simple 12v electret mic to earbud/headphone amp

Thread Starter

heykarch

Joined Feb 1, 2021
1
hello
im looking for help to build a simple 12v electret mic to earbud/headphone amp as in a car/aero intercom

i have tried many of the layouts on the internet with lm386 and NE5532 but not been able to get them to work...

any help would be appreciated, iam a beginner and just trying to learn

thanks
 

Boatman47

Joined Jan 22, 2021
11
My circuit shows a 9V supply but will work from 12V.
You do not learn anything by copying my circuit:
Actually, one does learn something both by analyzing your circuit and by building it. One can also adapt it to a Bluetooth wireless mode, as well as gain ideas on miniaturization. Op amps are peculiar circuits that still puzzle me, especially choosing RC pairs. Thanks for the suggested circuit.
 

Delta Prime

Joined Nov 15, 2019
996
You do not learn anything by copying my circuit
I have been copying your circuits for over... well a lot of years now along with the other rock stars of science on AAC. There are rumors going around that you are out of luck unless you have gone duck. In part because of all of you I graduated Summa Cum Laude.
 

LowQCab

Joined Nov 6, 2012
517
While you're learning,
you also need to find out about "Noise-Cancelling" vs "Omni-Directional" Microphones.
Also about Noise-Gates, Compressors, and
Frequency-Response-Shaping for increased Speech-Intelligibility in Voice-Communications.
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Audioguru again

Joined Oct 21, 2019
3,173
Frequency-Response-Shaping for increased Speech-Intelligibility in Voice-Communications.
Its cuts low frequencies so that people sound like chipmunks and cuts all important consonants sound in speech so that words sound like vowels, grunts and groans. The frequencies of consonants reach 14kHz, far above the 3kHz of AM radio and old telephones.
 

LowQCab

Joined Nov 6, 2012
517
Its cuts low frequencies so that people sound like chipmunks and cuts all important consonants sound in speech so that words sound like vowels, grunts and groans. The frequencies of consonants reach 14kHz, far above the 3kHz of AM radio and old telephones.
That's only because
"down & dirty" and "super-cheap" and "good enough" are normally the first priorities in the design.
I've designed Circuits that will "part-your-hair" with precision clarity,
and that will cut through any external noise you can imagine,
with ~150% modulation, virtually 100% of the time,
using Multi-Band, Super-Fast-Compression to limit Low-Frequency Response to around 300hz,
and "Soft-Clipping" to limit High-Frequency-Response to around 10-Khz.
You won't believe your Ears while you are watching a "pegged" Modulation-Meter,
with virtually zero unwanted Harmonics, and excellent clarity.
Notice that I didn't say there was no Distortion,
it's just that certain types or "characters" of distortion are useful,
and yet, not particularly irritating to the Ears.
Part of this is why Tube Amps are not particularly irritating when pushed hard into clipping,
but Solid-State Amps are very irritating when clipped hard.
Odd-Order vs Even-Order Harmonic Distortion,
and lots of Asymmetrical "Amplitude" Distortion ..........

And,
AM Radio is perfectly capable of "20 to 20" Frequency Response, with no issues,
but the Engineers know that ~98% of the listening devices out there in Radio-Land
can't reproduce those Frequencies, so why bother.

You can also push "20 to 20" Frequency response down a 6-mile long isolated Phone Line Pair.
I know because a buddy and I did these very things back
in the '70's at a local "Top-40" AM-Radio Station.
We routinely did Control-Room Quality Remote-Broadcasts over dedicated Phone-Lines using
2- 27-Band EQ's hooked-up in series, and a ~1000 Watt Audio Amp to push the Phone-Line .
That is, until we managed to obtain a "Marti" FM Transmitter and Receiver Pair,
and some rather large Yagi Antennas for the UHF Link.

It's usually not the equipment's capabilities that are the limiting factor,
it's the Engineer's capabilities in using that equipment that count.
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AnalogKid

Joined Aug 1, 2013
9,248
"These" are just "three" of the "top ten" "things" I "disagree" with.
with ~150% modulation, virtually 100% of the time,
What does that even mean?
AM Radio is perfectly capable of "20 to 20" Frequency Response, with no issues,
Ummm ... FCC - ? Part 73 - ? (ps. They probably have an opinion about "150% modulation", also.)
using Multi-Band, Super-Fast-Compression
and
using 2- 27-Band EQ's hooked-up in series, and a ~1000 Watt Audio Amp to push the Phone-Line .
Did you read any of the words in post #1? Words like "simple" and "beginner" - ? ? ?

