tube head amp vs. solid state mic and tube preamp

[Paul W]

Do tube head amps in microphones sound different from tube preamps? Do they saturate / distort differently in some systematic way, due to the different levels involved, or something like that?

I'm trying to figure out why people like tube mics, as opposed to clean solid state mics plus tube stages later in the signal chain.

At first glance, the microphone seems like the worst place to put a tube amp, because you can't adjust the degree of saturation independently of the volume of the acoustic signal hitting the mic. In engineering terms, there's no "separation of concerns" of volume and saturation, or modularity so that you can mix and match transducers and colorizing stages.

Am I missing something?

If I am, and there's a good reason for tube head amps, it seems like you'd want modularity by having swappable capsules. Why is that scheme not more common?

 

[MagnetoSound]

Microphones are colorizing stages, just as preamps are. Whether they have tubes in or not. The whole thing is an aesthetic exercise. If you wish to colour the sound in a particular way, what does it matter how you do it?

 

[Paul W]

Microphones are colorizing stages, just as preamps are. Whether they have tubes in or not. The whole thing is an aesthetic exercise. If you wish to colour the sound in a particular way, what does it matter how you do it?

Flexibility and cost savings.

If I have 4 great capsules of different types, and 4 great head amps of different types, I'd like to be able to mix and match them to give me 16 combinations. (And if headbaskets are swappable, too, I might have 4 of those giving me 16 x 4 = 64 different combinations, so I can do things like a U47 vs U47 fet vs. U497, or variants of all of those but with a very different not-Neumann-like capsule, like a Beezneez CK12.)

But maybe more importantly, I want to be able to control the degree of saturation independently of the volume. My impression is that with a tube head amp you generally don't get much saturation at all until you get to fairly high SPLs, and then you get a lot more when things get modestly louder. It would be nice to be able to turn up the gain in soft passages and turn it down in loud ones to control the amount of saturation and not go from too little to way too much as the volume changes.

I do that with my electric guitar all the time, adjusting the guitar volume control or input gain to increase or decrease distortion, and adjusting the output volume to give me the volume I want. I find it bizarre that people have amps that they like for distortion, but don't separate those concerns.

 

[RuudNL]

My biggest concern when using a tube microphone during a session is always: 'Will the microphone keep working without noise or crackling?' (I usually feel more relaxed when using solid-state microphones...)

 

[MagnetoSound]

You want to be able to drive your mic into distortion on quiet sources?

 

[Paul W]

You want to be able to drive your mic into distortion on quiet sources?

Sure. Relatively speaking, at least, and in terms of what the mic hears at different distances. Some people sing a whole lot louder than other people, like an opera singer friend of mine. I’d think that any mic that adds noticeable color for me belting it out is going to distort too much when she does. I could put the mic further away from her, but I’d rather choose mic distances for other reasons, like adjusting the direct vs reverberant sound.

Should I only want tube color in the loudest parts? That is far from clear to me, especially given the ways people usually talk about tube “warmth” and such. I never hear people say things like “it makes the screamiest screams warmer.”

 

[MagnetoSound]

If I hear people talk about ‘tube colour’, or if I were to use that phrase myself, it’s doubtful whether saturation or distortion is necessarily what one means.

Tubes simply sound different to FET amps, whether driven hard or not.

If you want it to sound like John Lennon on acid, you generally do that in the preamp.

 

[Accelerator]

@Paul W​

Do tube head amps in microphones sound different from tube preamps? Do they saturate / distort differently in some systematic way, due to the different levels involved, or something like that?

I'm trying to figure out why people like tube mics, as opposed to clean solid state mics plus tube stages later in the signal chain.

At first glance, the microphone seems like the worst place to put a tube amp, because you can't adjust the degree of saturation independently of the volume of the acoustic signal hitting the mic. In engineering terms, there's no "separation of concerns" of volume and saturation, or modularity so that you can mix and match transducers and colorizing stages.

Am I missing something?

