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Author Topic: What's so good about valve microphones?  (Read 43088 times)

danlavry

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Re: What's so good about valve microphones?
« Reply #30 on: February 15, 2006, 12:56:51 PM »

maxdimario wrote on Wed, 15 February 2006 15:40

The ac701 is a specifically designed miniature triode, and it sounds great....As you probably know, no-feedback mics such as c12 u47 etc. are generally thought of as being superior to mics with feedback in the amp.


You said:
“first of all I begin with the idea that the least amount of active components make for the most direct sound.”

I say:
Here is another audio “old wives tales” for you. It is simply WRONG!
For example (and I will stay with amplifiers, because that is what we are talking about), each device (tube, transistor, fet) has a quantity called “Gain-bandwidth product”. The more gain you use in a circuit, the less bandwidth is left for amplifying the signal. So say you take a device with 1MHz gain bandwidth, and you decide to use a single stage amplifier to get 60dB gain (that is 1000 gain). The bandwidth left is 1KHZ (=1MHz /1000). On the other hand, if you took a 3 stage approach, with 20dB each stage, the bandwidth of each stage is 20dB (gain =10) so each stage will yield 100KHz and the 3 in series will more then cover the audio. Sure beats 1KHz!

In general, the idea of less devices do a better job is ABSOLUTLY RIDICULES.

You said:
“this is due to the increasing complexity of the distortion as an amplifier increases in component count. the product of any system becomes more unpredictable as the system becomes more complex.”

That too is unfounded “out of mid air” WRONG statement!

”if one is to pick what are deemed to be the best high gain amps made, usually the standard choices will go back to discrete gear with simple circuits.”

You are invited again to STOP THROWING SUBJECTIOVE WORDS LIKE “WHAT IS BEST”, WHICH GO AGAINST THE RULES OF THIS FORUM!

You said
“I remember looking at the schematics for a HG desk built by a very famous german engineer for the german broadcast institute, in the late 70's or early 80's and the transistor circuitry inside had a topology similar to tube design.”

I say:
A transistor CAN NOT BE put into a tube circuit!

You said:
“comparing a tube to an op-amp for noise is not the same thing, since an op-amp is an integrated circuit with more than 10 transistors inside, usually.”

I say:
YES! YOU ARE GETTING IT! THER IS NO REASON TO REPLACE A TUBER WITH ONE DEVICE WHEN YOU CAN HAVE A WHOLE CIRCUIT.

You say:
”The FET transistor as you say is the only transistor that can be used without feedback, being a voltage-driven device and having the capacity for a higher input voltage. There is no need do convert voltage to current using a resistor.”

I say:
You obviously have not designed FET circuits either.

You say:
”So theoretically you can build an all FET design with no feedback, but no one has been able to do it with SUCCESS.”

I say:
Ridicules! No one has built a house of all stone. The door is wood, the electrical wiring is copper, the kitchen counter is a different material. FET’s have some advantages so you use them when needed. The idea of constructing a circuit out of a restricted list of parts makes no sense at all, one should use the best suitable combination of what is available!

You said:
“As you probably know, no-feedback mics such as c12 u47 etc. are generally thought of as being superior to mics with feedback in the amp.”

I say:
As a moderator of this forum, I insist that you stop stating subjective comments. See the rules of the forum under the first thread "Introduction".

Dan Lavry
www.lavryengineering.com
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danlavry

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Re: What's so good about valve microphones?
« Reply #31 on: February 15, 2006, 01:25:45 PM »

danickstr wrote on Wed, 15 February 2006 17:16

to respond to the original poster's question:

The reason tubes are still in use is because the complexity of their sonic shaping still eludes the best designers of solid state attempts to emulate them, as a general rule.  You mention that tube harmonics and other alterations could be "easily duplicated".   Well, get to it.  You have millions of dollars to make for yourself.

They can be duplicated on a case by case basis with static signals, but there is no circuit that can react like a tube to a real live musical performance, because of the dynamic relationship between the electronics and the input signal.  If there were, then all the great producers would use it.  They don't.  They use tube gear, well the ones who like the sound of a good piece of tube equipment.

Til you are done showing the world how easy it is, however, I will stick with a good classic tube, for all the magic is has in it's little body.