I don't think you have an accurate read of either the skill set of the TS or the scope of the project. In my own experience, I think *two* ( "2" ) 27-band EQs are a bit much for a voice-band intercom.

ak

Code of Federal Regulations (CFR),
Title 47,
Chapter 1,
Sub-Chapter C,
Part 73,
Paragraph 44,
Sub-Paragraph b

https://www.ecfr.gov/cgi-bin/text-i...mc=true&node=pt47.4.73&rgn=div5#se47.4.73_144
 
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LowQCab

Joined Nov 6, 2012
517
What's wrong with giving a "Noob" some ideas they may
never have known about otherwise ?????

Next .......
--------------------------------------------------------------------------------------
""(b) Emissions 10.2 kHz to 20 kHz removed from the carrier must be
attenuated at least 25 dB below the unmodulated carrier level,
emissions 20 kHz to 30 kHz removed from the carrier must be
attenuated at least 35 dB below the unmodulated carrier level ......... ""

This is new to me, this was not specifically in place in 1975,
or at least the FCC decided not to mention it when
they paid us a visit for an un-announced, surprise Inspection.
Only "Undesirable-Interference" was not permitted,
and could result in a hefty fine,
if you pissed-off the FCC Inspector.
-----------------------------------------------------------------------------------
Next ........

We actually did several Frequency Spectrum Analyses late at night,
just to verify what was actually being Broadcast over the Air.
We found that 20-Khz was not an issue at all,
but chopped it at ~12-Khz, because few, if any,
listeners had receiving equipment that could reproduce those High-Frequencies.
So, chopping it early took some load off of the Modulator Tubes,
which already had to be replaced about every ~60 days of operation.
--------------------------------------------------------------------------------------

""§73.1570 Modulation levels: AM, FM, TV and Class A TV aural.

(a) The percentage of modulation is to be maintained at as high a level as is consistent with
good quality of transmission and good broadcast service,
with maximum levels not to exceed the values specified in paragraph (b)..........

(b) Maximum modulation levels must meet the following limitations:

(1) AM stations.
In no case shall the amplitude modulation of the carrier wave
exceed 100% on negative peaks of frequent recurrence,
or 125% on positive peaks at any time. ""

-------------------------------------------------------------------------------------------
The Modulation Monitor was "bangin'" on 125% continuously when the FCC Man dropped by.
And this was a nice big 5" X 7" Analogue Meter that could easily be seen from across the room.
If you listened very carefully, you could even hear the Needle "clicking"
and bouncing off of the Needle Stop Pin.
We were lucky,
sometimes we'd crank it even higher just for kicks,
and to mess with the other local competing AM Station.
------------------------------------------------------------------------------------------

With CB Radio, you can get away with much crazier Modulation Levels,
it's only the "Negative-Peaks" that create "Hash", so they need strict control.
"Class-A" Tube distortion works hand-in-hand with these requirements quite nicely.
--------------------------------------------------------------------------------------------

Intercom Systems are their own special animal,
where any actual Amplifier Clipping needs to be totally avoided,
by careful use of substantial, clean power,
and heavy Dynamic Range Compression,
and Noise-Gating,
and well engineered Noise-Canceling-Mics.
Proper "EQ" is just icing on the Cake.
-------------------------------------------------------------------------------------------
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Audioguru again

Joined Oct 21, 2019
3,173
Telephones and AM radio were invented such a long time ago that the engineers did not know that reproduced sound could be better. They were also made to be cheap.

AM radios must completely cut 10kHz therefore their lowpass filter begins cutting 2.7kHz audio to prevent a 10kHz interference tone when two stations are 10khz apart. I think there were a few AM radios made with the bandwidth adjustable.

Today, Polycom makes speakerphones that use two telephone lines for double the bandwidth and AM stations produce pre-emphasis of treble sounds so that a good AM radio can have a frequency response flat to about 6kHz.
 

AnalogKid

Joined Aug 1, 2013
9,248
I really wonder where some of this stuff comes from.

The 10 kHz sideband limit for commercial AM broadcasting in the US was in place in the 1950's.

"must" - ? No. In terms of signal bandwidth, AM radios do not have to comply with anything. Of course, if they sound like crap no one will buy them, but there are no governmental rules. And the bandwidth shaping does not happen at baseband. The tuning of resonant transformers in the IF signal path is what sets the bandwidth of the final signal. AND - that also is where adjacent-channel signal rejection ("selectivity") is achieved (with help from the tuned antenna).