If I am, and there's a good reason for tube head amps, it seems like you'd want modularity by having swappable capsules. Why is that scheme not more common?

First of all, a tube microphone uses only pre-amplifier tubes, so in a tube microphone there isn’t any combination between pre-amp. tubes and power tubes as there is in a Tube Guitar Head Amplifier and for this reason a tube microphone does not described as a “Tube Head Amp.” but rather as “Tube Pre-Amp. Microphone”…

Secondly, the “hybrid” tube / solid state microphone with the variable gain and “all the bells and whistles” that you are looking / describe for, already exist and you can buy it at Sweetwater if you have got the $3,499.00 in your hand for the Lewitt LCT 1040 Tube Microphone System …

 

[Paul W]

First of all, a tube microphone uses only pre-amplifier tubes, so in a tube microphone there isn’t any combination between pre-amp. tubes and power tubes as there is in a Tube Guitar Head Amplifier and for this reason a tube microphone does not described as a “Tube Head Amp.” but rather as “Tube Pre-Amp. Microphone”…

AFAICT "Head amp" is a reasonably standard term for the amp inside a condenser microphone, often as opposed to a "preamp" you plug the mic into. (It's a pre-preamp, not what's usually called the "preamp.") I'm not confusing it with guitar amp terminology FWIW.

This page at Shure, for example, gives a quote of that usage going back to 1938 (but I've seen it in recent things too):
https://www.shure.com/en-US/insight...ophones-and-artifacts-from-the-shure-archives

Secondly, the “hybrid” tube / solid state microphone with the variable gain and “all the bells and whistles” that you are looking / describe for, already exist and you can buy it at Sweetwater if you have got the $3,499.00 in your hand for the Lewitt LCT 1040 Tube Microphone System …

That's interesting, thanks. It's a common feature on guitar practice amps costing about 70 times less, which is why I've been wondering wonder I've never seen it on reasonably affordable mics.

 

[kingkorg]

Do tube head amps in microphones sound different from tube preamps? Do they saturate / distort differently in some systematic way, due to the different levels involved, or something like that?

I'm trying to figure out why people like tube mics, as opposed to clean solid state mics plus tube stages later in the signal chain.

At first glance, the microphone seems like the worst place to put a tube amp, because you can't adjust the degree of saturation independently of the volume of the acoustic signal hitting the mic. In engineering terms, there's no "separation of concerns" of volume and saturation, or modularity so that you can mix and match transducers and colorizing stages.

Am I missing something?

If I am, and there's a good reason for tube head amps, it seems like you'd want modularity by having swappable capsules. Why is that scheme not more common?

Most gear is designed to NOT have imprint on the sound. All the coloration that comes out of vintage gear is due to the limitations of technology at the time, or limited knowledge. During the years we learned how to appreciate and exploit these ''weaknesses''.

That being said, tube mic with cathode output into high plate voltage clean tube pre will give you less coloration than km84 into 1073. So it's about how it's designed.

But in general, you get more control over how much coloration you get from a preamp, vs any mic. Mic saturation is dependent on SPL which you can't control. Any serious mic is designed to have as low as possible THD and coloration, so we are talking high SPL to get tiny amount of coloration. Unless it's something like unfortunate Apex460.

Enough me rambling, here's a constructive idea i was cagey about for longest time, as i don't like to inspire commercial products for free...

I have made a hardware plugin which is basically u47 circuit with EF14 but without capsule. I use it as U47 type color box.

XLR - Balanced input opamp stage - Opamp gain stage - 60pf cap instead of the capsule - u47 circuit powered by standard chinese psu. +-15v for opamps so i can drive the tube harder than any capsule could. And then you can play with various switches switching, swapping, changing various components, values, bias, voltages....

 

[Paul W]

If I hear people talk about ‘tube colour’, or if I were to use that phrase myself, it’s doubtful whether saturation or distortion is necessarily what one means.

Tubes simply sound different to FET amps, whether driven hard or not.

