The circuit has serious design faults and it is arrogant to put it in the same league with U89
syn08 said:
Your SPICE is definately different. our NJF defaults to the earliest JFET models where your model gives very non-physical characteristic curves. Pinchoff is abrupt and always obviously at VTO (it looks like a bipolar). After asking around I think I can get a better model running. Did you intend for VTO (VP) to be the same across the entire range. The first model was labeled for the 2SK170_BL so I just assumed there would be a mean value for each color code in yours with the beta adjusted over a more limited range. That's what I thought I was missing, the same VP for the entire 4:1 Idss range is not very physically real. It's funny we do almost no design with JFETs where a good fit matters.
With modern lithography the old planar FETs have absolutely cavernous dimensions. Since the parameter spread has not improved much I would think the implant dose and drive which enter into the VP and IDSS equations to essentially keep beta constant are more important.
The short channel FETs add some additional variation but accounting for 4:1 Idss variation by geometry alone I would doubt.
dimitri said:
Show them, please! 😉
Your claim is very serious, so please be prepared to answer.
While you are thinking, here is the record made by this mics:
http://wavebourn.com/music/alisovskiy/SebeNaBis.mp3
scott wurcer said:
Most of the simulators available for mortals are based on the old SPICE3 implementation, algorithms and model templates. Mine is Cadence PSpice.
I agree that keeping Vp constant for the entire range (which is what I am doing) is not entirely correct. But then if you keep Beta constant and start adjusting Vp you'll need a range of variation which in turn will have little technology (ion implantation + annealing) meaning. OTOH, the very large W/L in short channel devices hides the devil; very small variations in L (litography, these devices are not self aligned!) will have a major impact in W/L and hence Beta. I have never built a JFET, but I build enough ion implanted MOS devices to know that ion implantation and annealing is way more controlled than litography (including etching). Now, I don't know how the Toshiba JFETs are manufactured, but somehow I doubt they are using for devices worth pennies steppers and reactive ion etching to define the critical layers. FWIW it's probably projection and wet etching.
Probably the most (physical) correct way would be to parametrize both Vp and Beta, but then how to do this? One equation and two unknown allows an infinity of solutions.
If you can think of a better parametrization/model, just let me know...
scott wurcer said:
By the way, this slight modification of U89 don't have a parallel feedback...
http://www.angelfire.com/az3/dimitri/images/riaa.pdf
Edit: it was a joke. I like theoretical articles about obvious things; mathematical formulas in them remind me schoolbooks and my happy days in TIASUR and NIIPP when I was young and the whole life was still in the future. 😉
This is a sad situation. We have all kinds of amateurs designing microphones. Unfortunately, they are not the best possible solutions. Yet, nobody seems to know the difference.
john curl said:
Funny thing, it is where everything begins and brands whatever comes behind, except in the case of purely synthetic performances (and then not in all cases).
Rodolfo
I have been working on microphone design for 35 years or more, but only B & K and a few AES articles have ever taught me how to make the best possible microphone circuits. Of course, I have interacted with Neumann and Schoeps, etc., but they are compromised designs and I have often been called in to upgrade them, over the years.
Hi John,
I'm sorry to have to point this out to you.
If you made the only true low noise, high quality preamplifier stages, then your circuits would be used in close to every recording studio and high quality piece of audio equipment. I should think we would also see your work figure prominently in test equipment. Well, there appears to be more than one way to skin a cat. More than one way to compromise to create audio circuits.
Look, I'm not after you at all. It's your opinion and manner of speaking to other people here. You do make good stuff, but please allow the possibility that other people can also create very good circuitry. The way you talk, you are putting everyone else down. That is not fair, nor is it wise. I am sure that you can learn some things from others.
John, your attitude is not very good. You need to look in the mirror and accept that there are other people who can (and do) design circuitry every bit as good as your own. There is nothing one person can do that can't be done or bettered by another person. Also accept that your approach adheres to your idea of what is important. That does not mean that your approach is the only valid one.
I have not put you down, that is not my intent. I just want you to recognize the abilities others have. What would you say to a younger you? You did start somewhere, and that was not at the top.