Engineers knew *a lot* about frequency response and fidelity - in the 1920's, and super-het (supersonic-heterodyne) radios with IF stages dominated the market in the 1930's. If you'll recall, Bell was an audiologist and a speech and hearing therapist. His early work on the telephone came out of his experiments into - wait for it - an electric hearing aid. The Fletcher-Munson curves were published in 1933, way before the current rules for AM broadcasting were enacted. But Bell's own research predates them by decades. So yes, we in fact *did* know about better reproduced sound.

My broadcast days are waaay behind me, so I might have to dig up one of the old xmtr guys for an update.

ak
 

Audioguru again

Joined Oct 21, 2019
3,173
When I was a teen I assembled a Heathkit amplifier with tubes and made a pretty big speaker enclosure. My friend bought every Shure high price new phono cartridge and gave me his "old" one that was still like new. But my radio was still lo-fi AM. I assembled an Eico FM tuner kit with tubes and when stereo came out I assembled its stereo adapter, a new stereo tubes amplifer and a second speaker. I never listened to music on an AM radio again.

I phoned an FM radio station and told them their stereo channels were out-of-phase so that mono was cancelled. They agreed and fixed it.

I worked with a very large high quality business intercom system then Canada's Airports Authority put out a bid for a new PA system with intercom stations as the inputs. The spec was for high fidelity frequency response and my modifications made the intercom system I worked with meet the spec and it won the bid. The company I worked for sold only my prototype system because the Airports Authority bought more themselves from the manufacturer that did not have my modification for hi-fi.
For businesses who bought the standard intercom system I made a bass-boost equalizer for background music.

When I worked with telephone boardroom conference systems, sounds were very muffled so I made a call on one telephone line and received the call on another line. I measured 3khz to be down at -12dB. But Bell's spec is -15dB so they did not fix it.
I designed and made an equalizer that boosted transmitted sounds around 3kHz and every demo I made sold two or more.
 

LowQCab

Joined Nov 6, 2012
517
hello
im looking for help to build a simple 12v electret mic to earbud/headphone amp as in a car/aero intercom

i have tried many of the layouts on the internet with lm386 and NE5532 but not been able to get them to work...

any help would be appreciated, iam a beginner and just trying to learn

thanks
It occurred to me that nobody answered your question .......
OK, what follows is a Schematic for a very high quality Mic-Pre-Amp/Head-Phone-Amp Combination.
It's a good project to get you feet wet with,
but I think you will be disappointed in what you will get performance-wise,
so I included a Schematic for what I think you really want, also.

A little more than what you asked for ............
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Attachments

DickCappels

Joined Aug 21, 2008
7,426
Now you can choose between the deluxe versions in post #13 or if you want to put something together a little more quickly there is the simpler circuit in post #2. Or you might want to make the simple one, and once you see you it works, see whether the more complex solutions give significantly improved performance.
 

AnalogKid

Joined Aug 1, 2013
9,248
i have tried many of the layouts on the internet with lm386 and NE5532 but not been able to get them to work...
To help us help you, post the schematics of the circuits you tried, and tell us what did not work with them. Be sure to include details about power sources, links to the original circuits, etc.

ak
 

LowQCab

Joined Nov 6, 2012
517
hello
im looking for help to build a simple 12v electret mic to earbud/headphone amp as in a car/aero intercom

i have tried many of the layouts on the internet with lm386 and NE5532 but not been able to get them to work...

any help would be appreciated, iam a beginner and just trying to learn

thanks
.
I missed a mistake on the simple Mic Pre-Amp ..........
The 2-Stage Mic Preamp sections were supposed to have ~22-X Gain each, not 2-point-2-X,
That "should-be" a total of 22 X 22 = ~484-X Gain.

( 0.010-Volts Peak-to-Peak-Maximum-Output from the Mic, Times,
484 = 4.84-Volts Peak-to-Peak Output from the Pre-Amp Section ).
Which, when doubled by the "Power-Amp" Section = 4.84 X 2 = 9.68 Volts-Peak-to-Peak-Output.
Actually, at this point, there will probably be some Output Clipping,
and you have already lost ~20% of your hearing.

I just missed that extra zero on the Feedback Resistors.
It's fixed now.
Don't go by the first version,
a total of 4-X gain in the first version is no where near close to enough Gain for any Microphone.
My bad, I missed that.
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