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Author Topic: New AMI Transfomer For Shure SM57/58/AKG D12  (Read 53281 times)

rodabod

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Re: New AMI Transfomer For Shure SM57/58/AKG D12
« Reply #45 on: July 30, 2007, 12:34:12 PM »

Just a few notes.

With the AKG D12, adding the transformer in the standard step-up configuration will result in an output impedance which is too high and this will result in low-end losses when paired with a  standard mic preamp.

I think even with the lower output impedance of the AKG 60 Ohm models you might be pushing it. As far as theory goes, I don't really see the need in using a transformer in these mics unless it offers some sonic benefit (as it did for JJ in reverse with his D12).

I'm interested in the results with the D12 paired with the transformer in reverse. Could it be that the lower impedance presented by the combination worked better with JJ's preamp? Who knows.

As far as the D19 is concerned, there would only be a transformer use inside if it were a multiple output impedance model as far as I know.

Roddy

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Roddy Bell

maxdimario

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Re: New AMI Transfomer For Shure SM57/58/AKG D12
« Reply #46 on: July 30, 2007, 03:37:40 PM »

JJ, as you use the transformer with different source impedances and load impedances you will change the frequency response of the system as well as the overload characteristics..

Oliver's transformer was designed for the voice coil of the sm 57 which I am GUESSING (so please someone correct me) is very low, like less than 10-20 ohms.

placing a d12 with a source of 200 ohms will reduce high end and possibly cut off bottom.

by turning the transformer around you are actually raising the impedance that the d12 sees and lowering the impedance to the mic pre, which results in more extreme bottom and top.. depending on overload. In this case the transformer acts as a step-down.

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jrmintz

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Re: AMI transfomer for sm57/58 anyone know anything about it?
« Reply #47 on: April 24, 2009, 08:43:29 PM »

panman wrote on Tue, 17 July 2007 11:27

Tomas Danko wrote on Tue, 17 July 2007 13:46


My D19C says "Impedanz Var. 15 Hi" on the original cardboard box. Not that it matters in the end, but it'd be nice to know the impedance value on that mic as well. Any ideas?


D19:s only have 60 or 200ohm coils. The "Hi"-impedance(50`000 ohm) is achieved with a transformer. These "Hi"-models usually have a cable instead of a connector on the end. There are also those with variable impedance and a five-pin XLR-connector(D19E)and then you can choose 60,200 or 50`000 ohm.

            Esa
 


I resurrected this thread because I have a Norelco D12 HI with attached cable. The sound of it has never killed me, but I'm just realizing that I've been using a high-impedance microphone into a low impedance preamp input. Can I just bypass the transformer to get a 200 Ohm output? Would it be better to use a line transformer, or even a direct box?

Thanks,

Seth
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panman

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Re: AMI transfomer for sm57/58 anyone know anything about it?
« Reply #48 on: April 25, 2009, 06:19:03 AM »

jrmintz wrote on Sat, 25 April 2009 02:43

I resurrected this thread because I have a Norelco D12 HI with attached cable. The sound of it has never killed me, but I'm just realizing that I've been using a high-impedance microphone into a low impedance preamp input. Can I just bypass the transformer to get a 200 Ohm output?


Hi Seth, first to answer your question: bypassing the transformer will get you 60ohms output and a decent sound if the capsule(60ohms) itself is ok. This unfortunately is usually not the case. I`ve seen only one of these Norelco D12Hi:s and it had the same transformer as the slightly different looking Philips D12:s sold in Europe, just wired differently. They have 50/500/50000ohms (unbalanced)depending on how the special connector is twisted around. This trafo is filling up all the space inside the bass-chamber and has to be removed to get full bass-responce. For 200ohms a proper transformer would be needed to step up 60 to 200ohms.

Regards,
       Esa
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jrmintz

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Re: New AMI Transfomer For Shure SM57/58/AKG D12
« Reply #49 on: April 25, 2009, 11:50:49 AM »

Hi Esa,

Thanks for your help. I don't see a switch anywhere, but I do see the transformer potted in some sort of hard resin in the bass chamber. Is it possible to remove the trafo without destroying the mic?

Seth

index.php/fa/12066/0/
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jrmintz

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Re: New AMI Transfomer For Shure SM57/58/AKG D12
« Reply #50 on: April 25, 2009, 11:52:15 AM »

And a rear view.

index.php/fa/12067/0/
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panman

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Re: New AMI Transfomer For Shure SM57/58/AKG D12
« Reply #51 on: April 25, 2009, 05:34:51 PM »

Seth,

Is it possible to remove the trafo without destroying the mic?

Sure it is, but I suggest you just bypass the trafo first and see how it sounds. Just disconnect the four wires(yellow, brown, blue and green)going to the trafo and tape the ends to prevent them causing a short. Then you have to connect the blue wire coming from the capsule with the brown wire of the mic-cable and the green with the white one. On the other end you should have a normal balanced wired XLR. Now the mic unplugged, if you measure between blue and green wire with an ohmic-meter, it should read about 50 ohms. That normally means, the capsule is 60 ohms. However, if it reads about 230-240 ohms, the capsule is then the so called 200 ohms one. This may be possible, because your second pic shows the humbucking coil, which suspiciously looks like of a 200 ohms capsule. The measuring or a sidewiew-pic of the capsule would clear that out.

To remove the trafo you need to unscrew the four retaining screws that hold the bass-chamber and then you can carefully tap the rear-cap loose and remove it. If you don`t want to use the trafo, you can just pull it off and the wires will be destroyed. then replace the cap tapping it back carefully and sealing it with glue. Now just attach the chamber on the capsule. That`s it.

