mic pre theory

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pdaniels

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Maybe this is common knowledge, and I'm just out of the loop. If it is, please don't laugh (loudly).

I was just looking at frequency responses of different mic pre's, and I noticed that some of them said "frequency responce at max levels" and then gave their 20-20000hz stats.

We all know by now that the pre changes the sound coming from the mic when it amplifies it, and that is why some pre's cost a lot more than others--some just sound better. I've always assumed that the sonic qualities of the pre gets stamped uniformly on all audio that goes through it, but now I'm not so sure...

Because if the manufacturer goes to the trouble to state that their frequency measurements are at "max levels", then would the responce be different at less than max levels? I mean, who cranks up a mic pre all the way anyway?

What I'm getting at is this: if I use a mic with a "hot" output (like SP C1), would it take on less of the sound of the pre (because it needs less amplification) than if I used a ribbon mic (or another quieter mic) that needs to be amplified a lot? Taking it a step further, if I have a pre set to unity, would it affect the sound of the imput at all, and would the sound gradually be changed the louder I turn it? Or does the fact that the imput gets passed through all those circuits mean a change to the sound anyway, regardless of degree of amplification?
 
It's a pretty complicated answer, because many things affect the signal on the way through the preamp.

It's different with each different topology of preamp.

The input interface has a big effect on this. If it is transformer coupled, the transformers' non-linearities all contribute to variations. In transformerless preamps the first amplifier stages are usually pretty unobtrusive to the mic, but they may not have the best performance when the gain is high.

The actual gain of the circuit can be a determining part of the sound. Some amplifiers don't have enough feedback to maintain a consistant sound from one end of the gain setting to the other. If the closed loop gain is close to the open loop gain of the circuit, the sound will definitely change at different settings, since at higher closed loop gains there is less control of error.

The only preamp I know of that is designed to specifically combat this problem is the Gordon Audio unit.

In a well designed preamp, this is not a really a problem, in a cheap POS, it is.

Most good preamps have a consistant sound from one end of the range to the other.
 
Dan Kennedy a Newbie!!! ROFLOL :D

pdaniels - I hope you appreciate who just answered your question.
 
DigitMus said:
Dan Kennedy a Newbie!!! ROFLOL :D

pdaniels - I hope you appreciate who just answered your question.
Click to expand...

Please enlighten us! I'm in Japan and completely out of the loop on the who's who's and the where's and whys in the States right now.
 
This would be Dan's day job... he has somewhat of a handle on mic amp design... at least I think he does, YMMV.
 
Hey Dan, I have an old Shure Model 300 Ribbon, would a Great River Pre be the best match for it? Can you reccomend a certain model?

It sounds too noisy with everything else I've tried.

Thanks:D
 
HI Maestro...

I have one too. There isn't a preamp that will make that mic work real well.

Loud sources, yes, but nice little subtle things like it sounds good on? Nope.

I've heard that the output transformer is quite the limiting factor in these things, and a new Jensen, if you could shoehorn it in would really spiff it up. But then you'd have more in it than you paid for the mic.

I think they are what they are, 1950's middle class mics that can sound cool on some things and just not work so well on others.

To get that kind of sound, and really good performance, the AEA84 or the Royer 121 are the real tickets.
 
Thanks, that's extremely helpful to me. I didn't pay anything for the mic, and I wouldn't want to mod it anyway, I like having it as a showpiece if for nothing else. It's a cool looking mic.

What kind of loud source do you think it sounds good on? I will experiment with it some more if it's worth it. Would I damage it with loud sources like kick drum or snare or even guitar amp?

It's got that figure 8 Pickup pattern, is that useful too?
 
No sweat, I read a lot of forums, just usually keep quiet, thanks.

The 300 and it's cousins have a halfway decent blast screen, they were PA mics afterall, so I wouldn't be too afraid to stick them on just about anything.

If you can feel a puff of air from the source, don't put it there. Get it to the side and angle it in to the source.

Loud voices, with pop screen can work.

Horns, from a couple of feet.

Figure 8 can help, and it can hurt. If you have some space behind whatever you're miking it isn't much of a problem, if you have close walls, the quick reflections can really muck things up.

Don't worry about it too much, just remember to twist the mic, the angle can often really make or break what you are hearing.
 
DigitMus said:
Dan Kennedy a Newbie!!! ROFLOL :D

pdaniels - I hope you appreciate who just answered your question.
Click to expand...
Yeah, so you think Dan's special 'cause he designed some of the world's best preamps?!?! Sheesh...you're easily impressed! Truth be told, his dog probably designed them while he was out on his boat getting...er..."three sheets to the wind" and Dan just took credit for it all!!!! Or maybe, Dan actually had a "close encounter" and just stole the technology from aliens!!! Yeah...THAT'S IT!!! No, no...wait! I got it: DAN IS ACTUALLY AN ALIEN PRETENDING TO BE AN AUDIO DESIGNER AND HAS THE ADVANTAGE OF UTILIZING THE COLLECTIVE KNOWLEDGE OF AN ADVANCED ALIEN CIVILIZATION TO BEAT THE HELL OUT OF THE COMPETITION BY MAKING ONE OF THE SWEETEST (or BALLSYest...MP2 or NV...take your pick) SOUNDING PREAMPS THIS SIDE OF URANUS!!!!!

Dazed, beaten and just a little bitter in Austin (wimper, wimper),
McQ
 
Dan Kennedy said:
No sweat, I read a lot of forums, just usually keep quiet, thanks...
Click to expand...
Yeah, I see you've been here longer than me.

I greatly appreciate any and all wisdom I can soak up from guys like yourself. I love learning about microphone and mic preamp designs. I guess you could say it’s a part-time passion, or rather, “obsession” of mine. People ask “Did you see the such & such movie with so & so?” And I say “No, but I can give you the specs of several Jensen and Lundahl, transformers.” Pretty sick, huh? :D

Of course life has a way of getting in the way of things I'm passionate about and bogging them down, so learning is a slow process for me.
 
Don't fret, McQ, I use and recommend your stuff too. If you'd answered the guy first, I'd have posted the same dang thing. :D

Scott
 
McQ said:
Dazed, beaten and just a little bitter in Austin (wimper, wimper), McQ
Click to expand...
Austin?? Hey, I just figured out who McQ is! Wow! Is this cool or what?:D Well, maybe "really nice" would be a better choice of words. ;)

Welcome McQ, and a great big "howdy" from Tennesse!
:cool:
 
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