Thanks to all for the explanation.

I was asking this because I have in mind to get 10 or more AOM-5024L-HD-R. See if I have the luck to find matched capsules and then, make a SASS mic. A few more questions:

1- Theoretically, If I use a 32-bit recorder I can boost the signal in DAW with almost no problem using only 1 capsule instead of wiring them in parallel because I can get nearly the same signal later in DAW, right?

2-Is it doable or recommended to wire more than 2 capsules in parallel? For example, let's say I wire 3 capsules in parallel instead of 2, of course, I will put all of them really close to avoid problems with a phase of the audio signal

3-In case I can get matched capsules, I read somewhere I can "manually match" them using a resistor?

4-And lastly: I understand I can apply here the Simple p48 with this kind of mic as is FET based, right?

Thanks to you all again
Cheers

Ari,

I tried to email you offlist, but gmail thinks I am spam and bounced my message. Could you email me offlist?

Thet

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Exactly. Phase combination (cancellation as well as enhancement) is what changes the directivity pattern in a multiple capsule arrangement.

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The concept is that the audio signal from the capsules is correlated and the def noise is not. ?The math part says that adding two capsules gives you a 6dB increase in signal. But the noise only adds 3dB. ?Real world is close. ?The challenge is if the environment is noisy and that is picked up by the capsules, that is correlated between them and is part of the signal. ?

All this is correct, however, one must consider the changes in directivity pattern.
Depending on the physical arrangement (side by side, colinear, back-to-back...) the results may change significantly.
The side-by-side arrangement is the one that gives the best improvement in S/N, but it also results in some narrowing of the pattern at HF, which may or may not be desirable.

Best Regards,

Jules Ryckebusch?

On Jun 8, 2022, at 13:13, a45porhora@... wrote:

?I was trying to find information online but didn't find a good explanation

Reading at??I see Jared use 2 pair of Primo em272 per channel because:

Using 4 capsules lowers the noise floor slightly.?

Also, he mentions his friend? Douglas who did a test



Does anyone know more info about this?

Cheers

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The concept is that the audio signal from the capsules is correlated and the def noise is not. ?The math part says that adding two capsules gives you a 6dB increase in signal. But the noise only adds 3dB. ?Real world is close. ?The challenge is if the environment is noisy and that is picked up by the capsules, that is correlated between them and is part of the signal. ??

I was trying to find information online but didn't find a good explanation

Reading at??I see Jared use 2 pair of Primo em272 per channel because:

Using 4 capsules lowers the noise floor slightly.?

Also, he mentions his friend? Douglas who did a test



Does anyone know more info about this?

Cheers

--

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Maybe I'll make some. Took me ages to figure out how this thing was constructed geometrically. I don’t measure and copy hole patterns when I model capsules, I figure out how the patterns are constructed geometrically and reconstruct them from scratch. K47 and K67 was easy to do that with. This one…not so much. Unlike the k67 where it’s a 12 by 12 grid where the holes are 2mm apart exactly with only the holes inside the bound of the circle drilled, this is a 15 by 17 grid with holes 1.4mm apart, and the rotationally symmetrical drilling pattern is bizarre.

--

There have been third party K47, k67, CK12 capsules etc, but I've never seen someone sell a K103. Would anyone buy one?

latest revision:



Initial layout suggests that the board will be about 40mmx65mm though I will try to make it smaller.

Thickness will be about 15mm because of the capacitor height.

It has to hold 2 pots at a distance where they can be adjusted separately, so it can't be too small anyway.

R1, R4 etc are the source resistors for the fets in the capsules. the capsules are not depicted as they wouldn't be on the board.

As I mentioned earlier it might be desirable to make these trimpots, but that would be bulky. Also remember that we have no access to the gate of the fet, so we can't bias it directly, like in a schoeps, but only by varying the source resistor size.

On 07/06/2022 14:09, Arjay 1949 wrote:

I'm guessing these 'simulation' programs are for the 'obedience of fools and the guidance of wise men' ?...
Listing voltages to 3 decimal places is clearly nonsense. No two 'real world' examples of that same circuit are going to have anything like the same voltages present!
Still, I'm guessing these simulations can give useful 'guidance ' ? - they certainly seem to be popular among some electronic hobbyists.

In this case all the simulator is doing is ohms law, so it is trustworthy - purely for the avoidance of stupid mistakes rather than any great insight. I wouldn't trust it in some more complex scenarios, but it is fine for this. 3 decimal places was just the default for the simulator.

You don't therefore actually need a JFET input op-amp in this case, strictly speaking.? Are there perhaps other op-amps with a lower input impedance - and lower current requirements - that might serve better here?....

yes I have some low current bipolar opamps that would do - but I'd like to leave opamp options open with parts value adjustments as required. The 1642 is so good it is hard to better with lower current even allowing bipolar inputs.

it makes no difference to the basic circuit design though, just the values would change not the topology.

I don't have specs on the fets in the capsules, and indeed they may vary if different capsules are used so I don't know what current they will actually draw - except that I assume it should be under 1ma per capsule.

I'm guessing these 'simulation' programs are for the 'obedience of fools and the guidance of wise men' ?...
Listing voltages to 3 decimal places is clearly nonsense. No two 'real world' examples of that same circuit are going to have anything like the same voltages present!
Still, I'm guessing these simulations can give useful 'guidance ' ? - they certainly seem to be popular among some electronic hobbyists.

I had forgotten that this circuit is not complete, and you have FET 'front ends' that need (presumably) to be calibrated for minimum distortion? (similar to the Schoeps G-S calibration pot?)
That will of course need a regulated supply.
You don't therefore actually need a JFET input op-amp in this case, strictly speaking.? Are there perhaps other op-amps with a lower input impedance - and lower current requirements - that might serve better here?....

OH NO the actual link is this:

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Yes there were some obvious stupid mistakes notably I showed 48v at the XLR pins and worked down from there which is rubbish. sorry it was really just to show the topology.

I have done an improved one checked on a simulator.

and here are just a couple of scenarios in the simulator: both at 2ma with and without the zener.

The opamp regulator may not be necessary, but the 10v one for the capsules certainly is.

The capsules and the opamp plus VG resistors need to draw *exactly* the same current. If they don't then the voltages drift off, sometimes way off. That might be ok for the opamp, but the capsules voltage needs to be kept below 10v and not too low either.

The zener on the 9/10v supply dynamically takes up the variable difference in the current drawn by the opamp and that drawn by the capsules.

Reducing the 10k feed resistors allows better zener regulation yes. As you can see from the simulations I might be able to do away with the opamp zener - though not the 10v one.

I'm not sure if a varying supply voltage with signal has other adverse effects on an opamp other than variable headroom.

With 10k supply resistors and no regulation on the opamp part of the supply the opamp power voltage varies from 15v at 2ma right down to 6v at 3ma.

With 5k supply resistors the resistors the opamp power voltage varies from 20v at 2ma down to 12v at 3ma.

with a zener on the opamp supply and 5k supply resistors (as per the full schem above) the opamp power voltage varies from 13.6v at 2ma down to 11.6v at 3ma - the small difference being caused only by the filter resistor R7.

This is more challenging than a schoeps zenerless circuit because in a schoeps the (average) current is constant in both sections (class A) wheras in this one the opamp current varies with signal.

I don't know how much extra current it needs with signal - I think it may be quiescent plus however much it delivers to the load. Very roughly, if the opamp were to produce 2v rms into a 2k load that would be 1ma extra. More to allow for not being 100% efficient. That might be a worst case scenario since the output level wouldn't be that high. Anyway it seems 2ma and 3ma are reasonable test conditions for one opamp.