Bargain or Bust?

[MicMaven]

Good Day Mic Mavens. I purchased a used KSM44 microphone at a ham radio swap meet for $15 today. It appears in reasonably good condition, but it exhibits a substantial level of noise and much lower signal levels than other condenser microphones. Photos and sound clip attached.

What might I do to boost the output level and minimize noise? Any suspicious characters in view? Should I suspect problems with the circuit boards, or capsule, or both?

Have I purchased a microphone project or a parts rig? Boon or Bane? Bargain or junk? I recognize I provide precious little to chew on, but I do not know where else to start. Any ideas ? James - K8JHR -

First test - all original parts.
View attachment KSM 44 Mic test 1.wav

View attachment E50 versus KSM44 test G.mp3

 

[kingkorg]

You might have an issue like this.
I had the same issue with my ksm44. I replaced the whole board eventually for original one i got from Shure distributor.

If nothing, for that price you got a mic with exceptional capsule, so you can build something else inside it, or transplant the capsule into another body. The original board is nothing special really, probably over engineered.

 

[Icantthinkofaname]

You might have an issue like this.
I had the same issue with my ksm44. I replaced the whole board eventually for original one i got from Shure distributor.

If nothing, for that price you got a mic with exceptional capsule, so you can build something else inside it, or transplant the capsule into another body. The original board is nothing special really, probably over engineered.

It's probably a really solid body too.

 

[MicMaven]

Thank you, Gentlemen, for the initial response.

YES, the body feels heavy and solid. I figured it would, at the very least, be a nice $15 donor body. It was so cheap, I acquired it without a definite plan for it!

I presume, from KingKorg's initial take, the capsule may be OK, and the problem is more likely in the circuit board(s)? Should I try the capsule in another microphone to see if is OK? Or, should I try a different capsule with the original KSM44 boards to see if they is OK? Are there easier and better ways to determine whether board or capsule or both are futzed? (Assume I have no proper test equipment outside simple multi meters on my electronics bench.)

Considering the shell as a donor body, what could/should I put in it? How about a set of Alice OPA boards with either the original KSM 44 capsule or a new dual or single-sided capsule, or ... what else? I am not particularly interested in a multi-pattern microphone, so a single cardiod type capsule would probably be sufficient, but then, should I be thinking bigger? Do you suppose I could use just one side of the original Shure capsule with another microphone designed for a single sided capsule.

Thanks for any additional insight. James - K8JHR -

 

[Icantthinkofaname]

One of first things I would do is put it in a bag with some sort of desiccant in case there's moisture on the capsule. I had an MK-012 that went quiet and noisy after cleaning, I think a bit of isopropyl or acetone got on the diaphragm and drying it out for a few days fixed the issue.

If something does need servicing (either capsule or part of the board) I would use the parts Shure intended, unless you can make some sort of improvement (maybe increased voltage, quieter components, etc).

 

[MicMaven]

Roger the desiccant - it surely won't hurt to try it.

I am not sure what you mean by "use the parts Shure intended." Do you mean I should replace any defective part with a genuine Shure replacement part? Or have I missed the point?

Sidebar comment - After visiting the Shure web site, it sort of appears it is not selling replacement parts, and offering a Flat Fee Repair Service for a whopping $500 ! Ouch. So much for my bargain microphone! Double Ouch.

James - K8JHR

 

[Icantthinkofaname]

Roger the desiccant - it surely won't hurt to try it.

I am not sure what you mean by "use the parts Shure intended." Do you mean I should replace any defective part with a genuine Shure replacement part? Or have I missed the point?

Sidebar comment - After visiting the Shure web site, it sort of appears it is not selling replacement parts, and offering a Flat Fee Repair Service for a whopping $500 ! Ouch. So much for my bargain microphone! Double Ouch.

James - K8JHR

I would email them to inquire about getting replacement parts, or check a site like Full Compass. If they don't sell them then it's kind of a moot point, but yes I would use the KSM44 capsule and PCB and just replace whatever faulty components are there. That's not to say you couldn't build something else in there, you could easily use an M7 capsule or an accurate K67 replica like the one Soliloqueen sells (or even a CK12) and have PCBs made that would fit the Shure body. It'd still cost you a couple hundred bucks to make a good mic in that body if it can't be repaired, which is why I suggested using whatever replacement parts there are designed for the mic.

 

[Khron]

As per my (successful) thread that @kingkorg mentioned earlier here, i'd go ahead and replace all the tiny light-gray capacitors with 100-120pF C0G/NP0 ceramics (pretty sure they were 0603-sized). Yes, it's a bit labor-intensive, but hey - how much does a new (or used, working) KSM44 go for?

