amplifier for "BIG EAR" listening device

[4pyros]

Brownout look here;Parabolic microphone - Wikipedia, the free encyclopedia

and I quote

Parabolas only focus waves with a wavelength much smaller than the diameter of the parabola. Since sound waves travel at 342 m/s through the air (speed of sound), obtaining hi-fidelity sound (down to 20 Hz, the lower limit of human hearing) would require a parabola with a diameter greater than 17 meters (= 342 m/s / 20 Hz). Most parabolic microphones sacrifice low-end fidelity to get a more manageable size.

I saw the same thing mentioned many times the other night when I was looking for evidence that a 1/2 round would be better than a dish.

Andy

 

[BrownOut]

Brownout look here;Parabolic microphone - Wikipedia, the free encyclopedia

and I quote

I saw the same thing mentioned many times the other night when I was looking for evidence that a 1/2 round would be better than a dish.

Andy

OK, but what is there to hear at 20hz anyway?

 

[4pyros]

OK, but what is there to hear at 20hz anyway?

Not much but wind. LOL Thay say it makes human speech sound funny but you can EQ it some to make it sound more normal.

 

[gary350]

Here is the circuit drawing for the Big Ear Listening device. A brand new 9 volt battery works great for a small compact portable unit. 8 AAA batteries work excellent too.

When the volume control is turned up about 2/3 of the way it over drives the second stage causing it to make clicking sounds. It would probably be good to put a 2K or 3K resistor between pin 3 and the variable resistor I have not tried this but I always figured it would stop the over driving of the second stage.

Use capacitors rated for about 15 to 16 volts. Both of my .05 uf caps are 10 volts and are working fine. I tried 10 volts for both the 10 uf capacitors but they went bad so I had to change them both to a higher voltage the only thing I had available was 25 volts.

The best amplification is when the volume control is up in the range of about 60% to 65% volume. The volume control is very sensitive you move it just a tiny amount and it makes a big difference in that range. You might experement a little and fix this problem. I was thinking a 1K volume control with a fixed 6K resistor on the negative side and a 3K fixed resistor on the positive side might work. Best thing to do is adjust the volume control for best volume then unsolder the variable resistor and check the resistance both sides of the center tap with a meter.

If you put a 1K variable resistor in series with each 10 uf capacitor pin 1 and 8 only you can adjust the amplification of each stage from 200 down to about 50. Zero ohms = 200 amplification 1.2K = 50 amplification. If you do this for a volume control on the first stage it might stop over driving the second stage and the 10K variable resistor can be changed to a 10K fixed resistor.

**broken link removed**

 

[MrDEB]

thanks will try out your suggested circuit.
need tolocate transformer I have.

 

[chemelec]

Here is the circuit drawing for the Big Ear Listening device. A brand new 9 volt battery works great for a small compact portable unit. 8 AAA batteries work excellent too.

When the volume control is turned up about 2/3 of the way it over drives the second stage causing it to make clicking sounds. It would probably be good to put a 2K or 3K resistor between pin 3 and the variable resistor I have not tried this but I always figured it would stop the over driving of the second stage.

Use capacitors rated for about 15 to 16 volts. Both of my .05 uf caps are 10 volts and are working fine. I tried 10 volts for both the 10 uf capacitors but they went bad so I had to change them both to a higher voltage the only thing I had available was 25 volts.

The best amplification is when the volume control is up in the range of about 60% to 65% volume. The volume control is very sensitive you move it just a tiny amount and it makes a big difference in that range. You might experement a little and fix this problem. I was thinking a 1K volume control with a fixed 6K resistor on the negative side and a 3K fixed resistor on the positive side might work. Best thing to do is adjust the volume control for best volume then unsolder the variable resistor and check the resistance both sides of the center tap with a meter.

**broken link removed**

You should put DIODE DECOUPLING Between EACH LM386 and a Suitable Bypass cap from each Pin 6 To V-

 

[gary350]

You should put DIODE DECOUPLING Between EACH LM386 and a Suitable Bypass cap from each Pin 6 To V-

I been looking at all the circuits I can find online I see only 2 circuits with a .05 up capacitor from pin 6 to ground I'm not real sure what that cap does. I found one circuit that has a 1K variable resistor between pin 1 and 8 in series with the 10 uf capacitor so that proves my idea will work for a volume control. I don't find any circuits with diode coupling draw us a circuit lets see what it looks like, how will that be better?

