C800G

[dukasound]

Hi
We started to talking about PSU. Jakob sent us one pic.
We know that Sony used tube rectifier.
If anybody have a schematic to disscus about it.
Why two tubes?
How stabilize heaters voltage (LM317T)?
How much RC circuit?
Choke?
Thanks
Duka

 

[Marik]

[quote author="Tim Campbell"]

Marik, I haven't seen anywhere that reducing the resistance in this network would increase mids. [/quote]

Tim,

The main reason for acoustical resistance is damping of tuning resonance of the diaphragm. Let's have two extremes.
1) capsule with no acoustical resistance
2) capsule with max (or optimum) acoustical resistance.

In 1) we have max boost at resonance point
In 2) flattest response

Anything in between, will show boost of midrange. I found these graths in "The Microphone Book", by John Eargle, p.77.

 

[Marik]

[quote author="Tim Campbell"]Thanks Marik,
But acoustical resistance as you describe and a phase resistive network are not exactly the same.

A capsule with no sound reaching the back of the membrane is an omni capsule.
A capsule with equal amounts of sound reaching both sides of the membrane is a figure 8.
A capsule with a strong signal reaching the front of the membrane and a weak signal (because the sound has passed through a network that reduces it's velocity) is a cardiod.

A phase resistive network doesn't play as big a part in the tuning of the membrane as the design of the rest of the backplate and if the capsule itself is sealed.

An Omni version of a capsule ( a capsule with an infinite amount of resistance on the sound reaching the back of the membrane) doesn't exhibit a scooped midrange or more noise than a cardiod version of the same capsule.

The resistance as I understand it that you're describing is the back pressure exherted on the membrane by trapped air between the backplate and membrane.[/quote]

Tim,

Probably there is something that I am missing--I just cannot find it at the moment. My understanding is that an equation for acoustical loading of the diaphragm involves two parameters-- R and C, where R is an acoustical resistance, and C is a trapped volume of air between diaphragms, which also forms a phase network. If you increase value of R, C should be decreased and vs. versa.
I think that is what happens in M7, which is a thinner capsule, so the absolute value of C is bigger and thus the value of R can be made smaller (or more "primitive"). Since, as I wrote before, C also affects a phase network, smaller volume creates less phase artifacts.

Does it make any sense?

 

[dukasound]

Does anyone read on page 3 about PSU questions?
Duka

 

[Flatpicker]

...I only wish someone with more experience than us ( Josephson, Shoeps, Neumann) would pipe in here...

We could always send them an email with links to The Lab and this thread and ask if they are intrested. Never hurts to ask. (Well, almost never... :wink: )

 

[Gus]

I was also thinking of enlarging the holes that connect to the center chamber made by the washer in a neumann style capsule capsule backplates in stock postion .

I think I have some number 70 drills...................

 

[Marik]

Dear Tim,

There is one detail though, I forgot to mention, which as I see it now, is very important. The value of C, I mentioned is a COMPLIANCE of enclosed air volume. I need sometime to think about some things, though. I will get back later.

 

[Marik]

BTW,

Jacob, how about splitting this thread for C800 part and mic capsule one, so the microphone questions would not get burried?

 

[zebra50]

[quote author="Marik"]BTW,

Jacob, how about splitting this thread for C800 part and mic capsule one, so the microphone questions would not get burried?[/quote]

Marik,
Good thinking. I can put two links in from the microphone META unde capsule and C800.
Stewart

 

[Marik]

[quote author="Tim Campbell"]Thanks Marik,
But acoustical resistance as you describe and a phase resistive network are not exactly the same.

A capsule with no sound reaching the back of the membrane is an omni capsule.
A capsule with equal amounts of sound reaching both sides of the membrane is a figure 8.
A capsule with a strong signal reaching the front of the membrane and a weak signal (because the sound has passed through a network that reduces it's velocity) is a cardiod.

A phase resistive network doesn't play as big a part in the tuning of the membrane as the design of the rest of the backplate and if the capsule itself is sealed.

