The very noisy Cmos opamps will produce lots of hiss when used in a mic preamp.
Their input bias current is extremely low then the fairly high current 2.5V reference circuit using 2 paralleled opamps can be replaced by 2 resistors and 1 capacitor.

 

Here's the Schematic for a Low-Voltage-Mic-Mixer designed to
provide Bias-Power to Electret-Condenser-Mics.
Dynamic-Mics will probably work too.
If perfect extremely-High-Frequency-Response is important to You,
then You will need Op-Amps that cost ~10-times as much,
but these cheapo-chips should do just fine.
All of the Resistors need to be "Metal-Film", 0.5% tolerance, 1/2-Watt rated,
to keep the background noise to a minimum.
All Capacitors, 1uf and smaller, are Ceramic, and at least 10%,
You get what You pay for.
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View attachment 245024

I like the bias arrangement for the mic - very neat.
Not sure about 200n/1k for bass roll-off that's 800Hz, and you have two which make a 2nd order high-pass.

 

Opamp #11 has a 50 ohms (!) feedback resistor.

 

Opamp #11 has a 50 ohms (!) feedback resistor.

And the input is connected to PSU ground (but signal ground is at half supply)

 

And the input is connected to PSU ground (but signal ground is at half supply)

No.
The black triangles are the mixing buss.
The green triangles are ground.
The pink triangles are the 2.5V bias voltage for the opamps and the zero signal for the level controls.

 

It's good to see that somebody's paying attention.
I was fighting to keep my eyes open when I made this,
so there are bound to be some mistakes.

I've also found what I think is a better Op-Amp, for only twice the price.
I don't like the low Slew-Rate in the cheap one that I specified, although it should be adequate.
Any comments/suggestions are welcome.
Spec-Sheet for the "better" part is attached below.

Audioguru again
A ~120db Noise-Floor is really not necessary, no need for exaggeration or perfection.
And remember, He wants a 5-Volt Supply.
50db down is way more than adequate when you're not in a Recording-Studio,
and you're using multiple Lavalier-Style Mics, ( in a room with bare walls and ceiling no-less ).
It's been ~40-years since I made a Mixer from scratch, and they worked great.
I can't imagine that CMOS technology is significantly noisier than
the fussy crap I had to work with back then,
and I think most of the bad-rap that CMOS gets for Noise is due mostly to people wanting to
take advantage of the extremely high Input-Impedances
by using extremely high-value Feed-Back-Resistors
in an effort to have a more "Battery-Friendly" Power-Consumption level.
High Value Resistors can easily contribute more noise than any Amplifier could hope to.
Notice that 0.5%, 1/2-Watt, Metal-Film-Resistors are specified, specifically for this reason.

The Half-Supply-Buss also "Grounds" all the very low-value Level-Pots,
the heavy-Current-Capacity and large Bypass Caps are to reduce, or eliminate,
Cross-Talk between Channels.

Most of the 100nf Caps on the 1/2-Supply-Buss are to insure against
External-Noise-Sources, and to suppress any odd tendencies towards creating Oscillations,
as I won't be assembling the Board for this Mixer and
watching for unintentional loops and Antennas.
Actually, the whole Circuit has such Low-Impedance, along with Low-Slew-Rate Op-Amps,
that generating Oscillations should be almost impossible.

"" Opamp #11 has a 50 ohms (!) feedback resistor. ""
Yeah, it's not "Best-Practices" to Amplify a Signal,
then turn right around and Attenuate it by minus ~23db, ( or whatever it was ).
It was an afterthought,
but I considered that it might be a desirable feature to have
an additional Output that is compatible with low, "Mic-Level" Inputs, on some equipment.
That Output, is of course, optional in any case.

Ian0
"" Not sure about 200n/1k for bass roll-off that's 800Hz,
and you have two which make a 2nd order high-pass. ""
OOps, wrong Resistor entered into the Formula ............
Thanks for catching that.
I'll correct it soon.

"" And the input is connected to PSU ground (but signal ground is at half supply) ""
All Inputs and Outputs of the Op-Amp are at a nominal 2.5-Volts.
( the Power-Supply-Voltage may vary quite a bit )

Thanks for all the input ............
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I would recommend a Dynamic-Range-Compressor,
a Soft-Clipping-Circuit,
and at least a 3-Band-Tone-Control added to this project.
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I also don't think that two summing mixers connected to the same virtual earth will work so well.
45nV/√Hz is a noisy op-amp, but if we're saving every last microamp of current it might just have to do. It must have better crossover distortion than an LM358 - because NOTHING has worse crossover distortion than an LM358!
Why all the low-value resistors? If noise isn't a problem, and current consumption is, then 10k pots would save a few more uA.

CMOS op-amps tend to have higher 1/f noise corner frequencies, which the cynic in me says is why the 1/f noise corner frequency isn't mentioned in the datasheet.

 

Resistors can be very noisy, and it's directly related to their Resistance-Value,
a lot of them together can easily create more noise than the Amps.
That's why they're specified as being "Metal-Film", 0.5%, and 1/2-Watt rated,
and not 1/8-Watt, 10%, Carbon-Composition.
It makes a serious difference.

High-Gains can also cause Noise, Distortion, Frequency-Response, and Oscillation problems,
that's why the maximum Gain in this Mixer design is only ~22.
Bonus, Gain-Stages don't add, they multiply.

With Op-Amps, You generally get what You Pay for.
I'd rather have specified some decent ones,
but the price makes some peoples knees get weak at almost ~$80.oo for 8-Dual Op-Amps.
So, for a Dollar each, for Quads, You're going to have to accept some compromises.
Oh-well, this is not going into a Recording Studio, and most likely nobody will ever notice.

Lack of Distortion, and especially Room-Resonances, are the biggest considerations
in Recording Clear-Conversational-Voices.
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The Schematic has now been up-dated and corrected, including new Op-Amp Part-Number.
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