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Author Topic: U47 schematic, component-by-component  (Read 32574 times)

Eric H.

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Re: U47 schematic, component-by-component
« Reply #45 on: January 24, 2011, 07:27:19 pm »

To this day, I still don't get why we still do audio tests whith sine waves. To me, it is like travelling on a horse.
Measurements with filtered pink noise, by octave or 1/3 octave, burst signals, sweeps and others I don't know about would probably give more info on the complexity of the phenomenons.
Softwares like matlab really make it available to any lab to do very complex comparisons of original and measured signals.
I am sure the real mic labs have all kinds of measurements that they just don't make public.
I'd like to see one day transient measurements in the brochure for exemple.
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eric harizanos

Klaus Heyne

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Re: U47 schematic, component-by-component
« Reply #46 on: January 24, 2011, 08:22:34 pm »

What would transient measurements tell you about how a microphone sounds, or how useful the mic may be for music recording?
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Klaus Heyne
German Masterworks
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volki

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Re: U47 schematic, component-by-component
« Reply #47 on: January 24, 2011, 09:09:08 pm »

The fact that I was summing up Peus' paper in my last post doesn't mean I subscribe to the view that distortion measurement with static signals were the ultimate method of evaluationg sonic qualities - even if I do think that it does lend itself to outline a basic direction thereof.

Of course even the envelopes of quasi-stationary signals (let alone transients) will interact with the characteristic linear and nonlinear distortion mechanisms of a given capsule and amp design (where I remember some posts of David Bock in the recent tube biasing thread quite making sense to me), resulting in a more or less unique signature.

I'm also not debating by default that distortion of the capsule may sometimes (or even most oftentimes) be dominant over the head amp. On the contrary, that would explain sonic properties of certain mic's which otherwise would only rather weakly be backed up by measurements of the electronics.

Quote:

 (Oliver)
The capsule of a 47, it does not matter M7 or K47, will start to distort earlier than the buffer amplifier itself,

Could you elaborate as to where this information comes from - listening, measurements, etc.?

Anyway - in this case, one could also argue "the other way round" and attribute negative properties (such as sibilance) in some modern mic's to those capsules producing gross acoustic distortion in the upper midrange - any comments?

Quote:

 (Klaus)
There is also the electro-mechanical interaction of the mic amp's high impedance stage coupled to the capsule.

Klaus, what exactly do you mean? Nonlinearities caused by the electric force due to the membrane's excursion towards the backplate and thus being increasingly attracted by it? Metal contacts between capsule and amplifier...? And then there's of course the nonlinear compression property of the air cushion between membrane and backplate... they all seem to matter somehow.



PS. I once briefly compared my Neumann UM57 to a Neumann/Gefell UM70 head (containing an M7 capsule) combined with an M582 head amp (same tube but different circuit and xformer), but wasn't able to spot a significant difference. Now would that be due to the nonliniear characteristic of that M7 dominating any circuit nonlinearities...?!?  Cool




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Volker Meitz

volki

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Re: U47 schematic, component-by-component
« Reply #48 on: January 24, 2011, 09:20:46 pm »

PPS. Maybe I’m mistaken , but it seems to me that  manufacturers used to get their published max. SPL data by simply measuring THD of the electronic part of the mic, assuming that this were the dominant figure.

Now for modern mic’s, with their low THD and high headroom figures,  this method would indeed be valid somehw since the clipping of the circuit - and thus the very audible sudden rise of a lot of harmonics - definitely determine the max. SPL possible. On the other hand, if the capsule has a higher distortion figure than the amp, the above might not hold true for all types of signals - even if the capsule’s distortion products are dominant low order and rising proportionally with level, a property much more tolerable to the ear...?
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Volker Meitz

Klaus Heyne

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Re: U47 schematic, component-by-component
« Reply #49 on: January 24, 2011, 09:27:25 pm »

volki wrote on Mon, 24 January 2011 18:20

PPS. Maybe I’m mistaken, but it seems to me that  manufacturers used to get their published max. SPL data by simply measuring THD of the electronic part of the mic, assuming that this were the dominant figure.
Correct. Unless David Josephson has new information to the contrary, amp + dummy load instead of amp + capsule is still the standard for measuring headroom of mics.
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Klaus Heyne
German Masterworks
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Oliver Archut

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Re: U47 schematic, component-by-component
« Reply #50 on: January 24, 2011, 11:59:16 pm »

Hello Volker,

the distortion of the capsule is not the dominant one, in a 47 the capsule starts to distort earlier than the electronics, but at one point the electronics will catch up and the final distortion is dominated by the amplifiers THD. My point is that the static value of testing distortion does not take this into account.

