Comparison of JFETs for mic applications

[jp8]

Submit it to a fading low-frequency sinewave. I used to do that with a simple potentiometer, but today I can use a tone generated by a DAW.
I believe this method is documented in a Studer paper.

Or did you mean Jensen? See chapter 4.2 here.

Jan

 

[thor.zmt]

Or did you mean Jensen? See chapter 4.2 here .

Bill is in part correct.

I found the results far les subtles than he intimates, back in the 80's.

Anyway, a module from a mixing desk to be serviced could not pass basic acceptance tests with a magnetized transformer. Many that came had some gotten "magged". Must have been these wicked western imperialists magnetizing upstanding socialist Transformers of the people.

Secondly, what we are trying to do is to "re-randomize" the magnetic dipoles in the magnetic material after they have become aligned into a specific polarity. This condition is kinda self-reinforcing. It usually takes to beyond saturation (hence my implied suggestion of 5Hz +20dBu) to overcome.

Another issue is that the fade must be very slow, an excessively fast fade doesn't guarantee sufficient randomization. We "Go gray" pretty slowly.



As the signals drops so does the number of magnetic dipoles moved. Adding a significant amount of white noise to the VLF sinewave can be more effective and allows faster fade out.

Magnetized cans be PITA to clear, but commercial TV Tube demaggers (if they can be found) will do.

Thor

A man in a desolate train station
A suitcase at his side
Cold, fixed eyes
Show fear when he
Turns to hide

Feel the rain like an English summer
Hear the notes of a distant song
Coming out from behind a poster
Hoping life wasn't so long

Turning gray

 

[dai h.]

Or did you mean Jensen? See chapter 4.2 here.

Jan

hi,

(check out page 50) :

https://www.worldradiohistory.com/A...ive-Studio-Sound/80s/Studio-Sound-1987-05.pdf

(and page 5--this is the same pdf from the Studer ftp link in the old thread below (which no longer works)) :

http://revoxsammler.ch/revoxsammler-neu/quellen/SwissSound/english/Swiss-Sound-18-1987-02-e.pdf


(the Studer info has been referenced a few times as in these 2009 threads) :

https://groupdiy.com/threads/studer-169-269-de-magnetizing-input-transformers.32851

https://groupdiy.com/threads/some-strange-audio-transformer-response-curves.31454/#post-382253

p.s.

this link also has the same Swiss Sound issue, but also lots of back issues as well:

https://www.reeltoreel.nl/studer/Public/SwissSound/

 

[ricardo]

For the rest...

View attachment 142938
Predicted is an unweighted 14dB 20dB self noise 20Hz-20kHz, so perhaps 10dB(A) 16dB(A) without accounting for Brownian Motion Noise and acoustic resistances etc. I would say "low enough for music recording" but not phantastically low.

Thanks for this Thor.

It's unfortunate your starting point is a particularly bad version of BM800. Some of its sins have passed into your circuit which would be noisier than Zephyr's version of the Schoeps from above 1kHz culminating in more than 11dB extra in the aurally important 4kHz and above.

I don't think you would get 16dB(A)

This BM800 circuit responds well to Muntzing for better performance. Your regulator improvements are worthwhile but replacing it entirely with cheapo resistors & capacitors gives even better performance ... unless you need the mike to work in P24 & P12 situations. There is at least 9.2dB S/N improvement available on top of this.

I would keep the HP filter. Condensor mikes need subsonic filtering.

Zephyr's mike with 34mm ISK 'C12' (2011 vintage) clone capsule is a very quiet mike but even here, the electronics contribute at least 1dB extra noise. So we are still far from Acoustic Resistance noise or Brownian angels dancing on the diaphragm.

Schoeps size SDCs would probably have enough acoustic resistance to dominate even Zephyr's circuit ... which has up to 6dB noise advantage for variable pattern LDCs in some modes.

Of course if the mike is only used for singers in a booth, these noise improvements are moot. But there would be certainly appreciated if they were the main Blumlein pair in the Royal Albert Hall for the Proms.

I hesitate to point out SimpleP48 has even better noise ...

Shut up ricardo ! Just SHUT UP !!!

 

[thor.zmt]

It's unfortunate your starting point is a particularly bad version of BM800.

Not at all. Here is what I make from it:

Some of its sins have passed into your circuit which would be noisier than Zephyr's version of the Schoeps from above 1kHz culminating in more than 11dB extra in the aurally important 4kHz and above.

