SM7a/b humbucker coil

[CoolCat]

more pictures of disassembly -

The stand nut screw was weird- a square screw, the new SM7b with standard Phillips much easier, but this is the old one a button head screw with 4pt "square" screw.
Pic 1-5
Backplate and EQ and capsule wiring
following pictures- noted inner body is painted and wiring colors.

 

[rob aylestone]

That's really good for identifying how it should look! thanks for this.

 

[CoolCat]

Its one early version at least to note a bit. Outside the no-humbucking coil and the humbucking coil there's not a lot of difference seen.

Looking at the newer SM7b's I have there are good improvements imo, over the original ones.
1.Putting the XLR in the front seems to be popular (which can be done with any model of these)
2.The mic stand is now a Phillips/cross screw instead of this old weird square screw.

Seems most everything is still to the same spec/design and interchangeable from old to current. Some decal/label changes, nothing important.
As with old vs new in sound? gets crazy....the capsules and magnets etc, and age seems to be the "sound" difference debated forevermore. For gear collectors the old ones will go up in value

Shure has a number for the tiny screws pn 30D443E but they don't seem to sell them. Not much info on them I could find. But then another Shure Product seemed to have used the screw p/n and there were details its M25, and that's a o.08 size! 80 thousandths of an inch, so many people seem to lose them. To be honest 2qty hold the back plate/EQ plate fine but 4qty is the full set. I found that interesting as I need to order some. $7 for 10 of them or something.
UPDATE: Seems the tiny tiny backplate screws are technically called "2-56 x 5/16" , ( .086 dia x .31x Long ), the ones I got were too short in length so don't buy the 1/8/.11.

I also found the XLR shield wire intentionally not connected, with the black and clear wire going to the mic PCB. Because the pin 1 is connected to the case of the SM7, shield wire. There is a fine wire jumper from Pin1 to case ground. Inside the mic there's no green wire from the XLR. Anyway the old one works and noise was identical to my new SM7b.

In the picture it shows only black and clear going into the mic body and the XLR shows the pin 1 green with heat shrink on it? wierd. It works fine!

 

[bouldersoundguy]

Is the noise the same when near a powered up wall wart or fluorescent light?

 

[CoolCat]

Just having the mics setup sitting idle, I didn't see any difference.

Thats the thing, my setup/room doesn't have a hum buzz issue.
I can only assume the engineers of Shure got it right.
Some mention in the older days of tubes and amps and radio station setups/rooms the humbucker -coil was needed.

My original curiosity was if the humbucker-coil changed the sound but if the humbucker coil is only active in the presences of noise, seems its just docile when not needed.
In guitars humbuckers and single coils sound different, so I wondered?
I haven't done anything in depth of the sound thing. I am impressed the old mic works fine and isn't too beaten up. Interesting history of the SM7...SM57 on steroids the Shure article said.

I don't know anything about setups in the 1970's or 1960's that would not only drive the SM7 but also the humbucker-coil being added.

 

[drtechno]

Just having the mics setup sitting idle, I didn't see any difference.

Thats the thing, my setup/room doesn't have a hum buzz issue.
I can only assume the engineers of Shure got it right.
Some mention in the older days of tubes and amps and radio station setups/rooms the humbucker -coil was needed.

My original curiosity was if the humbucker-coil changed the sound but if the humbucker coil is only active in the presences of noise, seems its just docile when not needed.
In guitars humbuckers and single coils sound different, so I wondered?
I haven't done anything in depth of the sound thing. I am impressed the old mic works fine and isn't too beaten up. Interesting history of the SM7...SM57 on steroids the Shure article said.

I don't know anything about setups in the 1970's or 1960's that would not only drive the SM7 but also the humbucker-coil being added.

The humbuker is just a counter-wind tied in series. so they act like a small inductor filtering way past the audio range and counteract proportionally when electro magnetic radiation imposes on the mic coil. But since the inductance is small they don't interfere like they do with guitar pickups.

Since the "presence" filter is a useless cut, I removed mine and installed a TAB-58 transformer because it needs a step up transformer. That made it well compatible to plug into any mic preamp. About a year later, a young guy who was an intern with the local public radio was impressed on how it sound when I played through it and bought it off me. Which later I found out, that kid, Bryan Carlstrom, made a lot of platinum albums with it.

