Adding filter to a INA217...

[Phil Allison]

gnuarm.del...@gmail.com wrote:


** Has all the personality traits of a pedofile.
==================================

To hear or record very faint sounds, you need two things:

1. A special ( read expensive) low noise microphone.

2. A *VERY* quite indoor environment.

You have neither.


Or a better microphone assembly. I\'ve never done it, but I\'ve read about shotgun mics.

** The pin-up boy talks and moves its arm and legs.

> I think each element needs it\'s own amplifier, but read up on it, maybe they combine them all into one amp.

** But makes no sense - like a robot.


> Or maybe it uses an acoustic coupling of the tubes into a single element.

** Maybe the Moon really IS constructed from green cheeze ??

I\'m talking to the OP,

** In his wet dreams, while pulling his tiny cock.


> Rick Cunt

 

[John S]

On 2/19/2022 1:28 PM, Lasse Langwadt Christensen wrote:

lørdag den 19. februar 2022 kl. 20.23.37 UTC+1 skrev John S:
On 2/19/2022 12:33 PM, Rick C wrote:
On Saturday, February 19, 2022 at 1:08:38 PM UTC-5, amdx wrote:
Is there a way to add a simple RC filter in the gain control circuit
(fixed gain) of a INA217 audio amp.

Circuit shown here.

https://www.dropbox.com/s/wjixn4jq464i1fj/INA217%20Gain%20control.jpg?dl=0
Yes, I\'m aware I can reduce the input caps to cause High pass
filtering, I would like a low pass filter

on the input, but I don\'t want to add noise. So, I may add it on the
output. 300Hz to 3300Hz.

Often filters are in front of significant gain stages to prevent overloading the state from out of band noise. A low pass filter only requires series resistors and capacitor between the inputs (after the filter) or to ground. Across the input pair gives differential filtering. Capacitors to ground give common mode filtering. The series resistors give a voltage reduction when paired to the existing input resistors R1, R2, R3, R4 and R5.

What do you know about your noise? Do you have noise? I mean, do you know what you wish to prevent, details?

What is the gain of your amplifier? What is the level of your input signal? What is the level of the output signal? What is the signal source complex impedance? What is your load?

I\'m not sure what all the input circuit is for. I suspect this design uses more than one type of signal source. It would be nice to actually understand the details. It makes a difference.

Where is R7?


https://www.ti.com/lit/ds/symlink/ina217.pdf page 13

Oh. Didn\'t realize it had to be found elsewhere.

 

[John S]

On 2/19/2022 2:41 PM, amdx wrote:

On 2/19/2022 1:23 PM, John S wrote:
On 2/19/2022 12:33 PM, Rick C wrote:
On Saturday, February 19, 2022 at 1:08:38 PM UTC-5, amdx wrote:
Is there a way to add a simple RC filter in the gain control circuit
(fixed gain) of a INA217 audio amp.

Circuit shown here.

https://www.dropbox.com/s/wjixn4jq464i1fj/INA217%20Gain%20control.jpg?dl=0

Yes, I\'m aware I can reduce the input caps to cause High pass
filtering,  I would like a low pass filter

on the input, but I don\'t want to add noise. So, I may add it on the
output. 300Hz to 3300Hz.

Often filters are in front of significant gain stages to prevent
overloading the state from out of band noise.  A low pass filter only
requires series resistors and capacitor between the inputs (after the
filter) or to ground.  Across the input pair gives differential
filtering.  Capacitors to ground give common mode filtering.  The
series resistors give a voltage reduction when paired to the existing
input resistors R1, R2, R3, R4 and R5.

What do you know about your noise?  Do you have noise?  I mean, do
you know what you wish to prevent, details?

What is the gain of your amplifier?  What is the level of your input
signal?  What is the level of the output signal?  What is the signal
source complex impedance?  What is your load?

I\'m not sure what all the input circuit is for.  I suspect this
design uses more than one type of signal source.  It would be nice to
actually understand the details.  It makes a difference.


Where is R7?

Do you mean the output load?

https://www.dropbox.com/s/4b8bn9fu5r0wkk2/INA217%20with%20filters%20DB.jpg?dl=0

It didn\'t appear to be labeled as R7.

 

[Lasse Langwadt Christensen]

søndag den 20. februar 2022 kl. 01.49.00 UTC+1 skrev John S:

On 2/19/2022 1:28 PM, Lasse Langwadt Christensen wrote:
lørdag den 19. februar 2022 kl. 20.23.37 UTC+1 skrev John S:
On 2/19/2022 12:33 PM, Rick C wrote:
On Saturday, February 19, 2022 at 1:08:38 PM UTC-5, amdx wrote:
Is there a way to add a simple RC filter in the gain control circuit
(fixed gain) of a INA217 audio amp.

Circuit shown here.

https://www.dropbox.com/s/wjixn4jq464i1fj/INA217%20Gain%20control.jpg?dl=0
Yes, I\'m aware I can reduce the input caps to cause High pass
filtering, I would like a low pass filter

on the input, but I don\'t want to add noise. So, I may add it on the
output. 300Hz to 3300Hz.

Often filters are in front of significant gain stages to prevent overloading the state from out of band noise. A low pass filter only requires series resistors and capacitor between the inputs (after the filter) or to ground. Across the input pair gives differential filtering. Capacitors to ground give common mode filtering. The series resistors give a voltage reduction when paired to the existing input resistors R1, R2, R3, R4 and R5.

