Tube Mics, vs FET Mics

[sound125]

I have a few questions about this. In your guy's opinion, which if these two categories do you find better sounding or more useful on vocals?

A lot of the gear that I used in the 1970's was tube based from the 1950's-60's. In microphone applications, I find the sound is somewhat dated and doesn't work in many applications. In general, I prefer the sound of a higher end FET mic over many of the tube mics out there. In fact, I think there are a lot of marginal tube mics on the market and for people who didn't grow up around vaccum tubes, they don't know the difference.

The tube era is over and they will never produce the quality of tubes to match the construction of classic tubes like Amperex *PQs*, Mullards, Brimar, Telefunkens, Seimans and many others.

 

[thebigcheese]

Led Zeppelin is my favorite band of all time, but I think the recorded vocals are crap. Mind you it was 1972 and most vocals sounded that way.

I have never used a tube mic and I'm curious what users would say. Most use a good tube pre, so would 2 tubes in front of vocals get the hot modern voice signal or would it actually be a detriment?

I've also always been curious about that. It seems silly to use two tubes, though I suppose my guitar amp has a couple in the preamp section, so maybe not.

 

[Marik]

There isn't a need for more than 4mA for the amplifier (less if there is an output transformer).

Well, yeah, but it is not really enough to drive long cables happily. I'd want to have some spare 60-80ma and try there some larger die power MOSFETs...

Best, M

 

[mshilarious]

Well, yeah, but it is not really enough to drive long cables happily. I'd want to have some spare 60-80ma and try there some larger die power MOSFETs...

Best, M

Better than 90% of users aren't going to go longer than 100m, and when they do, odds are the signal is going to pass through some class AB if not D amps before it's done being amplified . . . so put an AB in the mic, or a transformer.

 

[dgatwood]

Better than 90% of users aren't going to go longer than 100m....

You're inclined to understatement. I doubt more than 1% of users run mic cables more than a hundred feet, much less a hundred meters. That's almost the length of an entire football field, including the end zones. Running a mic cable that far is such a corner case that it almost doesn't even bear consideration, IMHO....

And I'm going to go out on a limb and say better than 99.9% of users aren't going to go longer than about 20-30 feet with a tube mic. Long runs are rare except for live concerts, and if you're using an expensive tube mic in a live concert, you should have your head examined. That's what inexpensive, Shure and AKG dynamics are for. That and hammering nails into the stage before the show....

Yeah, yeah, I know you have to design under the assumption that you might have a long run to a distant control room or something in a large studio setup. Still... a hundred meters? Do folks really design with that in mind?

 

[mshilarious]

Yeah, yeah, I know you have to design under the assumption that you might have a long run to a distant control room or something in a large studio setup. Still... a hundred meters? Do folks really design with that in mind?

Pro sound guys will often run that far, especially in a hall with installed sound. Often in that situation though cable capacitance is not a giant concern. So really we are talking about guys who do location recording, especially classical.

But yeah, designing a mic you want to keep output impedance low enough to drive 100m cables, at 100pF/m that means 150 ohm or less.

 

[Ty Ford]

I have a few questions about this. In your guy's opinion, which if these two categories do you find better sounding or more useful on vocals? OR, are they really equally useful and some just sound better on different people's voices? This is assuming you could have/afford any mic you chose in those two categories.
I ask this because I'm new to the world of mics, and there is a ton of hype around tube mics which seem to generally a lot more expensive, but it seems that the FET ones can be used very successfully as well. I read somewhere that Led Zeppelin vocals were done with a U67 fet. Can anyone confirm that?

Good FET is better than bad tube. Good tube is better than bad FET.

Don't forget. It's the preamp/mic combo that creates the total sound, not just the mic. The new TLM 67, btw, sounds nothing like a U 67, but I like it a lot.

Here's my published review: http://www.proaudioreview.com/article/18510

Regards,

Ty Ford

 

[Marik]

Better than 90% of users aren't going to go longer than 100m, and when they do, odds are the signal is going to pass through some class AB if not D amps before it's done being amplified . . . so put an AB in the mic, or a transformer.

Pro sound guys will often run that far, especially in a hall with installed sound. Often in that situation though cable capacitance is not a giant concern. So really we are talking about guys who do location recording, especially classical.

But yeah, designing a mic you want to keep output impedance low enough to drive 100m cables, at 100pF/m that means 150 ohm or less.

Some Canare star-quads are at 160pF/m, but that's not only about the output impedance, but also about what kind of distortions that kind of load introduces to the driving stage.

Indeed, to put a transformer is an attractive idea, however, besides the cost (which for a high quality unit can be much more than made in China separate PSU), it also introduces all kinds of other problems, mainly, in SD mics there is no enough space to put good size of the core, so it whether compromise of the SPL, or sound quality (in case of using DU core).

Sure enough, it is possible to overcome all of those and design a conical shaped SD (I can post here a picture of one of my designs like that), but in the end, it is all about design and compromise choices.

Best, M

 

[mshilarious]

Some Canare star-quads are at 160pF/m, but that's not only about the output impedance, but also about what kind of distortions that kind of load introduces to the driving stage.