-Chris
I'm sorry to have to point this out to you.
If you made the only true low noise, high quality preamplifier stages, then your circuits would be used in close to every recording studio and high quality piece of audio equipment. I should think we would also see your work figure prominently in test equipment. Well, there appears to be more than one way to skin a cat. More than one way to compromise to create audio circuits.
Look, I'm not after you at all. It's your opinion and manner of speaking to other people here. You do make good stuff, but please allow the possibility that other people can also create very good circuitry. The way you talk, you are putting everyone else down. That is not fair, nor is it wise. I am sure that you can learn some things from others.
John, your attitude is not very good. You need to look in the mirror and accept that there are other people who can (and do) design circuitry every bit as good as your own. There is nothing one person can do that can't be done or bettered by another person. Also accept that your approach adheres to your idea of what is important. That does not mean that your approach is the only valid one.
I have not put you down, that is not my intent. I just want you to recognize the abilities others have. What would you say to a younger you? You did start somewhere, and that was not at the top.
-Chris
Hi Anatoliy,
I listened to your link.
I don't understand what you are trying to prove here. The mp3 sound byte will degrade whatever you did. I think in this case some measurements would have been more helpful. Who knows what people are listening to on their computers? I don't. Your preamp circuit most probably contributes the least amount of distortion and noise in that system.
Besides, sound can mask high levels of distortion. Did you every quantify your circuit in terms of noise and distortion? How much distortion does the mic element itself contribute?
Nice recording BTW. Just not very relevant to the discussion.
-Chris
I listened to your link.
I don't understand what you are trying to prove here. The mp3 sound byte will degrade whatever you did. I think in this case some measurements would have been more helpful. Who knows what people are listening to on their computers? I don't. Your preamp circuit most probably contributes the least amount of distortion and noise in that system.
Besides, sound can mask high levels of distortion. Did you every quantify your circuit in terms of noise and distortion? How much distortion does the mic element itself contribute?
Nice recording BTW. Just not very relevant to the discussion.
-Chris
John; in TIASUR we were taught and trained to make compromises: any design had to start from set of criteria which we had to meet, and many of them were contradictory. Non-compromises design may live in SIMS only, or in another kind of virtual reality like scientifical articles.
Anatech, I appreciate your frank input.
Unfortunately, we have some objective problems with the microphone circuits listed.
Usually I have just made the microphone channels for hi end recording concerns like Crystal Clear and Wilson Audio. However, I have explored microphone design as well, and know something about it.
The first factor of concern to me is: What is the input capacitance of the input fet? This is more important than most here realize. That is why I brought the subject up. Sure the 170 will work, and it does have low voltage noise, BUT what about the distortion added to the capsule transfer function? Isn't that important as well?
I have found several RF fets that do have low input capacitance AND are pretty quiet as well. It is not so hard to find alternative devices that would work somewhat better. Does anybody know what I am talking about, does anybody have any suggestions?
Unfortunately, we have some objective problems with the microphone circuits listed.
Usually I have just made the microphone channels for hi end recording concerns like Crystal Clear and Wilson Audio. However, I have explored microphone design as well, and know something about it.
The first factor of concern to me is: What is the input capacitance of the input fet? This is more important than most here realize. That is why I brought the subject up. Sure the 170 will work, and it does have low voltage noise, BUT what about the distortion added to the capsule transfer function? Isn't that important as well?
I have found several RF fets that do have low input capacitance AND are pretty quiet as well. It is not so hard to find alternative devices that would work somewhat better. Does anybody know what I am talking about, does anybody have any suggestions?
It is easy to show that the FET capacitance in that U89 circuit adds no distortion, by theory, simulation, and measurement.
anatech said:
Let me disagree Chris; the recording is very relevant: it shows where the mics were designed to be used, in what conditions, and how they meet the criteria.
They were designed not for studio usage, and not for measurements, but for a new generation of High-End stage equipment. That means, listeners compare direct sounds with amplified ones imidiately so flaws are well heard immediately, so inaudible distortions were preferred VS easily measurable ones. That's why single ended cirquitry was choosen.