What do you know about your noise? Do you have noise? I mean, do you know what you wish to prevent, details?

What is the gain of your amplifier? What is the level of your input signal? What is the level of the output signal? What is the signal source complex impedance? What is your load?

I\'m not sure what all the input circuit is for. I suspect this design uses more than one type of signal source. It would be nice to actually understand the details. It makes a difference.

Where is R7?


https://www.ti.com/lit/ds/symlink/ina217.pdf page 13
Oh. Didn\'t realize it had to be found elsewhere.

someone took the image from the datasheet and modified it but didn\'t change the text

 

[amdx]

On 2/19/2022 6:11 PM, Rick C wrote:

On Saturday, February 19, 2022 at 4:15:52 PM UTC-5, palli...@gmail.com wrote:
amdx is an incorrigible IDIOT wrote:

==========================
Is there a way to add a simple RC filter in the gain control circuit
(fixed gain) of a INA217 audio amp.
** Yaaawnnnn......

To hear or record very faint sounds, you need two things:

1. A special ( read expensive) low noise microphone.

2. A *VERY* quite indoor environment.

You have neither.
Or a better microphone assembly. I\'ve never done it, but I\'ve read about shotgun mics. I think each element needs it\'s own amplifier, but read up on it, maybe they combine them all into one amp. Or maybe it uses an acoustic coupling of the tubes into a single element. I think it makes the mic less important since the acoustics boost the signal quite a bit.

https://sound.stackexchange.com/questions/281/really-weird-diy-shotgun-mic-old-yes-but-i-just-found-it-again

The OP\'s setup would only need a 2 foot tube to reach 300 Hz so rather smaller than shown.

A parabolic reflector also can greatly improve the sensitivity of the mic.

That shotgun mic is where this all started (and might end up). It does
use only a single condensor mic no longer available, but I\'m sure can
be  much improved on now.

I think the directivity is also an important if not more detail of the
parabolic, or the shotgun.

                                        Mikek



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[amdx]

On 2/19/2022 5:43 PM, Rick C wrote:

On Saturday, February 19, 2022 at 3:40:29 PM UTC-5, amdx wrote:
On 2/19/2022 12:33 PM, Rick C wrote:
On Saturday, February 19, 2022 at 1:08:38 PM UTC-5, amdx wrote:
Is there a way to add a simple RC filter in the gain control circuit
(fixed gain) of a INA217 audio amp.

Circuit shown here.

https://www.dropbox.com/s/wjixn4jq464i1fj/INA217%20Gain%20control.jpg?dl=0
Yes, I\'m aware I can reduce the input caps to cause High pass
filtering, I would like a low pass filter

on the input, but I don\'t want to add noise. So, I may add it on the
output. 300Hz to 3300Hz.
Often filters are in front of significant gain stages to prevent overloading the state from out of band noise. A low pass filter only requires series resistors and capacitor between the inputs (after the filter) or to ground. Across the input pair gives differential filtering. Capacitors to ground give common mode filtering. The series resistors give a voltage reduction when paired to the existing input resistors R1, R2, R3, R4 and R5.

What do you know about your noise?
Not really, I just want low noise and high gain. What is high gain, I
don\'t know yet, I\'m building a big ear.

I have experimented with an amp that has a gain of 3500 and could hear
the clock ticking and every car that went by.

I wrapped the mic in foam and put it in a lead pipe. I didn\'t hear those
things but I did hear hiss. I swapped the mic for resistors

but no longer remember what value my ears said had the equal noise.

Do you have noise?
Sure, but I can\'t quantify it.
I mean, do you know what you wish to prevent, details?
Because of the high gain, noise is also amplified. I have been told
that the mic I have chose is noisy, but for now it\'s what I have.

AOM5024

https://www.puiaudio.com/media/SpecSheet/AOM-5024L-HD-R.pdf
I\'m simply trying to make a low noise audio amplifier. It is probably
all over kill if I make decent filters to roll off both ends.

But, that is OK.
Ok, you want something to filter noise, but don\'t know what. You don\'t know anything about your noise. At least you know something about the mic. But it sounds like your mic is actually pretty good, producing about the same noise as a resistor. How much better do you think it\'s going to get?

The only advantage a filter will do is remove noise outside your passband which is not a lot. 300-3000 Hz vs 20-20,000, so about 1/3rd the noise?


What is the gain of your amplifier?
Probably an adjustable max of 4000 voltage gain.
What is the level of your input signal?
mic input, other than that, I don\'t know the max of that.
What is the level of the output signal?
Output to drive headphones.
What is the signal source complex impedance? What is your load?
I\'m not sure what all the input circuit is for. I suspect this design uses more than one type of signal source. It would be nice to actually understand the details. It makes a difference.
I think the 48V option is for a mic that needs a high DC bias. If you are using an electret mic, you probably can simplify the circuit a lot. For one thing, you don\'t need differential inputs. Makes the filtering simpler. Use a battery for the electret bias to avoid any added noise on the input.


Here is my proposed circuit,

https://www.dropbox.com/s/4b8bn9fu5r0wkk2/INA217%20with%20filters%20DB.jpg?dl=0
Just wondering if I can get some filtering in the Gain resistor circuit.
If you mean RG, no. Well, the answer is yes, but it will be high pass which you don\'t need.

