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I have a? Rode NT1 which is very simlar to the NT1A in many respects. There only appear to be minor differences to the schematic linked to in post #2 of this thread.
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I've had it for about 7 year now, and last year the sensitivity dropped dramatically. Almost no output.
I was surpised to find that the polarisation voltage across that capsule was way lower than it should have been - even though the voltage multiplier was outputting the correct ouput voltage.
It's not easy to measure the actual polaristion voltage directly with any accuracy -- connecting a DMM will shunt the output filter 4M7 resistor, so that the 73v voltage generator output will measure more like 50v.? ?In my case it was a lot lower than that - more like 10v !?
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I desoldered the final output capacitor ( on the NT1 that is C8 - the large 0.1uF cap adjacent to the? actual capsule termination pad. )? Underneath was what looked like dust. Removed that, and cleaned underneath with iso prop alcohol. Resoldered, and was able to measure the voltage across that capacior as 45v? (should be around 50v for the NT1-A).
Mic has performed perfectly since.....?
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(The actual voltage figures are slightly lower for the NT1 - it used a 13v zener as opposed to the 15v of the NT1-A.
The figures I describe above refer to the expected NT1-A figures).
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On Sun, Oct 27, 2024 at 05:06 PM, @jp8 wrote:
Found today. It seems I'm not the only one.?
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On Sun, Oct 27, 2024 at 05:06 PM, @jp8 wrote:
If you have a multimeter and you're willing to spend some time on fault analysis,? I can guide you through the process. By doing this, you can at least exclude the capsule from being the culprit.
Hi Jan. Yeah, it's a pity but not too bad either. ?At least we were able to achieve partial success and I no longer have any interruptions during the recording process. That's really something!
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I'm busy this week. But there's no rush anyway. Please let me know when it suits you best.
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Many thanks!
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Heinz
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On Sun, Oct 27, 2024 at 07:15 AM, Richards wrote:
While I am NOT an expert, it just sorta kinda almost seems it might perhaps possibly be a capacitor or two on the circuit board taking a long time to charge up - sorta like an old camera flash unit taking longer than normal to charge its thyrister so it can flash a full blast.
That's what I thought when I came across a pair of speakers from the 1970th that nobody wanted anymore and that were thrown at me because everyone knew that I like listening to sound and analogue equipment.
When I opened the speakers and saw the old crossovers, my first thought was, "Omg, how am I going to replace those ones?! They must have almost certainly dried out after occupying storage space for decades."
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The only thing I knew was that the speakers were from a Pioneer S-77M Turntable Stereo. I looked for technical information but couldn't find anything useful. So I tried to find information about these old metal caps and came across an interesting article that might also be of interest to some of you. The article was published in Italian by Emilio Ciardiello on the German site radiomuseum.org with the title “Replacing Old Capacitors” and contains, in my humble opinion, a lot of useful information about (old) capacitors in general and error analysis tips. This may not be relevant to micbuilders and would probably be difficult to understand for someone unfamiliar with the subject matter, like me :-). Anyway, I dropped the English translation of the article to the files section. ?
The following takeaways were relevant to me at that time:
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1.? Capacitance meter and insulation meter are usually required to trace faulty capacitors.? To this day I do not own either of these.
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2. The substitution of properly working parts with more or less similar components is useless, may impair the operation of the equipment and may also result in additional failures. Original components, when still good, are stable and not subjected to infant mortality.
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3.? When first handling any old equipment it is advisable to perform some preliminary operations before replacing components. After a good cleaning, a visual inspection returns a first list of damaged parts, as hardened rubber cables or cracked capacitors that must be replaced before power-up. As a general rule, if the equipment was stored for a long while, six months or more, regardless of its previous operative conditions, a soft wake-up procedure should be run to allow reforming of electrolytic capacitors and of selenium rectifiers, if any. It is advisable to run equipment at about half voltage for half an hour, monitoring B+ voltage and watching for fluid losses from electrolytic capacitors, for overheat of components, hum and other alarming conditions.
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So I removed and checked the speaker drivers for any defects (there were none...). (I replaced the aged and smelling needle felt inside the speaker housing...).
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Checked and replaced any faulty or loose connections (there were some...).? And connected the speakers in series to the amplifier, ?as a soft wake-up procedure to allow the reforming of the capacitors,? when switching it on and using it for the first time.