I hope that this clears it up.

Best regards,


 
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Oliver Archut
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zebra50

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Re: U47 schematic, component-by-component
« Reply #51 on: January 25, 2011, 03:25:06 am »

Thanks for the link, Volki!
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Stewart Tavener
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Eric H.

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Re: U47 schematic, component-by-component
« Reply #52 on: January 25, 2011, 09:28:18 am »

Klaus Heyne wrote on Tue, 25 January 2011 01:22

What would transient measurements tell you about how a microphone sounds, or how useful the mic may be for music recording?

Well, the same way we have transient measures for power amp to reproduce music.
Music is the contrary or static and the way any audio device can "track" those micro changes in the music/sound can get a good idea of how much accurate a mic would be in transducing a pressure or gradient point in the sound field.

More accurate transient response is one of the reason people will love condenser for example.
We could do more into detail about this, but it my conviction that when we mike a group/ensemble, the transient response of the different mics is a very important factor in creating our reconstructed sound stage.
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eric harizanos

David Bock

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Re: U47 schematic, component-by-component
« Reply #53 on: January 25, 2011, 01:00:26 pm »

Quote:

Well, the same way we have transient measures for power amp to reproduce music.
Music is the contrary or static and the way any audio device can "track" those micro changes in the music/sound can get a good idea of how much accurate a mic would be in transducing a pressure or gradient point in the sound field.
Sadly, or Greatly, measuring microphones is still far more complex than measuring an amplifier.
There are a number of measurements that can be taken of a microphone beyond fr, but I haven't seen a successful deconvolution into a meaningful characterization that would permit decisive differentiation between mics. And in those measurements, transient response doesn't come up so much. FWIW greater minds than mine have and are addressing this topic, with still, no overwhelming evidence that one could use measurements instead of listening.
Quote:

More accurate transient response is one of the reason people will love condenser for example.
You have proof or evidence to justify this?

KaiS

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Re: U47 schematic, component-by-component
« Reply #54 on: January 25, 2011, 03:56:11 pm »

David Bock wrote on Tue, 25 January 2011 12:00

Quote:

Well, the same way we have transient measures for power amp to reproduce music...
Sadly, or Greatly, measuring microphones is still far more complex than measuring an amplifier.
... in those measurements, transient response doesn't come up so much. FWIW greater minds than mine have and are addressing this topic, with still, no overwhelming evidence that one could use measurements instead of listening.
Quote:

More accurate transient response is one of the reason people will love condenser for example.
You have proof or evidence to justify this?
Measuring the transient response of a mic is simple:
Use a gunshot - compressed air pistols works very well delivering an almost perfect pulse of not to high SPL.

When I did comparisons with this type of measurement I found the following:
The B&K reference mic (1/8") recorded @ 96kHz/24bit delivered a sharp pulse of 1-2 Samples with no ringing (as hoped and expected).

The larger the condenser mic the broader the pulse became, but no obvious ringing (may be some in the low level range).
This complies with theory, as those mics have a more limited bandwidth, therefore the pulse must be broader.

Using dynamic mics there wasn't a sharp pulse, but more like a bell shaped form with evidence of pre- and post-ringing.

Does this help us - it just confirms what most of us know from our own listening experience - condenser mics have a better transient response.
As this is in the time domain it's not possible to change a dynamic into a condenser sound and vice versa.

But - I couldn't find any significant difference in the transient responses of obviously different sounding condensers.

My conclusion - listening is the final judge.
Measuring can help to track down problems when constructing a mic.

Regards
Kai
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Eric H.