I am not sure where you get that impression from.

This BM800 circuit responds well to Muntzing for better performance. Your regulator improvements are worthwhile but replacing it entirely with cheapo resistors & capacitors gives even better performance ...

Not in a compact format. We have a passive 100k/10uF filter to the base of a low noise, super beta npn transistor, a transistor others have used in MC Pre-Pre's.

The Zener Diode will have perhaps 10uV noise 20-20k, our RC filter will have 0.16Hz turnover, so -40dB at 16Hz, I wager the zenner noise is filtered out well enough, to not be of concern in the audio band.

unless you need the mike to work in P24 & P12 situations.

This Mic circuit I show is P48 only.

There is at least 9.2dB S/N improvement available on top of this.

I rather doubt that, at least where the power supply is concerned.

I would keep the HP filter.

I would ABSOLUTELY NOT keep it. Especially the exact one as shown.

If I need (V)LF filtering, I do it elsewhere.

I hesitate to point out SimpleP48 has even better noise ...

Does it now. Just how much better, as we are doing a contest?

Let's agree on the C-12 capsule. I'll pull the tech data.

2SK660 used for both? How do we bias the capsule in the Simple48P?

I find the TINA simulator quite close to reality, I'll run the numbers.

Noise, THD @ 94, 104, 114, 124 and 134dB if it still makes sense. Would you like something different.

Thor

 

[ricardo]

View attachment 143243
This Mic circuit I show is P48 only.

I hesitate to point out SimpleP48 has even better noise ...

Does it now. Just how much better, as we are doing a contest?
I find the TINA simulator quite close to reality, I'll run the numbers.

SimpleP48 has about a 1dB noise advantage over a properly designed classic Schoeps mike in the cases where the 'electronic' noise is sorta verging on being prominent. It has MUCH more advantage over poor implementations like BM800.

Let's agree on the C-12 capsule. I'll pull the tech data.

2SK660 used for both? How do we bias the capsule in the SimpleP48 ?

Alas, SimpleP48 only works with electrets

Can we use a hypothetical capsule with the same capacitance as CK12 and assume Vp 60V ?

Noise, THD @ 94, 104, 114, 124 and 134dB if it still makes sense. Would you like something different.

Can TINA produce a noise spectrum curve like the one on page 10 of Zephyr.doc ?

I'm interested in THD @ 94, 104, 114, 124 & 134dB spl of SimpleP48. But I concede your SupaDupa circuit will have lower THD.

The SimpleP48 contender for THD is SimpleP48RCA on page 12 of SimpleP48.pdf

As this is a sim. challenge, could we use that instead? THD of SimpleP48RCA would be of great interest to many including myself. Even then, I think it is 'good' only to 130dB spl.

Let me dream up the values for my incredibly complicated circuit

 

[ricardo]

Thor, who's 2sk660 SPICE model are we using?

I'm worried about the 'reverse diode' across G-S. Guru Scott Wurcer points out the reverse current at low voltage should be about 1pA.

No maker specifies anything that low as it's very temperature & voltage dependent. But that's what it needs to be.

eg MicUlli says only Infineon & NXP BAV199s are good enough for this purpose but their datasheets show reverse current in the nAs.

---

And forgive my asking but does TINA simulate resistor noise properly? We can test this by doing noise spectrums with just various resistors like I do on page 10 of Zephyr.doc

---

Can we use a hypothetical capsule with the same capacitance as CK12 and assume Vp 60V ?

This is just to get a 'sensitivity' figure. We could use -66dBV/Pa which would be within 2.5dB of Zephyr's Schoeps variant with the ISK 34mm capsule.

---

I want the 'capsule + FET' side to be LN enough to clearly see the differences in the rest of the electronics ... as is the case with Zephyr's mike.

This would be useful to all and sundry ... as would THD at different spls for this 'hypothetical' capsule with SimpleP48RCA.

Much better than a "mine is bigger than yours!" shootout Much better use of your time and effort too for which I'm sure everyone here will be grateful.

 

[ricardo]

Does anyone have a pukka Windows XP install disc they could send to a beach bum in Cooktown, Oz?

I need a real XP machine to run my own software in case Thor asks mi mo hud kwestens. My last one has died.

Moderators, please move this cry for help to an appropriate forum if required.