Op amps problem Gain Calculation

[Walter Harley]

"Pasquale" <spdrweb@NOTHNXtelusplanet.net> wrote in message
news:jBXBd.45974$KO5.45393@clgrps13...

I'm going to buy another 3.5mm jack for my adaptor and do a better
soldering. Now that I take a closer look at it, it's not so great.
Thinking about, I remember the tabs getting too hot because the tabs were
moving back-and-forth in the plastic core. I'm going to be more careful
this time.

Hopefully that will fix the problem. If not I'll try a repair shop or
Radio Shack and see what they have to say.

Based on everything you said - I suspect the problem is just a combination
of inappropriate preamp and defective soldering.

Rather than doing all this soldering, you might consider just purchasing
ready-made adapters. But don't do that until you have the mic preamp,
because what you need will depend on the connectors on the preamp; if you
get the right thing you might not need any adapters at all.

I'm inferring the mic you have is something like the Philips/Magnavox
PM62080 "Universal Mic", as shown at
http://www.gemini-usa.com/a5/modelDetail.asp?PkgID=370080&User=GemAudioAccessories.
This mic has what we'd call a "high impedance unbalanced" output. That is
different than most professional mics, which use "low impedance balanced"
outputs. That means that a typical mic preamp will *NOT* work properly with
it. The giveaway is that most mic preamps have "XLR" (three-pin)
connectors, rather than 1/4" mono connectors. You could build an adapter
but it wouldn't get you anywhere, because the signal levels are different.

It is hard to find preamps for this kind of microphone. Your best bet is
probably going to be to find a consumer-grade "mic mixer", even though you
aren't actually mixing anything. For instance, an excellent choice would be
the Radio Shack 32-2056:
http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&product%5Fid=32-2056.
This has 1/4" mono inputs for the mic (meaning it is intended for exactly
your kind of microphone); it has stereo RCA outputs, so you don't even need
to buy any adapters; and it can run on a 9V battery. It lists for $40. You
might also be able to find something like it cheaper somewhere else.
Another possibility would be to find a DJ mixer.

If any of that is unclear, let me know.

 

[Rich Grise]

On Sun, 02 Jan 2005 01:01:04 +0000, Pasquale wrote:

I put together a adaptor cable to go from the 3.5mm microphone jack to
the dual RCA ends. I think it may be from here where I am getting the
static/hum/noise. It seems that if it is held right the noise is pretty
much gone. Maybe poor solder or bad connection to the tail of the
microphone jack (ground).

Please be more specific.

Are you getting Static?

Are you getting Hum?

Are you getting Noise?

In the realm of electronics, these are three different things. Saying "I
have noise" is so vague as to be meaningless. A baby crying in the
background? An airport? Scratchy sounds when you move the microphone
around? A constant hum? A constant buzz? The sound of rainfall? What are
you trying to record?

Please answer these questions before we even get to the connector-type and
signal-level stuff.

Thanks!
Rich

 

[Rich Grise]

On Sun, 02 Jan 2005 12:49:53 -0800, Walter Harley wrote:

"Pasquale" <spdrweb@NOTHNXtelusplanet.net> wrote in message
news:jBXBd.45974$KO5.45393@clgrps13...
I'm going to buy another 3.5mm jack for my adaptor and do a better
soldering. Now that I take a closer look at it, it's not so great.
Thinking about, I remember the tabs getting too hot because the tabs were
moving back-and-forth in the plastic core. I'm going to be more careful
this time.

Hopefully that will fix the problem. If not I'll try a repair shop or
Radio Shack and see what they have to say.

Based on everything you said - I suspect the problem is just a combination
of inappropriate preamp and defective soldering.

From what I've been able to glean, it sounds like he's trying to put a
mono mic into right and left of a stereo preamp simultaneously, in which
case he has "The Jack" wired wrong. All three center conductors should be
connected, and all three shells should be connected, and if there's a
third contact on any of them, it's the wrong part.

The thing he's trying to make is called a "Y-adapter".