An Omni version of a capsule ( a capsule with an infinite amount of resistance on the sound reaching the back of the membrane) doesn't exhibit a scooped midrange or more noise than a cardiod version of the same capsule.

The resistance as I understand it that you're describing is the back pressure exherted on the membrane by trapped air between the backplate and membrane.[/quote]

Tim,

I am not sure I understand exactly what do you mean here. In dual diaphragm capsules different patterns of the mic are just an electrical summing of two outputs with different polarities and amount of polarization voltage on each half of the capsule, and I don't see how it affects acoustical arrangement of the capsule.

>You're leaving out the fact that the membrane itself has a resistance. It's tuned and if you've ever touched a membrane you'd realize it pretty stiff. Also the air does not constitute a resistive network by itself.<

The diaphragm resistance is a mere function of its tuning at midband, where below tuning point it is stiffness controlled, and above--mass controlled. The acoustical resistance equalizes these two different systems of operation, and, in some sense, reminds me negative feedback. More resistance--less sensitivity--flatter response, meaning that midrange is damped, but the resistance (stiffness) of the diaphragm itself, as opposed to acoustical resistance, remains constant.

>The M7's resistive network is the group of very small holes drilled directly through the backplate so that vibrations can pass from one side of the capsule through these holes to the other. They restrict the velocity of vibrations only by their small size.<

The compliance of the trapped air volume here is determined by viscousity of the air in the holes and since the capsule is thinner, by smaller amount of trapped air.

>The amount of change we're talking about making to the resistive network (allowing 10 holes to pass directly through from one membrane to the other) may change the midrange slightly but it's effect on smear/phase, pickup pattern and off axis frequency response would be far greater and probably mask the change if any in the midrange.<

May be. I don't think pickup pattern change will be THAT noticable. On the other hand, less effect on "smear/phase" does not contradict change of midrange. But it might be just my speculation. By the end of this week I will get back nice book-- "Microphones" by Robertson. I think I saw there something about it. I will check then.

>Remember, we're not talking about adding any new holes or changing the volume of air in the capsule or retensioning the diaphram.<

As I wrote in my previous message, the most important factor here is the compliance of trapped air, and it seems that different hole orientation changes it quite a bit.

 

[dukasound]

Hi
Please, I like a story and proceeding about capsules but, when we will return to C800G questions?.
Duka

 

[Marik]

[quote author="Tim Campbell"]The use of dampning on the membrane by trapped air has been grossly overstated in almost everything I've read. For example I have a beautiful sounding U47 fet cardiod only mic on my bench right now. I'm torn as to what I should do about this mic. It sounds wonderful but by your rational it should sound terrible. The mic has a 1mm square hole in the back membrane. Since the capsule is cardiod only it doesn't use this membrane electrically ,only for dampning. Air is not trapped within the capsule any longer and so cannot dampen the front membrane. [/quote]

Dear Tim,

I hear you. I am myself have been using one side of K67 capsule with a little hole in it, for years. The other side has a wrinkle. It still sounds beautiful.
I guess at this point the most important thing is to go to bench and start experimenting... I am still waiting for bits, precision vise, parallels, and rotary table for my new milling machine. So hopefully I will start soon.
I am thinking of making much smaller holes, but larger number of them--something that would be much harder and expensive to do in commercial design.

On the other hand, I am fascinated with Pearl PP capsules design. Guessing from the front look of the capsule, the back plate should have the same shape and size. If so, there is no other acoustical resistance applied to the diaphragm, than this of trapped air volume.
Huh, is it too much???

 

[Marik]

[quote author="dukasound"]Hi
Please, I like a story and proceeding about capsules but, when we will return to C800G questions?.
Duka[/quote]

Duka,

It is hard to discuss original C800G PSU without seeing its schematics, and it doesn't seem anybody here has it. You could use C37 circuit here as it is. If you want to use a tube rectifier for B+ and regulated heater, you could combine these parts of C37 and Gus' circuit. Just ask specific question.