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That was three years ago and the effort was worth it. To this day, I really appreciate the lovely sound of these aged speakers. Of course, I will never know whether the gentle wake-up procedure made a difference, but to my understanding this approach made sense. After so many years, the old crossovers in the speakers still work perfectly.
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Many thanks!
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Heinz
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@Richards
You are absolutely right. Repairing the NT1-a could quickly become expensive, especially since I do not have the original purchase receipt.
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Hmm, what a bummer! Could very well be the polarization voltage oscillator or voltage multiplier circuit following that oscillator that are not working. That's the 14-pin IC and surrounding parts on the board. My first suspect was C20, for which R?de has used an SMT film cap that was notorious for cracking. But C20 is a through-hole (wired) part on this board. A next likely, and not uncommon issue, is a cracked SMT capacitor in said oscillator circuit. But those cracks are in most cases microscopic and only visible by cutting the part and watching under an electron microscope. If you have a multimeter and you're willing to spend some time on fault analysis,? I can guide you through the process. By doing this, you can at least exclude the capsule from being the cullprit.
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Suppose you send in the mike to R?de for repair, I assume they will not do a repair at component level but simply do a board swap. Like others already mentioned, this is probably not economical. Ask for a quote before sending in the mike.
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Good luck!
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Jan
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My gut feeling tells me that it could be a defective capacitor. But that's pure speculation.
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That is my Wild Alex Guess, as well. While I am NOT an expert, it just sorta kinda almost seems it might perhaps possibly be a capacitor or two on the circuit board taking a long time to charge up - sorta like an old camera flash unit taking longer than normal to charge its thyrister so it can flash a full blast.
But then, sending it to RODE for service makes sense only if the repair bill, coupled with the cost of shipping AND the initial cost of acquisition is a comparative bargain versus the cost of a new one under warranty or another model you might prefer over the long haul.
Just saying - I am NOT being critical in any way. The same sort of economic considerations apply in other hobbies, such as the comparative cost to restore an old MG or Triumph sports car often exceeds its restored resale value, or the cost to restore an ancient fountain pen relative to its restored resale value, and so forth.
Good luck. James
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On Sat, Oct 26, 2024 at 06:48 AM, Richard Lee wrote:
I think the muck on your PCB coupled with humidity, was making the polarizing voltage generator wonky.? After 3 min. the warmth of the electronics dried the stuff enough for it to work again.? The polarizing voltage has some serious decoupling to remove any noise in the generator.
After yesterday's long-term recording test, I have good news and bad news.
The good news is that there were no unexpected interruptions during the entire recording process. The bad news is that the 3 minutes warm-up phenomenon occurred again this morning.
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The technical data of the NT1-a include:
Acoustic Principle: Externally polarized 25mm (1”) condenser
Features: True Condenser (externally biased)?
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From a beginner's point of view, I would like to properly understand what "True Condenser (externally biased)" means. Which might be boring for the pros.
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Shure describes it this way:
There are two types of condenser microphones: a permanently biased condenser, usually called an electret condenser, and an externally biased condenser, usually called a true condenser. These days, when people say "condenser microphone", they usually mean, "electret condenser microphone". Probably ninety-five percent of the condenser microphones on the market are the electret type.
The electret has a charged backplate that is created when the microphone is manufactured. A true condenser, on the other hand, continuously requires an external charge. This external charge may come in the form of any external box attached to the microphone, or it may come from the electronics built into the housing of the microphone. To put it simply, true condenser microphones have active electronics that need an external power source.? The basics are that it is a positive voltage (Phantom Power from 12 volts to 48 volts DC) that runs on pins 2 and 3 in an XLR cable. The word phantom is used because the power source is essentially invisible, running through the same cord that the audio signal flows through (Source: sageaudio).?
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Jules Ryckebusch described it very well this way. That voltage charges the mic capsule, which is a capacitor or “condenser” in 1930’s speak.
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According to a Sound on Sound condenser mic life discussion:
A DC-biased capacitor mic should go on forever. There is no inherent deterioration process in the capsule itself. Dirt on the diaphragm (or a very high humidity environment) will cause temporary charge leakage that will reduce the output level and lead to hissing and/or 'frying' noises, but that can be cleaned and performance fully restored by a skilled technician.
