Stock Rode NTK

[sr1200]

I've sent my NTK back to rode twice for some issues the mic was having where it would almost seem like the mic would shut down for an instant if there was a harsh plosive that was picked up by the mic.  I recently opened the mic up and had a look around.  Noticed the stock caps, (not really good quality and theres no telling on the SMD stuff, all looks the same).  I removed the tube , the leads from the capsule, and then the board.  Had a look around.  Looked like a 5 year old did the soldering on it and there was a TON of flux or some other residue on the board.  Cleaned that up, removed the caps, and replaced them with some more trusted versions.  Found an old article from GUS where he suggested replacing some other caps, but a few he gave no values for (if anyone knows what C10 is supposed to be let me know, this was one cap that looks especially suspect on the solder job).  Anywho, the LAST thing I look at is the tube... written in chinese except for 6N1P.  I decide to look this up:

A reply to another owner of the NTK from Rode:

The 6922 tube is basically electrically equivalent to the 6N11, 6DJ8, ECC88 and the 6N1P (Obviously the 6N1P uses 635mA max heater current which is twice as much than the other tubes.)

Now the NTK power supply was designed to supply 350mA to the tubes heater elements. The NTK power supply can supply up to 650mA heater currents which means the 6N1P will work in the NTK although I would want to have a listen. The power supply will maintain its 6.3Volt output even at 650mA heater load current.

Anyone think my plosive issue might have to do with this? Kinda like over loading the PS to begin with then to add extra insult by over working the diaphragm.  Any thoughts would be appreciated.  PS: i ordered some Phillips 6922's to replace (if anyone needs one, I'll have an extra, had to buy a "matched" pair, no great deal, were $20 each)

 

[Pip]

I've sent my NTK back to rode twice for some issues the mic was having where it would almost seem like the mic would shut down for an instant if there was a harsh plosive that was picked up by the mic.  I recently opened the mic up and had a look around.  Noticed the stock caps, (not really good quality and theres no telling on the SMD stuff, all looks the same).  I removed the tube , the leads from the capsule, and then the board.  Had a look around.  Looked like a 5 year old did the soldering on it and there was a TON of flux or some other residue on the board.  Cleaned that up, removed the caps, and replaced them with some more trusted versions.  Found an old article from GUS where he suggested replacing some other caps, but a few he gave no values for (if anyone knows what C10 is supposed to be let me know, this was one cap that looks especially suspect on the solder job).  Anywho, the LAST thing I look at is the tube... written in chinese except for 6N1P.  I decide to look this up:

A reply to another owner of the NTK from Rode:

The 6922 tube is basically electrically equivalent to the 6N11, 6DJ8, ECC88 and the 6N1P (Obviously the 6N1P uses 635mA max heater current which is twice as much than the other tubes.)

Now the NTK power supply was designed to supply 350mA to the tubes heater elements. The NTK power supply can supply up to 650mA heater currents which means the 6N1P will work in the NTK although I would want to have a listen. The power supply will maintain its 6.3Volt output even at 650mA heater load current.

Anyone think my plosive issue might have to do with this? Kinda like over loading the PS to begin with then to add extra insult by over working the diaphragm.  Any thoughts would be appreciated.  PS: i ordered some Phillips 6922's to replace (if anyone needs one, I'll have an extra, had to buy a "matched" pair, no great deal, were $20 each)

Sounds to me like the capsule has had it. This is a classic sign that the capsule is some how compromised. Could be moisture, failure of sputtering or stretching. It is what usually happens when some how its capacitance is way off.

It is a bigger question in my opinion. Is the design of the circuit meant to underheat the tube if so than that might answer your question as to whether it will work. Sounds to me like the NTK supply will though based on that quote.

Ah tubes. It really doesn't matter where the tube is made, it matters whether it's up to snuff. If a tube is tested for its end use and passes then it is fine for that use. Microphones being a very needy lot reguire low microphonics and stability which could mean 1 in 10 or more of a lot of tubes and then there are variations like plate size and grid design, which change the sound. Thats why the price of tested for microphone use tubes are 300% of the cost of the same tested good tube. Also why the price of certain no longer manufactured tubes are through the roof 'cause most of the good ones have been had and whats left is cast-off.

Check out this factoid of a guy who tests tubes for a living and knows a lot about it.

http://leedsradio.com/technical/testslikenew.html

Lastly RODE Mics makes a good product at a practical price. I myself own a lot of there product and have had problems. They have always gone the extra mile to make it right to the point of replacing a mic that had failed. It would pain me to think they have faultered in an area where they have always excelled.