Remove C2. Don\'t short it, disconnect it entirely. It is doing nothing. The output filter can be 1k and 47 nF/150 nF, slightly more convenient numbers, but whatever. The R4/R5 value loads the mic which is now a much higher input impedance reducing the gain. Maybe instead of using a 14k resistor to 15V, use a divider pair with a lower parallel resistance and a 3V reference. Then R4/R5 aren\'t so much a problem. Or increase the values of R4/R5. I\'m not sure if they have recommended values for some reason. Check the amp data sheet. Input bias is usually a factor, but your design is AC so maybe not important.

OK, now I\'m laughing at my self about C2. I know there are suggested
ways to connect an unbalanced mic to a balanced input.

As I understand it, the biggest reason for that is to prevent problems
with long cables. I won\'t have long cables. I still don\'t really
understand, if

I need a better mic connection circuit for unbal to bal or if this just
fine. I was going for lower values in the mic circuit for lower noise,

and the manufacturer of the low noise chip says, 2.2kΩ so I left them. I
was thinking it was some type of bias for the input. Still do.

 On the 14kΩ, it biases the mic at about 1000nV which is near
recommended, not sure why 3V and 2.2k would be better, but not opposed

to adding another resistor. Just would like to know the advantage or
disadvantage.

                                            Thanks, Mikek


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[amdx]

On 2/19/2022 5:10 PM, Rick C wrote:

On Saturday, February 19, 2022 at 3:11:21 PM UTC-5, whit3rd wrote:
On Saturday, February 19, 2022 at 11:11:25 AM UTC-8, whit3rd wrote:
On Saturday, February 19, 2022 at 10:08:38 AM UTC-8, amdx wrote:
Is there a way to add a simple RC filter in the gain control circuit
(fixed gain) of a INA217 audio amp.
I would like a low pass filter ...
If I\'m reading the schematic right, you can either put a ferrite bead in
series with R6 , or a capacitor or R-C in parallel with it, for low-pass filtering.
Oops; sign error. For low pass, you want capacitor in series with R6, or
inductor or L-R in parallel.
I\'m not sure that is going to do what you want. A series cap on R6 will produce less gain at the low end. Higher impedance in the reference leg of the negative feedback reduces gain to a minimum of 1. Parallel or serial is not the issue, both produce a higher impedance at low frequencies and so a lower gain. The problem is this leg is not the place to use a cap to create a low pass filter. Even a high pass filter at this point has the limitation of having 0dB as the floor, so not such a good filter. To make a low pass filter, the cap needs to be across the feedback resistor which is not accessible.

Consider this. If you could create a useful filter in this configuration, they would include it in the app notes in the data sheet I am sure.

Ya, I think we are past this now.

                                Thanks, Mikek


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[Phil Allison]

amdx = TROLLING CUNT wrote:

========================

** Tell me - what do it take to make a nut case, asshole like YOU

FUCK THE HELL OFF ????????????

Physical violence ?




...... Phil

 

[Rick C]

On Saturday, February 19, 2022 at 7:49:46 PM UTC-5, John S wrote:

On 2/19/2022 2:41 PM, amdx wrote:
On 2/19/2022 1:23 PM, John S wrote:
On 2/19/2022 12:33 PM, Rick C wrote:
On Saturday, February 19, 2022 at 1:08:38 PM UTC-5, amdx wrote:
Is there a way to add a simple RC filter in the gain control circuit
(fixed gain) of a INA217 audio amp.

Circuit shown here.

https://www.dropbox.com/s/wjixn4jq464i1fj/INA217%20Gain%20control.jpg?dl=0

Yes, I\'m aware I can reduce the input caps to cause High pass
filtering, I would like a low pass filter

on the input, but I don\'t want to add noise. So, I may add it on the
output. 300Hz to 3300Hz.

Often filters are in front of significant gain stages to prevent
overloading the state from out of band noise. A low pass filter only
requires series resistors and capacitor between the inputs (after the
filter) or to ground. Across the input pair gives differential
filtering. Capacitors to ground give common mode filtering. The
series resistors give a voltage reduction when paired to the existing
input resistors R1, R2, R3, R4 and R5.

What do you know about your noise? Do you have noise? I mean, do
you know what you wish to prevent, details?

What is the gain of your amplifier? What is the level of your input
signal? What is the level of the output signal? What is the signal
source complex impedance? What is your load?

I\'m not sure what all the input circuit is for. I suspect this
design uses more than one type of signal source. It would be nice to
actually understand the details. It makes a difference.


Where is R7?

Do you mean the output load?

https://www.dropbox.com/s/4b8bn9fu5r0wkk2/INA217%20with%20filters%20DB.jpg?dl=0

It didn\'t appear to be labeled as R7.

R7 is the adjustment potentiometer in series with R6.

--

Rick C.

+- Get 1,000 miles of free Supercharging
+- Tesla referral code - https://ts.la/richard11209

 

[Rick C]

On Saturday, February 19, 2022 at 8:40:27 PM UTC-5, amdx wrote:

On 2/19/2022 6:11 PM, Rick C wrote:
On Saturday, February 19, 2022 at 4:15:52 PM UTC-5, palli...@gmail.com wrote:
amdx is an incorrigible IDIOT wrote:

==========================
Is there a way to add a simple RC filter in the gain control circuit
(fixed gain) of a INA217 audio amp.
** Yaaawnnnn......