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On the other hand, an electret mic can lose the internal stored charge over time and that will also reduce output level and increase noise. Early electret mics (from the 70s and 80s) are much worse for this than modern designs which are vastly improved and can expect a life of 50 years or more.
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If a true condenser sounds dull it could be a contaminated diaphragm -- especially if it has been used a lot on close vocals without a pop screen, or in a smokey environment -- or it could conceivably be because the diaphragm has stretched if used in front of very loud sources (especially kick drums). Alternatively, it could be caused by deteriorating components -- especially aging capacitors -- in the impedance converter electronics.
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In case of the NT1-a I can't say how it was treated. The capsule doesn’t sound dull or noisy at all, as soon as it is operational. So, I’m tempted to conclude that a component in the impedance converter electronics seems to have deteriorated which results in the slow magnetizing process of the diaphragm. My gut feeling tells me that it could be a defective capacitor. But that's pure speculation.
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Since the NT1-a is a 2018 model and my electronic circuit troubleshooting skills are not sufficient to determine the root cause, I should send it to Rode for maintenance.
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If anyone has any other ideas, I would be happy to carry out further error analysis. But I'm afraid I'll definitely need detailed instructions.
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Otherwise I will send it to Rode next week.
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Many thanks to all of you!
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Have a nice weekend.
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Heinz
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In da 80s, I didn't like ANY of the conformal coatings for the HiZ part of any PCB.? Modern stuff might be OK but I have no experience. Supposedly you can solder through this stuff: ...I got some for a project but didn't actually end up using it (for other reasons). -c
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I've tried - the finest small soft artist's brush, distilled water, the slightest touch with wet bristles near parallel to the diaphragm -? the answer, for most of us mortals, is... no. Gold comes off. And from your photos, the capsule doesn't look that bad for its age, nor do I think it's the capsule that would cause the problem you're observing.
I would use a blower brush (for camera lenses) and VERY GENTLY remove any loose stuff.? I would NOT USE ANY LIQUID or ANY HIGH PRESSURE AIR.
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Yes, you might remove some Gold but actually the capsule will work fine with a bit of Gold missing :)? The real danger is your liquid moving yuck behind the diaphragm.? Then the mike will be forever / intermittently noisy. :(
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I think Josephson or one of the other commercial mike makers said you DON'T TRY CLEANING CAPSULES UNLESS YOU CAN REPLACE THE CAPSULE IF IT ALL GOES TO SHIT.? I second this as an ex commercial mike maker.
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From your description, I don't think you have a dirty capsule.? This would be VERY NOISY long before it stops working.
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I think the muck on your PCB coupled with humidity, was making the polarizing voltage generator wonky.? After 3 min. the warmth of the electronics dried the stuff enough for it to work again.? The polarizing voltage has some serious decoupling to remove any noise in the generator.
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In da 80s, I didn't like ANY of the conformal coatings for the HiZ part of any PCB.? Modern stuff might be OK but I have no experience.
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Happy to help, no problem! Nice to hear it seems the mic is working properly now!?
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Enjoy your purchase.
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Jan
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On Thu, Oct 24, 2024 at 10:18 PM, Jules Ryckebusch wrote:
Clean the flux and debris off with isopropyl alcohol the ?test.
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Hi Jules. I've put on my magnifying ocular and cleaned the flux, debris and the burned coating. When I looked more closely with the magnifying ocular, I also noticed a kind of greasy film all over the circuit board. I cleaned this too and dried it with paper towels that I normally use to clean lenses.
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When I turned the mic on, it worked! I'm going to do a test recording now and let it record for a couple of hours. I will inform you of the results.
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@JP8 (Jan)
Thanks again for the tip. Hopefully I've learned my lesson and will check any used microphones I buy more carefully before turning them on or bothering you guys when something is wrong. The NT1-a seems to be from March 2018. If it doesn't work as expected, I'll send it in.
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I will buy nail polish soon and use it as a coating.
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Many thanks!
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On Thu, Oct 24, 2024 at 10:18 PM, Jules Ryckebusch wrote:
Clean the flux and debris off with isopropyl alcohol the ?test. ?If you want to reseal it you can use clear nail polish. ?