Good Luck!
Rich

 

[Pasquale]

The mic is a Phillips P72080, essentially the same.
http://www.gemini-usa.com/a5/modelDetail.asp?PkgID=370076&User=GemAudioAccessories

I also have a XLR microphone that is probably 11 - 12 years old in
excellent condition. It is a Electro-Voice MC100 that is dynamic,
directional, low impedance. I couldn't find any info about it on their
web site. Probably because it is so old. I did find the sheet with specs
and info that came with it.
I didn't use it originally because I was going to RCA's on my A/V cable.
I would like to use the MC100 because I believe it is a better
microphone. I just need to find a set up that will allow me to use it
with a pre-amp out to the A/V cable. I'll try Radio Shack and then some
music shopss, and see if I can find what I need.

What's the difference between Directional and Uni-directional? Is one
better than the other?

Thanks for all your help and suggestions!


Walter Harley wrote:

"Pasquale" <spdrweb@NOTHNXtelusplanet.net> wrote in message
news:jBXBd.45974$KO5.45393@clgrps13...

I'm going to buy another 3.5mm jack for my adaptor and do a better
soldering. Now that I take a closer look at it, it's not so great.
Thinking about, I remember the tabs getting too hot because the tabs were
moving back-and-forth in the plastic core. I'm going to be more careful
this time.

Hopefully that will fix the problem. If not I'll try a repair shop or
Radio Shack and see what they have to say.


Based on everything you said - I suspect the problem is just a combination
of inappropriate preamp and defective soldering.

Rather than doing all this soldering, you might consider just purchasing
ready-made adapters. But don't do that until you have the mic preamp,
because what you need will depend on the connectors on the preamp; if you
get the right thing you might not need any adapters at all.

I'm inferring the mic you have is something like the Philips/Magnavox
PM62080 "Universal Mic", as shown at
http://www.gemini-usa.com/a5/modelDetail.asp?PkgID=370080&User=GemAudioAccessories.
This mic has what we'd call a "high impedance unbalanced" output. That is
different than most professional mics, which use "low impedance balanced"
outputs. That means that a typical mic preamp will *NOT* work properly with
it. The giveaway is that most mic preamps have "XLR" (three-pin)
connectors, rather than 1/4" mono connectors. You could build an adapter
but it wouldn't get you anywhere, because the signal levels are different.

It is hard to find preamps for this kind of microphone. Your best bet is
probably going to be to find a consumer-grade "mic mixer", even though you
aren't actually mixing anything. For instance, an excellent choice would be
the Radio Shack 32-2056:
http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&product%5Fid=32-2056.
This has 1/4" mono inputs for the mic (meaning it is intended for exactly
your kind of microphone); it has stereo RCA outputs, so you don't even need
to buy any adapters; and it can run on a 9V battery. It lists for $40. You
might also be able to find something like it cheaper somewhere else.
Another possibility would be to find a DJ mixer.

If any of that is unclear, let me know.

 

[Pasquale]

The mic is a Phillips P72080, essentially the same.
http://www.gemini-usa.com/a5/modelDetail.asp?PkgID=370076&User=GemAudioAccessories

I also have a XLR microphone that is probably 11 - 12 years old in
excellent condition. It is a Electro-Voice MC100 that is dynamic,
directional, low impedance. I couldn't find any info about it on their
web site. Probably because it is so old. I did find the sheet with specs
and info that came with it.
I didn't use it originally because I was going to RCA's on my A/V cable.
I would like to use the MC100 because I believe it is a better
microphone. I just need to find a set up that will allow me to use it
with a pre-amp out to the A/V cable. I'll try Radio Shack and then some
music shopss, and see if I can find what I need.

What's the difference between Directional and Uni-directional? Is one
better than the other?

Just curious, how much dB gain do you think you can get from a 2.5W or
10W mic pre-amp?

Thanks for all your help and suggestions!


Walter Harley wrote:

"Pasquale" <spdrweb@NOTHNXtelusplanet.net> wrote in message
news:jBXBd.45974$KO5.45393@clgrps13...

