How important is impedance matching between mic and amp?

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Mr Funk

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Most pre amps will work with most mics, irrespective of the mic's impedance, but they will work better with some loads than others.

This results in mics sounding different to how they are 'meant' to sound and why some mics work better with certain pre amps. This is not saying that a miss-match won't result in a subjectively better sound, just that it will not be how the mic is supposed to sound.

How important do you think this issue is? Is a pre amp that can switch its impedance preferable? This will allow a mic to work 'properly' or give the user extra flavours to play with by setting incorrect impedances.

Please give your opinions.
 
A pre that will switch impedances is all well and good... but hardly necessary. We had pre-amps that didn't switch impedance for the first lord only knows how many years of this industry... and not a single life was lost due to the lack of flexibility.

With that said... I think that it's pretty damn cool to have the ability to switch impedance on the input of the mic pre... the net result is several different tones and textures from the same unit... which in my world, is a good thing.

As always... YMMV
 
What would an input transformer's role be in all of this? Warning: I know nothing about this kind of thing.

Slackmaster 2000
 
Input/out transformer's are the best way to couple the impedance of two audio devices.... but Jenson transformer's are not cheap. Like Fletcher said, it's cool to use the preamp impedance switch kind of like an effect.

Fletcher, does this hold true wilth ribbon mic's also?
 
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So would an impendence switch on a preamp just be some kind of variable resistor?

Slackmaster 2000
 
Slackmaster2K said:
So would an impendence switch on a preamp just be some kind of variable resistor?

Slackmaster 2000
Click to expand...

More likely multiple taps (or multiple windings) on the input transformer; although a straight resistive load would change the impedence the mic sees, I would think a reactive load would be better.

SG
 
At the risk of being yelled at by everyone here..... I would like to correct the above answer. Impedance matching is important... and it's best to use the correct load. For example... if you were to use a 2 ohm speaker (load) with an 8 ohm guitar amplifier you could damage the amp..... poof, smoke, you know.... as in bye-bye. It's not a good idea to mismatch any amp.... it may not somke.... but over time it can damage it. Also mic preamps use either transformers (which are the best and not cheap) or little intergrated ciruits to couple the impedance. If impedance matching wasn't important... there would be no need for transformers and etc. The cost of a good Jenson audio transformer by itself can cost more than it costs a manufacture to build a little preamp that sells for about $200 or less.

Sorry...... my spelling sucks.
 
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Slackmaster2K said:
So would an impendence switch on a preamp just be some kind of variable resistor?

Slackmaster 2000
Click to expand...

Well yeah, on the cheap little op-amp type preamps.... it's just a resistor switched in or out.... you know, something like a 620 ohm resistor connecting the the audio input line to ground through the resistor for the Lo Z or switched out (no resisitor) for Hi Z.
 
I've played around quite a bit with the variable input impedence on my Avalon, and it produces very different sounds from the same mic. As Fletcher said, it is by no means necessary, but it is very cool. It also allows me to use the Shure SM82, which is a line level mic.-Richie
 
DJL said:
For example... if you were to use a 2 ohm speaker (load) with an 8 ohm guitar amplifier you could damage the amp..... poof, smoke, you know.... as in bye-bye.
Click to expand...

Dude, you're doing apples and oranges here... the output of an amplifier is a hell of a lot different than the input to a mic-pre.

You can't damage a microphone, nor a mic pre with a "mismatched" situation... you can gain different tones and textures depending on how a mic couples with a pre... the net result of that coupling can lead to an interesting and varied sounding track within the context of a recorded presentation.
 
Sure it sounds different when you mismatch the impedance of a microphone with a preamp.... because there is a loss of signal and it's subject to noise. Therefore proper impedance matching is important and necessary to get a powerful clean signal with a mic and pre.
 