 

[chemelec]

I been looking at all the circuits I can find online I see only 2 circuits with a .05 up capacitor from pin 6 to ground I'm not real sure what that cap does. I found one circuit that has a 1K variable resistor between pin 1 and 8 in series with the 10 uf capacitor so that proves my idea will work for a volume control. I don't find any circuits with diode coupling draw us a circuit lets see what it looks like, how will that be better?

Well in the First Place, Why would you use a POWER AMP AS A PRE-AMP?

It is not the Best Situation.
That is WHY they Make Pre-Amps.

And what I Suggested will Not be on the Internet because Only Beginners will use a LM386 as a Pre-Amp.

Your Clicking Sound is Most Likely Feedback Oscillation through the Power Supply.
The Diode De-Coupling will Help to Prevent that.

But Far MORE PRACTICAL would be to use an ACTUAL Preamp circuit.
Or just an LM358 as a Preamp.

As to that .05 you Mention, It is to help Prevent High Frequency Oscillations and Should be INCLUDED on Power Pin of ALL IC's. (.001 to .1 Values are Common for this)
And Many Schematics Don't Show this Capacitor, as its "Common Knowledge for a Good Design".

 

[audioguru]

Of course a low noise opamp should be used as a preamp.

I have one LM386 amplifier with a gain of 200. Its output has plenty of hiss. If it is amplified 100 times more then the hiss will be louder than any microphone signal.

An electret mic is an excellent mic. But a speaker will resonate like a bongo drum when it is used as a microphone.

 

[chemelec]

An electret mic is an excellent mic. But a speaker will resonate like a bongo drum when it is used as a microphone.

A Small Speaker with a Wind Screen, (Like used on Most Microphones) will work Quite Well, when Impedance Matched.
The Problem with an Electric Mic facing a Parabolic: Is it SMALL Size.
Unless it is a Really Pefect parabolic, a Considerable amount of sound will Miss hitting it.

Some systems use a Smaller Parabolic to Encompass a Electric Mic. And this Mic Faces Forward into the smaller parabolic.
Not Facing the Larger one.

Also a Transistor, Base Follower Circuit will Better Impedance Match the Speaker to the Amp.
Eliminating a lot of Inductance Resonances that a Transformer can create.

 

[gary350]

Well in the First Place, Why would you use a POWER AMP AS A PRE-AMP?

It is not the Best Situation.
That is WHY they Make Pre-Amps.

And what I Suggested will Not be on the Internet because Only Beginners will use a LM386 as a Pre-Amp.

Your Clicking Sound is Most Likely Feedback Oscillation through the Power Supply.
The Diode De-Coupling will Help to Prevent that.

But Far MORE PRACTICAL would be to use an ACTUAL Preamp circuit.
Or just an LM358 as a Preamp.

As to that .05 you Mention, It is to help Prevent High Frequency Oscillations and Should be INCLUDED on Power Pin of ALL IC's. (.001 to .1 Values are Common for this)
And Many Schematics Don't Show this Capacitor, as its "Common Knowledge for a Good Design".

Power Amp!!!.....Ha, Ha, Ha, .4 watt is not a power amp.

 

[audioguru]

The LM386 has an output of 0.45W into 8 ohms at clipping with a 9V supply.
An opamp has an output of only 0.004W into 2000 ohms at clipping with a 9V supply.
A huge difference.

The opamp cannot drive the high current, low impedance speaker.

The LM386 is made for cheap toys. A low cost low noise audio opamp makes an excellent preamp.
An LM358 dual opamp has crossover distortion, a high hiss level and reduced high frequencies like a telephone.

 

[chemelec]

Power Amp!!!.....Ha, Ha, Ha, .4 watt is not a power amp.

Maybe you should read at the DATA SHEET.

It May not be HIGH POWER, But it definately is a Power Amplifier.

And the LM386N-4 can produce 1 Watt with a 16 Volt supply.

 

[audioguru]

With a 9V supply the LM386 produces 0.45W into 8 ohms at clipping and dissipates 520mW of heat.
With a 16V supply the LM386 produces 0.53W into 8 ohms at clipping and melts with 1.35W of heat.
Its max allowed dissipation is 1.17W when the ambient is 25 degrees and its chip is at 150 degrees C.