To hear or record very faint sounds, you need two things:

1. A special ( read expensive) low noise microphone.

2. A *VERY* quite indoor environment.

You have neither.
Or a better microphone assembly. I\'ve never done it, but I\'ve read about shotgun mics. I think each element needs it\'s own amplifier, but read up on it, maybe they combine them all into one amp. Or maybe it uses an acoustic coupling of the tubes into a single element. I think it makes the mic less important since the acoustics boost the signal quite a bit.

https://sound.stackexchange.com/questions/281/really-weird-diy-shotgun-mic-old-yes-but-i-just-found-it-again

The OP\'s setup would only need a 2 foot tube to reach 300 Hz so rather smaller than shown.

A parabolic reflector also can greatly improve the sensitivity of the mic.


That shotgun mic is where this all started (and might end up). It does
use only a single condensor mic no longer available, but I\'m sure can
be much improved on now.

I think the directivity is also an important if not more detail of the
parabolic, or the shotgun.

What the commercial companies sell as \"shotgun\" uses slots in the side to allow multipath to reduce off center noises from reaching the mic. That has no gain. The parabolic definitely has gain. The multi-tube shotgun might have gain based on the resonances of the tubes. How many tubes you need depends on the frequency range (which you have restricted to voice) and the Q of the resonances (spacing of the resonance peaks). The higher the Q, the more gain, but also the need for more tubes to cover the frequency range without excessive ripple.

In one of the posts I read someone claimed the acoustic combining of the multiple tubes ruins the resonances. I\'m not sure how directional the multi-tube shotgun really is, but as long as it has gain, you are money ahead even with a little selectivity if your noise floor is set by your microphone.

I guess this would be a bit like a tuned loop antenna, getting gain from the resonance.

--

Rick C.

++ Get 1,000 miles of free Supercharging
++ Tesla referral code - https://ts.la/richard11209

 

[Rick C]

On Saturday, February 19, 2022 at 8:52:37 PM UTC-5, amdx wrote:

On 2/19/2022 5:43 PM, Rick C wrote:
On Saturday, February 19, 2022 at 3:40:29 PM UTC-5, amdx wrote:
On 2/19/2022 12:33 PM, Rick C wrote:
On Saturday, February 19, 2022 at 1:08:38 PM UTC-5, amdx wrote:
Is there a way to add a simple RC filter in the gain control circuit
(fixed gain) of a INA217 audio amp.

Circuit shown here.

https://www.dropbox.com/s/wjixn4jq464i1fj/INA217%20Gain%20control.jpg?dl=0
Yes, I\'m aware I can reduce the input caps to cause High pass
filtering, I would like a low pass filter

on the input, but I don\'t want to add noise. So, I may add it on the
output. 300Hz to 3300Hz.
Often filters are in front of significant gain stages to prevent overloading the state from out of band noise. A low pass filter only requires series resistors and capacitor between the inputs (after the filter) or to ground. Across the input pair gives differential filtering. Capacitors to ground give common mode filtering. The series resistors give a voltage reduction when paired to the existing input resistors R1, R2, R3, R4 and R5.

What do you know about your noise?
Not really, I just want low noise and high gain. What is high gain, I
don\'t know yet, I\'m building a big ear.

I have experimented with an amp that has a gain of 3500 and could hear
the clock ticking and every car that went by.

I wrapped the mic in foam and put it in a lead pipe. I didn\'t hear those
things but I did hear hiss. I swapped the mic for resistors

but no longer remember what value my ears said had the equal noise.

Do you have noise?
Sure, but I can\'t quantify it.
I mean, do you know what you wish to prevent, details?
Because of the high gain, noise is also amplified. I have been told
that the mic I have chose is noisy, but for now it\'s what I have.

AOM5024

https://www.puiaudio.com/media/SpecSheet/AOM-5024L-HD-R.pdf
I\'m simply trying to make a low noise audio amplifier. It is probably
all over kill if I make decent filters to roll off both ends.

But, that is OK.
Ok, you want something to filter noise, but don\'t know what. You don\'t know anything about your noise. At least you know something about the mic. But it sounds like your mic is actually pretty good, producing about the same noise as a resistor. How much better do you think it\'s going to get?

The only advantage a filter will do is remove noise outside your passband which is not a lot. 300-3000 Hz vs 20-20,000, so about 1/3rd the noise?


What is the gain of your amplifier?
Probably an adjustable max of 4000 voltage gain.
What is the level of your input signal?
mic input, other than that, I don\'t know the max of that.
What is the level of the output signal?
Output to drive headphones.
What is the signal source complex impedance? What is your load?
I\'m not sure what all the input circuit is for. I suspect this design uses more than one type of signal source. It would be nice to actually understand the details. It makes a difference.
I think the 48V option is for a mic that needs a high DC bias. If you are using an electret mic, you probably can simplify the circuit a lot. For one thing, you don\'t need differential inputs. Makes the filtering simpler. Use a battery for the electret bias to avoid any added noise on the input.


Here is my proposed circuit,

https://www.dropbox.com/s/4b8bn9fu5r0wkk2/INA217%20with%20filters%20DB.jpg?dl=0
Just wondering if I can get some filtering in the Gain resistor circuit.
If you mean RG, no. Well, the answer is yes, but it will be high pass which you don\'t need.

