Schematic Rode NT2-A

[LevinGuitar]

And yet it works.
NT2-a is different from NT1 black.
I put a 0.51nF capacitor (511) from the jFet source (pin C11) to ground.

I just tried 470pf and 4.7nf there, not much difference, just a hair less of top end

 

[micolas]

I just tried 470pf and 4.7nf there, not much difference, just a hair less of top end

Exactly what I said.
That's what I followed.
The 510pF value worked perfectly for me.
Already with 1nF it seemed more closed than I like.

 

[kingkorg]

And yet it works.
NT2-a is different from NT1 black.
I put a 0.51nF capacitor (511) from the jFet source (pin C11) to ground.

Glad if it works for you, source impedance is quite low, i can't see how 0.51nF would do anything, but i could be missing something.

 

[micolas]

Glad if it works for you, source impedance is quite low, i can't see how 0.51nF would do anything, but i could be missing something.

Kingkorg,
I approached the topic in the most pragmatic way. I soldered a 10nF capacitor to ground and went the reverse audio path to the input. I thought it was better to filter at the beginning of the audio chain. It worked after C12, between C11-C12, before C11. After some tweaking I decided to remove the treble that was bothering me, but with the desire to still keep a sound profile close to the U87ai (at least graphically, because I didn't have one at hand). I used Superlux 681 headphones, it's true that they have expanded highs. At the value of 511G (I hope I said 0.51nF correctly), I liked it. Radio-ready sound.
Please, If you have the possibility, in an NT2a of yours, make comparative measurements between stock and my mod. I'm curious if I attenuated about 0.5..0.7 dB after 8..9kHz, that's what I was hoping for.

 

[micolas]

I just tried 470pf and 4.7nf there, not much difference, just a hair less of top end

Did you try my mod simultaneously with your mod, or on the stock circuit?

 

[LevinGuitar]

I tried first yours one only, then both. Anyway none of them makes a real change. A small piece of foam under the capsule in my NT1000 did a bigger change.

Today I was wondering about desoldering C11, pick there the signal there and send it through a cap and a low? ratio transformer into the output and see if it works (to add later a classic deemphasis)

You don't like my ways, but I do learn somehow

 

[Khron]

I don't suppose you ever considered adding a capacitor in parallel with the JFET's drain resistor, have you?

 

[LevinGuitar]

No :/
Tomorrow will try!

 

[micolas]

I tried first yours one only, then both. Anyway none of them makes a real change. A small piece of foam under the capsule in my NT1000 did a bigger change.

Today I was wondering about desoldering C11, pick there the signal there and send it through a cap and a low? ratio transformer into the output and see if it works (to add later a classic deemphasis)

You don't like my ways, but I do learn somehow

I also thought about using the input part of the circuit (which ensures low noise) and a transformer or BJT+transformer (for some magnetic saturation). I'm still studying.
In another context I thought that a jumper over C11 would increase the equivalent capacitance (from about 41.1 nF now, (47nF in series with 330nF) to 330nF and lower the frequency response (but would invert the output phase probably xlr pins 2 and 3 should be reversed and would affect the Hi-Pass.
For treble, as I didn't want a classic attenuation of several dB, like for a very bright k67 capsule, in this case I was satisfied, the stock microphone is very close as FR to the U87ai, only a small peak above about 9khz more , it bothered me a bit.
I thought that changes towards the output would introduce greater distortions, phase changes (although passive multi-way filters in acoustic enclosures exist and work).
And one more thing, if the impedance at the input of C11 was too low, then for a good response to the bass, the values of C11 and C12 had to be several microFarads, and the resistance from them, component of the filter, put to ground would be should have been a few kohms (not 940kohms for 'flat').
The next mod will be a U87 headbasket for the NT2a (the one received on the HL-77).

 

[micolas]

I don't suppose you ever considered adding a capacitor in parallel with the JFET's drain resistor, have you?

Khron, yes.
I use it in the classic Shoeps circuit. Sometimes in combination with the mod used by MicParts.

 

[micolas]

Hey guys,
does anyone know if there is any similarity between the circuit diagram of NT2a and NT2000?

 

[LevinGuitar]

I don't suppose you ever considered adding a capacitor in parallel with the JFET's drain resistor, have you?

Tried today, it works a bit too, but cannot find a nice combination between all/some of them

 

[greg_is_not_a_bot]

In case anyone is still watching this discussion or comes across it, I have an issue I'd like to run by the group.

I had some issues with random popping and noise in my NT2a, replaced the capsule (was going to anyway) with an RK-47 (no change in the noise) and then proceeded to replace what I figured were all the caps in the high-impedance section before the JFET. (See photos) I used Wima FKPs where I could, but the two 0.1μF are MKPs due to space limitations. The popping is gone (nice!) but I have a weird problem. In cardioid the mic sounds fine, but in figure-8 there's a big difference in the sound from the front and rear of the mic. The front side sounds scooped, while the back side sounds mid-hyped. I haven't done any measurements, but it seems like the same frequencies attenuated on one side are enhanced on the other. In omni, the mic is quite dark. All 3 patterns work as expected from a directional standpoint.

Any clues as to where I should be looking? I have zero experience working on LDCs, so I'm a bit out of my depth here. I know the logical thing would be to try a different capsule, switch capsule leads, etc, but with the change of capacitors it's a tightly packed circuit board now and I'd prefer not to do too much desoldering / resoldering on those little smd pads just to get access.

Oh, and I used what I believe are the correct capacitor values, based on the schematic that @Drosselmeier supplied earlier in this thread. I wasn't sure about one of them that appears to be listed as 4700pF, since the numbers are a little fuzzy. Could that be my issue? Is that the wrong value for the cap?

Thanks in advance for any help, in case anyone actually ends up finding this post after so long.