 

[dukasound]

Duka,

It is hard to discuss original C800G PSU without seeing its schematics, and it doesn't seem anybody here has it. You could use C37 circuit here as it is. If you want to use a tube rectifier for B+ and regulated heater, you could combine these parts of C37 and Gus' circuit. Just ask specific question.[/quote]

Hi Marik
OK, I have a C37 schematic but I wanna make a stabilized voltage for heaters and B+ like on standard tube microphone PSU but with tube rectifier (or like in C37 maybe). If I use 250V-0-250V AC and 6X4 possible with choke input and than use a bigger caps I think that would be better solution.
Two or four caps is a question?
In original C800G PSU I saw two tubes?
In any case thanks for reply.
Duka

 

[Marik]

Last night I did some experiments and spent about 4 hours listening back and forth between rotated and stock Chinese 6um cardioid capsules. My initial response was WOW!--such a difference!! Mid-frequencies were so much clearer! After first shock was over, little by little I started paying attention at obvious lack of HF in rotated one, so I started playing with EQ, equalizing stock capsule, trying to make it sound identical. Finally, I ended up with HF EQ at -9:30, and MF at +3:00. Then I tried opposite EQ for rotated, and flat for stock. In both cases capsules sounded fairly similar, with the difference that rotated was more clean and clear. I tested it with close micing, where polar pattern does not affect the results in significant way.
I think this shows that both--I and Tim were right.
1)The compliance of enclosed air volume has a lot to do with diaphragm's damping and thus, frequency response.
2)The phase/smear has a lot to do with quality of the sound.

There is probably something I missed. Any ideas?

 

[Gus]

Marik

thanks for the feedback testing the capsule mod.

Might we want a capsule skin tuned higher than the stock tuning?

Has anyone else tried this?

 

[Gus]

Does anyone know what the screw sizes are in the china microphone capsule. The reason I ask I want to take two of the backplates and drill and tap them for the 10 hole pattern.

Marik, Tim I did not note a loss of highs with the two capsule I rotated. I will go back and check again.

This is a fun place!!!!!

 

[Marik]

>Now this lack of high end was it on or off axis? If you took a look at the M7's frequency response you'll see that above 8khz the top end's polar pattern becomes extremely narrow. Does the original capsule have a peak or lift in the top end? At what frequency? Could this lack of top simply be a reduction of this lift? A U89 sounds very dull compared to a U87 but in fact it's frequency response is flatter. Once our ears hear something bright everything less bright sounds dull.<

Tim,

I tested it on-axis with close micing. In fact, I compared it to M7 in my UM70, but I payed attention that both its sides are different, so I have to check what is the problem, first. Also, the electronics and grill are different, so it is not a fair comparison.
Right now we have visitors untill the end of this week. After that I will run and record all of the tests with pink noise, and see on spectrum analizer what ACTUALLY is going on.

>Have you tried achieving the same effect by placing thicker spacing matierial between the two halfs of the capsule as you mentioned before?<

No, not yet, but I will. There is one, as I think, very important detail. The K67's spacer between backplates has a slot, so it is not an "O", like this of Chinese capsule, but "C". Isn't it for "capsule breathing", Oliver Archut mentioned on Klause's forum? I will definitely try to do the same for Chinese capsule spacer. Also, I need to check if the thickness of Chinese spacer is the same as of K67.

Meanwhile, I got back "Microphones" by Robertson, and "Elements of Acoustical Engineering" by Harry Olson, so I gotta do some homework.

Gus,

I will measure the screws later tonight. And please report back your second listening impression. BTW, did you pay attention that the output was noticably higher?

 

[Marik]

[quote author="Gus"]Does anyone know what the screw sizes are in the china microphone capsule. The reason I ask I want to take two of the backplates and drill and tap them for the 10 hole pattern.
[/quote]

Gus,

My digital caliper shows 1.35 mm (0.0535") diameter.

 

[dukasound]

Hi Gus
Is it IT?????
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