SM57 - thin sound - fixed! Very unusual fault, but pictures xplain it all.

R

rob aylestone

Moderator
I did a video last week and compared some mics, and for the first time ever, an SM57 did a bad job. Just thin, but when I investigated pulling the plastic end ring away from the mic, it restored to normal.

This seemed odd and worthy of investigation, so I pulled out my collection of broken mics (the idea was to fix them over the quiet periods, but it never happened.

I pulled apart a dead one. I remembered that I started a spreadsheet with resistance values for capsule and transformer wires, and found that the transformer measured fine and the first mic had an open circuit capsule. I then removed that capsule, and took the end cap and perforated screen off. I repeated this process for the qeird sounding one and the capsule measured out normal. I removed the end cap and looked at the diaphragm. Dead centre was a little black 'microturd' - the best description I have. The end cap has plastic in the centre - sound gets through via 7 circular ports, so I am assuming the spec is a collection of tiny foam fragments that have gradually coalesced with spit into a little lump dead centre. eventually it grew to the size where it touched the centre of the cap, and that's what changed the tone. I'm pretty sure this is the very first one I bough from the 70s, so this probably isn't really bad, is it? Looking at the others in the box - there are two with open circuit capsules - I did look for a replacement, but the only so called genuine ones are clearly not.
 

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That's cool. It's exciting to actually find the cause of such a problem - especially when it's easily remedied. However, I don't believe you are aware of what you actually hold in your hand. You've stumbled onto a great modification. You can buy a bunch of SM57 clones, add your own (patented) "microturd" to each and sell them as SM57 Chris Squire Editions. Maybe a packaged set - regular SM57 clone paired with a Chris Squire Edition in a lined wooden box. Oh yeah. . . :guitar::p
 
I'm surprised that a microturd that small would make such a huge difference in the sound, especially in the low frequencies. I would have thought it would dampen the mids and highs and be all bass.
 
I think it possibly actually touched the underside of the dome in the cap. Difficult to know exactly what the clearance was, but when I tugged the cap away - it moved a tiny bit and the sound changed to normal, but pushed just a little, I suspect it pushed against the microturd?
 
If your microturd was kind of jammed in there it would impede movement of the diaphragm and bass would be the first thing to go.
That'd be similar to what happens if the whole coil and diaphragm assembly shifts such that the coil is rubbing against the magnet.
I've had that happen with a 57, even though they're glued down, and old AKG D12s which are clamped with a screw-down ring.

Gently put some pressure on a monitor woofer some time and you'll see what I mean. The bass just disappears.
 
rob aylestone said:
I did a video last week and compared some mics, and for the first time ever, an SM57 did a bad job. Just thin, but when I investigated pulling the plastic end ring away from the mic, it restored to normal.

This seemed odd and worthy of investigation, so I pulled out my collection of broken mics (the idea was to fix them over the quiet periods, but it never happened.

I pulled apart a dead one. I remembered that I started a spreadsheet with resistance values for capsule and transformer wires, and found that the transformer measured fine and the first mic had an open circuit capsule. I then removed that capsule, and took the end cap and perforated screen off. I repeated this process for the qeird sounding one and the capsule measured out normal. I removed the end cap and looked at the diaphragm. Dead centre was a little black 'microturd' - the best description I have. The end cap has plastic in the centre - sound gets through via 7 circular ports, so I am assuming the spec is a collection of tiny foam fragments that have gradually coalesced with spit into a little lump dead centre. eventually it grew to the size where it touched the centre of the cap, and that's what changed the tone. I'm pretty sure this is the very first one I bough from the 70s, so this probably isn't really bad, is it? Looking at the others in the box - there are two with open circuit capsules - I did look for a replacement, but the only so called genuine ones are clearly not.
Click to expand...

So this is not a common occurrence with SM57s? And you said you pulled apart your collection of broken mics - do you collect them to figure out the problems or do you break a bunch microphones? - I've never had an issue with my SM57s - I've think I've got around 21 - most of them are over 25 years old - never seen this in active mics.
 
