

> configuration you recommaned

... oh, you know what I mean
(what did they put in this glass of wine?)

--
Anahata
anahata@treewind.co.uk -+- http://www.treewind.co.uk
Home: 01638 720444 Mob: 07976 263827
Anonymous
June 8, 2005 2:20:21 AM

Archived from groups: rec.audio.pro (More info?)

anahata wrote:
> Bob Cain wrote:
>
>> As to noise, I just can't see how increasing voltage can do anything
>> to lower noise.
>
>
> I think buried in the article at the end of that link (up there
> somewhere in the thread) was a mention that higher volgatge gives more
> gain, hence larger signal output.

I don't think so. That would make it a VCA and those are
kinda hard to get by accident. A larger resistor in the
common source _will_ increase gain because the FET is a
voltage controled current source.

If a higher drain voltage moved the operating point up to
where the Gm is signifigantly greater I suppose that is
possible but if I remember the curves right, increaing drain
voltage moves it toward lower Gm at 0 Vgs and the Gm
sensitivity is not very pronounced at all.


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein
Anonymous
June 8, 2005 9:36:22 AM

Archived from groups: rec.audio.pro (More info?)

Bob Cain wrote:
>
>
> Les Cargill wrote:
>
>> I know this to be true of other battery powered condensers.
>
>
> I sure wish somebody could explain why that might be. I'd really like
> to know.

In this case, it was two Radio Shack mics ( from the
alt.music.4-track days). Both had more output. Both
were EXTREMELY cheap mics.

> It flies full in the face of all the microphone circuits that
> I've seen and those include most all the major players for which
> internal circuit diagrams can be found.
>

FWIW, in both cases, the "head amp" for the electret element
was internal to the capsule, so whatever schematic for the head
amp comes with the Panasonic electret elements might be the
right guess....

>
> Bob

--
Les Cargill
Anonymous
June 9, 2005 3:34:29 AM

Archived from groups: rec.audio.pro (More info?)

Before this thread dies or gets forever lost in technominutiae, I
would like to re-ask a part of the question posed earlier:

Would higher voltage batteries improve the performance of an AT-822 ?
Anonymous
June 9, 2005 3:34:30 AM

Archived from groups: rec.audio.pro (More info?)

Willie K. Yee, MD wrote:
> Before this thread dies or gets forever lost in technominutiae, I
> would like to re-ask a part of the question posed earlier:
>
> Would higher voltage batteries improve the performance of an AT-822 ?

Got a circuit to look at?


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein
Anonymous
June 9, 2005 1:14:42 PM

Archived from groups: rec.audio.pro (More info?)

In article <42a78016.911875@nntp.bestweb.net>,
Willie K. Yee, MD <wkyee@bestweb.net> wrote:
>Before this thread dies or gets forever lost in technominutiae, I
>would like to re-ask a part of the question posed earlier:
>
>Would higher voltage batteries improve the performance of an AT-822 ?

It might, but depending on the voltage rating of the blocking cap, it
might damage it also.

BUT, the Phil Rastoczny modifications for the PZM can probably be
adapted for the AT-822 also!
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
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