I see a couple of schems in the files area that show the neutrik NTE-4 used in mic circuits.

has anyone got any advice or experience about using that line of tiny neutrik transformers in mics regarding quality or level handling and so on?

I'm planning to try an opamp circuit with a NTE-1? (1:1)? There's also a NTE10/3 which could be good for something.

However they are so small and inexpensive I am sceptical about the likely quality.

Hey all. We're wrapping up development on the K67 capsule here, and since we're doing everything from scratch, I figured I might pick a color for the plastic ring other than white or ivory. I want something distinctive, but that still sort of scratches that ivory itch, isn't too ostentatious etc. Do you think people would go for something like this?

so I looked up the KM-88, interestingly it had a removable capsule with a 4 pin connector. looks like you needed a screwdriver to change capsules though...

Come to think of it you could make a 3 wire connector for a SCD capsule using an XLR plug.

But still finding a SDC capsule that had both diaphragm and backplate isolated from the housing would be impossible.

On 16/06/2022 14:14, henryspragens@... wrote:

So nearly all electrets and SDCs have the diaphragm connected to the body or outer shell.

yes, I stated this wrongly in my OP, assuming that it was the backplate that was connected to the outer shell.

It makes no difference to the main issue though.

Since a typical electret has an effective polarization of over 100V

I had wondered what level of polarisation electrets had, that explains why some are more sensitive than I had expected.

the objective for many mic hobbyists is adding new "flavors" of mics to your recording arsenal, so keep experimenting.

That is indeed my objective. Although I already have quite a few flavours the available parts tend to push one towards certain well-trodden paths. I'm now trying to diversify the sounds available, without actually increasing the (very large) number of finished mics I have.

I've yet to hear an electret that really excited me, although some are very functional and useful.

I wish there were more larger sized pure pressure (omni) capsules around, and more small capsules that don't have a built in fet and that can easily be mounted without grounding.

The one exception is a 35mm electret made a few years ago with metal diaphragm and K67 backplate

hmm what was this, are they still available?

Jerry pretty much covered the impedance angle. Tube mics typically used to use 100 Mohm resistors because grid current was too high for 1 Gohms, but noise was higher than in modern FETs too.

There are 2 common ways to make a connection to the diaphragm of a capsule.
In Small Diameter Capsules (SDCs) and Large Diameter Capsules (LDCs) with edge termination, the diaphragm is clamped to the body of the capsule. The backplate is insulated, nearly always with a plastic outer ring, and the connection to the backplate is made with a screw through the center at the back of the capsule. In the case of C12 style LDCs, the backplates are visible at the side of the capsule, and are drilled for screws to make connection for backplates. So nearly all electrets and SDCs have the diaphragm connected to the body or outer shell. In a pencil style mic where the capsule is screwed onto the body sleeve, the diaphragm is therefore grounded because of the way the capsule is built. In a larger body with a SDC, for instance the MXL 990, 770, etc. a plastic insulated capsule holder can be used, so the capsule body and diaphragm can be charged with a polarizing voltage. So: small diameter mic requires 2 large resistors and a coupling cap to separate the signal from the polarizing voltage since one side of the capsule is grounded.

The other way to make a connection to the diaphragm is to leave an insulating ring of un-sputtered (no gold) plastic around the edge of the diaphragm, and make contact via a screw in the center, Neumann style. In that case, the diaphragm is insulated from the capsule body and it's possible if the capsule mount is insulated to take signal from one side and polarize the other. Center termination just won't work with a small diaphragm.

A 3-terminal SDC could be built, but it would be fiddly and expensive. Probably would be prone to insulation leakage problems because of small gaps between parts. I can't think of an example. There have been 3 and 4-ring terminal SDCs but they have had the JFET inside the capsule, and the "extra" ring contacts were for power and polarization.

?I've been trying to figure out how to connect to the innards of an electret through the side of the capsule instead of a screw through the back. It's mechanically very difficult unless you build it like a C12. I'd like to have a dual-sided edge terminated electret, essentially an electret RK-12. Since a typical electret has an effective polarization of over 100V, it should make a very low noise capsule. On the other hand, a 34mm electret may put too much tension on the diaphragm to allow a C12 tuning. All the 34mm electrets I've tried are tuned a bit low, and fall off before 10KHz. They're good for vocal mics, but lack the famous "air" of AKG's LDCs. The one exception is a 35mm electret made a few years ago with metal diaphragm and K67 backplate. It doesn't sound like my other mics. Reminds me of a KM-88 which also has nickel diaphragms. After you get over the excitement of building a working microphone yourself, the objective for many mic hobbyists is adding new "flavors" of mics to your recording arsenal, so keep experimenting.

Thanks Jerry! That confirms what I thought but wasn't sure.

Are there any effects on frequency response or transient handling, or any other sound quality issues?

It seems odd to me that Neumann or AKG haven't made a 3 contact removable capsule system - they love over-engineering stuff and this seem to have more justification than many of their complex design decisions.

As others have said, yes they are true condensers.

PCBway do 5 pieces by default. Still very cheap. The quality is excellent. The PCB job configuration options are a little confusing, but if you stick with the default option where it asks about panellised boards, you'll get nicely cut out separate boards.

You will need both the and the boards.?

You will also want a saddle to sit your capsule in (e.g.?). However I've recently found that plastic 32mm pipe clips from hardware stores work rather well with a bit of electrical tape around the top edge to hold the capsule in and some double-sided sticky foam strip to affix to the mic body mount. Just be very careful when you fit it not to touch the membrane!

The capsules are very treble heavy. I'm personally getting good bass response with mine. I trim the treble and boost the bass in the mixer eq rather than do any filtering in the mic.