Hi,

I do not have a problem with what people choose to use, I have no interest in telling people to use or not to use tube guitar amps.
I agree with your comment that static emulation of a tube without the dynamic aspects is less then perfect. I disagree completely with the notion that one can not include the dynamic effect to great detail. Look at spice analysis. One can model the behaviour of inter electrode capacitance, of dielectric absorption of the coupling capacitors, one can model even the microphonics of the tube. How well can the model fit? It depends on the "level of commitment" of the designer. I do not see a tube as being more complex then say a transformer...  

Regarding your comment: "Well, get to it.  You have millions of dollars to make for yourself".

I did consider doing it, but decided against it (for now). I am into designing gear for recording and playback (AD, DA, micpre's) and such gear should yield the least amount of coloration. There is plenty of gear for sound coloration, but that is not what I am into. A tube may be useful as a part of say the sound generation of an electric guitar, but I am not making guitar amps...

I did make a tube emulator a few years back. It was not as detailed as I would do for a finished product, but it did include some of the dynamic aspects. I sent it to a very large and respected studio for a listen. The reports I got: There was a consensus that it did sound like a tube.

Regards
Dan Lavry
www.lavryengineeing.com
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dcollins

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Re: What's so good about valve microphones?
« Reply #32 on: February 15, 2006, 07:10:29 PM »

Triodes have a high amount of negative feedback inherent in the design!  The reason they are linear.....

DC

Terry Demol

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Re: What's so good about valve microphones?
« Reply #33 on: February 16, 2006, 05:18:05 AM »

dcollins wrote on Thu, 16 February 2006 00:10

Triodes have a high amount of negative feedback inherent in the design!  The reason they are linear.....

DC


It's a really interesting area to dabble in. I was checking some
FFT's of triodes with CCS loaded plate at various currents and
straight R degenerated cathodes.

They appear move 'in and out' of linearity depending on how much
current is drawn. Some triodes are really linear with CCS and heavy current, ie; no degeneration, others not so.

The spectrum also varies hugely. One of the most reverred
triodes, the 6SN7 is very linear but the spectrum often measures
H2 and H3 almost the same. So much for even order tubey stuff.

Kind of supports my long held theory that H3 is not nearly as
bad as it's cracked up to be. I mean we never complained about
mag tape Smile

Cheers,

Terry
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Terry Demol

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Re: What's so good about valve microphones?
« Reply #34 on: February 16, 2006, 05:49:57 AM »

maxdimario wrote on Sat, 11 February 2006 16:59

Quote:

Tubes tend to be much nosier then transistors and FETs. Tubes age very fast... And if you like the sound, that is subjective, not a technical comment.

All circuits based on tubes, transistors, FET's and Opamps Begin with parts containing some degree of non linearity, and the circuit design does correct for the non linearity to some degree, most often by use of negative feedback. Many tubes circuits have been incorporating feedback from day one (over a hindered years ago), and a tube designer knows that the reason for using feedback sparingly has been the fact that tubes have VERY LIMITED OPEN LOOP GAIN, thus tubes offer LIMITED AMOUNT OF NEGATIVE FEEDBACK. There is a TRAD OFF between circuit gain (closed loop) and linearity (more feedback).


What tubes are you talking about?

One EF804s can provide more gain with less noise than 1 trasistor or fet.




Max,

IP noise of a tube is loosely inversly proportional to it's
gm (transconductance).

So if you want ultra low noise, you need high gm.

About the highest gm tube I know of is the WE437A or 3A/167M.

These had a gm of about 50mS so the cathode impedance was around
20 ohms. This is about as low noise as tubes get and from memory
somewhere around 1.6 to 2 nV/rt Hz.

They are basically extinct now and if ou can find them will cost
around US$200 each. I have 1 pair.

Unfortunately' all these super gm tubes are frame grid types and
commonly suffer from microphonics so often didn't actually get
used for low noise IP apps. They also have relatively high
IP capacitance so I would imagine they are not really suitable
for microphone circuitry.

WRT usable gain both BJT's and FET's can be arranged to have as
much or more gain in a single stage zero FB circuit. It is just
a case of how much degeneration and current is run.

Cheers,

Terry
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danickstr

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Re: What's so good about valve microphones?
« Reply #35 on: February 16, 2006, 10:34:56 AM »

Dan

thanks for your response.  If anyone could do it, my guess is that you would be among those "any".  My post of course was referring to the originater of the thread, who seemed to brush by the technical difficulties in achieving such success as triviality.  I wish he were correct, but the list of current gear in use in top studios leads me to believe tube emulation is still a lab bench item.  