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Next question: phantom power is used to generate the internal voltage used by the mic electronics and a bias generator. The bias generator creates the capsule bias voltage which is usually 60VDC ?in run my mics at 80V ?rode goes higher. It is only present when the mic is powered on. That voltage charges the mic capsule, which is a capacitor or “condenser” in 1930’s speak. When sound vibrates the gold plated diaphragm the capacitance changes and that results in a vintage change in the capsule. Which is what we want.?
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I will clean the flux and debris off tomorrow.
Many thanks for the explanation, Jules. That would explain the newly discovered behavior.?
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Clean the flux and debris off with isopropyl alcohol the ?test. ?If you want to reseal it you can use clear nail polish. ?
Next question: phantom power is used to generate the internal voltage used by the mic electronics and a bias generator. The bias generator creates the capsule bias voltage which is usually 60VDC ?in run my mics at 80V ?rode goes higher. It is only present when the mic is powered on. That voltage charges the mic capsule, which is a capacitor or “condenser” in 1930’s speak. When sound vibrates the gold plated diaphragm the capacitance changes and that results in a vintage change in the capsule. Which is what we want.? Best Regards,
Jules Ryckebusch?
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On Oct 24, 2024, at 07:48, Heinz via groups.io <heinz.hartfiel@...> wrote:
? On Thu, Oct 24, 2024 at 02:55 PM, @jp8 wrote:
can you take a picture that zooms in on the high-Z area around the red wire?
Many thanks for pointing me to the area and the detailed instructions to clean it up!
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I will give it a try to remove the discolored coating and flux. It will take some time because I have to order the acrylic coating first. Any tips on which coating I should use?
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Rode uses a high polarization voltage of 100V or more?! That's interesting. I have a beginner question. Is polarization performed every time the microphone is switched on or every time phantom power is applied respectively? Without polarization the capsule doesn't work, right? What could be the reason that polarization takes time? Shouldn't the polarization be kept? I'm asking because I noticed a different behavior today.
If I don't use the microphone for several hours and then turn it on, the NT1-A needs 3 minutes to warm up before it starts working. If I then unplug the XLR cable and plug it back in after three minutes, no warm-up phase is necessary. The NT1-a is immediately ready for use. Apart from the fact that after a longer period of operation, there will be interruptions again. Which could indicate a problem between the capsule and the circuit board?! I'm just guessing. Many thanks, Jan!
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You will get emi and hum without the headbasket — it is a faraday cage? Best Regards,
Jules Ryckebusch?
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On Oct 24, 2024, at 06:34, Heinz via groups.io <heinz.hartfiel@...> wrote:
? On Thu, Oct 24, 2024 at 12:29 PM, kennjava wrote:
While the mic is open, connect it to your recorder or mixer, and gently tap the board and connections with the the back of a plastic pen while listening
I tried your suggestion. But as soon as I remove the cover, connect the XLR cable and switch on the phantom power, the mic is caught in a ground loop. Or is it because the EMI/RFI shield is missing? I recorded a bit... <inline.0.part>
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I gently tapped the board and connections with the back of a plastic pen while listening. The only thing I could hear was the humming. Even when I snapped my fingers directly in front of the capsule after 5 minutes, the level indicator didn't change.
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On Thu, Oct 24, 2024 at 02:55 PM, @jp8 wrote:
can you take a picture that zooms in on the high-Z area around the red wire?
Many thanks for pointing me to the area and the detailed instructions to clean it up!
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I will give it a try to remove the discolored coating and flux. It will take some time because I have to order the acrylic coating first. Any tips on which coating I should use?
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Rode uses a high polarization voltage of 100V or more?! That's interesting. I have a beginner question. Is polarization performed every time the microphone is switched on or every time phantom power is applied respectively? Without polarization the capsule doesn't work, right? What could be the reason that polarization takes time? Shouldn't the polarization be kept? I'm asking because I noticed a different behavior today.
If I don't use the microphone for several hours and then turn it on, the NT1-A needs 3 minutes to warm up before it starts working. If I then unplug the XLR cable and plug it back in after three minutes, no warm-up phase is necessary. The NT1-a is immediately ready for use. Apart from the fact that after a longer period of operation, there will be interruptions again. Which could indicate a problem between the capsule and the circuit board?! I'm just guessing. Many thanks, Jan!