I'm going to buy another 3.5mm jack for my adaptor and do a better
soldering. Now that I take a closer look at it, it's not so great.
Thinking about, I remember the tabs getting too hot because the tabs were
moving back-and-forth in the plastic core. I'm going to be more careful
this time.

Hopefully that will fix the problem. If not I'll try a repair shop or
Radio Shack and see what they have to say.


Based on everything you said - I suspect the problem is just a combination
of inappropriate preamp and defective soldering.

Rather than doing all this soldering, you might consider just purchasing
ready-made adapters. But don't do that until you have the mic preamp,
because what you need will depend on the connectors on the preamp; if you
get the right thing you might not need any adapters at all.

I'm inferring the mic you have is something like the Philips/Magnavox
PM62080 "Universal Mic", as shown at
http://www.gemini-usa.com/a5/modelDetail.asp?PkgID=370080&User=GemAudioAccessories.
This mic has what we'd call a "high impedance unbalanced" output. That is
different than most professional mics, which use "low impedance balanced"
outputs. That means that a typical mic preamp will *NOT* work properly with
it. The giveaway is that most mic preamps have "XLR" (three-pin)
connectors, rather than 1/4" mono connectors. You could build an adapter
but it wouldn't get you anywhere, because the signal levels are different.

It is hard to find preamps for this kind of microphone. Your best bet is
probably going to be to find a consumer-grade "mic mixer", even though you
aren't actually mixing anything. For instance, an excellent choice would be
the Radio Shack 32-2056:
http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&product%5Fid=32-2056.
This has 1/4" mono inputs for the mic (meaning it is intended for exactly
your kind of microphone); it has stereo RCA outputs, so you don't even need
to buy any adapters; and it can run on a 9V battery. It lists for $40. You
might also be able to find something like it cheaper somewhere else.
Another possibility would be to find a DJ mixer.

If any of that is unclear, let me know.

 

[Walter Harley]

"Pasquale" <spdrweb@NOTHNXtelusplanet.net> wrote in message
news:sMmCd.50368$KO5.42614@clgrps13...

I also have a XLR microphone that is probably 11 - 12 years old in
excellent condition. It is a Electro-Voice MC100 that is dynamic,
directional, low impedance. I couldn't find any info about it on their web
site. Probably because it is so old. I did find the sheet with specs and
info that came with it.

Yes, I'm sure that would be better sounding. You would need a mic preamp
for it. Something along the lines of the Rolls MP13 (Google for it) or an
equivalent. Then, you would come out of the 1/4" output, using a mono 1/4"
to dual RCA adapter from Radio Shack; and from there to the camcorder.

What's the difference between Directional and Uni-directional? Is one
better than the other?

Both of them are imprecise terms, too vague to tell apart.

Microphones are generally classified as "omnidirectional", "cardioid",
"supercardioid", "hypercardioid", or "figure-of-8". These refer to
different amounts and patterns of directionality, where "omnidirection"
means that it is about equally sensitive in all directions, and
"figure-of-8" is just what it sounds like.

What you have is somewhere in the spectrum of cardioid patterns, but there's
no way to tell which one other than by trying.

Directional mics do still pick up a bit of sound from the "off axis" -
particularly at low frequencies. So it's just an approximation.

 

[Rich Grise]

On Fri, 14 Jan 2005 11:54:54 -0600, danray wrote:

help if you can, I found the attached schematic, and text on a website
but cant get anyone to answer my questions.

The reason no one will answer your questions is because the nature of the
questions shows that you are not yet qualified to experimentally construct
circuits which connect directly to mains voltage. You would be almost
sure to kill yourself.

No one wants to be an accessory to suicide by ignorance.

Get your ass to the public library, or search the web for "elementary
electronics tutorial" or the like. Maybe even "basic electricity".

Good Luck!
Rich

 

[gmv]

You are probably right.
I am trying to go as cheap as absolutely possible.
Is it possible to use a diff amp on the input if there
is no center tap from the sensor ?

Surprisingly this circuit produces fairly good results
so long as there is no electrical disturbances in the vicinity.
I have found using electrolytic condensors works quite well
so long as you do not use them in a feedback type filter.