I for one would love to see another Lavry success in this field, to match the success you have had in conversion.

cheers

I live close to you so feel free to have me over to listen to the prototypes..haha.
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Nick Dellos - MCPE  

Food for thought for the future:              http://http://www.kurzweilai.net/" target="_blank">http://www.kurzweilai.net/www.physorg.com

maxdimario

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Re: What's so good about valve microphones?
« Reply #36 on: February 16, 2006, 01:10:15 PM »

Quote:

WRT usable gain both BJT's and FET's can be arranged to have as
much or more gain in a single stage zero FB circuit. It is just
a case of how much degeneration and current is run.


you can have a lot of gain, but it's not useable.

if you hav zero source impedance feeding a transistor you get a LOT of gain..
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maxdimario

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Re: What's so good about valve microphones?
« Reply #37 on: February 16, 2006, 01:31:01 PM »

Quote:

In general, the idea of less devices do a better job is ABSOLUTLY RIDICULES.


It's the basis of hi-end Hi-Fi and professional recording of acoustic music. The less active elements in the path, the better, given you can meet the same specs and demands.
Quote:

A transistor CAN NOT BE put into a tube circuit!



I said SIMILAR.
Of course transistors and tubes can't be interchanged, I am talking about design philosophy.

http://community.webshots.com/photo/373437952/13734390030726 18419EcewgR

This is a link taken from J. Bloemsma's site, who by the way has a full HG desk!

this is what I was talking about.. not exactly tube-type design but not typical solid state. Designed by an audio expert with no cost limits... why didn't he put 30 transistors in there?

Quote:

You obviously have not designed FET circuits either


Sure I have, you don't need to feed the gate with a resistor, other than to avoid oscillations (using the fet's inherent capacitance to form  a LPF. look at the schematic above.
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danlavry

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Re: What's so good about valve microphones?
« Reply #38 on: February 16, 2006, 02:34:06 PM »

At this point, one should be sure to make a distinction between a triod and a penthod, they are rather different animals!

A penthod is pretty much a current source when Looking at the device from a load side. The translation of tube current to anode voltage is relatively simple - multiply the current by the load impedance, thus the gain is A = gm * ZL (ZL is the load impedance).

The triode does not look like a current source, its output resistance is not that high thus the gain is
A = (mu * ZL)/ (Rp + ZL) where Rp represents the tube impedance.

When talking about linearity, the first thing to observe is what takes place is to look at the relationship between grid voltage and anode current. Say we take the EF804 that was mentioned earlier. Clearly the curves show much better linearity near 0V grid voltage, and as one goes to more negative grid voltage, the curves (grid voltage vs, anode current are EXTREMAL non linear.

But the above does not mean that one can get best linearity operating near grid at 0V. Operating near V grid = 0V means much higher tube current which does impact things -
more current means a higher dissipation and heat, and it may require lower loads to avoid operation at very low anode voltage, where the tube encounters another type of non linearity. Either way (high current and low load or low current and high load, or operating between), one ends up with limited gain.

Now, lets get some perspective. Say we take an open loop (no feedback) EF804 operating at say 140V anode voltage, with a grid bias of say 3V (pretty typical). Say we input a grid voltage of 1KHz sine wave with 1V peak.
At no signal Vg = -3V and Ia = 1.5mA
At positive peaks, Vg = -2V and Ia = 3mA
At negative peaks, Vg = -4V and Ia = 0.5mA

So the AC signal positive peak is 3-1.5 = 1.5mA
The AC signal negative peak is 1.5-.5 = 1mA

Now draw a sine wave where the negative peaks are 66% of the positive peaks. The distortions are HUGE! we are not talking about .001% linearity. We are not taking 1% linearitry either. We are talking about huge non linearity!

In fact, I do not believe the eye can see a difference between a .001% and a 1% curve, they both look like a stright line. The EF804 Vg vs Ia curves look like way over 10% distortions for a 1V peak signal. Open ended tubes are highly non linear, and of course, like all devices, they will get more linear when the input signals get to be very small.