Remove C2. Don\'t short it, disconnect it entirely. It is doing nothing. The output filter can be 1k and 47 nF/150 nF, slightly more convenient numbers, but whatever. The R4/R5 value loads the mic which is now a much higher input impedance reducing the gain. Maybe instead of using a 14k resistor to 15V, use a divider pair with a lower parallel resistance and a 3V reference. Then R4/R5 aren\'t so much a problem. Or increase the values of R4/R5. I\'m not sure if they have recommended values for some reason. Check the amp data sheet. Input bias is usually a factor, but your design is AC so maybe not important.

OK, now I\'m laughing at my self about C2. I know there are suggested
ways to connect an unbalanced mic to a balanced input.

As I understand it, the biggest reason for that is to prevent problems
with long cables. I won\'t have long cables. I still don\'t really
understand, if

I need a better mic connection circuit for unbal to bal or if this just
fine. I was going for lower values in the mic circuit for lower noise,

and the manufacturer of the low noise chip says, 2.2kΩ so I left them. I
was thinking it was some type of bias for the input. Still do.

On the 14kΩ, it biases the mic at about 1000nV which is near
recommended, not sure why 3V and 2.2k would be better, but not opposed

to adding another resistor. Just would like to know the advantage or
disadvantage.

I know why you picked 14k. The issue is it upsets the balance of the two inputs, but that is typically a DC issue with the bias currents, so maybe it\'s not important here. However, the 14k resistor sets the mic impedance. The 14k and 2.2 k act as a divider, losing almost 90% of the signal strength. That sounds like a bad idea. If you are worried about the noise in the resistor, I think this would be a bigger issue since it makes the resistor noise a lot more significant compared to the signal.

--

Rick C.

--- Get 1,000 miles of free Supercharging
--- Tesla referral code - https://ts.la/richard11209

 

[Phil Allison]

gnuarm.del...@gmail.com wrote:

========================

** The ass has all the guile and incorrigible cheek of a pedofile.

What the commercial companies sell as \"shotgun\"

** Is true in name only - it merely looks like one.

> uses slots in the side to allow multipath to reduce off center noises from reaching the mic. That has no gain.

** It has SFA directionality ( compared to cardiod ) under 2KHz too.

All audiophool fantasy - no fact.


...... Phil

 

[Jan Panteltje]

On a sunny day (Sat, 19 Feb 2022 15:01:36 -0600) it happened amdx
<amdx@knology.net> wrote in <surlrj$tld$1@dont-email.me>:

 Thanks Jan, for now, I\'m just going to use simple RC filters that I
can construct on the PCB I bought.

One thing about microphones that just happened to me.
I have to align my satellite dish again, and I use my software on the PC to move it to a reference point,
the software generates a tone so I can hear if it is pointing right,
But PC is far away from dish...

I have this little FM transmitter
http://panteltje.com/panteltje/pic/fm_pic/
and then go outside with earphones and a portable FM radio in my pocket. on a ladder moving the dish.

That FM transmitter is about 200 mV pp audio in.
Wanted to test if I could use a cheap electret clip on mike to pickup the beep from the PC, if the sensitivity was enough,
without pre-amp.
It was! I got feedback from my earplugs to the mike a meter away, LOAD !

So contemplate using simple cheap electret mikes, huge output signal!
No over-complicated input circuits needed.
With transmitter next to mike no cables... not sure if noise level is low enough for your application,
but a simple pre-amp and FM 100% is very powerful.

 

[John Walliker]

On Sunday, 20 February 2022 at 07:22:33 UTC, Jan Panteltje wrote:

On a sunny day (Sat, 19 Feb 2022 15:01:36 -0600) it happened amdx
am...@knology.net> wrote in <surlrj$tld$1...@dont-email.me>:
Thanks Jan, for now, I\'m just going to use simple RC filters that I
can construct on the PCB I bought.
One thing about microphones that just happened to me.
I have to align my satellite dish again, and I use my software on the PC to move it to a reference point,
the software generates a tone so I can hear if it is pointing right,
But PC is far away from dish...

I have this little FM transmitter
http://panteltje.com/panteltje/pic/fm_pic/
and then go outside with earphones and a portable FM radio in my pocket. on a ladder moving the dish.

That FM transmitter is about 200 mV pp audio in.
Wanted to test if I could use a cheap electret clip on mike to pickup the beep from the PC, if the sensitivity was enough,
without pre-amp.
It was! I got feedback from my earplugs to the mike a meter away, LOAD !

So contemplate using simple cheap electret mikes, huge output signal!
No over-complicated input circuits needed.
With transmitter next to mike no cables... not sure if noise level is low enough for your application,
but a simple pre-amp and FM 100% is very powerful.