"John Woodgate" <jmw@jmwa.demon.contraspam.yuk> wrote in message news:4Oy7VzD3Cs6BFwoo@jmwa.demon.co.uk...

I read in sci.electronics.design that gmv <noemail@please.123> wrote (in
iUyGd.9393$OF5.5238@attbi_s52&gt about 'Comments needed on this
circuit', on Sun, 16 Jan 2005:

I am seeking recommendations to stop or significantly reduce this
electrical disturbance. The offending device is actually a heat pump and
the signature of the disturbance is quite different depending upon
whether the device is heating or cooling.


The unbalanced input stage is wide open to every disturbance under the
sun. You need a balanced input stage and a twisted-pair shielded cable
to your sensor. With that huge gain in the first stage, I suspect the
whole design, frankly.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[Larry Brasfield]

"gmv" <noemail@please.123> wrote in message news:iUyGd.9393$OF5.5238@attbi_s52...

http://files.photojerk.com/gmvoeth/diagram1.gif


Hello,
Hi.

The circuit above has been used by me for the last year to
receive regional and teleseismic signals but I have been
plagued by a problem that requires me to seek help.

The lead in cable is a shielded, twisted pair,
microphone cable. Its shield stops maybe 2 feet from the sensor.
The sensor cable itself has no shield. Its entire length
is approximately 50 feet and parallels a major airconditioner
power supply line about 4 or 5 feet away for maybe 30 of the
50 feet.

Every time the Air conditioner comes on a tremendous
electrical disturbance is generated in the input
of this circuit causing the class "A" baseline to follow
a nonsymmetrical cycle of waveform maybe 30 to 60 seconds
in period.

I am seeking recommendations to stop or significantly
reduce this electrical disturbance. The offending device
is actually a heat pump and the signature of the disturbance
is quite different depending upon whether the device
is heating or cooling.

I am unable to relocate the sensor so other solutions are necessary.

Any help here is appreciated.

The first three steps should be to convert your single-ended
preamplifier into a differential configuration, extend the shield
to the rest of the cable and around the geophone, and tie the
shield to the same ground the input diff-amp uses as reference.

At the same time, I would redistribute the gain so that, rather
than x 2947 followed by x 1, you would have x 54 and x 54.5.
This would prevent overload of the input stage on signals that
are going to be rejected by subsequent filtering.

The circuit shown below has approximately the same input
impedance, gain, and frequency response as your original
two stages with the above suggestions incorporated.


||
.------||----.
| || |
| 12n |
___ | ___ |
.----o---|___|--o-o----|___|---o
| | | |
| | 1.07k | 57.6k |
| | | |\| |
| .-. '-|-\ | || |\
| | | | >---------o-----||----o---------------|+\
| | | 511 .-|+/ || | | >---.
| '-' | |/| .-. .---|-/ |
| | | 47u | | | |/ |
| | | | |348k .-. |
| | ___ | ___ '-' | | |
| .--o---|___|--o--o---|___|---. | | | 348k |
| | | | | '-' |
| | 1.07k | 57.6k | | ___ | ___ |
| | | | o---|___|---o---|___|--'
| | | || | |
| | .---| '-----||----o === 2.00k 107k
| '--| | || | GND
'----| | 12n |
'---| ===
GND
(created by AACircuit v1.28.4 beta 13/12/04 www.tech-chat.de)

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

 

[Rich Grise]

On Sun, 16 Jan 2005 13:37:00 -0800, Larry Brasfield wrote:

The circuit shown below has approximately the same input
impedance, gain, and frequency response as your original
two stages with the above suggestions incorporated.


I'd break this between the two opamps, and use a differential output amp

for U1, and put that part of the circuit at the sensor.

||
.------||---.
| || |
| 12n |
___ | ___ |
.----o---|___|--o-o----|___|--o
| | | |
| | 1.07k | 57.6k |
| | | |\| | |\
| .-. '-|-\---------o-----------||-----o---------------|+\
| | | | > cable |
| | | 511 .-|+/---------------------||---- | ----------.---|-/
| | | | '-' | |/|

At this point I gave up on trying to do ASCII art. Hopefully, it gets
the point across.