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Well, DJL, Avalon Design disagrees with you quite a bit. While in the broadest sense, impedence matching between mic and pre matters, and an outright mis-match can suck, all mics are capable of outputting a usable signal across a spectrum of input impedences. If the self noise of the pre is low enough (it's hard to beat the Avalon for that), the input can be impeded variably as a tone shaping tool. Avalon included the results of extensive experiments with a variety of mics with my AD2022, from cheap dynamics to high end Neumann tube mics, inputted at various impedences, with output plot graphs. What's interesting is that as the input impedence is altered, the frequency output curve of the mic changes, the peaks and valleys *actually move*. In virtually all cases, the signal to noise ratio was still well within usable parameters, at least until you get down to about 50 ohms, where most mics except my SM82 become pretty useless.
It seems that getting the hottest noise-free signal often is not as important as the frequency curve that's generated. There isn't an ideal input impedence for any mic. What there is is a spectrum of input impedence options, and there's one that's right for a given source, in a given room, in a given mix, with a given mic placement.
Also interestingly, Avalon says their research uncovered no discernable patterns when comparing mics of similar design, and often the results of input impedence shifts were more similar between 2 completely different mic designs than they were between 2 mics nearly identical in design, suggesting that every possible mic/input impedence combo must be evaluated on a case by case basis. I can tell you that generally on my voice, my Rode NTK prefers 600 ohms to the 1500 ohm mic level in, but on Maureen Fleming's voice (my main chirp), it wants mic input. Go figure. In conclusion, it is Avalon's contention that changing the impedence load across the mic is not just a matter of optomizing output, but is a tone shaping tool, which can also be used to compensate for the capacitance of varying length runs of cable.-Richie
 
I can't decide (yet) if a EV 635a sounds "better" either at 200 Ohms or 50 Ohms on my voice.
200 Ohms is clearer, 50 Ohms is thicker.

Chris

P.S. Fletcher (or anyone else who knows), what does Shure's
"50/150 dual impedance" mean? TIA.
 
Well Richard, it wouldn't be the first time someone has disagreed with me and I'm sure it won't be the last.

However, I believe my statement "Sure it sounds different when you mismatch the impedance of a microphone with a preamp.... because there is a loss of signal and it's subject to noise. Therefore proper impedance matching is important and necessary to get a powerful clean signal with a mic and pre." to be true.

Maybe you can call or email Avalon's engineering department and ask them what part of my above statement is false.... and post their reply here. Also advise them that when I made the statement that I was speaking in general... and not necessary about your particular device. Also, if you don't believe me that impedance matching is important, maybe you can email Harvey Gerst and ask him "How important is impedance matching between mic and amp" and share what he tells you here also. Thanks.
 
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DJL, I think you're missing the point. If you start with almost no noise, the loss of signal strength is irrelevent for all intents and purposes. Getting the strongest, cleanest signal is not the most important thing . What's important is getting a signal that *sounds good*, which is strong enough, and clean enough to use. The best preamps in the world are *not* the cleanest reference amplifiers. They are prized not just for providing gain. What's important is how the frequency curve of the mic and pre interact with the source. There's a reason why you don't sing into measurement mics. Variable impedence changes the frequency response of microphones, which is a useful tool. I am not looking for ruler flat response from a mic, or a preamp.-Richie
 
I didn't miss the point...... the question was "How important is impedance matching between mic and amp?"

My answer was, and still is..... impedance matching is important.

Email Harvey Gerst and ask him "How important is impedance matching between mic and amp" and share what he tells you here. Thanks.
 
I think Fletcher covered this concern in his first response DJL.

Flipping between 50 and 200 Ohms on various microphones
gives me the impression of the frequency response being
modified, much more than any issue over noise.

Chris
 
Ok, whatever......

Mr Funk asked how important proper impedance matching was between a mic and a preamp was.

And the answer is..... "It's Very Important".

Because if you were to load down the mic it would lose level, distort, and sound crappy.

I think what Fletcher is talking about is varying the input impedance of the preamp while still maintaining a proper impedance match higher than the mic output impedance, which is cool with the new stuff... just make sure you maintain a proper impedance match by keeping the preamp input impedance higher than the mic output impedance so it doesn't load down the mic. And with the older vintage vacuum-tube devices the mic output impedance and the preamp input impedance must match so you don't load down the mic.

So, how important is the proper impedance match between a mic and a preamp? It's Very Important.

Ok, I'm done with this thread
 
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