EDIT: I posted the following before seeing kingkorg's comment above it, so it's a bit out of context.

Opinions on that seem to vary a lot. Some people think that un-driven amps, operating in their very-nearly-linear regimes, are hard to tell apart and that often the noticeable differences have more to do with things like slight frequency response differences than any special "tube sound."

As I understand it, blind listening tests make it clear that the differences are often not noticeable, or not nearly as clear as people expect, or not the kinds of differences people expect, like in the Sound On Sound tests with a Disklavier player piano, or the funny thread at GS comparing a Great River preamp to a starved-plate ART Tube MP Studio costing next to nothing.

It's also my understanding that some preamps are designed to be particularly clean, and others are supposed to be more or less colorful, and that clean preamps really can amplify things very nearly linearly, with little distortion of any kind, if they're not driven hard.

To the extent that's true, I'd think it would be desirable to get the "tube sound" (if that's what you want) from a later stage, where it's controllable independently of source volume and mic distance.

My question is really whether there's some cool sound you can get from a tube mic that you can achieve in the head amp inside the microphone, but not with a clean solid state head amp and subsequent tube preamp.

If you want it to sound like John Lennon on acid, you generally do that in the preamp.

Not what I'm talking about. I'm not talking about using distortion as an obvious "effect," as with "distorted" electric guitar. The guitar analogy was just about the desirability of controlling the degree of saturation, even if the level of saturation is always much subtler than in the guitar example.

And even if what we're talking about isn't exactly "saturation," or what you'd normally call "distortion," is it something you have to do in the head amp, or can you do it just as well in a subsequent stage, where you have more control?

 

[Paul W]

I have made a hardware plugin which is basically u47 circuit with EF14 but without capsule. I use it as U47 type color box.

XLR - Balanced input opamp stage - Opamp gain stage - 60pf cap instead of the capsule - u47 circuit powered by standard chinese psu. +-15v for opamps so i can drive the tube harder than any capsule could. And then you can play with various switches switching, swapping, changing various components, values, bias, voltages....

Now THAT sounds very cool!

I'm not sure I understand the details, though. I guess you're buffering but then attenuating the signal to get it back down to the voltage range (plus a bit extra) that a U47-type circuit expects, and the 60pF cap is to match impedance too. Is that right? (My understanding of analog circuits and impedance is very weak.)

That brings me back to my earlier question: is there tube-head-amp goodness that you can only get with something very like a head amp, operating on the kinds of signals you get from a capsule, rather than mic-level signals into a preamp?

As far as I understand it, or misunderstand it, head amps are typically low gain (even unity gain) and mainly used for increasing current, leaving it to the preamp to actually increase the voltage.

Do low-level low-gain tube amps distort characteristically differently from higher-level higher-gain tube amps? Does head amp distortion therefore have a different "tube sound" than preamp distortion?

 

[kingkorg]

I'm not sure I understand the details, though. I guess you're buffering but then attenuating the signal to get it back down to the voltage range (plus a bit extra) that a U47-type circuit expects, and the 60pF cap is to match impedance too. Is that right? (My understanding of analog circuits and impedance is very weak.)

There must be a ton of ways to do this, it was just most logical to my non-electrical engineer way of thinking.

First balanced unity gain opamp is to get rid of any noise the cable picks up, it comes from my audio interface, line level. But it could from any outboard gear. If i want to attenuate signal, i do it from my audio interface. k67 (probably the same as k47) puts out 390mV RMS polarized at 60v, at 117db of spl.

Line output puts out more than this, so there is no boost really needed if you want to drive the tube as a capsule would. 60pf can really be omitted, but this would eliminate capsule - grid resistor interaction which forms hpf filter. So i keep it in. k47 has about 80pF capacitance, so that cap should in reality be a bit higher. 80pF and 60Meg grid resistor form hpf at 31.9 hz. This is important to have in place as low end content affects tremendously how things sound when saturated. 60Meg sets tube input impedance, and since you have that pF range cap emulating capsule in place, the tube doesn't really care what came before it, is it an op-amp, or a real capsule generating the signal.

