Connecting multiple mics to a preamp?

Hello all:

What considerations do I need to take when connecting multiple microphones to a pre-amp? Can I even do that?

Just by looking at it, I know that I'm paralleling multiple capacitances. This will probably change the frequency response of the mics, right?

I got some samples for a MAX4468 and wanted to see if I can use it to connect three condenser mics to the same input. The mics would be setup in a small box enclosure. One mic for each side except for one.

Datasheet:

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Thanks!

Reply to
MRW
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I think in general you can't. For example, when I was in college I had an amp and a friend of mine brought his guitar over. We had one amp and two guitars. I hooked spliced the lines together and guess what? One volumn control controlled the other guitar. I didn't realize it at the time(I was a math student) but its quite simple now.

Its possible for all the loads of the mics to interfer with each other(although for mics it may not be an issue but I bet it is) because they will load each other. This is why mic preamps probably exist.

Yes, this is essentially what I mean. If you have a cascade of filters then its possible for the the succeeding stages to load the previous ones. Think of trying ot put two LP filters together. Do you get the effect of two acting "independently"? It depends on the resister and capacitor values. I can't explain it well but I'm sure you can find more info on it if you want. The AOE has a very good explination of it and how to fix it.

Yep, AFAIK and see it looks like this is exactly what you want.

Essentially what you want to do is use the op amps to make the mic see an infinite load so the voltage does not depend on the load. This is what an op amp does.

I'm not quite sure the exact configuration as I've not messed with this stuff to much and its been a while sense I've read AOE but basically you want to use some type of op amp for each mic such as a unity gain buffer(this loads the mic at the load you want but essentially seperates mic and what comes after the mic from interfering with each other) then after those use a summing op amp configuration to do the mixing(might be able to just using the summing op amp though but not sure as the mics might interfer with each other).

You would have variable resisters on one of the stages to control how its mixed. If you don't have to much experience in electronics you might and to find a schematic already made or ask here about it more. Theres probably a lot of nuances that can cause problems for you. I also imagine that you have to worry about the capacitances in the mic since AFAIK the op amp loading is mainly dealing with resistance and not reactance.

Anyways, since these are mic preamps it looks like you have everything you need. You just gotta figure out how to put them together ;) (and some ways will be better than others).

Jon

Reply to
Jon Slaughter

There may be exceptions (aren't there always?), but in general, you need a mixer to individually preamp each mic and adjust each mic's volume and mix them all together to make a single audio signal.

Reply to
John Popelish

You need a mixer circuit. It needn't be complex.

Reply to
Homer J Simpson

What is your application? These things aren't likely to sound very good - check out that noise figure of 40nV.

Reply to
tempus fugit

For sure these are *not* condensor mics, but cheap electret ones. Choose the bias resistor accordingly and parallel them into a transimpedance opamp configuration. Since these are basically current sinks, the output current will add up fine. Since the summing node has very low impedance, the frequency response of the single mike will not change, but because of different path length comb filtering will happen at higher frequencies, depending on incident angle. A box will create awful interference patterns at those sharp bends, better put them in a small sphere.

--
ciao Ban
Apricale, Italy
Reply to
Ban

That was my original thought ...... using multiple pre-amps and send their output to a mixer. But I wanted to check if I can get away from using multiple pre-amps.

Reply to
MRW

I saw a circuit online where the guy made a grenade-like sound detector. The idea was to throw this box containing mics at a certain distance and then you can listen on in via a wireless connection. I think the person was inspired after playing too much Halo.

I think this application has some use when playing a friendly game of paintball.

Reply to
MRW

You can often uses resistors to mix the signals.

Reply to
Homer J Simpson

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