The OP is already using a high-sensitivity electret mic. The AOM5024 has a
sensitivity of -24dBV/Pa when used with a 3V supply and 2.2k resistor. The noise
floor is 14dB(A) spl which is very good. This mic is one of the best in its class
and its cheap and readily available. It is VERY hard to find an outdoors environment
which is as quiet as 14dB(A), so the noise performance of this mic is good enough.
There is no point in using the 14k pullup resistor and higher bias voltage
(of up to a maximum of about 9V) UNLESS the mic is fed directly into the
virtual earth of an op-amp with a very short connection. The op-amp that has been
selected is over-complicated for this application as it has been designed for
differential amplification. This makes it harder to use than a simple op-amp.
There are plenty of better choices.
For example, the Texas Instruments OPA1641 (single) or OPA1642 (dual)
are low-noise J-FET input op-amps that would work well from a 9V battery
which could also provide the mic bias voltage. There are plenty
of other good choices, some with lower power consumption and/or
lower cost. The circuit can be very simple - as has already been suggested.
Capacitor couple the junction of the mic and pullup resistor to the -ve input
of the op-amp. Keep the connection very short. Select a feedback resistor
from output to -ve input to give the gain you want. (I did the calculation for
you a while back.) Shunt the feedback resistor with a capacitor to low-pass
filter the output. Set the +ve input of the op-amp to a mid-point voltage
obtained with a pair of high-value resistors between ground and power.
Decouple the mid-point with a large capacitor to ground.
If you have feedback problems from fluctuations in the power supply voltage
getting into the mic bias circuit, buffer the mid-point supply with the other half
of a dual op-amp configured as a unity gain buffer and feed the mic bias resistor
from the output of that buffer. By doing this you get a very well filtered bias
supply. Reduce the mic bias resistor to work with the reduced supply. The resistor
can be calculated on the basis that this mic draws about 0.5mA and works well
when the voltage at the junction of the mic and bias resistor is about 2V.
So if you have a total supply of 9V and use a buffered mid-point supply for the mic
of 4.5V then the best bias resistor would be about 5k.

John

 

[Jan Panteltje]

On a sunny day (Sun, 20 Feb 2022 02:00:35 -0800 (PST)) it happened John
Walliker <jrwalliker@gmail.com> wrote in
<dfe731fc-67bf-4ebc-abe2-466e4572f2ean@googlegroups.com>:

On Sunday, 20 February 2022 at 07:22:33 UTC, Jan Panteltje wrote:
On a sunny day (Sat, 19 Feb 2022 15:01:36 -0600) it happened amdx
am...@knology.net> wrote in <surlrj$tld$1...@dont-email.me>:
Thanks Jan, for now, I\'m just going to use simple RC filters that I
can construct on the PCB I bought.
One thing about microphones that just happened to me.
I have to align my satellite dish again, and I use my software on the PC to move it to a reference point,
the software generates a tone so I can hear if it is pointing right,
But PC is far away from dish...

I have this little FM transmitter
http://panteltje.com/panteltje/pic/fm_pic/
and then go outside with earphones and a portable FM radio in my pocket. on a ladder moving the dish.

That FM transmitter is about 200 mV pp audio in.
Wanted to test if I could use a cheap electret clip on mike to pickup the beep from the PC, if the sensitivity was enough,
without pre-amp.
It was! I got feedback from my earplugs to the mike a meter away, LOAD !

So contemplate using simple cheap electret mikes, huge output signal!
No over-complicated input circuits needed.
With transmitter next to mike no cables... not sure if noise level is low enough for your application,
but a simple pre-amp and FM 100% is very powerful.

The OP is already using a high-sensitivity electret mic. The AOM5024 has a
sensitivity of -24dBV/Pa when used with a 3V supply and 2.2k resistor. The noise
floor is 14dB(A) spl which is very good. This mic is one of the best in its class
and its cheap and readily available. It is VERY hard to find an outdoors environment
which is as quiet as 14dB(A), so the noise performance of this mic is good enough.
There is no point in using the 14k pullup resistor and higher bias voltage
(of up to a maximum of about 9V) UNLESS the mic is fed directly into the
virtual earth of an op-amp with a very short connection. The op-amp that has been
selected is over-complicated for this application as it has been designed for
differential amplification. This makes it harder to use than a simple op-amp.
There are plenty of better choices.
For example, the Texas Instruments OPA1641 (single) or OPA1642 (dual)
are low-noise J-FET input op-amps that would work well from a 9V battery
which could also provide the mic bias voltage. There are plenty
of other good choices, some with lower power consumption and/or
lower cost. The circuit can be very simple - as has already been suggested.
Capacitor couple the junction of the mic and pullup resistor to the -ve input
of the op-amp. Keep the connection very short. Select a feedback resistor
from output to -ve input to give the gain you want. (I did the calculation for
you a while back.) Shunt the feedback resistor with a capacitor to low-pass
filter the output. Set the +ve input of the op-amp to a mid-point voltage
obtained with a pair of high-value resistors between ground and power.
Decouple the mid-point with a large capacitor to ground.
If you have feedback problems from fluctuations in the power supply voltage
getting into the mic bias circuit, buffer the mid-point supply with the other half
of a dual op-amp configured as a unity gain buffer and feed the mic bias resistor
from the output of that buffer. By doing this you get a very well filtered bias
supply. Reduce the mic bias resistor to work with the reduced supply. The resistor
can be calculated on the basis that this mic draws about 0.5mA and works well
when the voltage at the junction of the mic and bias resistor is about 2V.
So if you have a total supply of 9V and use a buffered mid-point supply for the mic
of 4.5V then the best bias resistor would be about 5k.