Le 16/06/2022 à 12:09, thet a écrit?:

There are two scenarios for connecting a single sided capsule with external polarisation.

1. In a typical LDC you would normally connect one side of the capsule to the polarisation voltage and take signal from the other side. Neither side is DC grounded, although the polarised side is at AC ground.

2. In most SDC mics the backplate is grounded through the body and you have to apply polarisation voltage to the signal side of the capsule.

This requires a second 1G resistor and a blocking cap.

It lowers the input impedance of the headmp to 500M instead of 1G and puts an extra capacitor in the signal path.

So it seems like an obviously inferior arrangement.

So why do people do it? Why not make the effort for SDCs to have a 3 contact connection for removable capsules.

Probably a matter of tooling.

Would using 2G resistors in both positions help or cause other problems?

Yes. There are a few examples that use higher values. Although with higher values, the circuit becomes extremely vulnerable to moisture. FET gate leakage may also be an issue.

Does it even matter that much? If it doesn't matter why not use 500M resistors in scenario 1?

It does. The perceived noise level is proportional to the cut-off frequency of the HPF constituted by the capsule capacitance and the gate and bias resistors in parallels.

My motivation for asking is that I'm building a mic where I have a choice between making the capsules interchangeable but using a #2 polarisation scheme, or fixing the one capsule in place with a #1 polarisation scheme.

There are two scenarios for connecting a single sided capsule with external polarisation.

1. In a typical LDC you would normally connect one side of the capsule to the polarisation voltage and take signal from the other side. Neither side is DC grounded, although the polarised side is at AC ground.

2. In most SDC mics the backplate is grounded through the body and you have to apply polarisation voltage to the signal side of the capsule.

This requires a second 1G resistor and a blocking cap.

It lowers the input impedance of the headmp to 500M instead of 1G and puts an extra capacitor in the signal path.

So it seems like an obviously inferior arrangement.

So why do people do it? Why not make the effort for SDCs to have a 3 contact connection for removable capsules.

Would using 2G resistors in both positions help or cause other problems?

Does it even matter that much? If it doesn't matter why not use 500M resistors in scenario 1?

My motivation for asking is that I'm building a mic where I have a choice between making the capsules interchangeable but using a #2 polarisation scheme, or fixing the one capsule in place with a #1 polarisation scheme.

Ok I'm not sure if this should be a new thread, as it is not about a TSB2555

It is relevant to padding in general and to drum mics though.

Yesterday I received a new batch of PCBs including a version of my single opamp mic board. I assembled a mic using one of those 25mm (20mm membrane dia) chunky brass electret capsules, and ran the opamp at 13v (+/- 6.5v)

The mic is really clean and crisp sounding. Pic is here:

I tried it in a tom, and the output was waaay too high for the mic preamp. With the 20dB pad engaged on the mic pre I could mostly avoid clipping if I didn't play too loud.

I also tried some other condenser mics.

All the other mics I tried clipped internally if used on a tom without an internal pad - however the opamp mic did not clip internally - which is not surprising since the headroom in the circuit is much higher than in most mics.

The issue was purely excessive output level.

This suggests to me that capacitative padding at the input of an opamp mic may not be the only or best way to make it compatible with close micing drums.

The next things I am going to try are:

1. connecting the mic to a line level input (I will have to rig some phantom power though, and that means more caps in the signal chain)

2. using an alternate version of the opamp pcb that I also received yesterday that allows a transformer output. This was intended for a 1:1 transformer, but if I were to use a stepdown transformer that would act as an output pad, and just possibly do something nice to the drum transients.

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You will have to add components to the PCB’s. Good luck! If you need help we are here.?

Capsules arrived.
Are these true condenser type?

They look like typical Chinese K67 style capsules.

You will want to implement some aggressive high-frequency rolloff in the circuit to correct the response of these capsules. Otherwise the microphones will (most likely) have a harsh top end.

You will also want to test the low frequency response. Many cheap K67s are thin below 300 Hz.?

1st time on pcbway, they do 5 pcs by default?

I believe 5 pieces is the minimum.?

?Do they include the components with the pcb?

Board houses rarely supply components. Components are definitely not included in the cost of manufacturing the PCB.?

—
matt.

Capsules arrived.?
Are these true condenser type?
I was thinking going the pcbway and buy your pcb's, the Dual Alice and the Hex Inverter.?
1st time on pcbway, they do 5 pcs by default? Do they include the components with the pcb?
I am using single capsule per microphone.?
Thanks for your work!

--

ok, the picture turned out pretty small, try it now as a pdf

the cap values are 0, 100pF and 270pF?

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Thank you!!!! This is great?

I measured the freq-response of a mic with Jules OPA circuit, TSB2555 and different values of the pad cap.

As Jules said above, I made some mics with a switch, but I also made some with headers (is this the right english term?) so I can change the caps pretty easy and experiment with different values and types.

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I love the simpleP48. As Roger mentions the downside is the case is not at ground potential. ?Checkout out files area for R values of the various capsules we have tried. ?I’ve done the EM200. I have some 204’s but don’t like them as much as the 200’s most of my builds with the this circuit are AOM 5024’s and TSB 2590’s?

Further to my post above, I should mention that if you need to interface an unbalanced electret - as used with TRS mini jacks for? PIP inputs - then I've found works well.

Not balanced of course, but quite usable with PIP 2 terminal electrets, connected with a screened cable, and a 3.5mm jack plug (....and 'shortish' cable runs? - say 5m or less)

Commercial versions of that type of interface are available - like this one:?https://rode.com/en/accessories/adaptors-cables/vxlr-plus