RODE NT2 J.W. MOD - schematic attached

[ln76d]

Thank you guys for help!

Other symptom is huge difference between cardioid and  omni pattern.

Was this 'feature' in the original NT2?

It's hard to tell, truly i don't remember Even if it was, this "feautre" for sure couldn't make that big difference.
Please tell me ricardo, what should i change to remove hi-pass filter? Keeping only the Pad would be ok in your opinion?

My question was whether the original NT2 had the 'huge difference between cardioid & omni".

If both original & modded circuits are JW's, they both have some really bad faults.

Yes, get rid of R33.

So again, i don't remember  ;D
Even if, now the difference is really huge and for sure it couldn't be in the original circuit.
At omni level of the signal is really low and the bass response is weak.

What do you think about keeping C21 and C15 in the circuit?

 

[ricardo]

Even if, now the difference is really huge and for sure it couldn't be in the original circuit. At omni level of the signal is really low and the bass response is weak.

What do you think about keeping C21 and C15 in the circuit?

Are the circuits you posted in #10 from JW or are they from Rode?

There is a way to get rid of both caps but as it stands, you need at least one of them.

 

[ln76d]

The upper one is genuine Rode circuit, lower is my variation about all of those JW recepies.

Tomorrow i will try to remove hi-pass filter and check all of the options with both of caps and let you know

 

[ln76d]

Ok... In attachment is the last version of my circuit.

This is the version without hi-pass filter and without both capacitors.

Capacitors comparision:

- with C21 Cardiod sounds pretty good and is most "bass-y", Omni sounds weak (lower signal, weak bass response, difference between both sides of the capsule)

- with C15 Cardiod sounds little bit worse, Omni sounds better but only on the front side (huge difference between both sides, better bass response), overall signal level is a little bit worse

- with C15 and C21 everything is worse than after...

- without both capacitors Cardioid sounds the best - very balanced, Omni sounds similar to the setup with C21 - so weak

Any ideas?

Maybe i miss something in the J.W. descriptions?
Should i put somewhere the removed 1Gohm resistor (R32)?

 

[ricardo]

The upper one is genuine Rode circuit, lower is my variation about all of those JW recepies.

I'm asking if you drew the circuit, or JW, or Rode.

You have the circuit as it should be.  Don't put back R32, the 2nd 1G resistor.

Try turning the capsule round.  It sounds like the two diaphragms are mismatched.

 

[ln76d]

I'm asking if you drew the circuit, or JW, or Rode.

You have the circuit as it should be.  Don't put back R32, the 2nd 1G resistor.

Try turning the capsule round.  It sounds like the two diaphragms are mismatched.

Thanks ricardo!

Sorry, i was thinking that i wrote it obvious. But is not Upper circuit was drawn by Rode and the lower only changed by me.
In the first step of mounting this capsule, i've wired it backwards and the back side sounds (on cardioid) the same as the front sounds now. I will do that today again and check it.

 

[ln76d]

Both sides of the capsule sounds same when changeing front-back connection, so there is something with the circuit. Capsule is practically new. Any ideas where look for fault?

 

[ricardo]

Anyone have an unmodified NT2 and can check if omni & cardioid sound very different?

 

[Krumlee]

Did you make any progress with this? I'm interested because I've got an NT2 that I'm gradually upgrading using similar mods to the ones you're doing. I've just ordered an RK-47 capsule that I'm planning to wire directly to the fet using similar setup.

I hadn't thought about simply wiring the capsule directly across the polarising voltage and amp input. I was intending to use a path to ground with a 1G resistor in series and connecting the fet gate between them. Looking around the web at other similar designs, I see that your method is a common one.

To answer your question: The front and back of my NT2 sound the same in omni mode - a bit quieter than in cardioid setting, but otherwise the same. I suspect you may have a capsule issue. Also make sure you carefully clean all the solder connections and board using isopropyl alcohol.

Thanks for posting details of your mod.

 

[Krumlee]

Just to help other people...

I carried out this mod, as described above; basically wiring the common side of the card/omni switch directly to the fet, and wiring the capsule so that the backplates are polarised. I elected to remove the resistor R33 but left that pcb position open, unlike the schematic - that way the high-pass switch position does nothing.

It all worked great. I did this mod alongside a capsule replacement, so I can't comment on how the rewiring itself affects the sound.

I haven't done the other mods. The replacement capsule I used doesn't need any high end tweaking, so C12 and C13 are fine as they are. There doesn't seem to be anything wrong with the low end, so I'm leaving C11 and C14 unchanged - I'm only recording vocals though, other people may find that mod useful.

I'm not sure about the mod for the polarising voltage - I've ordered a better multimeter so I can measure the existing voltage more accurately.

Thanks for everyone who posted in this thread - very helpful.

 

[micaddict]

Not to hijack, but if I recall well the Behringer B2 was basically the Rode NT2 in new disguise. (?)

(If that is the case, owners of those could chime in, as well.)

And going from there, the B2 Pro (with figure eight added) shouldn't be too different. (?)

Could be wrong, though. Been a while.



