MRW said:
Hello all:
What considerations do I need to take when connecting multiple
microphones to a pre-amp? Can I even do that?
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.
Just by looking at it, I know that I'm paralleling multiple
capacitances. This will probably change the frequency response of the
mics, right?
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.
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.
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