That can be dealt with a bit of series resistance. But of course then we are increasing output impedance again.

These are still problems of the few, I don't think the solution is 80mA microphones for location recording, especially if those fellows happen to be running on battery. In the studio, I don't expect engineers to select star quad and use long cable runs; if they do that's a sign their studio wasn't designed very well.

I also haven't noticed much of a correlation between thirsty microphones and output impedance. It seems to me that some manufacturers are taking the current because it's there, without necessarily much benefit to the user. This is the opposite trend from the rest of the electronic industry. It seems odd to me that a microphone can consume as much as 480mW in its attempt to generate less than 10mW into its ultimate load, if a converter. That efficiency would never be acceptable in a power amp, even in a class A tube amp. I would like to do a microphone at 10mW; a few more parts and I'll be below 20mW for all supply voltages.

 

[Marik]

That can be dealt with a bit of series resistance. But of course then we are increasing output impedance again.

I made some experiments with that long ago. In a double blind test the series resistance introduces some very noticeable adverse sonic qualities.

These are still problems of the few, I don't think the solution is 80mA microphones for location recording, especially if those fellows happen to be running on battery. In the studio, I don't expect engineers to select star quad and use long cable runs; if they do that's a sign their studio wasn't designed very well.

I also haven't noticed much of a correlation between thirsty microphones and output impedance. It seems to me that some manufacturers are taking the current because it's there, without necessarily much benefit to the user. This is the opposite trend from the rest of the electronic industry. It seems odd to me that a microphone can consume as much as 480mW in its attempt to generate less than 10mW into its ultimate load, if a converter. That efficiency would never be acceptable in a power amp, even in a class A tube amp. I would like to do a microphone at 10mW; a few more parts and I'll be below 20mW for all supply voltages.

Ah, clearly, you are a studio guy, as opposed to me, who records classical on locations. When you are on location, even if the straight distance between stage and the booth is some 100ft, when the cable needs to go around the wall, the length easily goes to 300ft. Also, not every hall was designed for the recording in mind. I have one commercial CD where the hum is quite noticeable (if you listen on headphones with higher volume--for understandable reason I dont' tell ya what CD was that), but the only way to avoid it was to use the star-quad Canare. It is a challenge to drive those.

Best, M

 

[mshilarious]

I made some experiments with that long ago. In a double blind test the series resistance introduces some very noticeable adverse sonic qualities.

Interesting. Is that from rolloff, or some other factor?

Ah, clearly, you are a studio guy, as opposed to me, who records classical on locations. When you are on location, even if the straight distance between stage and the booth is some 100ft, when the cable needs to go around the wall, the length easily goes to 300ft.

I'm a studio guy, but also a live sound guy. Our hall has similar issues, but then we also have an audience who is old enough that none of them can hear over 10kHz I can hear the problems in the PA--noise mostly--but the EMI isn't too bad. But then probably half of our acts play without amplification, which is a refreshing reminder of the total inferiority of all transducers, on both ends.

Yes, I have said that such problems are mostly experienced by the classical location recording set, but that's a small world. Another solution is a digital microphone.

Anyway, I design almost strictly for battery power these days, and not much of it.

 

[TimOBrien]

Short short answer: Use . What. Works. For. YOU

If the singer sounds great with a U87, use a U87.
If she/he insists or sounds great with an SM58, then go for it.

Arguing what is TECHNICALLY better (or just for pissing rights) doesn't get the track done.

 

[mshilarious]

Short short answer: Use . What. Works. For. YOU

If the singer sounds great with a U87, use a U87.
If she/he insists or sounds great with an SM58, then go for it.

Arguing what is TECHNICALLY better (or just for pissing rights) doesn't get the track done.

Funny how you don't feel that way about Soundblasters and USB mics . . . I could make a passable track with either.

Anyway, output impedance and power consumption are real specifications that have a measurable impact on performance criteria. And also the effects of transformers, etc., these are real differences that should be considered in the question of tube vs. FET mics.

There are plenty of other threads if this discussion bothers you . . .

 

[dgatwood]

Pro sound guys will often run that far, especially in a hall with installed sound. Often in that situation though cable capacitance is not a giant concern. So really we are talking about guys who do location recording, especially classical.

When I said I'd never gone over a hundred feet, that was location work I was talking about. I used a mic near the front of the audience, and ran cables between the seats, straight up the center. If I had been in the booth (I never was), I'd probably have done what those guys did---slide the glass window open and toss the cable through.... These days, I'd probably just use a Zoom recorder taped to the mic stand, and synchronize it with the video in post.

One big difference between what you're talking about and my situation, of course, was that I wasn't the house; I couldn't install cables up on catwalks and hang mics down from the ceiling. It was always "get in, set up, wait a few hours, do the shoot, tear down, go home".

Either way, my point was that installed large hall location recording is like a niche of a niche when you compare that with the number of people using mics for other stuff---house sound in a small club, rockers in their garage, people recording in studios, etc. For all those other folks, if they're running a cable twenty feet, that's a long way for them....

Seems like maybe the folks who need the long range hardware should just either use mics specifically for installed sound or add a phantom powered inline amp stage and let everybody else's mics draw a tenth the power.