Steenamaroo said:
If your microturd was kind of jammed in there it would impede movement of the diaphragm and bass would be the first thing to go.
That'd be similar to what happens if the whole coil and diaphragm assembly shifts such that the coil is rubbing against the magnet.
I've had that happen with a 57, even though they're glued down, and old AKG D12s which are clamped with a screw-down ring.

Gently put some pressure on a monitor woofer some time and you'll see what I mean. The bass just disappears.
Click to expand...

Sounds like that's what happened. Like a HPF set at 700 Hz or so.

Papanate said:
So this is not a common occurrence with SM57s? And you said you pulled apart your collection of broken mics - do you collect them to figure out the problems or do you break a bunch microphones? - I've never had an issue with my SM57s - I've think I've got around 21 - most of them are over 25 years old - never seen this in active mics.
Click to expand...

There's obviously something wrong in the way you handle your equipment. You should send yours to Rob so he can fix them for you :p
 
No No - I felt guilty today so took one of the duff ones - the other one in the picture and it's open circuit, so I got a jewellers eyeglass and spotted that the microthin copper wire from the solder tag that goes down the side under a layer of tape was physically broken. I filed the tip of the soldering iron - found another bit of wire and delicately soldered it on. I attached it to the tag, and bingo - the meter gave good news. I started to reassemble it, keeping the fragile diaphragm safe and then the nasty spring clip assembly to put the cap back on. The tube slides over and that's a tight fit, and I slipped and snapped the copper coil wire off where it entered the capsule. Ruined!

I have never broken a 57 - but I know exactly how these two suddenly became faulty. I loaned them to the PA company for the band at a theatre when they were short, and they handed two back after the show. I put them in the mic box. These two mics are dead. When you unscrew a 57 or a 58, I write 'ears' in sharpie on the capsule. My two dead ones do not have 'ears' inside - so the PA guys gave me two of theirs. The cynic in me thinks they had two duff ones, so borrowed my two good ones, and deliberately ripped me off. It's probably a year ago, so my fault.

In the duff box at the moment are the following mics:
AKG D190 - dead
Audio Technica 815 shotgun - hums
Samson S02 - dead
Samson S02 - hisses
Sennheiser e609 - rattles
AKG C451E - capsule hisses


Rainy day projects.
 
I have 4 dead mics.

AKG D160e Omni (very old.. open circuit in the capsule)
2 CAD TSM411 (open circuit in both mic capsules.... I THINK due to phantom power.. only reason I that was a common denominator).
Shure 55 1950s era (besides being 60+ years old, it was underwater. It has the Amphenol connector and HML impedance switch)

Everything else works.
 
Seriously though, the diaphragm was really clean and the foam totally intact. No obvious sign of goo or nasty stuff or crumbled foam. All clean and tidy, but just the tiny black micro turf. It was so small, I used a scalpel blade to slice it off the mylar.

Two open circuit 57 mics seems wrong to have at the same time. And they’ve just say in the mic box if you buy a new capsule, you get it with the complete set of bits. The disassembly is not too bad, but if it’s simply not a dry joint, then it really is micro surgery. I’ll have a look today at the one I have left that is dead. An open circuit coil is just something that shouldn’t happen. The transformer makes DC damage impossible, but the actual coil wire is very fine, scraping the insulation off is really hard. Maybe I’ll get a camera out and see if I can show you what’s actually inside the bits people don’t normally have to take apart?
 
I started to do a video and decided to sacrfice the faulty capsule and I sliced off the mylar diaphragm to have a look inside - to be fair I'd decided my smallest soldering iron was by comparison huge to the wires, so I knew my clumsy talents in that department wouldn't let me fix it, but I found the actual design really clever - especially for something 50 years old, design wise. I also dug out a fake 57 to compare it to - and discovered the fake had the transformer in the head end, not the body tube sealed in epoxy. I wondered about the design inside the Chinese one and discovered they actually sell spare capsules claimed to fit in the Shure body and even feature the rotating end cap - these ones don't feature the transformer, so I have ordered a couple to see if I can fix the genuine Made in Mexico SM57s that are dead. Less than £10 for two! They will either fit, or not - but if they do, I can then compare what they sound like. I discovered replacement capsules for 57, 58 and Beta 58 are available at very low prices. The sources for genuine ones are very limited now - my usual supplier for Shure spares doesn't have any, but the one that did wanted over £70, and I can get a new 57 for not much more than that. £91 from a trusted genuine source.