The difference in loudness is almost nothing but the heat becomes 2.6 times more.

 

[MrDEB]

suprised audioguru took so long to jump in. Morning Audio or ?? what ever time of day it is.
I still question the use of descrete componets vers an op amp preamplifyer circuit (link at begining of this thread somewhere)

 

[MrDEB]

link to schematic using transistors for preamp, op amps for bandpass filter and an lm386 for amp
**broken link removed**
what I am after is a per amp followed by perhaps a bandpass filter to limit the static then an amp that can input into a set of headphones AND a switch to turn on an amp say 7-10 watts so several cubscouts can hear at one time.



i

 

[gary350]

Maybe you should read at the DATA SHEET.

It May not be HIGH POWER, But it definately is a Power Amplifier.

And the LM386N-4 can produce 1 Watt with a 16 Volt supply.

I built this in 1977. Got the circuit out of a book. Someone some where designed the one IC amp all I did was put 2 of them together and I had a BIG EAR. I had a lot of fun with it. It doesn't matter to me that it produces 1 watt on 16 volts. I never operator it on more than 15 volts I killed a few ICs on 16 volts. I know data sheet says it is rated 18 volts and it does work on 18 volts for a short time then it fries the chip. A brand new 9 volt battery only lasts a short time AAA or AA batteries are better.

There is no noise or static the circuit is crystal clear sound. The only unwanted sound is when you turn the volume up too loud.

 

[chemelec]

I still question the use of descrete componets vers an op amp preamplifyer circuit (link at begining of this thread somewhere
----------------------------------------------------------------------------------------------

link to schematic using transistors for preamp, op amps for bandpass filter and an lm386 for amp
**broken link removed**
what I am after is a per amp followed by perhaps a bandpass filter to limit the static then an amp that can input into a set of headphones AND a switch to turn on an amp say 7-10 watts so several cubscouts can hear at one time.

Re: Transistor Preamp.....And What do you Think makes up an Integrated Circuit?
It May be Smaller, But its still comprised of Transistors.

A Band Pass Filter Won't Remove STATIC.
It will Only help Narrow the Bandwidth to help picking up certain Frequencies better.
Such as a Higher Frequency to Hear a Bird, while Limiting Lower Frequency sounds, like a car going by.

Reguardless of What Power Amp, your using, To Eliminate HISS from the Amp into Headphones, You need to put a Resistor in Series with your HeadPhones. Usually a 1/4 watt resistor, with a Value of Between 47 and 100 Ohms is Good.

And with 9 volt supply, an LM386 can Easily Drive 10 sets of Headphones.
Use a Seperate Resistor to EACH Headset.
7 to 10 Watts is really an Overkill for Head Phones.
And if you use it to drive a Speaker, you will just wind up with Lots of Feedback SQEELING

 

[audioguru]

suprised audioguru took so long to jump in. Morning Audio or ??

I was busy viewing a tutorial about Windows 7 that I will get soon. My time is Eastern Standard Time.

I still question the use of descrete componets vers an op amp preamplifier circuit.

Transistors were used in preamps in the 60's and 70's. They had plenty of distortion.
Audio opamps are much better and make a very simple circuit.

what I am after is a preamp followed by perhaps a bandpass filter to limit the static

What static? Keep away from lightning storms and high voltage lines.

then an amp that can input into a set of headphones AND a switch to turn on an amp say 7-10 watts so several cubscouts can hear at one time.

You can't play a speaker when there is a very sensitive mic nearby or you will have acoustic feedback howling. Record it, turn off the mic then play it back through a speaker.

 

[chemelec]

Transistors were used in preamps in the 60's and 70's. They had plenty of distortion.
Audio opamps are much better and make a very simple circuit.

The Transistor Pre-Amp I show on my site is Quite low both distortion and noise and has a good frequency response.

The Better OP-Amps Typically require a +/- Supply voltage. (like an LM381.)
And if you use a Single Supply Op-Amp, like the LM358, Its not all that good for Noise and Frequency Response.
Actually Probably Worse than my transistor pre-amp.

But to each to there own ideas.