John

Agreed, electret mikes are cool, there is even one on one of the mars rovers,
I have heard the sound from the wind on mars.
https://www.dpamicrophones.com/mars-rover
tooks them some tohide it is a normal electret:
https://www.dpamicrophones.com/pencil/4006-omnidirectional-microphone
Cartridge type Pre-polarized condenser
to get those $$$$$$$$$$$$$$

As to filtering, using the mike outside gives you, if it catches wind, huge low frequency variations
(maybe up to a volt pp on the mike output) so a bandpass is not a bad idea.
No idea _what_ he exactly wants to measure, all depends on that of course,

 

[amdx]

On 2/20/2022 4:30 AM, Jan Panteltje wrote:

On a sunny day (Sun, 20 Feb 2022 02:00:35 -0800 (PST)) it happened John
Walliker <jrwalliker@gmail.com> wrote in
dfe731fc-67bf-4ebc-abe2-466e4572f2ean@googlegroups.com>:

On Sunday, 20 February 2022 at 07:22:33 UTC, Jan Panteltje wrote:
On a sunny day (Sat, 19 Feb 2022 15:01:36 -0600) it happened amdx
am...@knology.net> wrote in <surlrj$tld$1...@dont-email.me>:
Thanks Jan, for now, I\'m just going to use simple RC filters that I
can construct on the PCB I bought.
One thing about microphones that just happened to me.
I have to align my satellite dish again, and I use my software on the PC to move it to a reference point,
the software generates a tone so I can hear if it is pointing right,
But PC is far away from dish...

I have this little FM transmitter
http://panteltje.com/panteltje/pic/fm_pic/
and then go outside with earphones and a portable FM radio in my pocket. on a ladder moving the dish.

That FM transmitter is about 200 mV pp audio in.
Wanted to test if I could use a cheap electret clip on mike to pickup the beep from the PC, if the sensitivity was enough,
without pre-amp.
It was! I got feedback from my earplugs to the mike a meter away, LOAD !

So contemplate using simple cheap electret mikes, huge output signal!
No over-complicated input circuits needed.
With transmitter next to mike no cables... not sure if noise level is low enough for your application,
but a simple pre-amp and FM 100% is very powerful.
The OP is already using a high-sensitivity electret mic. The AOM5024 has a
sensitivity of -24dBV/Pa when used with a 3V supply and 2.2k resistor. The noise
floor is 14dB(A) spl which is very good. This mic is one of the best in its class
and its cheap and readily available. It is VERY hard to find an outdoors environment
which is as quiet as 14dB(A), so the noise performance of this mic is good enough.
There is no point in using the 14k pullup resistor and higher bias voltage
(of up to a maximum of about 9V) UNLESS the mic is fed directly into the
virtual earth of an op-amp with a very short connection. The op-amp that has been
selected is over-complicated for this application as it has been designed for
differential amplification. This makes it harder to use than a simple op-amp.
There are plenty of better choices.
For example, the Texas Instruments OPA1641 (single) or OPA1642 (dual)
are low-noise J-FET input op-amps that would work well from a 9V battery
which could also provide the mic bias voltage. There are plenty
of other good choices, some with lower power consumption and/or
lower cost. The circuit can be very simple - as has already been suggested.
Capacitor couple the junction of the mic and pullup resistor to the -ve input
of the op-amp. Keep the connection very short. Select a feedback resistor
from output to -ve input to give the gain you want. (I did the calculation for
you a while back.) Shunt the feedback resistor with a capacitor to low-pass
filter the output. Set the +ve input of the op-amp to a mid-point voltage
obtained with a pair of high-value resistors between ground and power.
Decouple the mid-point with a large capacitor to ground.
If you have feedback problems from fluctuations in the power supply voltage
getting into the mic bias circuit, buffer the mid-point supply with the other half
of a dual op-amp configured as a unity gain buffer and feed the mic bias resistor
from the output of that buffer. By doing this you get a very well filtered bias
supply. Reduce the mic bias resistor to work with the reduced supply. The resistor
can be calculated on the basis that this mic draws about 0.5mA and works well
when the voltage at the junction of the mic and bias resistor is about 2V.
So if you have a total supply of 9V and use a buffered mid-point supply for the mic
of 4.5V then the best bias resistor would be about 5k.

John
Agreed, electret mikes are cool, there is even one on one of the mars rovers,
I have heard the sound from the wind on mars.
https://www.dpamicrophones.com/mars-rover
tooks them some tohide it is a normal electret:
https://www.dpamicrophones.com/pencil/4006-omnidirectional-microphone
Cartridge type Pre-polarized condenser
to get those $$$$$$$$$$$$$$

As to filtering, using the mike outside gives you, if it catches wind, huge low frequency variations
(maybe up to a volt pp on the mike output) so a bandpass is not a bad idea.
No idea _what_ he exactly wants to measure, all depends on that of course,

 If that happens I may need a sharper filter. I need a first iteration
and adjust from there.

Not measuring, just want to listen to the drug deals across the street.

And then what ever else. May need to be able to switch filters in and
out at some point

to make it more versatile.

                                                   Mikek


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[Rick C]

On Sunday, February 20, 2022 at 9:53:45 AM UTC-5, amdx wrote:

If that happens I may need a sharper filter. I need a first iteration
and adjust from there.

Not measuring, just want to listen to the drug deals across the street.

And then what ever else. May need to be able to switch filters in and
out at some point

to make it more versatile.

If you really want to listen to drug deals, the parabolic reflector is what you want. It doesn\'t even need to be large. An old satellite dish would do a decent job and be more inconspicuous than a typical reflector microphone. Just mount your preamp amp next to the electret mic. I second the idea of ditching the differential amp, but there\'s really nothing wrong with it other than being hard to modify. A single, simple op amp can be the preamp next to the mic and provide your low pass and high pass filtering with one pole each. The main concern on the preamp is to not overload the preamp.. Then you can add more filtering on the main amp to prevent that amp from overloading if needed.