.-. | |/

| | | 47u | | |
| | | | |348k .-. |
| | ___ | ___ '-' | | |
| .--o---|___|--o--o---|___|--. | | | 348k |
| | | | | '-' |
| | 1.07k | 57.6k | | ___ | ___ |
| | | | o---|___|---o---|___|--'
| | | || | |
| | .---| '-----||---o === 2.00k 107k
| '--| | || | GND
'----| | 12n |
'---| ===
GND
(created by AACircuit v1.28.4 beta 13/12/04 www.tech-chat.de)
(royally munged by Rich Grise)

Cheers!
Rich

 

[Larry Brasfield]

"Rich Grise" <richgrise@example.net> wrote in message newsan.2005.01.16.22.33.07.300919@example.net...

On Sun, 16 Jan 2005 13:37:00 -0800, Larry Brasfield wrote:

The circuit shown below has approximately the same input
impedance, gain, and frequency response as your original
two stages with the above suggestions incorporated.


I'd break this between the two opamps, and use a differential output amp
for U1, and put that part of the circuit at the sensor.

I agree that such a solution would provide lower
susceptibility to noise pickup. However, given that
the OP has gotten useful results already, and that
line-frequency noise is not particularly significant in
seismic signals, I figured the simpler solution would
be to revise the existing circuit. It will likely work
well enough to keep the noise from taking the input
stage into overload, so whatever measures were
good enough before to take out the 60 Hz and low
harmonics should be more than good enough after
applying those changes.

Another consideration: This is obviously a one-off,
amateur solution. The concept of good-enough applies
more than usual in such situations.

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

 

[Jamie]

gmv wrote:

http://files.photojerk.com/gmvoeth/diagram1.gif


Hello,

The circuit above has been used by me for the last year to
receive regional and teleseismic signals but I have been
plagued by a problem that requires me to seek help.

The lead in cable is a shielded, twisted pair,
microphone cable. Its shield stops maybe 2 feet from the sensor.
The sensor cable itself has no shield. Its entire length
is approximately 50 feet and parallels a major airconditioner
power supply line about 4 or 5 feet away for maybe 30 of the
50 feet.

Every time the Air conditioner comes on a tremendous
electrical disturbance is generated in the input
of this circuit causing the class "A" baseline to follow
a nonsymmetrical cycle of waveform maybe 30 to 60 seconds
in period.

I am seeking recommendations to stop or significantly
reduce this electrical disturbance. The offending device
is actually a heat pump and the signature of the disturbance
is quite different depending upon whether the device
is heating or cooling.

I am unable to relocate the sensor so other solutions are necessary.

Any help here is appreciated.

gmv


its obviously a Hi-Z problem due to the nature of your app.

Microphone wire is crap most of the time from what i have
seen.
you could try some tightly shielded RG174..

in any case, after looking at your circuit i think moving it
all to the location of the sensor and having a low Z output.
or at least move one stage to give you a unity gain with
low Z, make sure you use Large by pass caps in the sensor
end for the +/- lines to keep the EMF out of that.
your basicly picking up the EMF and your cable is the secondary.

 

[Nico Coesel]

Jamie <jamie_5_not_valid_after_5_Please@charter.net> wrote:

gmv wrote:

http://files.photojerk.com/gmvoeth/diagram1.gif


Hello,

The circuit above has been used by me for the last year to
receive regional and teleseismic signals but I have been
plagued by a problem that requires me to seek help.

The lead in cable is a shielded, twisted pair,
microphone cable. Its shield stops maybe 2 feet from the sensor.
The sensor cable itself has no shield. Its entire length
is approximately 50 feet and parallels a major airconditioner
power supply line about 4 or 5 feet away for maybe 30 of the
50 feet.


gmv


its obviously a Hi-Z problem due to the nature of your app.
Microphone wire is crap most of the time from what i have
seen.
you could try some tightly shielded RG174..

