Mavis Prima MPA-81s is a very nice donor mic platform

[micolas]

@AdamFrisen ,
Draw on a piece of paper the physical correspondence between the wires of the two capsules:
MPA-81 and Arienne K47Flat.
Then retry the correct connection again.
*
You can also measure, check if there is electric continuity between the diaphragms and the backplate.

 

[Wordsushi]

View attachment MPA-81s-FlatK47-OnAxis-OffAxis.wav
On axis and off axis with flat k47

My mic came wired with the front and back capsule connections soldered to F and R on the top right of the PCB respectively. And the blue wire to backplate. All of which I replicated when I put the Flat k47 in there.

There were a bunch of BFL V47's that did leave the factory wired with reversed polarity and pins 2 and 3 reversed. I noticed it in mine and also the V47s of at least 3 other people whose samples I heard. I let BFL know and they fixed the problem, which was not present in an updated V47 they sent me. I can say with certainty that my MPA 81s arrived with the polarity correct.

 

[micolas]

View attachment 132221
On axis and off axis with flat k47

My mic came wired with the front and back capsule connections soldered to F and R on the top right of the PCB respectively. And the blue wire to backplate. All of which I replicated when I put the Flat k47 in there.

There were a bunch of BFL V47's that did leave the factory wired with reversed polarity and pins 2 and 3 reversed. I noticed it in mine and also the V47s of at least 3 other people whose samples I heard. I let BFL know and they fixed the problem, which was not present in an updated V47 they sent me. I can say with certainty that my MPA 81s arrived with the polarity correct.

@Wordsushi ,
You did the test in an acoustically untreated room. It is felt that due to the reflections at 90° and 180° sufficient attenuation is not obtained.
(maybe in a hotel in Hawaii?)

 

[Wordsushi]

View attachment MPA-81s-K47-Axis test - Desk.wav
Here is on/off axis test from my desk in my office. Sadly, I'm back home from Hawaii.

 

[AdamFrisen]

Thanks Wordsushi for the info about the wires and in your recordings I hear attenuations from 90 degrees and 180 degrees off-axis clearly.

I expected the sound from the rear capsule in cardioid mode would sound much less than from 90 degrees off-axis.

I myself am unfortunately not in a nice hotel in Hawaii .
Just basic acoustic treatment on the back wall using t.akustik wall absorber.

But as I was hearing in your Youtube video, changing the capsule to Arienne K47 flat was all worth it and more.

I will try with another body and fit in one of the U87 ORS circuit without de-emphasis with a K47 flat as well.

 

[Khron]

U87 ORS circuit without de-emphasi

"Technically", FET847 then...

 

[AdamFrisen]

@micolas

More pictures of MPA-81s capsule. I was being very gentle with it so it was in this state inside the microphone.

 

[micolas]

@micolas

More pictures of MPA-81s capsule. I was being very gentle with it so it was in this state inside the microphone.

View attachment 132254

View attachment 132255

View attachment 132256

Thanks for the detailed pictures. I'm sure I've seen similar capsules on Ali...
But with good sounding Takstar,797,3U capsules, and others more from Ali...purchased over time, plus a few dozen microphones, I think I need to take some GAS pills.

 

[AdamFrisen]

View attachment 132230
Here is on/off axis test from my desk in my office. Sadly, I'm back home from Hawaii.

It looks like in the cardioid mode, the sound is rejected less than 90 degrees off-axis at the rear?

Reading about polar patterns: https://www.soundguys.com/how-to-read-a-polar-pattern-chart-16272/

The mic/capsule could be super- or hypercardiod?

 

[micolas]

It looks like in the cardioid mode, the sound is rejected less than 90 degrees off-axis at the rear?

Reading about polar patterns: https://www.soundguys.com/how-to-read-a-polar-pattern-chart-16272/

The mic/capsule could be super- or hypercardiod?


View attachment 132259

There could be something wrong with the tension on the rear diaphragm in different patterns, or maybe even with the physical construction of the capsule.
But the specificity of the capsule construction is decisive in the behavior of different patterns.

Edit: I was speculating thinking about the MPA-81 capsule.

 

[AdamFrisen]

There could be something wrong with the tension on the rear diaphragm in different patterns, or maybe even with the physical construction of the capsule.

So it is the capsule itself being primarily responsible for the characteristics of a certain polar pattern?

As Wordsushi's and also mine K47 flat capsule show similar and much less pronounced cardioid polar pattern, it could be by design?

 

[micolas]

So it is the capsule itself being primarily responsible for the characteristics of a certain polar pattern?

As Wordsushi's and also mine K47 flat capsule show similar and much less pronounced cardioid polar pattern, it could be by design?

In addition to the intrinsic parameters, characteristics, of the capsule, the applied voltages (or lack thereof) determine the spatial behavior, the polar pattern. Consider that some microphones (for example the Rode K2) have a continuous variation between the main polar patterns, which is achieved by the variation of the applied voltage.