Of course, a preliminary test would be to (temporarily) connect another known-good capsule (even cardioid-only) to the front diaphragm and backplate connections, and see if the noise remains the same. It very much did, in my KSM27. If it does, it'll likely be those capacitors. If not, then it's worth trying out the capsule in a known-good circuit, and see if that's noisy.

 

[MicMaven]

Gentlemen - I appreciate the clarification provided by each reply.

My wife can acquire a substantial quantity of dessicant from her place of work, so I will try that in a day or two. No harm, no foul - certainly worth trying as I have no idea how this was handled or stored by its previous owner. I am fussy about how I handle delicate electronics, musical instruments, radios, etc., especially allowing items to reach room temperature before opening boxes previously in the cold, and that sort of care.

I contacted Shure over the weekend, and await its response concerning replacement parts. I also checked Marketek, Full Compass, BSW, B&HPHotovideo, and a couple other likely suspects looking for replacement parts, with no joy. I recall seeing replacement capsules somewhere sometime in the past, but I cannot find them now. Sheesh! You know how it goes ... everyone is flush with parts, until you need them!

Unfortunately, I am a bit of a rookie at electronics, with limited experience troubleshooting and replacing SMD components. While I am a reasonably skilled project builder with through hole components, and actually own a basic L/C meter, I lack the competence and reflow equipment to competently replace SMD bits. I am, however, working to expand my skill set as everything is going in that direction. (My career as a licensed professional was in a vastly different field, but like the AVIS company, I try really hard.)

Spending just $15 to for this item, I had no expectation it would work at all, and figured it would be a parts rig or donor body. I will test the capsule and boards as per your suggestions, and see what gives. It is OK if it becomes something very different from an original KSM44. I will be pleased if ANY part of it proves useful, whether that is capsule, boards, or body/shell. Considering the magnitude of my initial investment, I will be pleased if I can make anything useful with it. Shoot! It is heavy enough to anchor a small skiff! It will find its purpose, eventually.

I truly appreciate your looking over my shoulder as I approach this project. I realize this is a small potatoes sort of project, but I will learn something from it, so I cannot lose. James - K8JHR -

 

[Khron]

No particularly fancy reflow equipment needed for these still-reasonably-sized two-terminal passive components.

My favourite soldering iron tip is a knife-blade style. Nice fat flat sides for good heat transfer into big joints, as well as a nice pointy-enough tip for finer work.

You should be fine even with a pretty normal 1.2-1.6mm-wide wedge tip.

For removing parts, i like to add some fresh solder to each end of the part, as well as plenty on the tip, and angle the iron so that the tip (with molten solder) reaches both ends of the component at once. Then you can pick it off with some nice sharp tweezers, or even just "wipe" it off with the iron tip itself. Clean off the pads with some (rosin / flux infused) solder wick, and you're good to go to solder in the new capacitor(s).

I'm moderately proud of my stubbornness and persistence, allowing me to still comfortably-enough maneuver 0402-sized components without additional vision-aids

 

[peterc]

I had a KSM44 for many years and it was an axcellent mic. Seems to have dissappeared from my mic box, really sad about that.
In my studio at the time, I had a very small booth (for voice overs) and my U87 sounded awful. Put in the Shure and, bingo, sounded great. A keeper in my opinion if you can get it sorted.

 

[MicMaven]

Good Day, Mr. @Kron. Perhaps you are merely "determined" and not as "stubborn" as you claim. In contrast, my wife is stubborn.

But seriously folks, I appreciate the nudge to upgrade my skill set reworking SMD components. Unfortunately, that remains a work in progress. Do you ever use a hot air device for SMD rework jobs? I have one, but I am far from proficient using it.

Your preference for blade-shape solder tips intrigues me. I need to get to know them better. I typically use conical or 1.2mm screw driver (chisel) tips on circuit boards, or the thickest heaviest tip possible installing large RF connectors because those have more "heat mass" to give away. Melting Teflon center insulators on PL-259 connectors is both costly and embarrassing, and easy to avoid with the correct tool for the job.

Thanks for the uptake. James - K8JHR

PS - to @Icantthinkofaname -- Shure tech support proffers no help and passed the buck to another department, so the the saga continues. JR

 

[Khron]

https://assets.testequity.com/te1/product-images/large/10140964_1.jpg
I use an Ersa iCon nano as my "daily driver", and the item code for the blade-type tip is 0102BDLF2, if you want to look up more pictures.

And i use a cheapie hot-air wand for non-iron-able packages, like QFN's or QFP's. I'll still manually solder on QFP's though, for reliability's sake (even if i often bridge together sets of 2-3 pins and have to then wick off the excess )

 

[MicMaven]

Mr. K - Your Ersa iCon nano solder station looks good. I have 2 Weller stations, a Hakko 936 knock-off station, and a low cost hot air gun/wand.

