Phantom Power Capacitors

[ruffrecords]

Ideally we want to have a noise that significantly ( > 6dB) lower than microphone noise. That is what really matters in the real world.

Let's say I have STC 4104A ribbon Mic, my Z is 30R. Suddenly a Noise factor of 3dB at 150 Ohm seems not so great.

Hence I do not consider noise figure or Ein stated at a specific impedance all that useful.

I agree which is why an EIN at zero ohms is no better than at 150 ohms. What we really need , but are unlikely to get, is a plot of EIN versus source impedance.

In the absence of that, a figure at the most common source impedance is the best choice.

And we have not even touched on how EIN varies with gain.

Cheers

Ian

 

[MicMaven]

I'm too lazy to work that hard. So I'm always looking for someone easy. / Thor

THIS, I believe !

James

 

[k brown]

The correct type and vlue of phantom power blocking capacitor is whatever sounds best and has no longterm problems. You can use your own ears to determine what sounds best but there's not enough time to test for long term problems but in theory and practice film caps will have fewer if any long term problems. Electrolytic caps from major manufacturers (but not made in PRC but ok if from ROC) are all going to be similar as all the manufacturers know what each other knows and is doing. Japanese and German parts are probably the best due to cultural influences fostering integrity. BUT.... a mic pre without input and output transformers is like a vegan meal....it won't satisfy and can lead to sarcopenia.

Not true if one is recording Classical music where one is after minimal coloration and phase shift.

For example, renowned Classical engineer Tony Faulkner is using primarily transformerless Audient pres.

 

[abbey road d enfer]

Actually, Ein with input short is best, IMNSHO. Here is why.

The noise of a system is always that of all noise sources.

By lumping multiple separate noise sources into one, it becomes hard to determine what is what.

That is acceptable only if noise current is also specified.
Without it it's an object of speculation.
Alternatively, several noise figures pertaining to various source impedances would be pertinent and useful.

 

[abbey road d enfer]

. a mic pre without input and output transformers is like a vegan meal....it won't satisfy and can lead to sarcopenia.

!?

 

[abbey road d enfer]

We have two separate tests.

Self noise and system noise.

A system noise where electronics do not increase noise would have a noise factor of 0dB and an Ein (0R source) of -oo dBu.

Can you explain this cryptic concept?

 

[abbey road d enfer]

Not one person said: "If you make a kit that sells at 100 USD each, I take eight!"

Not intrested, since I can make a Cohen that works good enough for me for less than 10 bucks, using dreaded capacitors, which, BTW, have provided good service for the last 40 years or so.

 

[sahib]

..............

I have a problem with this article. See.

...... of music passing through a capacitor (it doesn't really)...

It does.

Note: This is not directed at Abbey as he will remember from a past discussion.

 

[abbey road d enfer]

Cryptic?

Let's say I have a microphone with around 74dB SNR at 1Pa and -34dB(V) sensitivity, output Impedance < 10 Ohm.

Thus with this microphone in my system, my best system noise at the system input cannot really be better than -105dBu.

Yet my Microphone Preamp may offer -129dBu (re 150 to keep those with torches and pitchforks happy).

But system noise will invariably be 24dB worse, no matter what I do on my Mic-Pre, like for example "electronic cooling" (aka synthetic impedance) to reduce the noise from resistance's in the circuit.

I'm quite familiar with this concept, when it's exposed clearly.
I've never seen it referenced as "system noise", that's all.
It's just a global noise consideration, that generally concludes that the noise performance of a system is constrained by the first stage, in this case the diaphragm, where S/N is constrained by thermal agitation of air particles and ambient noise.

Please do. Anything I have to offer is obviously not for those who, unlike me, already know everything. Enjoy what have.

I believe this jab is addressed at me. If you knew me, you would realize that I'm much more humble than you think. OTOH I hate BS and braggarts.
Unlike you, as a mod, I have a duty to members to make sure that the content of posts is understandable, documented, open to contradiction and educative.

 

[abbey road d enfer]

It does.

Note: This is not directed at Abbey as he will remember from a past discussion.

I don't remember such a discussion, honest.
The idea of "music passing through a capacitor" is a tad romantic.
The electrons need more space for a piano than for a flute, ain't they? That's why the capacitor is bigger.
But what really makes me twinge is considering a capacitor as something that definitely imprints "character" to signals that pass through it, this "character" being intrinsic to the capacitor and not to its surroundings.
That's very much this belief that vendors of snake-oil capacitors exploit. Very pregnant with guitars and guitar amps.
Now, even the fact that signal passes through capacitors is debatable. Maxwell would disagree.
But Maxwell himself was just an ensemble of propagation waves, as we all are.
It's all a matter of point of view.

 

[sahib]

I'll need to find the thread but a forum member argued that the current did not actually pass through a capacitor (common belief) because of the insulator between the two plates. You commented saying the current passes through it in whatever form that it is. I tackled it from leakage current point of view. Another forum member (who taught analogue electronics) briefly mentioned of displacement current.

There are a number of description problems in electrical engineering and this is one of them. The source of the problem is the word "flow" which automatically conditions us to think of current as a river flowing. Somehow the electrons march from one end to the other end and for that to happen there has to be something that facilitates it (conductor). This thinking is wrong. Current is not a stuff. It does not flow like water does in a river. It is due to charge and we should take it that way.