Here is an interesting preamp candidate with compression.

file:///C:/Users/Rick/AppData/Local/Temp/ssm2167.pdf

https://www.ebay.com/itm/143774994752

About $8 from ebay. You can adjust C1 or C2 for the high pass filter and add a low pass filter between the mic and the amp.

The compression will help to hear quiet sounds without louder sounds overloading the amps.

--

Rick C.

--+ Get 1,000 miles of free Supercharging
--+ Tesla referral code - https://ts.la/richard11209

 

[amdx]

On 2/20/2022 12:43 PM, Rick C wrote:

On Sunday, February 20, 2022 at 9:53:45 AM UTC-5, amdx wrote:
If that happens I may need a sharper filter. I need a first iteration
and adjust from there.

Not measuring, just want to listen to the drug deals across the street.

And then what ever else. May need to be able to switch filters in and
out at some point

to make it more versatile.
If you really want to listen to drug deals, the parabolic reflector is what you want. It doesn\'t even need to be large.
An old satellite dish would do a decent job and be more inconspicuous than a typical reflector microphone.

Yes, I\'m kicking myself, I had 3 of them and in a recent clean up, I
threw the all out. I\'m now looking for another one.

Just mount your preamp amp next to the electret mic. I second the idea of ditching the differential amp, but there\'s really nothing wrong with it other than being hard to modify. A single, simple op amp can be the preamp next to the mic and provide your low pass and high pass filtering with one pole each. The main concern on the preamp is to not overload the preamp. Then you can add more filtering on the main amp to prevent that amp from overloading if needed.

Here is an interesting preamp candidate with compression.

file:///C:/Users/Rick/AppData/Local/Temp/ssm2167.pdf

Yes, I ordered a cornucopia of mic amps! I have on hand PCBs with the
SSM2167, TS472 and the INA217, and then a Headphone driver amp

https://www.ebay.com/itm/143774994752

About $8 from ebay. You can adjust C1 or C2 for the high pass filter and add a low pass filter between the mic and the amp.

The compression will help to hear quiet sounds without louder sounds overloading the amps.

 That Ebay PCB is the one I have.

Yes, I liked the idea of compression, I had a few issues with loud sound
on my ears using the Gain of 3,500 amp I built first.

Here\'s the 3,500 Voltage gain amp.

https://sound-au.com/project13.htm
Anything I do now, is to compare to that amp.

Although, I now have the headphone amp which has a gain of 4 too add
after the preamps.

 Just need to do something

                                     Mikek



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[Phil Allison]

amdx wrote:
===========

Not measuring, just want to listen to the drug deals across the street.

** Monitoring private conversations is ILLEGAL !!

Both fines an jail time are penalties.
So you go right ahead - asshole.

....... Phil

 

[amdx]

On 2/20/2022 3:40 PM, Rick C wrote:

On Sunday, February 20, 2022 at 3:06:25 PM UTC-5, amdx wrote:
On 2/20/2022 12:43 PM, Rick C wrote:
On Sunday, February 20, 2022 at 9:53:45 AM UTC-5, amdx wrote:
If that happens I may need a sharper filter. I need a first iteration
and adjust from there.

Not measuring, just want to listen to the drug deals across the street.

And then what ever else. May need to be able to switch filters in and
out at some point

to make it more versatile.
If you really want to listen to drug deals, the parabolic reflector is what you want. It doesn\'t even need to be large.
An old satellite dish would do a decent job and be more inconspicuous than a typical reflector microphone.
Yes, I\'m kicking myself, I had 3 of them and in a recent clean up, I
threw the all out. I\'m now looking for another one.
Just mount your preamp amp next to the electret mic. I second the idea of ditching the differential amp, but there\'s really nothing wrong with it other than being hard to modify. A single, simple op amp can be the preamp next to the mic and provide your low pass and high pass filtering with one pole each. The main concern on the preamp is to not overload the preamp. Then you can add more filtering on the main amp to prevent that amp from overloading if needed.

Here is an interesting preamp candidate with compression.

file:///C:/Users/Rick/AppData/Local/Temp/ssm2167.pdf
Yes, I ordered a cornucopia of mic amps! I have on hand PCBs with the
SSM2167, TS472 and the INA217, and then a Headphone driver amp
https://www.ebay.com/itm/143774994752

About $8 from ebay. You can adjust C1 or C2 for the high pass filter and add a low pass filter between the mic and the amp.

The compression will help to hear quiet sounds without louder sounds overloading the amps.

That Ebay PCB is the one I have.
So what is wrong with that circuit?


Yes, I liked the idea of compression, I had a few issues with loud sound
on my ears using the Gain of 3,500 amp I built first.

Here\'s the 3,500 Voltage gain amp.

https://sound-au.com/project13.htm
Anything I do now, is to compare to that amp.
If the only problem is too much gain, adjust the gain to something lower.


Although, I now have the headphone amp which has a gain of 4 too add
after the preamps.

Just need to do something
That doesn\'t narrow the field much. What problems are you having that you need to solve? Which circuit are you using? Which circuit do you want to use?

 The only thing I\'m doing noise is to see if I get less noise with in
other preamp. Just more experimentation than anything.

 I see Phil is still posting, has he said anything good that you want
to pass along. I\'m not reading his posts.


                                                     Mikek


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