Modify the Shure SM57 Microphone

[mikep]

[quote author="colinmade"] I'm going to do a break out box with a switcher between original transformer, a good replacement and no transformer.

[/quote]

not a bad idea at all. also, there are many variants of the 57, some with an on-off switch. perhaps, if it is a double pole switch, that could be used as a transformer bypass? alternativly you could drill a hole and mount a switch right on the side of a regular 57. you'll probably have to remove the transformer and then re-install it. maybe I will mod my 57 afterall.

mike

 

[soundguy]

CJ-

gus didnt modify my 57, I did...

thats not a beta, its a regular 57. betas have a different grille and have that blue stripe around them. I always wondered if the capsules were the same. Ive heard that the 58, 57 and 7 all have the same capsule, would stand to reason the beta is the same with a different grille, but Im absolutely pulling that out of my ass, I have no idea.

the easiest way to get the transformer out is unscrewing the XLR connector and knocking it through with a screwdriver and hammer.

you guys should realize that this is hardly anything new. A friend of mine showed me some stuff and when I discussed this with great excitement with "real" engineers I knew I was met with nearly %100 dead stares, "yeah, we've been doing that for 25 years". I guess there's always someone one step ahead of you.

was a really good secret for a while.

dave

 

[Emperor-TK]

[quote author="soundguy"]CJ-

gus didnt modify my 57, I did...

thats not a beta, its a regular 57. betas have a different grille and have that blue stripe around them. I always wondered if the capsules were the same. Ive heard that the 58, 57 and 7 all have the same capsule, would stand to reason the beta is the same with a different grille, but Im absolutely pulling that out of my ass, I have no idea.

dave[/quote]

Dave, like I mentioned above, the beta series use Neodymium magnets vs. the ceramic used in the classic SM microphones, so they are definitely diferent. The beta series came out shortly after the Electovoice ND (neodymium) series. EV marketed the ND mics as having better S/N ratios and being less feedback than thier ceramic counterparts (the Shures). My guess is that the Beta series was Shure's response to EV, and the Betas took off while the ND's didn't.

-Chris

 

[Flatpicker]

I never mic drums or guitar/bass cabs so the no-transformer mod is useless to me. However, if a re-lam can give me a significantly improved sound, or better yet, approach the sound of an SM7 for the price of a $50 transformer, I?m there.

 

[rodabod]

I'm a little dubious about the suggestion that the mic without the transformer might sound like an SM7.

I think the SM7 probably uses venting of some sorts to achieve a better response than the SM57.

Would anyone care to open up an SM7? I don't own one. Maybe the spec. sheet will detail this....

 

[soundguy]

the sm57's I modified sound bigger and better than my stock sm7b which rarely gets used. I say this with the utmost authority, nobody has ever picked the 7 when compared to the 57 in this studio, not one single time. The sm7b is a really decent sounding mic too... The sm7b uses a multitapped transformer for the hi/lo pass functions. Ive never torn mine apart but would really love to know if its the same capsules, they certainly sound similar. The spec sheet that comes with the mic shows how the transformer is wired.

dave

 

[CJ]

this is pretty funny, i am running the signal generator into the xlr end of the 57 and i can hear the 1 k hz tone coming out of the capsule!

weird, ratio changes from 1:3 to 1:4 and then 1:5 as the level goes up.

looks like xfmr is sucking a lot of signal, will do current draw test...

about 5 henries on the sec.

pri henries are all over the place, this will change afdter disconnecting xfmr from capsule hopefully.

a lot of capacvitance as this acts like an API output, sags a bit around 20 k, then stays there til 1 meg.

 

[mikep]

[quote author="CJ"]this is pretty funny, i am running the signal generator into the xlr end of the 57 and i can hear the 1 k hz tone coming out of the capsule!
[/quote]

I know someone who used to work for sennheiser in the service deptartment. he says this is actually one of the ways they test dynamic mics! buzzy "electric shaver sound" at all levels is an indication of voice coil rub. different models have a different voltage spec that they should be able to reproduce "cleanly", but I think most ordinary low-Z moving coil dynamic mics should be ok to about .2 volts. from memory, a 421 should be able to take something like a .7vRMS signal at 500Hz before bottoming out. you can hear it go all buzzy when it runs out of headroom. interestingly, the voltage it can take is proportional to the max SPL it can handle and is also somewhat related to the sound the mic will have. if you sort mics this way you can find "best" ones for loud sources. the guy I mentioned has several selected 421s that can handle 2 to 3 times the spec. I can testify that those particular mics do indeed sound better than the average 421 on toms. a little bit smoother, and more impact.

mike p

 

[CJ]

Very cool! Thanks Mike!

This is a reverse tweeter, yes indeed.

Can't wait to hear 20 hz from this thing.

Here is freq plot for xfmr both connected in the mic and seperate from the capsule.
No res peaks, just a lot of stray C and L.
Starts to droop before 20 K, might be a good thing.