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On Thu, Oct 24, 2024 at 12:29 PM, kennjava wrote:
While the mic is open, connect it to your recorder or mixer, and gently tap the board and connections with the the back of a plastic pen while listening
I tried your suggestion. But as soon as I remove the cover, connect the XLR cable and switch on the phantom power, the mic is caught in a ground loop. Or is it because the EMI/RFI shield is missing? I recorded a bit... 
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I gently tapped the board and connections with the back of a plastic pen while listening. The only thing I could hear was the humming. Even when I snapped my fingers directly in front of the capsule after 5 minutes, the level indicator didn't change.
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Heinz, can you take a picture that zooms in on the high-Z area around the red wire? The picture becomes too blurry to see all the details when zooming in, but it looks like there has been some soldering going on there. And it looks like there are charred remanents of damaged conformal coating and flux residues. These can become conductive and short out the signal. The coating is there for a good reason and should be intact! Rode uses a high polarization voltage of 100V or more. Good for SNR, but it increases moisture sensitivity and accelerates tracking and dendrite growth.
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Carefully remove discolored coating and flux, then clean with IPA and a brush. Finally, rinse off with abundantly applied IPA. I use an IPA aerosol can for that. Dry with hot air and apply new conformal coating. I'm not sure, but I think it's acrylic coating they used. Epoxy could be used as well, but may be harder to remove in case you have to solder on new wires of a new capsule.
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Good luck with it!
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Jan
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On Wed, Oct 23, 2024 at 09:09 PM, Heinz wrote:
Is there a way to clean a capsule without kicking it in the bucket?!
I've tried - the finest small soft artist's brush, distilled water, the slightest touch with wet bristles near parallel to the diaphragm -? the answer, for most of us mortals, is... no. Gold comes off. And from your photos, the capsule doesn't look that bad for its age, nor do I think it's the capsule that would cause the problem you're observing.
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While the mic is open, connect it to your recorder or mixer, and gently tap the board and connections with the the back of a plastic pen while listening (at safe levels!) , to see if there's something loose.
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Here are the capsule photos you requested. I added two photos from the circuit board as well. From the images posted the capsule doesn't look too bad, honestly, i.e. pretty normal for an older/used mic I'd say, but I'm not an expert. (Of course you can't tell for sure from a visual inspection whether there would be issues.) In terms of DIY cleaning, I read enough about the process to be scared to attempt it myself with a mic I cared about. I started to try but ended up sending it away. That video seems way more aggressive than I would ever dare be, but I'm no expert and will let others more knowledgeable weigh in. And of course this could be a good practice mic for your technique, so there's that. But I wouldn't bother heading down that road until/unless an expert here agrees that it's a potential explanation for your symptoms. Btw: Yesterday I registered the microphone with Rode. They promptly issued an extended warranty for the product until 2034. Maybe I'll send it in and ask for a cost estimate for a repair. Heck yeah -- especially if it's under warranty that would definitely be the way to go. :-) -c
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On Thu, Oct 24, 2024 at 01:50 AM, Casey wrote:
It just makes me wonder if the dirty capsule might be reacting to changes in temperature/humidity. Might be a dumb long shot, but maybe Heinz should post pics of the capsule just to sanity check the situation?
High humidity is a real problem here. I usually store microphones in dry boxes. Especially during the hot and humid summer season. The NT1-a seems to be particularly susceptible to moisture.
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Here are the capsule photos you requested. I added two photos from the circuit board as well.
It doesn't look very promising. I wonder what the other side of the capsule might look like, but I was afraid to take the back plate off. I guess Casey is not entirely wrong in the estimate. It could well be moisture damage.
 ---  Btw: Yesterday I registered the microphone with Rode. They promptly issued an extended warranty for the product until 2034. Maybe I'll send it in and ask for a cost estimate for a repair. Considering that the NT1-a came out in 1995, there may still be an additional defect in the circuit.
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I'm aware this is a Micbuilder and maybe not a Micrepairer group, so I really appreciate your responses.
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Perhaps one final question about cleaning large diaphragm capsules. I found many contradictory statements on the Internet. Is there a way to clean a capsule without kicking it in the bucket?! I saw that looked trustworthy and somehow made sense to me. Have any of you tried this method or perhaps know a more reliable way? I'm just wondering.
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Many thanks!
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Heinz
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