I added the second stage op-amp after first buffer stage just in case i want to go crazy, and if the signal i'm sending from the daw is low for whatever reason.

That brings me back to my earlier question: is there tube-head-amp goodness that you can only get with something very like a head amp, operating on the kinds of signals you get from a capsule, rather than mic-level signals into a preamp?

I would say most definitely yes, because pre-amps, tube or not, have quite different topology, probably multiple stages, before if any transformer. There's also a question of existence of input transformer. There's that interaction between EF14 (VF14) through coupling cap to BV8 style transformer, to whatever preamp you use. And i do go back into a mic pre, just like i would with a mic!
Maybe you would presume my color box sounds always great, and i can promise it does not, just like regular mic it sounds best at moderate levels, just like a real capsule would create. Overdriven heavily sounds like typical one stage triode. Can be fun, but often not.

As far as I understand it, or misunderstand it, head amps are typically low gain (even unity gain) and mainly used for increasing current, leaving it to the preamp to actually increase the voltage.

Yes, at the end of the mic circuit, but in a typical c12, u47... type circuit there is quite a bit of gain from the tube, the voltage swing is determined by plate voltage, so it can go quite high in c800, c12, less in u47... That voltage goes back down to output level, and is lowered by the output transformer. So there's that interaction when tube pushes the OT transformer at those voltages, and how it can saturate it's core. And then that OT transformer interacts with pre that follows. BV8, T14, and other transformers are quite different than your preamp transformers.

Do low-level low-gain tube amps distort characteristically differently from higher-level higher-gain tube amps? Does head amp distortion therefore have a different "tube sound" than preamp distortion?

I think i already touched upon this, it will depend on the topology, but in general yes.


To add further to the madness, I made an IR from VF14 shootout files posted here, which generates characteristic VF14 microphonic ''reverb'' effect, which comes from the sound hitting the tube, and has nothing to do with signal going through the circuit....


What a marvelous idea for a commercial product i just gave away for free
I hope i, at least, get credited if it ever comes to fruition. On the other hand, the concept is so logical to me, and I thought of it the second i injected the signal for measurement of the first mic circuit i measured. So it could be there are people who have already done this.

 

[k brown]

AFAICT "Head amp" is a reasonably standard term for the amp inside a condenser microphone, often as opposed to a "preamp" you plug the mic into. (It's a pre-preamp, not what's usually called the "preamp.") I'm not confusing it with guitar amp terminology FWIW.

This page at Shure, for example, gives a quote of that usage going back to 1938 (but I've seen it in recent things too):
https://www.shure.com/en-US/insight...ophones-and-artifacts-from-the-shure-archives



That's interesting, thanks. It's a common feature on guitar practice amps costing about 70 times less, which is why I've been wondering wonder I've never seen it on reasonably affordable mics.

The more accurate term for the circuits in most mics is 'impedance converter'; that's their main job - that and producing a balanced output. They're not really 'preamps' or 'head amps'; head amp is really a term from the guitar world.

Two of the most unfortunate and confusing conventions that have established themselves in the microphone world is calling the circuits inside mics 'preamps' (then what's the thing you plug the mic into?), and referring to externally polarized capsules as 'true condensers'; like electrets are 'fake' condensers? Silliness.

 

[Paul W]

They're not really 'preamps' or 'head amps'; head amp is really a term from the guitar world.

I suspect that the term "head amplifier" predates electric guitar amplifier terminology. (And conflicts with it.)

I found a reference to a 1933 book "The Condenser Microphone and Head Amplifier." That makes it sound like the term was well-established by 1933 and who knows how much earlier.

I also found a 1936 description of an early British TV system that talks about the head amplifier in the video scanning unit, whose output goes to the "A amplifier" in the console, which is the first amp in the console.

It seems that "head amplifier" was used early on to describe a first amplifier housed with a sensor, separate from downstream amplifiers in the main processing system or user console.