So what does one do? One weighs the many variables (including heat and reliability) and one optimizes a circuit by considering various trade offs, no different then the design of any circuit. When it comes to linearity, one can trade off some (or all) of the open loop gain of a device for linearizing the circuit. Say one has 60dB of open loop gain AOL (gain of 1000), and a certain amount of distortion POL (percent distortions open loop). The device also has a certain given bandwidth BWOL (open loop bandwidth in Hz).

One can keep the circuit as open loop with AOL, POL and BWOL (gain distortions and bandwidth under open loop conditions).

Or one can apply negative feedback. Applying negative feedback WILL REDUCE THE GAIN OF THE CIRCUIT. The more feedback, the lower the gain. If the feedback amount is say 10dB, the "left over gain", the circuit gain with feedback is 60dB - 10 dB = 50dB (open loop gain - feedback = closed loop gain). If the feedback is say 30dB, the close loop gain is 60-30 =30dB. If the feedback is 60dB the closed loop is 0dB (gain = 1, no gain)as is the case with a follower circuit.

So why waste the open loop gain? The reason is - one gets an improvement in BOTH distortion and bandwidth. Say the open loop gain was 60dB, the distortion was 10%, the bandwidth was 10KHz. With feedback of say 40dB (100), we end up with circuit gain of only 20dB, but the distortion is down from 10% to
10/100 = .1%, and the bandwidth of the closed loop circuit went way up as well...

So it is about the circuit design and tradoffs one makes.

But the facts are:

While one can get a lot of open loop gain from cascading devices, tubes are expansive and most designs do not use a lot of tubes to raise the open loop gain, therefore the distortions tend to be higher, especially at signals higher then a few millivolts.

Having less devices in the circuits would be great if the devices were perfect to Begin with. In fact, going for less distortions would take a gradual step by step buildup, many stages in series. In my above example, one can not get a 60dB  
and .1% in one step, because the single device yields 10% at 60dB. But 3 stages of 20dB each, with 40dB negative feedback per stage will almost get you there and 4 stages with 45dB feedback in each, will yield even better linearity.


Now, .1% is still a lot of distortions in my book, and the above was just an example. There are many people in audio that like tube sound, and are willing to accept and acknowledge the reality, that tubes circuits have distortions. In fact many people openly state that they like the coloration (distortion) due to 2nd harmonics and so on.

But here I saw some comments by some claiming that tubes are linear.

The facts are: Tubes are not linear. Transistors are not linear. Fets are not linear. The nature of the non linearity of tridoes, penthodes, bipolar transistors FET's are all different. Those devices all have huge device to device tolerances, temperature dependent behaviour... At the end of the day, it is the circuit that counts. One can choose to retain some of the open loop device characteristics in a circuit, and in that sense, a tube will sound different then a FET and a FET is different then a bipolar. That is because a square law is different then an exponential curve, the "inter electrode" capacitance in a semiconductor changes differently in a semiconductor then in a tube, and so on. But At the end of the day, it is the circuit that counts.    

Like the tube sound? That is OK with me. You want to claim that tubes are less noisy and distort less then transistors? I have an issue with it - tubes and transistors distortions and noise should not be examined out of the context of real circuits, and there are many different circuits and component values that make for different outcomes.

Regards
Dan Lavry
www.lavryengineering
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dcollins

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Re: What's so good about valve microphones?
« Reply #39 on: February 16, 2006, 09:11:32 PM »

danlavry wrote on Thu, 16 February 2006 11:34


But here I saw some comments by some claiming that tubes are linear.



Well, nothing's perfect!

But triodes do have a large linear operating area due to the internal NFB.  This was the origin of the pentode, as you could only get so much gain out of triodes.

  http://www.next-power.net/next-tube/articles/Stockman/Stockm an.pdf

DC

maxdimario

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Re: What's so good about valve microphones?
« Reply #40 on: February 17, 2006, 09:24:55 AM »

I like to use ef804's in mics wired as triodes for the same reason.

I prefer the 'internal feedback' due to the plate modulation affecting the flow of electrons to external feedback through a network etc.

tubes can be quite linear. and they have a very wide bandwidth.
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danlavry

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Re: What's so good about valve microphones?
« Reply #41 on: February 17, 2006, 04:27:32 PM »

dcollins wrote on Fri, 17 February 2006 02:11

danlavry wrote on Thu, 16 February 2006 11:34


But here I saw some comments by some claiming that tubes are linear.



Well, nothing's perfect!