Pri- DCR - 1.50 ohms L = 386 mH Leakage - 150 uH
Sec- DCR - 24.18 Ohms L = 7.95 H Leakage - 4.26 mH (horendous!)

That sec to pri leakage is 4 times higher than the output transformer for a Macintosh Stereo Power Amp! There is room for improvement here, do not know if it will help sound, hopefully, yes.

Impedance Ratio: 1:20.6
Turns Ratio: 1:4.53

Turns ratio changed with level. This is probably the core. Or too much distance between the wire and the core.

 

[CJ]

BH curve for the 57 xfmr.

unstable ringing:

I'm out.

 

[craigmorris74]

Nice work CJ. Any transformers come to mind?

 

[ramjet]

so is the long and short of all this is that a sm7b is simply a sm57 but with decent electronics and a different body??????????

 

[Flatpicker]

Closest thing I can find at the moment:

?Sowter 9760 1:10 2 ohm Ribbon microphone Transformer
Very high performance transformer for use with ribbon microphones with an impedance of 1 to 3 ohms to match to a 200 ohm input. Bandwidth 10 Hz to 50 kHz.?

Sowter doesn't have a data sheet, so I'm not sure of the size, but looks like 34mm, so it won't fit the 57 body, I don't think. Maybe if you hammered it a little, lol!

 

[Emperor-TK]

[quote author="ramjet"]so is the long and short of all this is that a sm7b is simply a sm57 but with decent electronics and a different body??????????[/quote]

I think that is just speculation so far, until someone can come up with some real evidence.

 

[khstudio]

[quote author="mikep"][quote author="CJ"]this is pretty funny, i am running the signal generator into the xlr end of the 57 and i can hear the 1 k hz tone coming out of the capsule!
[/quote]

I know someone who used to work for sennheiser in the service deptartment. he says this is actually one of the ways they test dynamic mics! buzzy "electric shaver sound" at all levels is an indication of voice coil rub. different models have a different voltage spec that they should be able to reproduce "cleanly", but I think most ordinary low-Z moving coil dynamic mics should be ok to about .2 volts. from memory, a 421 should be able to take something like a .7vRMS signal at 500Hz before bottoming out. you can hear it go all buzzy when it runs out of headroom. interestingly, the voltage it can take is proportional to the max SPL it can handle and is also somewhat related to the sound the mic will have. if you sort mics this way you can find "best" ones for loud sources. the guy I mentioned has several selected 421s that can handle 2 to 3 times the spec. I can testify that those particular mics do indeed sound better than the average 421 on toms. a little bit smoother, and more impact.

mike p[/quote]

Great info.. thanks
I have a few originals (white/cream body) 421's from Germany.
Can this test hurt the mics at all?

Soundguy,
...very interesting if all the capsules are the same. I wish you could share your mod... it seems that at one time it was also new & exciting to you like it is to me now.

The reason I haven't tried it yet is ALL my (5) 57's sound different & I want to try it on one of my least favorite's, need time to check them. + I'm working on a few mic pre's. Being as good as the sm7 or better is KILLER.

Thanks for your input :thumb:

Kevin

 

[khstudio]

CJ,
Those pics show a regular 57.

I asked about an old Shure PE54D I have earlier... can anyone help with that? I wonder if it has a better transfomer... anybody?

Also, it has a switch so if it's not fixable, transplanting a good capsule in there & using the switch to bypass the trans (like mention earlier :thumb sound like a good idea. Plus I always liked the silver body :green:

 

[pucho812]

did some inital testing last night recording drums. On top snare we had a stock 57 and next to it a trafoless 57. Did some A/B testing and the conclusion was

1. Trafo less had lower volume and had to crank the mic pre more to volume match however this didn't add any noticable noise

2.the trafoless one sounded tighter and didn't pick up the snare ringing as much as the stock one

3. THe trafoless one sounded "phatter" then the stock one

4. Trafoless one was not as midrangy as the stock one

Yeah a good mod but not an end all be all expecially since a stock 57 sounds good on certain things.

 

[khstudio]

I must say the only 2 places I use a 57 are on snare & guitar cabs... so reduced gain & more headroom (not to mention not needing a pad for the snare) might be just what I'm looking for.

Thanks for the feedback. Your finding are in line with the artical & what others say. I'm curious to see what a better transformer could do but know very little about mics.

 

[RoyM]

I have one of these: http://www.electromusic.co.uk/pa/en-gb/dept_430.html (scroll down). It's labeled a "special 57" and I think it's transformerless. I've never really used it but I do remember it having less output than a regular 57. If I get a chance I'll go to the studio and do some comparisons.

Roy

 

[Flatpicker]

[quote author="khstudio"]...I'm curious to see what a better transformer could do but know very little about mics...[/quote]
You don't need to know any more than this: Contact all the companies in the transformer meta and tell them that you need an improved version of the SM57?s transformer, reference the article in Tape Op, give them CJs? data, and see what they recommend. Then, give one (or some) a try and let us know how it sounds. I plan to do this when funds permit, but you may grow a very long beard or raise a few kids waiting on me. :wink: