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You can do the "Jerry Lee Marcel" mod. Check Stefano's or Ricardo's files. It will reduce sensitivity by about 10dB and about 15dB more max SPL, with a 2.2k resistor.
But you need to make the 3-wire "Linkwitz" mod.

You can also drop the value of the drain resistor. Output level is directly proportional to the drain resistor value. However, this will not increase the max SPL.

I apologize for not being more specific about the capsule type and microphone circuit. I need to reduce the sensitivity of the Primo EM200 capsule in the KM84 circuit. I have a working microphone, but it is very sensitive for "normal" studio use.

I don't know if I understand correctly from the mentioned documents, can I achieve the sensitivity reduction by adding an RC link between drain and source?

Also, do I understand correctly that the EM200 is a three cable capsule, so there is no need to do the linkwitz mod?

Do you have a resistor between drain and source?
Primo recommend 5.6KOhm but you can adjust that value to change the sensitivity.
Cheers
Jack

Here is my actual schematic:
/g/MicBuilders/message/32232

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One of the challenges here is that this methodology lowers the voltage out of the FET ?it may reduce output but not headroom/maxSPL ? Ideally we want to lower the signal going into the Fet. ?It’s easy with a fetless capsule. Not sure the best methodology for one with built in FET?

On Sun, Jan 7, 2024 at 08:37 PM, jack wrote:

Primo recommend 5.6KOhm but you can adjust that value to change the sensitivity.

Increasing this resistor would not change the sensitivity if the capacitor is still there. It would just decrease headroom.

On Sun, Jan 7, 2024 at 08:26 PM, <mildavaca@...> wrote:

Also, do I understand correctly that the EM200 is a three cable capsule, so there is no need to do the linkwitz mod?

That's right, you don't need to do the mod.
Just remove the 22uF capacitor across the 5k6 resistor.

I've got this problem also, but with a two-wire Primo em258 capsule — since I believe drain and ground are already connected inside the capsule, is there another way to reduce the sensitivity, or is that an impossibility for such a capsule?

Here's the diagram from the em258 spec sheet:

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Have you tried recreasing the resistor ?

1kohm should reduce level by 6dB, 620 ohms by 10dB, and so on.

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"decreasing", not recreasing.

You can reduce gain of the internal jfet to unity if you disconnect capsule gnd from ground and instead connect it directly to capsule drain.
That way you make it a charge amp just like the km84, just with lower gain (unity).
This works the same way as the simplep48RCA.?
This also works very well for reducing gain of pip mics, by the way.
This works only with 3 wire or linkwitzed capsules.
I wish had figured this out in the old days when I went out and recorded live concerts...

Jerry Lee Marcel:

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Jerry Lee Marcel:

>Have you tried decreasing the resistor ?

>1kohm should reduce level by 6dB, 620 ohms by 10dB, and so on.

The drain resistor also sets the dc operating point of the inbuilt JFET transistor.

There is only one optimum value of that resistor that nets you reasonably symmetrical?

clipping at high spl levels from the jfet.

That would matter if the voltage source was a stiff one, but in most cases it has some resistance, which tends to average teh bias point.
It is always possible, when teh optimal combination of voltage AND resistance, to split teh resistance in two and bypass their junction point with a capacitor of suitabe value.

In fact that resistor should be adjusted individually for each capsule for symmetrical?

clipping at high spl?level and not be changed at all for other reasons.

That's true, but the values indicated in teh datasheet seem to work reasonably well without adjustment.

If that resistor is adjusted to decrease the gain of the JFET then the?dc operating point is

wrong that the clipping point is severely affected to become highly asymmetrical clipping?

on one side of the output signal only.

"Severely" is debatable.

is there another way to reduce the sensitivity, ...?
_______________________________________

While I believe this was mentioned previously, ... I generally use an L or T attenuation pad made from appropriate value resistors. I make a simple L pad circuit to attenuate hot computer type electret condenser capsules so they better match and seem like a dynamic cartridge to amateur radio transceivers - which tames hot condenser capsules so they do not overload and leave plenty of headroom for adjusting volume, EQ settings, etc.

Just my take ... James

Is "recreasing" the opposite of "inducing"?? :)

-Scott

--
---- Scott Helmke ---- scott@... ---- (734) 604-9340 ----
"I have ceased distinguishing between the religious and the secular,
for everything is holy" - Joe Henry

As per James, I'm wondering about this too - whether the ones posing the question are trying to raise the max possible sound pressure level they can accommodate (ie their mic is being overloaded by desired sounds), or that they're simply finding the mic's output too hot compared to their other mics (eg overloading their preamps).

Zander, can you tell us what circuit will use with the EM258?? What recorder?? What recording situation etc?

The 'best' solution to your problem depend on these.

IMHO, the options are

• convert to a charge amp as from page 10 of simpleP48.pdf? You need to get at the Gate & Drain of the internal FET
• Rene's solution as page 12.? You need to convert the 2 wire capsule to 3 wire
• Jerry Lee Marcel's mod as page 7? You need to convert to 3 wire

Here is my actual schematic:
/g/MicBuilders/message/32232

Why do you need to reduce the sensitivity?? You only need to do this if the mike itself is overloading.? Otherwise just turn the preamp gain down.

Thanks for the advice and sorry for not being clear about what I want to do — I was hoping to increase the max SPL that I can capture without overloading the mic, to make a quite sensitive mic more versatile. However it it seems like that's a limitation of the capsule and I should stop trying to make it be something it isn't... or get a FET-less or 3-wire capsule with similar properties that I can use one of the suggested approaches with.