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Author Topic: Fet Mic Vs. Tube Mic: Do They Sound Different?  (Read 14298 times)

ricknroll

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Re: Good Question!
« Reply #15 on: October 25, 2007, 01:07:21 pm »

J.J. Blair wrote on Wed, 24 October 2007 18:07

The mics sound very different to me.  U67 doesn't have that honkiness around 1kHz that I don't care for in U87s.

I just got back from selling one of my U87s to Jerry at Coast, btw.
J.J.,

My guess is you've never owned a U87 that Klaus modded, but correct me if I'm wrong.  You really owe it to yourself to try one - it might change your mind about the U87.  I just got back my U87 from Klaus with Oliver's new transformer in it (literally last night), so I need some more time to play with it, but given its improved midrange, I'm eager to borrow a friend's M269 again to do another comparison.  There's nothing about the sound of my U87 that I would characterize as honky.  I'm also going to borrow a stock U87 to compare with, so maybe I'll hear some of that honkiness you referred to in the unmodified version of the mic.

Rick Hedges
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J.J. Blair

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Re: Good Question!
« Reply #16 on: October 25, 2007, 01:39:47 pm »

Rick, I'm talking about stock mics.  Klaus could mod an Audio Technica and make it sound exceptional.  Trust me.  Stock U87s are notorious for that 1kHz presence.  

I'm on Klaus' wait list.  But I'm going to send him an M49.
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rphilbeck

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Re: Good Question!
« Reply #17 on: October 25, 2007, 06:53:40 pm »

ricknroll wrote on Thu, 25 October 2007 13:07



My guess is you've never owned a U87 that Klaus modded, but correct me if I'm wrong.  You really owe it to yourself to try one - it might change your mind about the U87.  I just got back my U87 from Klaus with Oliver's new transformer in it (literally last night), so I need some more time to play with it, but given its improved midrange, I'm eager to borrow a friend's M269 again to do another comparison.  There's nothing about the sound of my U87 that I would characterize as honky.  I'm also going to borrow a stock U87 to compare with, so maybe I'll hear some of that honkiness you referred to in the unmodified version of the mic.

Rick Hedges




Nice!  Please report back on your findings!  I have considered sending mine to Klaus for modification, but worried that since I like the mic as is, I might like it less after his mod and that would depress the bejesus out of me.  

Robert
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Klaus Heyne

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Re: Good Question!
« Reply #18 on: October 25, 2007, 07:07:22 pm »

Schallfeldnebel wrote on Thu, 25 October 2007 02:26

Klaus wrote:"The one area where the single FET mic will always do more poorly is high sound pressure."
I agree when you would add to it "48V phantom powered without a DC-DC converter". 48V DC-DC converter equipped designs already do a better job, but the problem with FET microphones is phantom power.

In my opinion the drawback of the new microphone generation after the tube mikes is not the FET, it is phantom power.


Eric,
I know, high voltage microphone supplies are your hobby horse and credo, but that's not the commonly available method:  48V phantom powering is and will remain for the foreseeable future the studio standard, rather than schlepping dedicated and proprietary power supplies along.

You state that phantom mics with DC converters have higher headroom.
The opposite is true, and confirms a FET's problems with high input voltages into its gate:
Neumann's U87Ai uses a DC converter to boost the capsule pol. voltage to 60VDC, with the result that the FET cannot take the capsule's output in high SPL situations, and in the U87Ai the already low headroom of the old U87 is further reduced 5-6dB.

Gustav,
Using a specific European-made FET has helped me improve the headroom by ca. 3-4 dB, all else being equal, and no circuit changes undertaken.
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ricknroll

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Re: Good Question!
« Reply #19 on: October 25, 2007, 07:40:06 pm »

RPhilbeck wrote on Thu, 25 October 2007 15:53


Nice!  Please report back on your findings!  I have considered sending mine to Klaus for modification, but worried that since I like the mic as is, I might like it less after his mod and that would depress the bejesus out of me.  

Robert
Robert,

The stock U87 is now on its way to me, and as soon as it arrives I'm going to borrow a friend's M269 (modded by Klaus) and will report back my findings.  I'll probably upload a few sound clips for a rough comparison, although obviously there's no substitute for firsthand experience.

Rick
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Schallfeldnebel

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Re: Good Question!
« Reply #20 on: October 26, 2007, 06:43:03 am »

Klaus,

The example of the U87Ai is the worst example you could mention.

You are right, and my opinion is that the design of the U87Ai does not earn an award in electronic design, nor the U87.

I wanted to point out that the limited current of phantom power is the bottleneck, not the FET's.