 

[Gus]

FWIW  I currently would not do the all the changes from my posts in the past.
I did trace the NTK and it was on the web in the past.

I own a K2 and I changed some parts in it, it did not change that much.  I even changed the tube to another tube (not 6dj8 type had to cut and jump a trace) not much change if at all.

Are you using a transformer input preamp? if so try a transformerless input preamp

Is the issue with a person singing close to the microphone and/or a loud sound? 

Have you tried  a different preamp? 

Transformless microphones can have high outputs

If it is voice can you place a loud speaker close to the microphone and play back a voice to sim the issue without human breath and mosture?

 

[Kingston]

PS: i ordered some Phillips 6922's to replace (if anyone needs one, I'll have an extra, had to buy a "matched" pair, no great deal, were $20 each)

Ouch! Maybe you should have checked here before buying. These Jan Philips 6922 tend to be *very* microphonic. One of the worst I've heard. A good friend was using these specifically in Rode NTK for years and once happened to ask me why he was hearing this high pitched ringing on all the sounds. Had had been notch filtering that stuff out for years not knowing better.

I'm using Jan Philips 6922 in a certain line level stage and when I tap the front panel I can hear a faint *ping*. They are that bad.

For the price of your "matched" tubes you could have bought sixteen CCCP era 6N1P's from Ukraine. They are the better tube here anyway, besides the steep heater requirement. But it's actually not even electronically equivalent to ECC88. It has lower plate resistance. Non issue in this mic output transformer task.

But 6922, ECC88, 6N23P and 6DJ8 are quite equal and can be swapped around freely.

 

[Pip]

I had a thought regarding the ECC88/6922 tube issue and remembered that JJ tubes makes a really nice one.

 

[sr1200]

Lol Pip & Kingston, sounds like ill be ordering other tubes in the VERY near future.  Checkin the link now. Thanks

As far as the voice thing, the only one that uses it is me (partially because I know about the issue and wouldnt want that happening to a client, would look real bad on my part)  I use it for voice over work, although, i recently got one of chungers C12 knock offs and really enjoyed the sound of that last time.  I'd love to save up the scratch to make the full clone one day.

Gus, thanks for chiming in, the caps in the stock mic looked about as cheap as the solder job. (the mic has a pretty low serial, under 4000 if memory serves, its probably 10 years old or more at this point)

Unfortunately I think all my pre's have Tx's in them (from the tube pre's to the germaniums... Not too sure about the AEA RPQ pre, i recall that being pretty heavy though.  (everything else is either API clone or Neve clone  ;D )  I do have a focusrite thats gotta be IC, but its kinda decommissioned at this point, perhaps ill fire it up just to try though. thanks for the tip.

Any suggestion on what to replace the capsule with?

 

[Pip]

As far as the voice thing, the only one that uses it is me (partially because I know about the issue and wouldnt want that happening to a client, would look real bad on my part)  I use it for voice over work, although, i recently got one of chungers C12 knock offs and really enjoyed the sound of that last time.  I'd love to save up the scratch to make the full clone one day.

The build is not that expensive and right now he has the whole kit available on his web site http://store.studio939.com/. You must really read matadors build thread as there are some PSU tweaking things to be aware of.

Any suggestion on what to replace the capsule with?

First I would ascertain what the capacitance of the existing Capsule is and try to get in the ballpark. Then you might find one of these fits the bill electrically even though I believe the NTK capsule is center terminated and obviously cardioid so you only really need one diaphragm and backplate. Finding that in small quantities might be a task.

http://www.microphone-parts.com
I have used these very affordable capsules with good results.

http://www.pelusomicrophonelab.com/parts/Capsules.html
These capsules keep getting really good reviews. I myself have no experience with them.

http://tab-funkenwerk.com/id131.html
So far I have used a lot of Mr. Archuts transformers and not been dissappointed. Its a good price.

http://www.cathedralpipes.com/zen-cart/index.php?main_page=index&cPath=65&zenid=a4ae6dc14bf9b4030e77da3b27e566cb
I just used one of the M7 clones in a build. It is a good upperscale item.

Want the real deal:
http://www.thiersch-mic.de/en/estm_produkte.html
The best M7 copy out there.

Lastly Chunger has some capsules he is selling at a very reasonable rate.

Good Luck.