And lose the twisted pair? Bad idea. With a differential input
amplifier and shielded microphone wire, you can have several hundred
feet of wire between the microphone and the amplifier without any
problems. I see no problem in the setup of the OP.

--
Reply to nico@nctdevpuntnl (punt=.)
Bedrijven en winkels vindt U op www.adresboekje.nl

 

[Fred Bloggs]

gmv wrote:

http://files.photojerk.com/gmvoeth/diagram1.gif


Hello,

The circuit above has been used by me for the last year to
receive regional and teleseismic signals but I have been
plagued by a problem that requires me to seek help.

The lead in cable is a shielded, twisted pair,
microphone cable. Its shield stops maybe 2 feet from the sensor.
The sensor cable itself has no shield. Its entire length
is approximately 50 feet and parallels a major airconditioner
power supply line about 4 or 5 feet away for maybe 30 of the
50 feet.

Every time the Air conditioner comes on a tremendous
electrical disturbance is generated in the input
of this circuit causing the class "A" baseline to follow
a nonsymmetrical cycle of waveform maybe 30 to 60 seconds
in period.

I am seeking recommendations to stop or significantly
reduce this electrical disturbance. The offending device
is actually a heat pump and the signature of the disturbance
is quite different depending upon whether the device
is heating or cooling.

Is that 432 ohm at the sensor something you added or is it internal to
the geophone? Your input lines are not "balanced", a terminology which
simply means each input line from the sensor has identical impedance to
your circuit common over all frequencies in this case. Your interference
problem runs deeper than just electrical. From your description, it is
clear that the heat pump assembly is transmitting shock and/or acoustic
wave components into the ground that are within the frequency range of
the geophone.

 

[Larry Brasfield]

"gmv" <noemail@please.123> wrote in message news:yLXGd.11857$EG1.6658@attbi_s53...

http://files.photojerk.com/gmvoeth/circuita.gif


http://files.photojerk.com/gmvoeth/circuitb.gif


Thanks to input from you guys I tried an instrumentation amplifier
on my input and that seems to have eliminated the 60HZ noise I had
in my first stage.

circuita.gif is the noisy devil.
circuitb.gif is the one I am now using.

That circuit would reject common-mode noise better if the
two branches consisting of 2.2k+120k resistors both had
equal capacitors across the 120k resistors.

You should also be aware that using 3 op-amps for an
instrumentation amplifier can be done with better common
mode rejection using the popular circuit diagrammed below:

|\
----------|+\
| >-------o---------.
.-|-/ | |
| |/ .-. | 100k 100k
| | | | ___ ___
| | | 20k '--|___|--o---|___|-
| '-' | |
| | | |
| | | |
'------------o | |
| | |\| |
.-. '--|-\ |
| | | >---'
| | 2k .--|+/
'-' | |/|
| |
.------------o |
| | |
| | 100k | 100k
| .-. ___ | ___
| | | .--|___|--o---|___|-.
| | | 20k | |
| |\| '-' | |
'-|-\ | | ===
| >-------o---------' GND
---------|+/
|/|

(created by AACircuit v1.28.4 beta 13/12/04 www.tech-chat.de)

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

 

[Ray]

Rich Grise <richgrise@example.net> wrote in
newsan.2005.01.16.03.09.56.589505@example.net:

On Fri, 14 Jan 2005 11:54:54 -0600, danray wrote:

help if you can, I found the attached schematic, and text on a
website but cant get anyone to answer my questions.

The reason no one will answer your questions is because the nature of
the questions shows that you are not yet qualified to experimentally
construct circuits which connect directly to mains voltage. You would
be almost sure to kill yourself.

No one wants to be an accessory to suicide by ignorance.

Get your ass to the public library, or search the web for "elementary
electronics tutorial" or the like. Maybe even "basic electricity".

Good Luck!
Rich

Rich I am an electrician by trade, I deal with voltages that will make your
body explode on a daily basis, I am not ignorant to what electricity can
do. I am ignorant to how it can be manipulated with electronic circuits.