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Re: U47 schematic, component-by-component
« Reply #55 on: January 25, 2011, 04:49:26 pm »

Maybe what I wanted to say is that the requisite to have more info on a mic behaviour is to gather dynamic info vs. static info of either sine waves or pink noise. On the path to the measurements of a mic, there must be something something smarter than sweeping the mic with an HP in front.
Maybe scientist should go back to how hour hearing works to get there. To me that would probably be the most rewarding path.
And we know that our hearing is a comparison machine, and not an absolute one(except maybe some highly trained and specialized people). The only parameter we have more ability to judge absolutely (and it is only for a handful of humans) is the frequency.


Note that I don't know much about measurements, but I do know that to achieve something visually palpable is no picnic.

David, if you have some reference to those paper on new ways to measure microphones, I'd love to know about them.
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eric harizanos

volki

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Re: U47 schematic, component-by-component
« Reply #56 on: January 25, 2011, 04:57:05 pm »

Oliver Archut wrote on Tue, 25 January 2011 05:59

 in a 47 the capsule starts to distort earlier than the electronics (...) My point is that the static value of testing distortion does not take this into account.  


Point well taken - but again, is there anything you can back up your statement with?
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Volker Meitz

Klaus Heyne

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Re: U47 schematic, component-by-component
« Reply #57 on: January 25, 2011, 05:31:03 pm »

Yes, I too would like to know some kind of method, even if it's just empirical, that Oliver uses to isolate capsule distortion from amp distortion.

My best guess would be: it won't be a linear, easily repeatable, method to reliably pinpoint capsule distortion.

For example, if sound waves hitting the membrane are accompanied by strong capsule exertion caused by exhaled breath, that might easily distort the fairly linear swinging process of a diaphragm* sooner than the amp distorting. On the other end of the application spectrum for a microphone, I cannot quite imagine diaphragm distortion with sound sources at great physical distance from the capsule.

* a conventionally constructed capsule- diaphragm swings against a closely spaced polarized backplate - is inherently incapable of a 100% symmetrical, and therefore linear, distortion-free swinging process. The backplate's electrostatic attraction prevents this.
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Klaus Heyne
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David Bock

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Re: U47 schematic, component-by-component
« Reply #58 on: January 25, 2011, 07:32:14 pm »

Quote:

For example, if sound waves hitting the membrane are accompanied by strong capsule exertion caused by exhaled breath, that might easily distort the fairly linear swinging process of a diaphragm* sooner than the amp distorting.
Are you saying LF modulates mid and HF?
@Kai: I wasn't questioning the superior transient response of condensers over dynamics. That is well documented. I was questioning this statement:
"More accurate transient response is one of the reason people will love condenser for example."
Quote:


David, if you have some reference to those paper on new ways to measure microphones, I'd love to know about them.
Can't think of any books but there have been a few AES papers in the last 30 years addressing the subject, but nothing groundbreaking or conclusive. Besides the Peus paper nothing comes to mind as published "new methods".
Jackie Green wrote one that attempted to correlate measurements with adjectives and other verbal descriptors, but it didn't result in a useful, repeatable language. You should read it to see how far they went, for such a non-result.

Oliver Archut

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Re: U47 schematic, component-by-component
« Reply #59 on: January 25, 2011, 08:44:30 pm »

Point well taken - but again, is there anything you can back up your statement with?

Most of the statement are based on my own measurements.

As Klaus pointed it out the polarization voltage is the first problem of nonlinearities with condensers, LDC in particular.
The higher the polarization the earlier the nonlinearities show up. The capsule is bound by design and there are a few parameters that can be changed, but like everything you change one and the rest will change as well.

The membrane material is the 2nd problem, most capsules are not 100% tensioned with reference to dead center of the capsule. There are only a few capsule out of any given series that collapse uniformly when the polarization voltage is pushed up, most capsules need a 5 to 10V window before the entire membrane is collapsed. In my measurements the less uniform the capsule collapses the more the distortion.
Additional the material itself is one factor itself for distortion, as an example a multiple layer membrane will produce less distortion. AKG did a couple of test membranes for Telefunken that were at least 4 individual layers fused/sintered together. The problem this process was to expensive for production so it never reached perfection. At a later point AKG rolled the mylar with a special pattern aside several other production advantages it did reduced the capsule distortion.

Best regards,



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Oliver Archut
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We are so advanced, that we can develop technology that can determine how much damage the earth has taken from the development of that technology.
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