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Cheap microphone - simple amp circuit
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Richard Crowley:

--- Quote from: mikeinfodoc on September 27, 2018, 10:19:37 pm ---If I follow with LM386 stage, what is the advantage of using the ne5532 at all?
I ask this earnestly as I am wondering when the ne5532 would/should be used...

--- End quote ---
The LM386 is designed for a line-level signal input.  So you need some amount of additional voltage gain if your source is a low-level source like a microphone.  The NE5532 is designed for amplifying low-level signals (microphone, phonograph pickup, electric guitar, etc.) up to line-level.  And with better signal-to-noise ratio than common general-purpose monolithic op-amps.


--- Quote ---Also is the term "line level" considered a norm for small signal transfer between devices?
--- End quote ---
Yes most audio gear uses "line-level" internally.  And also "line-level" externally to connect between different pieces of gear.
There are roughly three levels of audio signal standards:

1. Low-level - this includes mic-level, phono-level, instrument-level, etc. Typically down at a few millivolts.  Modern microphones are low-impedance sources (a few hundred ohms), Phono-level are typically 47K ohm impedance, and electric instruments (guitar, bass, etc.) expect to see no lower than 100K load impedance (or higher)
2. Line-level - There are two varieties of this, Consumer line-level is typically -10dBv (somewhere around 300mV), and Professional line-level (+4dBv to +10dBv) which is typically around 1.2V  Modern gear has rather low output impedance (perhaps a few hundred ohms to maybe 1K ohm source impedance.  And modern gear typically has rather high input impedance (perhaps 5K to 10K or 20K ohms.  That convention generally eliminates cable effects (parallel capacitance and series resistance) from consideration, and makes "impedance matching" something that only our grandfathers remember.
3. Speaker-level  - Typically a very low source-impedance from a power amplifier designed to drive a 8 ohms (or 4 or 16 ohms) load from a passive speaker cabinet.  Voltage depends on the amplifier power.  Around 9V for 10 Watts into 8 ohms, or 28V for a 100 Watts into 8 ohms.  Ohm's law will translate watts into volts for a given impedance (http://rcrowley.com/eirp.htm)


--- Quote ---(I take it that LINE LEVEL means kohms and very small millivolts, but I could be wrong about that also)
--- End quote ---
No. Line-level does not mean K ohms of impedance, and certainly does not mean small mV of signal level.  See outline above.

As @Hero999 observed, you are trying to use an electret microphone capsule. Electret microphones do not generate any signal on their own (as a dynamic microphone would).  They actually have a FET transistor inside with "sound" connected to the gate.  So you must put some current through it in order to get a voltage signal out of it.  There are hundreds of representative circuits on the interweb showing electret condenser microphone circuits connected to the input of an NE5532.
6PTsocket:
Because there are other uses for  op amps  used in audio circuits than to drive speakers. The word audio does not make it a power amp/ speaker driver.
--- Quote from: mikeinfodoc on September 26, 2018, 01:39:59 pm ---Thank you for your reply/feedback.

I agree the datasheet indicates they use 600ohm, however I am not sure why.

That seems very impractical for an audio op amp.

When I drive my small pc speak using my existing circuit with 5v dc (which gets split), the volume seems plenty high/loud enough.

I will likely have more follow up question, but let me ask this one first:

Why would an audio opamp be spec'ed for 600ohm load?
     (As most speakers are no where NEAR that reactance in typical audio frequency ranges).

--- End quote ---

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mikeinfodoc:
Your feedback is immensely useful.

You cleared up several concepts for me which I have wondered about for a while.

It seems in electronics, there are those who know a lot, and those who know a little, and not many "in betweener's" (which is where I find myself).

My day job is oracle database programming and IT related stuff (30 years strong), but I have a keen interest in electronics as a hobby (and wish I had more time to devote to it).  My son is 10 yrs old, so not quite old enough to help dad with this stuff yet :-)
mikeinfodoc:

--- Quote from: 6PTsocket on September 28, 2018, 11:57:48 am ---Because there are other uses for  op amps  used in audio circuits than to drive speakers. The word audio does not make it a power amp/ speaker driver.

--- End quote ---

Thank you, as I understand now, there are often situations in which you only need to take low-level to line-level, etc...

I have ordered some LM386 power audio amp dip's.  Once they arrive, I hope to add a 2nd stage to take my line level to speaker level.

I welcome any guidance on doing that (or schematics) if you so choose.
Audioguru:
If you split 5V then the NE5532 has plus and minus 2.5V power supply, but its minimum allowed is plus and minus 3V for a 6V total. Maybe you are lucky yours works.
Since your pc speaker is plenty loud enough then does it have a built-in power amplifier?
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