Henk

 

[Krumlee]

Hi Henk,
I was on the verge of getting a B2 pro on ebay yesterday. As you say it's an OEM version of the NT2 built by 797 audio so I expect that all of the NT2 mods would work well on it. In the end I didn't buy it because having another NT2 wouldn't really add anything to my range of mics. I love the NT2 though - I've been playing around modding mine for a few months, but in the end I concluded that there isn't much wrong with it at all. I elected to change the capsule just to see what difference it makes, and I really like the RK-47. I also rewired the output capacitor on the oscillator board, as described above, and fitted a copper shield to the back of it.

One question for the group: Can anyone think of a good way to reinstate the low-cut switch? The way that it's done in the original NT2 isn't a good design, and the direct capsule wiring requires it to be taken out. Could it be reinstated after the FET? The only way I could think of doing it would be a double pole switch doing something identical to both legs of the amplifier. Can anyone see a better way?

 

[micaddict]

Thanks, Krumlee.

Oh, and welcome! 

 

[ln76d]

BehriBehri B2 and 797 NT2s have different circuits than Jim Williams NT2 circuit. Similar body and same capsule only.

 

[micaddict]

Yeah, now that you mention it, I do recall others stating they are in fact not the same.

Is there a B2 or B2 Pro schematic available somewhere?

BehriBehri?  ;D



Henk

 

[ln76d]

I've never searched for schematic, but there's many pictures of the circuit pcb over the web.
Few years ago i've read somwhere, that the circuit was designed by 797. Maybe on the GS forum?!?

For example:
http://recordinghacks.com/microphones/Behringer/B-2Pro

 

[micaddict]

I once even posted some pics myself ...
Unfortunately, I'm not able to reconstruct to a written schematic.
Yeah, I know ...
:-[
But I know someone who can.

I'll ask him.

Carry on.

 

[Krumlee]

I'm sure you're right about the B2 Pro. I've also been looking for a schematic because it looks like an interesting mic to mod, but I can't find one. Wouldn't be too hard to derive one - I'm sure the NT2 schemo would be a close starting point.

Getting back to my NT2 mod - which is sounding really nice. I've now got a better multimeter with 10M input impedance.
The output from the oscillator board (with the capsule removed) measures about 42v. I'm sure many of the NT2 mod threads (some by Jim Williams) claim that the original capsule voltage was too high - so I'm a bit confused. Many people seem to shoot for about 60v so if my readings are close to true then I'm on the low side.

I'm not sure what I'll gain from changing the polarising voltage anyway - I'm not sure it will change the tone of the mic, and I'm fairly happy with the sensitivity, so I may pass on it. I'd be interested to hear from anyone who's done this mod, or who has an opinion. Thanks in advance...

 

[dhammer]

Thanks to all the great info on this thread, I'm making my NT2 the object of my first real mod work on a mic.  I have already made the changes to the capsule wiring but am waiting for a Mouser delivery so I can add the bypass caps at C11 and C14.  I put an RK7 in this mic a year or so ago so I'm going to leave the 470pf caps alone. 

The numbering on my boards doesn't match the schemo Piotr put up.  I added the numbers on my board to help me keep things straight.  I'm posting it here in case its a help to somebody else.  Pix of my boards are here:

https://www.dropbox.com/sc/247tlf5mygunc2b/Yn-gSTN3Tm

There is one thing on the amp board that doesn't match the schemo:  there is a 10-ohm resistor added in series with the zener at D3.

Two questions from a newb:

1 - my understanding for testing the polarisation voltage is that I give the mic 48v phantom and test at the 1gig resistor at the jfet – is this correct?  and can I do it with the capsule head disconnected?

2 - copper foil between the boards - how is this done? 
Mouser has a 3M foil with non-conductive adhesive – would this do it?
http://www.mouser.com/ProductDetail/3M-Electronic-Specialty/1194-1-4x36yd/?qs=sGAEpiMZZMuwwZaQzCsHbAXRJ9p9NoJkgTgslASRPIM%3d

Thanks to all 

 

[Krumlee]

Yeah, I don't think the numbering on my board matches the schemo on the web that everyone seems to refer to either.

1 - If you disconnect the capsule head then there won't be a polarising voltage at that point. I measured mine at the output of the oscillator board - CAP-B connection on the standard schemo.

2 - I can only speak for my approach. I think I bought similar stuff - lots of ebay sellers seem to sell it for people to use on their electric guitars. I elected not to stick it to the back of the oscillator board simply because if you ever want to do any work on that board (mods are always a work in progress) then you'll have to pull it off and probably clean up a mess.
So my approach was this:
- cut a piece to the size of the oscillator board
- make 'cutouts' at the edges to accomodate the connections on the rear of the board
- leave the backing paper in place
- cut small rectangles of foil from another piece and use these to secure the shield to the back of the board by sticking them to the shield and wrapping them over the edge of the board and on to the component side. [Hope that makes sense - it really needs pictures!]. The copper shield lays against the mic chassis when the board is replaced, providing a ground - I'm not sure if a better ground connection should really be soldered to the copper, but this works for now.

Let us know what capsule voltage you discover - the RK7 is a bit more robust, so it may pay to raise it a bit, but I'm not convinced in my case.