Second, it had to be cheap so mass production parts were taken for the prototype.
Third, it has to work with all available consoles, that's why so strict requirements to output impedance were applied.
Forth, it has to work in field conditions where RMI will present, that's why (among other things) a transformer output was choosen.
Also, during live events on peaks power falls down to 90 Volt and below and in some consoles phantom power voltage regulators fail to work, that's why so high time constants in powering filters were used.
There are different SPL and ambient noise levels in studio VS live concerts, so my microphone can't be directly compared to Neumann designed for studio usage. It is like to compare apples VS oranges. I don't know why Dimitri decided to compare them and comment so rude.
My single point was, let me repeat, that 2SK170 transistors work well on microcurrents, so I don't understand why they can't work much better on currents higher with lower imput source impedances: teoreticians attacking John according to my experience were wrong.
john curl said:
Yes, it is!
In Newmann's microphone feedback capacitance is dominated (Miller-type, parallel by voltage), in my microphone it is dramatically reduced by serial feedback by voltage that bootstraps source against gate.
In both cases the issue was addressed and solved well, though diferently.
Hi John,
I am reasonable sure I have a handle on the concepts. Don't ask me to design one. That's your job!
-Chris
Never questioned that at all. I'm sure you know far more about that than many of us here, including myself. I've only used mics in stage productions.
Wouldn't the stability and linearity of that capacitance be most important? As long as the FET gate capacitance does not introduce distortion (thinking non C0G / NPO ceramic cap type here), it can be compensated for. Beyond that, we are only talking about system noise I would think. That has little to do with gate capacitance.
I am reasonable sure I have a handle on the concepts. Don't ask me to design one. That's your job!
-Chris
myhrrhleine said:
john curl said:
Far be it from me to argue with my good friend John. 😀
He's absolutely right.
Hi Anatoliy,
How were we to know that? The only reference you can give us are measurements. Then offer the target specifications and budget. Then we are looking at your options. The mp3 tells us nothing of that. We can't even compare anything which was your stated point of that recording.
Anatoliy, I was only trying to point out that you did not prove or show anything with the mp3 link. I even have real home speakers, amp and sub on my system using a good Creative X-Fi Music card. I could hear pretty well, but nothing that proved anything at all. I'm sure the mp3 was of lower quality than the original recording. Those are the only points I was attempting to make.
-Chris
No, it doesn't. Imagine a member listening to your mp3 through some really bad computer speakers, no sub. What on earth does he take away from that?? Nothing. Besides, you can record that from a roof or back lot. Video is required to show the location and even that can be faked.
How were we to know that? The only reference you can give us are measurements. Then offer the target specifications and budget. Then we are looking at your options. The mp3 tells us nothing of that. We can't even compare anything which was your stated point of that recording.
Kind of goes without saying, doesn't it? The device had a target budget is really all you have said.
This is the reason why there are standards that sound equipment adheres to (hopefully). Designing for all circumstances tends to increase the price or create unwelcome decreases in quality. So, you built to normal specs (I hope!). Phantom power does vary a lot with cheaper semi-pro equipment. Some supplies have too much supply noise too.
I have not seen a mic that didn't have RFI measures designed in. Maybe the really cheap ones don't. Also, using a transformer is the easiest way to handle the phantom power supply.
Already covered above.
That is a non-issue. SPL levels vary a huge amount no matter where you are recording. Besides, I wasn't comparing to the Neumann. They are to delicate to use outside on a constant basis.
Okay. I didn't question you on that at all. I can accept your point.
Anatoliy, I was only trying to point out that you did not prove or show anything with the mp3 link. I even have real home speakers, amp and sub on my system using a good Creative X-Fi Music card. I could hear pretty well, but nothing that proved anything at all. I'm sure the mp3 was of lower quality than the original recording. Those are the only points I was attempting to make.
-Chris
anatech said:
So, let's go back to where this branch started from: to the buffer in John's amp that uses 2SK170. As an audio engineer I would be glad to see such attention to details in design of professional amplifiers as John applies to his designs.
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