If you want to save the trafo for some other purpose, you need to carefully solder the wiring loose before pulling the trafo out. That is very tricky, but can be done, if you know exactly what to do. I`d say, better leave it for someone more experienced to do.

Regards,
       Esa



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jrmintz

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Re: New AMI Transfomer For Shure SM57/58/AKG D12
« Reply #52 on: April 27, 2009, 02:11:43 PM »

Success! Thanks for your help Esa. I took out the transformer and the metal liner that was in the chamber to hold the trafo. I soldered the capsule leads directly to the cable leads. I resealed the chamber with epoxy, put everything back together and it works fine. I won't be able to try it on a bass drum for a few days, but it sounds pretty rich and warm just speaking into it. I was wondering what all the fuss about the D12 was. Mine certainly wasn't anything special - I think it's going to be much different now.

Seth
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J.J. Blair

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Re: New AMI Transfomer For Shure SM57/58/AKG D12
« Reply #53 on: April 27, 2009, 03:17:12 PM »

I've bypassed the xformer in both of my D12s, but is there really any benefit to removing the transformer?  Even in the D12E, they use a plastic dummy, to keeps that space filled, even though there is no transformer.  What's the acoustic difference with that space there?
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compasspnt

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Re: New AMI Transfomer For Shure SM57/58/AKG D12
« Reply #54 on: April 27, 2009, 05:21:22 PM »

So JJ, are you running it straight in with no xfrmr, or going through an AMI (or other) with those D12's?
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jrmintz

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Re: New AMI Transfomer For Shure SM57/58/AKG D12
« Reply #55 on: April 27, 2009, 05:23:11 PM »

J.J. Blair wrote on Mon, 27 April 2009 15:17

but is there really any benefit to removing the transformer?


I'll let you know next time I cut drums. Unfortunately, I didn't think to do a reference recording before I took the trafo out.
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jrmintz

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Re: New AMI Transfomer For Shure SM57/58/AKG D12
« Reply #56 on: April 28, 2009, 10:03:14 AM »

Here's a link to a brief 16-bit 44.1k sample of my D12 with the transformer removed, nothing in the chamber and the capsule connected directly to the cable. This is my daughter practicing a Roy Haynes solo for her jury next week, so it's not really hard groove drumming. The drum is a DW with the mic about three inches outside the hole in the front head, through a Daking preamp flat, and into my 192. The mic is much, much punchier than it used to be.

Seth


http://files.me.com/jrmintz/dig1iu.wav  Modified_D12-test
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J.J. Blair

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Re: New AMI Transfomer For Shure SM57/58/AKG D12
« Reply #57 on: April 28, 2009, 01:12:41 PM »

compasspnt wrote on Mon, 27 April 2009 14:21

So JJ, are you running it straight in with no xfrmr, or going through an AMI (or other) with those D12's?



Terry, it depends.  When recording kick, into my 1073, I have been liking it through the TAB, but reversed.  

But in general, if I'm going to use it for something, I don't use the transformer or my little film cannister thing.
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studio info

They say the heart of Rock & Roll is still beating, which is amazing if you consider all the blow it's done over the years.

"The Internet enables pompous blowhards to interact with other pompous blowhards in a big circle jerk of pomposity." - Bill Maher

"The negative aspects of this business, not only will continue to prevail, but will continue to accelerate in madness. Conditions aren't going to get better, because the economics of rock and roll are getting closer and closer to the economics of Big Business America." - Bill Graham

panman

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Re: New AMI Transfomer For Shure SM57/58/AKG D12
« Reply #58 on: April 28, 2009, 02:58:25 PM »

J.J. Blair wrote on Mon, 27 April 2009 21:17

Even in the D12E, they use a plastic dummy, to keeps that space filled, even though there is no transformer.  What's the acoustic difference with that space there?


J.J., that „dummy“ is just the the same size and form inside as the older metal chambers. Even sonically it is replaceable with the older one.

As for your question, I`ve been experimenting a lot with the older type bass-chambers limiting its volume and found out, that the more volume, the more bass and of course reducing the space you get bass-rolloff. In fact I have been using D12:s with acoustical bass-rolloffs like that for close micing purposes. Also the form is important. You can take exactly the same volume, but different form like Echolette Top 12 using the same capsule. The chamber is right there in the rear of the capsule and is very short giving a strong bass-boost, but not extending as low as with the"normal" long chamber. Then there are the D30/D36/D45 just both capsules sharing the chamber. It is a fact that transformers in D12:s were somewhat different in size in different badges and times, but I also noticed that the vents sometimes were filled with some filtering stuff, but mostly not. So, it is again not that simple. It is all about manipulating the rear wave, that the mic will give that bass-boost. The idea is to get the sound reflecting back in the right phase. This can also be achieved by putting obstacles on the way. If the transformer is filling exactly the right space, it can really be ideal for bass-boosting.  As it happens, I have a D20/60ohms, that I converted to 200ohms by swapping the bass-chamber with one, that has the transformer inside. Well, that is the one with the most bass and extending lowest of all the D12-type mics that I posses and I do have quite a few, plus the sound is more pleasant in general. Maybe a coincidence? One of these days perhaps I will open up the chamber to find out the secret, but not until I find one that is as good, because this mic is my favorite for too many things.

Regards,
       Esa
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muddy

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Re: New AMI Transfomer For Shure SM57/58/AKG D12
« Reply #59 on: June 04, 2009, 06:26:30 PM »

what about removing the resonator, ala joly's electrovoice (i think) mod? i did this to my us made 58 (which i also removed the wind/foam from), and though the output is now lower, it SOUNDS a LOT clearer & more flat. btw, i've only used it for guitar. here (excuse the goop):

http://soundclick.com/share?songid=7618823


ml
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