So ...

This evening I am testing original KSM44 boards with a couple of different capsules to see if they are OK or can be used with a different capsule. I will try the original sure capsule on a different mic/board if I have time. I am postponing troubleshooting the original boards at component level on a work-from-outside-in basis.

QUESTION: What happens if I test the original KSM board(s) with an electret capsule, or pair of capsules, which have their own permanently charged plates and which are not "true" condenser capsules? A large 34 mm condenser capsule does not fit in the KSM44 head basket without modifying the head basket, and I do not want to alter it unless I must later on. Using another mic basket and holding it all all together with aluminum foil to cover the gaps between basket and body is hardly an ideal test arrangement !

Thanks - James -

 

[MicMaven]

Initial CRUDE TEST of the KSM44 Capsule -

Attached mp3 compares (a) a new CAD E50 microphone, with (b) one side of the KSM44 capsule on a set of Alice OPA boards, and (c) a low cost 34mm Chinese condenser capsule on the same set pf Alice OPA boards. Recorded with an M-Audio Preamp on a computer sound card at about 6-8 inches. Not high end gear, but a handy bit of kit for quick testing. Does it tell us anything? -James-
View attachment E50 vs KSM44 with JLI boards vs Chinese capsule JLI boards.mp3
View attachment E50 vs KSM44 with JLI boards vs Chinese capsule JLI boards.mp3

 

[kingkorg]

What happens if I test the original KSM board(s) with an electret capsule

You can just do it, no problem.

 

[Icantthinkofaname]

Initial CRUDE TEST of the KSM44 Capsule -

Attached mp3 compares (a) a new CAD E50 microphone, with (b) one side of the KSM44 capsule on a set of Alice OPA boards, and (c) a low cost 34mm Chinese condenser capsule on the same set pf Alice OPA boards. Recorded with an M-Audio Preamp on a computer sound card at about 6-8 inches. Not high end gear, but a handy bit of kit for quick testing. Does it tell us anything? -James-

So what were the results? I'm getting an XML file error clicking the attachment.

 

[MicMaven]

what were the results? I'm getting an XML file error
____________________________________

Sheesh ! First nothing, now two copies appear. I edited the origininal post and they should appear now. Um ... I think.

Also - here is a sample of the E50 versus the KSM44 original boards with a low cost 25mm Chinese capsule (which was previously discussed in positive terms in another thread) - and a second sound sample of the E50 compared with the KSM44 boards and a BM-800 capsule I had in the parts closet. ( A rather crude test because I recorded them in a hurry late last night whist doing umpteen other things. I just hate when real life interferes with my hobbies. James


View attachment CAD e50 vs KSM44 boards and BM800 capsule .mp3

View attachment e50 vs 25mm capsule and original KSM44 boards test 1.mp3

 

[MicMaven]

OK, guys, I think all the sound samples can bee played right from the main screen. The rookie did not fully "insert" the files the first time ... duh.

Now that you can hear them, any traction or suggestions? James

But WAIT ... there is MORE !

PS - @Icantthinkofaname asked about cost of replacementparts, and Shure replied today with the following information. I think I could afford to replace the boards easily enough - and then either use the oroginal capsule or some other capsule that may not be as expensive, although this would make me a very expensive mic for relatively low cost - considering Shure would repair and refurbish the unit for a whopping $500, and a new one costs more than $900. Still, it would be swell if I could use any /most/ all of the original parts for a super bargain on my initial investment.

p/n description price

RPM131 CARTRIDGE - KSM44A/SL - SERVICE ONLY $181.77
90A13940 PCB-KSM44A POWER SUPPLY 25.76
90A13942 PCB-KSM44A AUDIO BOARD 37.49
90A13944 PCB-KSM44A FET INTERFACE 23.73

 

[kingkorg]

90A13940 PCB-KSM44A POWER SUPPLY 25.76
90A13942 PCB-KSM44A AUDIO BOARD 37.49
90A13944 PCB-KSM44A FET INTERFACE 23.73

This is more than fair price. I've been quited 300$ for the audio board by Norwegian Shure distributor. And since i still have some Shure contacts in Europe, after being irritated by the distributor, I reported them to Shure Europe and got suddenly an quote of 114$ for the same part, followed by phone call and apology from the distributor.

The files sound exactly as my faulty mic. I would bet the capsule is ok, and the audio board, and/or psu board are faulty.

Now if you could persuade them to sell you the boards that would be a win. Extremely easy to replace, just snap in, all you need is a screwdriver.