But triodes do have a large linear operating area due to the internal NFB.  This was the origin of the pentode, as you could only get so much gain out of triodes.

   http://www.next-power.net/next-tube/articles/Stockman/Stockm an.pdf

DC



Hi Dave,

The article is talking about linear operating range is very relative terms. It views some of the internal mechanism of the tube as is it were negative feedback, and indeed, low mu triode is more linear then high mu. That is all nice but the minute you get of the mode of comparing tubes (which one is more linear and which one is less), one gains a different perspective. Non of them are linear, in context of say 1v peak input (grid) signal.

One needs to QUANTIFY things. When doing so, we immediately realize that transistors are not linear either. The fundamentals of electronics suggest to us that negative feedback is one hack of a major building block to linearize circuits.

We do not make a big deal out of feedback when dealing with modern electronics. Why? Because semiconductors are cheap,  you can put many of them on a substrate and make an opamp, or you can use them discreetly or in match pairs... Each stand alone transistor is often a rather "terribly unpredictable device", the tolerances on gain (beta or hfe) is huge! One can find a transistor with beta range between 40 and 400. One can find a FET with gm range in the 300%.... But we do not need to worry about such stuff, because as long as we build enough open loop gain, and use much of it for feedback, the tolerance issues, the errors, the distortions all get divided by the access gain (the open loop gain access over the desired circuit gain).

In theory, we could approach perfection if we kept building open loop gain. In practice, there are real world issues that limit such practice (limits such as system stability issues, circuits start to oscillate...)

But it is easy and cheap to "build open loop gain" with transistors. Say each transistor can yield at least a gain of 10 (very low number). Then with 6 transistors you have 120dB open loop (10*10*10*10*10*10 =1000000). Say each transistor yields a gain of 20.

However, it is not cheap and easy to do the same with tubes. Each one is an expansive power hog, not to mention reliability aging, size and so on. That is why in "tube circles" there is so much talk about feedback, and so many attempts to minimize the use of feedback, which demands as much linearity prior to feedback.

Sadly, such attitude of going for as linear device as possible, and using minimal amount of feedback, has been "carried forward" from the tube age to the much newer transistor age, where it really does not apply. The arguments for low feedback and open loop circuits had some merit in the tube age. Adding tubes was a "big deal" so it was desirable to push tubes as far as possible, with as little negative feedback as one could get by. With tubes, using gain for negative feedback cost dearly because gain was dear and to be used sparingly.

But carrying the old concepts to the transistor age is void from any technical explanation, and inappropriate carry over of a concepts that do not apply, form days of old technology. Much of it has been exploited by marketing, and as always in audio, when no credible technical explanations exist, when measurements can not prove an argument either, the sales guys come put with the "it sounds better" argument. and most often without a credible double blind ABX.

I am a design engineer. I looked at the article you pointed out, and it all looks correct to me, including that rehash of the old gain block "A" with the feedback block "beta" that I learn when I was 14 years old. Fine article, but not a single plot of a single tube! You want to talk about linearity? You want to calculate it? Go and find the plots of some tubes. I can assure you that you will not find straight lines showing the relationships between current and voltage. Linearity is about straight lines.

You can take devices that have a bent transfer curves, and make a circuit with less bent transfer - less distortions. That is why I keep talking about circuits. But lets face it, a "stand alone" tube, transistor, fet, prior to being put in a circuit, are all so far away from any resemblance to anything linear, that anyone saying that such devices are linear is way off, unless linear means many percents or tenth of percent of distortions.

Forget the BS and all the baseless claims. Go look at the curves, and you will see what is correct and what is hot air, presented by people that refuse to look at what they are taking about. How else can any one call a tube linear?

Regards
Dan Lavry
www.lavryengineering.com



 

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Terry Demol

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Re: What's so good about valve microphones?
« Reply #42 on: February 17, 2006, 08:51:21 PM »

maxdimario wrote on Thu, 16 February 2006 18:10

Quote:

WRT usable gain both BJT's and FET's can be arranged to have as
much or more gain in a single stage zero FB circuit. It is just
a case of how much degeneration and current is run.


you can have a lot of gain, but it's not useable.

if you hav zero source impedance feeding a transistor you get a LOT of gain..


Hi Max,

You are making comments here with a lot of enthusiasm, which is
good. However a lot of what you say is, unfortunately, not really
technically correct.

You -can- get a lot of gain from 1 SS gain stage and it -can- be
of -similar- linearity to an eqivalent tube stage.