That makes sense given other analogous uses of the word "head" like hammer head, headwaters, and hydraulic head. The "head" is the first or source part, or the distal "business end" of a tool, or the uppermost encapsulated module, and in this kind of case, all three.

Edited to add: I found three references to "head amplifier" in snippets from "Projection Engineering" from 1930 but I can't see much context in Google Books. There seems to be an amplifier in the "sound head" of a sound-on-film projector. One says "The development of a new improved preliminary (head) amplifier , for use with sound-on-film equipment, is announced by the G-M Laboratories, Inc., of Chicago. It can be used on all makes of sound equipment..."

Another edit: and something from 1929 also about sound-on-film, and sounding like it's not a new term then either.

Still another... maybe something from 1924, about x-ray detectors. If so, that makes the term 100 years old or more.

What an odd little rabbit hole. (Yeah, I'm a nerd.)

 

[kingkorg]

On the other hand, what we call today preamplifiers are also doing the work of impedance conversion.

 

[MagnetoSound]

Paul is correct, both AKG and Neumann, as well as others I’m sure, have described the impedance converters of their modular mic systems as ‘head amplifiers’.

Not to be confused with an ‘amp head’ for a guitar stack. A popular colloquialism from days of yore was ‘Marshall head’.

The problem nowadays is the way people will change ‘amp head’ to ‘head amplifier’ without a second thought. It seems there is nothing to be done about that.

 

[rock soderstrom]

I suspect that the term "head amplifier" predates electric guitar amplifier terminology. (And conflicts with it.)

+1

The term head amplifier was already in use before the appearance of the first separate guitar amplifiers and has nothing to do with them. It is the direct translation of the German word "Kopfverstärker" (this was commonly used for the first amplifier in the signal chain), which is not surprising as some mayor developments of the condenser microphone had their origins in German-speaking countries.

BTW, condenser microphone also comes some how from the German language, the "Kondensator" was called at first a condenser in English before it became a capacitor, which is in my opinion the better term. The true origin of the word condenser is in Latin. "condensare"

 

[BGroen]

Nice thread! Funny I had the exact same train of thoughts this week...

Just some thoughts of mine on tube mic vs. Solid state here. I'm definitely not an expert!!

I imagine that you can use a tube mic safer on sources than can get loud, but are not loud necessarily.
Like an accidental rim shot or up-close heart felt scream, as the tube saturates in a nicer way than solid state. Maybe it could safe a take, that otherwise needed a (partly) re-take?

Also, doesn't the fact that a tube mic always has a separate power supply play a part in this discussion too? Being forced to use 48V affects mic designs I imagine. Having a separate box to house the power supply must have benefits...

Another also, and a question, does tube vs solid state affects loading on the capsule, and does this affect the response?

I guess the whole topology of the circuit, and how components interact, has an effect on how the mic sounds and I don't think choosing a tube mic only for saturation is the right reason, but I also don't think you can simulate a tube mic sound using a tube stage afterwards..

 

[pasarski]

Yes, also me, an enthusiastic microphone enjoyer with limited knowledge about electronics also thinks topology really matters.

Phantom power is a limiting factor that makes a single active device solid state circuit saturate early and abruptly. Solid state mics usually have more complex circuits because of that (and for lower noise, lower over all THD etc..). You could get more tube mic kind of behavior using a dedicated PSU and a simple JFET circuit, but that kind of mics don't seem to be very popular. You can also build a solid state sounding tube mic (think Ref C).

The capsule biasing and loading is not vastly different in solid state and tube mics AFAIK. Input capacitance of the active device matters, but you can find good and bad devices in both tubes and fets regarding that.

Edit: want to add this quote from late Oliver Archut from an other forum regarding saturation in U47 because I find it very interesting:

"...the distortion of the capsule is not the dominant one, in a 47 the capsule starts to distort earlier than the electronics, but at one point the electronics will catch up and the final distortion is dominated by the amplifiers THD."