Erik Sikkema
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Klaus Heyne

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Re: Good Question!
« Reply #21 on: October 27, 2007, 12:29:29 am »

...and my contention is that, as long as we are stuck with 48V Phantom Power, and when using a single FET design, like the U87, A or not, the headroom ceiling is caused primarily by the FET's limitations to process high input without distorting.
Do you agree?
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John Monforte

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Re: Fet Mic Vs. Tube Mic: Do They Sound Different?
« Reply #22 on: October 27, 2007, 12:46:52 am »

Personally, I don't see Phantom Power as a headroom problem either. I wish it were possible to prove that one way or another, but it is hard to make a definitive test.

In practice, the FET does not see all the phantom voltage. I think a U87 has about 22 volts on the FET supply.

Meanwhile, people rave about the class A Neve gear which is powered by 24 volts and is working at line level. That's about a 40dB greater (1000x) signal.

Even still, it is possible to get a 170mW from a standard phantom circuit. Stick an inverter on that and you should have plenty to make a FET work at a high voltage with a low output impedance.

There's more going on here than can be blamed on Phantom Power.
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John Stafford

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Re: Fet Mic Vs. Tube Mic: Do They Sound Different?
« Reply #23 on: October 27, 2007, 08:19:55 pm »

Oliver Archut wrote on Thu, 25 October 2007 14:11


Some Neumann Berlin close sources point out that Neumanns next U87 revision will be a TLM version....




That's interesting Oliver.

Given that the TLM103 was originally marketed as a cardioid TLM U87 with a capsule 'based on' the K87, and the TLM 127 as a multi-pattern TLM103, I had assumed that this is what the 127 was aiming at, but then it appeared with a capsule based on a capsule based on a capsule......



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Schallfeldnebel

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Re: Fet Mic Vs. Tube Mic: Do They Sound Different?
« Reply #24 on: October 28, 2007, 04:45:54 am »

There has already been a TLM version from the U87, named the TLM171. Only a few on special request were made, and this microphone was nothing more than the TLM170 electronics and the capsule from the U87(A?).

Since there was no electrical compensation for the large peak of the capsule, this microphone sounded very bright. I assume when Neumann comes with a new TLM version, the capsule's peak will be controlled like the U87 and U67 models.

If I may give Neumann's developing staff a suggestion, make this electronical compensation switchable.

Erik Sikkema
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volki

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Re: Fet Mic Vs. Tube Mic: Do They Sound Different?
« Reply #25 on: November 06, 2007, 10:10:20 am »

hi all, just to get back to the initial question...

the factors involved in judging mic's regarding the tube vs fet issue can be so various.
my 2 cents, next to the things mentioned already:

amount and balance of low vs. higher order distortion
even order distortion (often referred to as "2nd harmonic") is dominant in both tube and early single ended FET designs. however, the ratio between 2nd and higher order harmonics can vary greatly within both tube and and FET circuits, depending on tube / FET type & biasing, amount of negative feedback. tube designs usually have more relative level of 2nd harmonic that FET circuits, with higher order harmonics rising in level later as overall input signal level increases. for both designs, distortion rises gently with input level even well above the usually cited max. SPL @ THD of 0,5 or 1%.
thus, a) real world signals passed through these mic's can exhibit a richer structure of harmonics / intermodulation products, b) especially in tube designs, transients may exceed the max. SPL by a considerable amount without sounding grossly distorted. Early FET's tend to sound less forgiving there, since at that point, the amount of higher order harmonics is already greater, increasing the risk that the resulting distortion is actually being percieved as unpleasant.

there are exceptions such as the schoeps circuit with one FET followed by an active balanced BJT output stage. here, you get dominant odd order distortion (3rd harmonic), but with less relative level than the above designs.

modern FET mic`s mostly include several active stages with high amounts of negative feedback, resulting in high headroom but also lack significant distortion of any order within their dynamic range, until just above the max. SPL point, hard clipping occurs... so these mic's amps sound "clean" within their operating range but will reveal gross distortion even when slightly overdriven.


the transformers of tube mics can vary greatly in design - some metal alloys can exhibit high distortion (dominant 3rd harmonic) especially at low (!) levels, so depending on the materials used, low level signals may also sound different regarding harmonic /IM structure. besides, some metal alloys tend to rise gently in distortion as input is increased, others retain low distortion up to a certain point, beyond which they will rise rather steep (compareable to soft clipping). Some designs will exhibit considerable rise of low freq. dist. at high levels, others only a marginal rise thereof.

not to mention possible interactions between freq-dependent and non-dependent resistances of mic output and mic-pre input (properties of maybe present transformers, varying overall input impedances...)

so IMO it's not all that easy =o)



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