I made a couple of more for my own use, when I find someone to play with from time to time. They still freak the sound guys out because they think they are not going to work. Then when I played through them they freaked out because they decided to turn the mic gain up too much.

 

[CoolCat]

interesting. I looked for a picture of a bucker-coil wire, it must be tiny. The wire is so tiny, so I might assume the hum-180 coil wire is the same gauge?

modding a SM7abd , the TAB58 seems is 1inch x .7inch pretty large but the SM7 has more room I suppose somewhere in the body. Any pictures?
Bryan , wow...I was just listening to Americana this week, love Offspring, the guitars and vocal "sound" screaming tube compression vibe, good article in TapeOps.

 

[drtechno]

interesting. I looked for a picture of a bucker-coil wire, it must be tiny. The wire is so tiny, so I might assume the hum-180 coil wire is the same gauge?

modding a SM7abd , the TAB58 seems is 1inch x .7inch pretty large but the SM7 has more room I suppose somewhere in the body. Any pictures?
Bryan , wow...I was just listening to Americana this week, love Offspring, the guitars and vocal "sound" screaming tube compression vibe, good article in TapeOps.

I'll dig one out and take a picture when I have time this weekend. But the hardest thing was figuring out a way to mount it.
The last time I saw him was a couple of months before his accident and he was using it in this one corner space area that was enclosed on one side with a glass sliding door. He was distant micing a Marshall stack with using a modified marshall amp that had a bogden SRPP input stage made by a like minded modder. That later I modded again to clean it up more.

I tried to share my mod and even offer to sell ones on Gearslutz years ago. But they were more into pushing the cloudlifter which isn't a true fix for the microphone. Putting a step up transformer in it is the proper solution.

Long ago, I researched and tried out different preamps to find what kind of preamp that would interface it correctly. Which I found that it was DC coupled mic preamp channel. First one I found was from a sadies broadcasting board that is used in television and radio studios and others like a harrison (can't remember which model) and an AMEK M2500 were the other ones that worked instantly with a stock sm7.

 

[CoolCat]

Part of my question was trying to find a picture of the hum-bucker coil wire in the capsule. Just curious what it physically looks like.
The capsule wiring can be seen in repair- videos but Im trying to see what this SM7 coil- that was added, looks like. It's all just curiosity...
so you mentioned its wrapped in a opposite right vs left, and its not a "part" like the schematic shows the coil as a wave-y symbol.
Is it equal number of windings turns or only one wire wrap? sorry too many questions! lol

I don't even think Shure cared that much, its a company with many products and shipping it to Mexico and changing stickers, or changing the paint
is just not documented in their spec's much and they do this. Looking at pictures you see they changed stickers decals, paint types, none of it is really documented on why they
did it.

interesting your comment on the DC Coupled preamp for the stock SM7.
not sure what a DC Coupled is, and how it helps. some reading to do. I might have one around an not know it.

Did you ever witness in a working environment the hums and buzzes of the SM7 vs SM7a-b?
Someone in Shure made the change driven by customers seems logical. Why else would they bother?

I guess this all born from the SM5, did you ever use one of those? Wonder why they stopped making them?

 

[ecc83]

Hi Cool Cat, I can answer some of your questions I think from "first principles?

But first let me nail down the operation of the Hum Bucker Guitar Pup? Yes, this has two coiis but they are not 'contra wound' merely connected out of phase*, usually in series. This would normally give a very weak output akin to the "reedy" sound you get with a Strat with the selctor switch mid way betwen two pups. The HBGP is clever though and they REVERSE the polarity of one of the magnet strips. Thus the output voltages add.

A "DC coupled pre amp" (or AI for that matter) is one where no capacitors are used in the signal path. The idea is that this avoids the use of electrolytic capacitors which, it is claimed cause distortion. Well yes they do but for coupling duties (one part of a circuit to another) the simple solution is to make them large enough in value that distortion is next to nothing down to any desired LF limit. 10Hz say? DC coupled amps are more vulnerable to external voltages e.g. phantom power and difficult to protect, especially in the knockabout world of the studio and PA!
Yer pays yer money!

Re the SM7b bucker? AFAIK the mic was developed mainly for use in talk studios, radio, later TV where there was always a high incidence of meaty gear around with large 50/60Hz transformers. Home bods rarely have such problems and of course we all have HPFs in us DAWs!

*More correctly "Polarity" but leave us not get pedantic and poncy!

Dave.