 

[jeremynothman]

K47s are renown for having a "cardioid" pattern that is closer to Hypercardioid, but I'm sure @soliloqueen can chime in about that, but hearing the recordings, i'm still surprised!

According to Recording Hacks
"Martin Schneider

The standard K47/49, just like the M7 is an in-between capsule. Cardioid somewhere below 1kHz, super/hypercardioid the higher you go. That’s the way the capsule came out of the design process in 1935. And that’s why the manual for U47fet said ‘supercardioid’."

 

[micolas]

K47s are renown for having a "cardioid" pattern that is closer to Hypercardioid, but I'm sure @soliloqueen can chime in about that, but hearing the recordings, i'm still surprised!

According to Recording Hacks
"Martin Schneider

The standard K47/49, just like the M7 is an in-between capsule. Cardioid somewhere below 1kHz, super/hypercardioid the higher you go. That’s the way the capsule came out of the design process in 1935. And that’s why the manual for U47fet said ‘supercardioid’."

Yes, that's right, K47 has a toward hypercardioid behavior

 

[AdamFrisen]

Ok, that makes sense it's hypercardioid with the observations. Thanks.

https://www.syncoaudio.com/blogs/news/hypercardioid-microphone-explained

 

[micolas]

Is it an exaggeration to think that due to the tendency towards hypercardioid and the collection of more spatial informations, microphones with K47 are often described by some as having 3D properties?

 

[Paul W]

Yes, that's right, K47 has a toward hypercardioid behavior

I seem to recall Arienne saying that the flat 47's polar pattern is somewhere in between that and plain cardioid, so only a little super.

 

[VanguardAudioLabs]

There are quite a few knowledgeable people here whom do advanced stuff with capsules and mics in general. Quite a few with direct connections to OEM manufacturers whom make all these capsules for, among others, Telefunken.

I, for example, measure all imaginable aspects of all the capsules i can get my hands on. I also modify them.

The reason i asked about your capsule, is because i dare to say i know exactly where it comes from, and how different it could be to other, widely available inexpensive capsules on the market.

What Gyraf alluded to is that there are now way too many mic "manufacturers" whom claim their version of these OEM capsules are special, each in their own respect, without providing any kind of hard evidence for it.

I would personally like to experience your unique capsule myself, and take a look at it, however i am not in a situation to buy one of your mics.

What i can offer is detailed measurements of your model, comparisons against stock OEM capsule which looks exactly like yours, and publish results. I will happily send the capsule back to you upon examination.

I have offered this to many mic manufacturers, only one accepted it, and it turned out extremely well for them. As for the others, most of these mics end up on my bench anyways, so i get to put them to the test sooner or later.

If you are interested, feel free to drop me a DM.

Edit:
As usual, it gets pretty quiet after this kind of proposal.

Apologies, I don't check these forums often.

I'd be interested in this although I have a few questions about it. I will DM you.

When you say "Quite a few with direct connections to OEM manufacturers" I will give you a 'grain of salt' story from my Avantone days. Ken being gone now, I'd set the record straight on something. We have all the original drawings for the Avantone BV-1 (I guess what the new owner calls the "first generation") that he worked on for several years and talked to several OEM/ODMs about manufacturing. I've still got them on my drive on this computer, in fact. The manufacturer he finally ended up going with ended up taking the design and selling it to T-Bone (Thomann), ART, and a few others before we even got our first shipment - which they had stored improperly and had all sorts of corrosion issues for the metal parts, at which point they accused us of running "saltwater testing" on all our metalwork.

It was a nightmare. To this day, that manufacturer insists that it was "their design". Ken never sent any NNN agreements or anything of the sort to manufacturers, and several things got lifted over the years and it always caused problems.

EDIT: can you DM me? I cannot for the life of me figure out how to send you a DM.

 

[micolas]

I seem to recall Arienne saying that the flat 47's polar pattern is somewhere in between that and plain cardioid, so only a little super.

I meant a normal K47 capsule, not the Arienne K47F
That's why I posted the FR for the Neumann U47/48

 

[VanguardAudioLabs]

I put the red wire from the center of one side of the capsule to pad on the circuit board with letter 'F'. The white wire from the center of the other side of the capsule to the pad with letter 'B', The blue wire in the picture was connected to the side of the capsule so I attached that to the side of the new capsule as well.

given that i still have the files for that PCB design they lifted - yep, F is front and R is rear.

Replacing the MKS2-series WIMAs with MKP2s (and upping the C3/C4 ones to .22/250V) will yield a much better result.

One funny thing they goofed was the placement of the F/R capsule connections in regards to the chassis rails. Those full-bend rails (that's what i call them anyways) take away what i consider valuable PCB real estate, I've always avoided those.

Since F is grounded it's less of an issue in theory, but in practice can give some grief in assembly - thus their "green tape" solution.

At least they didn't keep my memoriam note to Marty, or the Tom Petty lyrics on the inside of the rear PCB, or i would have been even more miffed.