 

[sr1200]

Ive used a peluso and tab tx in my u87 clone (sound REALLY good). 
Good call on the mic parts site, totally forgot about them.  The capsules i was lookin at for the c12 were over $300 (well over).  This kind of brings it back to the realm of possibility now.  ;D ;D ;D  I smell a weekend project... or is that just lack of hygene? hmm... anyway.  You're right about finding a single back plate capsule, like hens teeth.  Ill take a look at chungs caps when i order my C12 bundle   My guess is that they would be no worse or better than whats in there since my mic was made way before rode started making their own capsules.

 

[Pip]

.....since my mic was made way before rode started making their own capsules.

I wonder if maybe the NTK you have has already had some "work" done to it before it came to be in your possession. Because I think RODE has been making there own capsules since the early to mid 90's.

As a footnote good capsules cost. Tim Campbells C12 capsule and Thiersch's capsule are the real deals and thats why they cost.

 

[sr1200]

I bought the mic new in the late 90's or early 00's.  Eventually I think im going to go for Thiersch's capsule, just not in the budget right now.  The one from micparts I'm hoping will suffice for now.  Just ordered a GE tube for the C12 and a JJ for the Rode.  Kingston was right on about the Phillips... yuck.  Back to the Bay they go lol.

 

[sr1200]

K after swapping out the tube and touching up the board with the iron, theres not much change in the reaction to plosives.  The slightest breath in the mic's direction cuts it out.  When i took it apart, i did notice a small what almost seemed to be crack in the diaphragm where the lead connects to the capsule.  Perhaps I should try throwing one of the M7 capsules in there. 

 

[sr1200]

or not... just swapped out the capsule for another i had laying around that i know had no issues... same issue.  any thoughts?  At this point i almost want to suspect the powersupply since that is the only thing that was different when Rode checked it.  Could off voltages cause that problem?

 

[sr1200]

Opened up the PSU.  Manufactured Jan of 01. So early 00's.  There are 2 voltages listed, one of them adjustable.  there is a -125 volt test point which im reading at about 123 volts and a -5.8 volt point with a trimmer.  That test point was reading about 5v.  I adjusted the trimmer so that it read -5.8.  No real change in performance.

edit, also checked the voltage to the capsule which was at 48.9 ( a lil high but not crazy)

 

[Pip]

Do you have schematic of mic? If so could you post?

Could be output caps? That mic has an output buffer circuit not a transformer if Im not mistaken? I would check that and see if it is the caps feeding that circuit.


Have you put meter on various points and watched for sudden drops in voltage?

 

[Kingston]

Kingston was right on about the Phillips... yuck.  Back to the Bay they go lol.

save them for some other project where you will need ecc88. They are very good sounding tubes, just not for microphones or anything that might vibrate.

 

[sr1200]

I wish i had a schematc for it.  Would be a lot easier to troubleshoot. The closest thibg i have is gus' hand scrawled schemo which has been pretty helpful thusfar.

 

[Gus]

Are you sure it is not the preamp overloading?  Have you tried it with different preamps both transformerless and transformer input?  You could be causing a DC shift in the preamp with an overload.

Transformerless microphones can have high outputs. 

Have you tried a pad at the preamp to hear if it changes?

If you are sure is not the capsule and the preamp.

I would check for DC shifts in the circuit when exposed to a high level.
http://web.archive.org/web/20110219163852/http://www.diyfactory.com/projects/gus/ntk2.GIF
That was a fast trace of the circuit it could have errors.
Also I would leave the microphone stock.  The cap changes I made to my K2 did not seem to change the sound

Are the LEDs glowing?
Do you have phantom power on or off?

 

[sr1200]

K... lets see if i can get all these answered.  The LED below the tube take a min to come up but comes on full and strong.  the LED to the right of the valve comes on eventually but kind of dim.  The preamp is set VERY VERY low (because of the high output) and yes phantom is def. off.  I did try to put on the pad. And it does actually get a bit better. HMMMMMM.....  k, i plugged the mic into my old joe meek pre, which has a bit of a roll off on the top end.  I think you found it Gus.... wow... Mic sounds amazing through this pre, still spikes a bit on plosives but nowhere near what was going on on my 610, neve, api, aea or MA1 pres.  guess this might be one of those perfect match situations.  Bright mic + Dull pre = happy time!  PS the JJ tube sounds great and is dead quiet thanks Pip (and Kingston) for the tip there!