Without cluttering the thread too much, there are three forms of current. Conducting current which happens in conductors, convection current which happens in thermionic valves/tubes, and displacement current (also referred to as polarization current) which happens in capacitors. So, in brief there is no conduction current through a capacitor but there is displacement current (which as you said coined by Maxwell). There is no charge inside the insulator hence no current, but there is disturbance of the atoms on the surface (polarization) which gives rise to current. To reconcile with the maths displacement current is taken as equal to conduction current.

 

[abbey road d enfer]

OK, now I remember I made a fool of myself by posting a stupidity I can attribute to old age and typing in the middle of the night.

 

[sahib]

.... I made a fool of myself by posting a stupidity ...

Certainly not.

I can attribute to old age...

Tell me about it.

 

[abbey road d enfer]

Certainly not.

But there is proof! I didn't delete my flub.

 

[Matt Syson]

In the good/bad old days when I was testing gear as my day job manufacturers would state the EIN but with a range of test conditions such as two or three resistive terminations (to represent likely mic output impedances) and 4 or 5 meter meadurements with 20 to 20K flat measured with RMS and peak reading meters and also with various weightings CCIR AES etc because some of the 'results' can reveal intersting artifacts such as low end rumble (or power supply noise) or influences from the mains supply, All of which can have a bearing on how 'good' a preamp may be. NOW we get talk of how many flashing lights you can have and actual real world measurements are forgotten.

 

[rh001]

I'm guessing you never heard Forssell, Gordon, or GML, or had an Ital meal.

Italian cuisine will satisfy though it works against good health. I've heard GML micpres...very transparent but because of that not all that compelling...it's definately a vegan mic pre. Totally transparent pro audio gear is a waste of time as nothing really sounds as good in person as it can be made to sound after recording with hot & fat gear, punchy or smooth as needed,....with the exception of some instruments used to make classical music and the like especially when there is a desire to hear how good that instrument is...a multi-million dollar violin for example....but then the loudspeakers' coloration will swamp out a lot of micpre and recording chain differences. There is a winning sound but people not into winning often fail to notice.

 

[abbey road d enfer]

Please, not the old subjective vs. objective debate.
It's beaten to death, though still alive.
No winners, only losers.

 

[abbey road d enfer]

In the good/bad old days when I was testing gear as my day job manufacturers would state the EIN but with a range of test conditions such as two or three resistive terminations (to represent likely mic output impedances) and 4 or 5 meter meadurements with 20 to 20K flat measured with RMS and peak reading meters and also with various weightings CCIR AES etc because some of the 'results' can reveal intersting artifacts such as low end rumble (or power supply noise) or influences from the mains supply, All of which can have a bearing on how 'good' a preamp may be. NOW we get talk of how many flashing lights you can have and actual real world measurements are forgotten.

That's to say that noise performance evaluation is never a single digit. Also true for distortion.
Somewhat akin to evaluate the performance of a car by only measuring its time to 60mph.

 

[rh001]

Not true if one is recording Classical music where one is after minimal coloration and phase shift.

For example, renowned Classical engineer Tony Faulkner is using primarily transformerless Audient pres.

At the end of the day things like "minimal coloration and phase shift" don't really matter.....the buying public wants whatever is delicious. A lot of even modestly priced mic pres can achieve minimal colorationa and phase shift. Music is supposed to be enjoyed...it's not a science experiment. (how many of those old wrinkled players in the orchestra can actually hear above 8 khz?) Recordings of Drew Henderson on YouTube are pleasant and his playing is phenomenal, and sometimes he is playing with another phenomeal guitarist, but while the recorded sound is smooth it's a wee bit dull, like there's high humidity, but aside from all that there is significant room tone....most of his recordings are in churches famous for their musical acoustics.....we don;t really know what his guitars sound like in an anechoic chamber with our ear 10 inches from the sound hole.

 

[JohnRoberts]

At the end of the day things like "minimal coloration and phase shift" don't really matter.....the buying public wants whatever is delicious. A lot of even modestly priced mic pres can achieve minimal colorationa and phase shift. Music is supposed to be enjoyed...it's not a science experiment. (how many of those old wrinkled players in the orchestra can actually hear above 8 khz?) Recordings of Drew Henderson on YouTube are pleasant and his playing is phenomenal, and sometimes he is playing with another phenomeal guitarist, but while the recorded sound is smooth it's a wee bit dull, like there's high humidity, but aside from all that there is significant room tone....most of his recordings are in churches famous for their musical acoustics.....we don;t really know what his guitars sound like in an anechoic chamber with our ear 10 inches from the sound hole.

In 15 years of designing audio SKU for lots of value customers (price conscious). I don't recall one customer ever complaining that the audio paths I sold them were too clean, and they wanted more coloration (distortion*****).

JR

***** I haven't shared this story in a while. Back last century when I advised the analog group in their design of high performance vacuum tube mic preamp (VMP-2). I cautioned about making the audio path too clean. I asked the senior design engineer (Jack Sondermeyer RIP) to add a jumper that could be removed to reduce the amount of negative feedback and allow more of the vacuum tube path open loop distortion to express. After about a year in the market, not one customer complained that it was too clean and we hard-wired across the jumper for the "clean" position.