I'll report back

I thought you might like to see £100 vanishing in a very small crunch.
 
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I wouldn't bother with fakes, myself.
Any I've seen are an extremely lightweight assembly, like a headphone driver, with an empty plastic tube taking up the space where the heavy magnet would go in the real deal.
That might even be why they've put the transformer up front in the one you describe - to make the weight discrepancy less obvious.

Of course what you've bought might not be the same as what I saw but I thought it was worth mentioning.
There's often a huge difference between a clone and a fake.
 
Yep - but there are also some that are impossible to hear - Thomann do their own brand - it's sold as a 75, not 57, and no Shure markings, but you'd be hard pressed to tell. Some are absolutely awful - but a £12 57 vs £40 57, then £50 one and things really change.
 
Sure. You would hope Thomann would be aiming at a capsule of similar design, weight, and quality,
although I couldn't find any disassembly pics or videos online. 🤷‍♂️
 
I had a very old mic some time ago that had virtually no signal output and the magnet gap had corroded, white and green ***t and the diaphragm was solid.

Re cheap, not ripoff mics? I have mentioned before the Behringer XM8500, more like a 58 but not really trying to copy one. The sound is very acceptable, especially for $25ish! It is a decent weight and would stand some abuse but not, perhaps as much as a genuine Shure. It does not have a transformer and has a quote impedance of 300 Ohms. DC resistance is 250R.

The 57/58s AFAICT have a capsule impedance of about 12 Ohms and so if you take the mic's source impedance as 150R* then it uses an about 1:3.5 step up transformer. I would guess way back when the mic was designed it was easier to wind a coil of a few turns of a relatively thick wire which would be more robust than much thinner stuff. A transformer also makes the mic pretty bombproof against phantom power in the event of a cable miss wire.

*Shure's spec says "150 Ohms (310 actual) NO idea WTF that means!

"Such fun!"

Dave.
 
That's useful info Dave - the resistance of the capsule , from direct connection to the terminals was 12.1 Ohms which fits in well. I'm left wondering if both of the open circuit ones failed due to breakage of the wire?
 
rob aylestone said:
That's useful info Dave - the resistance of the capsule , from direct connection to the terminals was 12.1 Ohms which fits in well. I'm left wondering if both of the open circuit ones failed due to breakage of the wire?
Click to expand...
Forgot to say, the Behrry is a couple of dBs more sensitive than a 57. All helps!

Looked in vain for a true value for the transformer ratio but did find shedloads of sites offering transformers some as low as six quid for two!

Dave.
 
rob aylestone said:
I discovered replacement capsules for 57, 58 and Beta 58 are available at very low prices. The sources for genuine ones are very limited now - my usual supplier for Shure spares doesn't have any, but the one that did wanted over £70, and I can get a new 57 for not much more than that. £91 from a trusted genuine source.
Click to expand...
that was my vote too, I had one or two destroyed 57's in the sons punk band that was about music and breaking stuff ..50/50.
I looked into the 57 and priced capsules and I thought? I can get a whole mic, brand new 57 for a little more cash. ..no work. Thought the capsules were way overpriced.
 
ecc83 said:
I have mentioned before the Behringer XM8500, more like a 58 but not really trying to copy one. The sound is very acceptable, especially for $25ish! It is a decent weight and would stand some abuse but not, perhaps as much as a genuine Shure. It does not have a transformer and has a quote impedance of 300 Ohms. DC resistance is 250R.
Click to expand...
Thats more appealing to me than a fake lookalike, the XM8500 price $25 and its their own design.
For HR on budget too, 25% the cost ..HR land is usually gentle compared to live environment.
How does anyone make a "decent legit mic with transformer" for $25 retail? Thats maybe another thread, but its mind boggling to me.
 
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