It's all a matter of fully understanding the intrinsic generators
of non linearity.

The source Z -generally- has little to do with gain of the
circuit.

Cheers,

Terry
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Sahib

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Re: What's so good about valve microphones?
« Reply #43 on: February 18, 2006, 04:21:40 PM »

Hi Martin,

The thread started with the comments about tube (valve) mics sounding better in general. I hope we all agree that he tube mics sounding better is a subjective comment. A million sound engineers around the world may like the sound of it, prefer it or whatever. It is still subjective.

Then the subject got onto linearity and now onto the NFB.

I think Klaus Heyne's comments do not fit here either. They are all subjective and not technical. I hope I am offending anybody here by saying this but there is a wide spread snobbery among the "high end audio community" about the NFB.  The NFB did not appear in solid state times, it dates back to valve era. So for the "pro-valve" activists to come up with statements such as NFB being a crime is silly. Why should NFB be have to be a crime? It is like saying stabilising the emitter current of a transistor with a resistor is a crime. NFB is a technique to linearise a circuit and it is there to be used when needed and prefered. I also do not agree with the statement solid state (described as high gain chips) being dirt cheap way of implementing mic processing. Perhaps a cost effective solution but not dirt cheap.

Cemal



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danlavry

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Re: What's so good about valve microphones?
« Reply #44 on: February 18, 2006, 05:07:52 PM »

Sahib wrote on Sat, 18 February 2006 21:21

Hi Martin,

The thread started with the comments about tube (valve) mics sounding better in general. I hope we all agree that he tube mics sounding better is a subjective comment. A million sound engineers around the world may like the sound of it, prefer it or whatever. It is still subjective.

Then the subject got onto linearity and now onto the NFB.

I think Klaus Heyne's comments do not fit here either. They are all subjective and not technical. I hope I am offending anybody here by saying this but there is a wide spread snobbery among the "high end audio community" about the NFB.  The NFB did not appear in solid state times, it dates back to valve era. So for the "pro-valve" activists to come up with statements such as NFB being a crime is silly. Why should NFB be have to be a crime? It is like saying stabilising the emitter current of a transistor with a resistor is a crime. NFB is a technique to linearise a circuit and it is there to be used when needed and prefered. I also do not agree with the statement solid state (described as high gain chips) being dirt cheap way of implementing mic processing. Perhaps a cost effective solution but not dirt cheap.

Cemal




Good comments.

Negative feedback is not a crime when it fixes your signal distortions. Negative feedback is the reason one puts a resistor to ground at the tube cathod, to help stabilize the operating point. Unfortunately, most tube amplifier circuits needed a bypass cap across that resistor, to disable the feedback at frequencies above 20Hz-50Hz or so, because the resistor feedback reduced gain were gain is so precious (tubes). But it was negative feedback that kept the tube biased. The open loop is less linear because of lack of open loop gain. One can always remove that cathode cap, and the linearity will improve greatly, but the gain will drop way down...

At this point let me put a link for an easily accessible link to the data sheet of the FE804 tube that max likes:

http://www.mif.pg.gda.pl/homepages/frank/sheets/128/e/EF804. pdf

Go to the last page and look at the graph on the left - the X axis is grid voltage, the Y axis is the tube current. Does any of the 4 curves look linear? In the context of a 1V signal I would call it "big time distortion city".

One can string words together all day long. Words such as "tubes are linear" or "tubes do not distort" or tubes are less noisy". Such practice of connecting words does not at all assure that the sentence conveyed is real.

Also check the EF804S (more detailed specifications) for the same linearity plot (pg 335), and the noise figure at pg 333 (under noise, shown as 2uV at typical set of conditions, and that is high noise compared to semiconductor technology:

See it at
http://www.mif.pg.gda.pl/homepages/frank/sheets/128/e/EF804S .pdf  
And while at it look at the site for triodes which are teribly non linear. Check the EL84

http://www.mif.pg.gda.pl/homepages/frank/sheets/128/e/E84L.p df

Or any and all the tubes, and you realize that the devices are extremely non linear, not particularly low noise.

Again, I am not saying that other devices are linear outside a circuit. Transistors are not linear and I did not hear anyone say they are. Tubes are not linear, and there is a crowed of people claiming they are linear...

Regards
Dan Lavry
www.lavryengineering.com



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