Røde NT3 Mod - 6Khz Hype Circuit Removal

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kingkorg

Well-known member
Joined
Apr 15, 2017
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Hello guys,

I saw yesterday this whole series of great videos with Doug Ford. This one caught my attention as i have two of Røde NT3s and i love them for their practicality, versatility, reliability... They have been my  main live vocal mics for years.

However i had to use de esser all the time, and 6khz range was killing me. Only to realize in this video that it was intentionally hyped (+4db!) but not by designer Doug Ford, but marketing department xD

The story begins at 11.43, tho i recommend watching the whole thing.
https://youtu.be/niZizzHBanA?t=11m43s

He added bridged t circuit in the feedback network i hope i managed to bypass in this mod. But i am not 100% certain i did it right, the hype is gone, i adore this mic now,  the difference is HUGE! However it seems i should bypass one more resistor after removing one resistor and two caps, but i cant figure out which one it is. Maybe it's not necessary at all.

I removed components in the picture, but the hype was already gone after removing the resistor. Maybe i shouldn't have removed the caps at all? Did i mess something up?

Clips side by side unmoded and moded one.
Unmoded NT3
https://app.box.com/s/rz1vshqb55ugb1jmb3w5530t0yk18rmr
Moded NT3
https://app.box.com/s/ngw9a832ezs2zkethm8rkl2tfh5m2ke7

Spoiler! CIA is being mentioned in the video! But you have to watch from the beginning. :D
 

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Oh well, a bit sad no one else wants to chime in, but i got a reply from Doug himself today via eMail. I am sure someone will be interested in moding this guy in future and this will be simplest mod ever by removing only one resistor. I can tel you one thing, for what ever reason this moded mic sounds  identical to my Shure KSM44. Almost identical frequency response, and they cancel out almost completely in phase flip test with pink noise. So you get poor mans cardioid KSM44. And believe me, even stock (with some extra EQ) this is an amazing mic.

Here is what Doug said:

¨When I left Rode, I did not take any of the design files with me.
What a silly bugger!
So, I cannot give you a nicely labelled PCB overlay which shows the bridged-T circuit.
However, I believe that you have correctly identified the T-circuit in your photo.
The bridging resistor is the 680-ohm (6800) resistor at the top-right of the IFND89 fet.

I believe that you can eliminate the HF boost by simply removing the bottom T-resistor.
The two capacitors, and the bridging resistor, will then have no effect on response and will give a flat preamp response.

You may like to try this: Lift the ‘ground’ end of the resistor, and connect a very small switch between the resistor and ground.
This will allow you to compare the ‘flat’ and ‘boosted’ responses.

Thanks for identifying the IFND89.
The fet we were using originally came from Siliconix, who were bought out by Vishay.
It seems that Interfet have either purchased the rights to this component, or it has fallen out of copyright and can be manufactured by anyone.
I have had good success with Interfet fets; For example - the IF4500 has extremely low noise, moderate capacitance and low gate leakage current.
The IFND89 has very low capacitances (and the advantage of the inbuilt diodes) but higher channel-noise. It’s still a nice fet, though.

I am pleased that you are willing and capable of modifying your microphones (and, I suppose, other electronics).
I applaud you!

Cheers –

Doug''
 
Very nice that he replied!
I noticed the forum is a little quieter indeed than a year ago, or it may be my imagination :)

 
Hello King Korg!

I was inspired to join this community today after stumbling on your posts here regarding your NT3 mod.

I’ve just bought a cheap second hand one here in Adelaide, Australia…for use as a boom dialogue mic indoors. Serial number approx. 0065000.

I’m very curious about the modification you talk about. I am a fairly novice audio guy…am yet to put my soldering iron to use…but it sounds like this mod might be an easy one.

I couldn’t view your YouTube video from the above link, as the video appears to be private. It it somehow possible to get the link to this video please?

Any other advice you’d have to share would be greatly appreciated also.

Cheers from Australia!

Andrew
 
Hello King Korg!

I was inspired to join this community today after stumbling on your posts here regarding your NT3 mod.

I’ve just bought a cheap second hand one here in Adelaide, Australia…for use as a boom dialogue mic indoors. Serial number approx. 0065000.

I’m very curious about the modification you talk about. I am a fairly novice audio guy…am yet to put my soldering iron to use…but it sounds like this mod might be an easy one.

I couldn’t view your YouTube video from the above link, as the video appears to be private. It it somehow possible to get the link to this video please?

Any other advice you’d have to share would be greatly appreciated also.

Cheers from Australia!

Andrew
Hello. I had to take the video down due to some copyright crap. There's just one resistor that should be removed to deactivate the 6K boost. I'll try to dig up which one it is.
 
Hello King Korg!

I was inspired to join this community today after stumbling on your posts here regarding your NT3 mod.

I’ve just bought a cheap second hand one here in Adelaide, Australia…for use as a boom dialogue mic indoors. Serial number approx. 0065000.

I’m very curious about the modification you talk about. I am a fairly novice audio guy…am yet to put my soldering iron to use…but it sounds like this mod might be an easy one.

I couldn’t view your YouTube video from the above link, as the video appears to be private. It it somehow possible to get the link to this video please?

Any other advice you’d have to share would be greatly appreciated also.

Cheers from Australia!

Andrew
Here's the reupload
 
Thank you so much for sharing this video. Do you find that you actually actually use the switch and go back to 'boosted' setting on occasion ?
No, eventually i removed the switch. I've been using NT3 for 10 years as my main vocal mic. When i made the mod i was still uncertain if i was to miss that HF boost at some point, but that never happened.

I also used a pair of modded ones for overheads for about 5 years, once i discovered Line Audio CM4, NT3 had to go unfortunately. I tried CM4 on vocals, but they are very sensitive to plosives, which NT3 isn't (with some extra foam under the grille). So modded NT3 remains my favorite live vocal mic. It even won over kms104/105 and ksm9.
 
I see no difference. The new nt1a have a different layout and bigger output caps (and less pol.voltage) but should be the same. Have to check out but maybe the NT5 have a similar circuit too
 

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Doesn't look that much like the Primo to me; plus, unless Rode is outright lying, they say the mic is externally polarized. The Primo capsule is an electret.

Also, Rode say the mic is supercardioid, and the EM21 is cardioid; they also say the diaphragm is gold sputtered, and the Primo is aluminized.

Current production NT3 capsules look quite different from that photo, and even less like the EM21.
 

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Last edited:
photos of the front grille and it looked like a Primo EM21…
they say the mic is externally polarized. The Primo capsule is an electret.

If it was an electret, they wouldn't need the 40106-based oscillator (that 14-pin chip on the bottom side of the board) to achieve the 40-60v bias voltage for the capsule...
 

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