----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups
---= East/West-Coast Server Farms - Total Privacy via Encryption =---

 

[JeffM]

I am not ignorant to what electricity can do
Ray

It appears that Rich was responding to the *nature of the questions*,
not to the actual schematic.
It is likely he never saw it.
The reason for that was you don't know much about Usenet either.

Unless the newsgroup has *binary* or *binaries* in its name
you are not permitted to post graphics or other attachments.
They are stripped off by most servers.

The standard way is to draw your circuit with ASCII characters
(Andy's ASCII Circuit by Andreas Weber
http://www.tech-chat.de/download.html is a nice tool)
or post the graphic it to a website
and include a link to the page in your post.
http://www.google.com/search?&q=updated+2004+best+free+space+Tripod+Angelfire+Geocities+Freeservers
if you don't have your own site.

 

[Fred Bloggs]

gmv wrote:

http://files.photojerk.com/gmvoeth/circuita.gif


http://files.photojerk.com/gmvoeth/circuitb.gif


Thanks to input from you guys I tried an instrumentation amplifier
on my input and that seems to have eliminated the 60HZ noise I had
in my first stage.

circuita.gif is the noisy devil.
circuitb.gif is the one I am now using.

gmv






"gmv" <noemail@please.123> wrote in message news:iUyGd.9393$OF5.5238@attbi_s52...


http://files.photojerk.com/gmvoeth/diagram1.gif


this file is now circuita.gif




Hello,

The circuit above has been used by me for the last year to
receive regional and teleseismic signals but I have been
plagued by a problem that requires me to seek help.

The lead in cable is a shielded, twisted pair,
microphone cable. Its shield stops maybe 2 feet from the sensor.
The sensor cable itself has no shield. Its entire length
is approximately 50 feet and parallels a major airconditioner
power supply line about 4 or 5 feet away for maybe 30 of the
50 feet.

Every time the Air conditioner comes on a tremendous
electrical disturbance is generated in the input
of this circuit causing the class "A" baseline to follow
a nonsymmetrical cycle of waveform maybe 30 to 60 seconds
in period.

I am seeking recommendations to stop or significantly
reduce this electrical disturbance. The offending device
is actually a heat pump and the signature of the disturbance
is quite different depending upon whether the device
is heating or cooling.

I am unable to relocate the sensor so other solutions are necessary.

Any help here is appreciated.

gmv

That's a lie if I ever heard one.

 

[cb]

I wanted to use an ATX power supply to provide 12vdc to car radio in my
house, but was told that it would not operate unless it was physically
connected to a motherboard.

Is there a way to use it without it being connected to a motherboard?

Thanks.
"Dick Johnson" <RLJinPA@comcast.net> wrote in message
news:aNWdnZX_8pGwyGjcRVn-uA@comcast.com...

Try a computer vendor who takes trade-ins.

A non operative unit is usually very cheap and the Power supply may still
be
working.

You get 12 v. and lots of 5 v capability from a ATX machine.

Not a lab supply but reasonably well regulated

Poppa J

 

[Sylvan Butler]

On Wed, 26 Jan 2005 15:03:02 +1100, cb <clarkb@nospamplease.com> wrote:

I wanted to use an ATX power supply to provide 12vdc to car radio in my
house, but was told that it would not operate unless it was physically
connected to a motherboard.

Is there a way to use it without it being connected to a motherboard?

Sure, not a problem. Two requirements...

First the power supply will need a reasonable load to operate properly.
I attach one of the connectors to an old disk drive that draws an amp or
two of +5v and also an amp or two of +12v. Works well.

Second, one of the wires on the ATX connector needs to be connected to
ground (also known as "common") to turn on the power supply. This wire
is in the middle of the connector, and a ground is adjacent. The pin
number is 14, and the wire is supposed to be green (and the ground
black). I usually use a little pair of spring-closing tweezers to
connect the two.

Here is the google "lucky" reference for a pinout diagram:
http://xtronics.com/reference/atx_pinout.htm

sdb

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