The Transformer's Role

The=20 Transformer's Role

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New updates: =

An update: Good quality transformers are available on = the=20 Noisyhaus website for $21.95 plus shipping. In = fact=20 all the parts need to build a great mic are there. Check it=20 out.

http://make_a_ribbon_mic.tripod.com/noisyhaus/

This is an incredibly important part of the design, = and I=20 recommend finding a transformer before you get started, = =20 unless you decide to use a record player preamp, or you want to = screw=20 around and make one that is intended to show the principles = =20 only.

I've used the Ludahls, the Cinemags, Jensens, = and a=20 whole host of other transformers (even winding a few = =20 myself here and there). All the = commercially=20 available ones are all great in certain types of = =20 microphones. Almost all of them are very affordable = now. If=20 you want quality vs. price, I suggest the Lundahl. = =20 But I have to tell you, there has always been something about the = Jensen=20 that just sounded so sweet.

Just do a search on google for the names above = followed by=20 "ribbon microphone transformer," and you'll get there. = =20

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Transformers. A basic = rundown of=20 what they are.

Transformers are (usually) cores of = metal=20 (mostly a soft iron) that have two sides: one = is=20 called the primary and one is called the secondary. Both of = these=20 sides are wrapped in wire to achieve a desired = effect for=20 a circuit. The primary serves to change whatever is put into it = into a=20 magnet field, then the secondary takes the = magnetic field=20 and changes it into an electrical source again. The number = of=20 windings on each side expressed in a ration like = 1:1,=20 2:1, 10:1, 1:10, etc. In the case of 2:1, there are twice as = many=20 windings on the primary than on the secondary. Here = =20 is an example of the ratio and how it relates:

One effect of a transformer is = that it=20 blocks Direct Current. So one can get a transformer = that=20 has the same number of wire windings on each side (1:1), also = known as an=20 isolation transformer. This allows an A.C. = signal=20 to pass through (but there is no physical connection between the = two=20 sides) , and D.C is blocked. Another = =20 effect is the ability of transformers to step-up or step-down=20 Voltage. Yet another is the changing or matching of = impedences =20 from one piece of gear to another. Lots of uses, = and lots=20 of importance.

The voltage induced by the Ribbon = mic is, of=20 course, Alternating Current. But the amount = of=20 voltage is so little, how do we get great sounds out of something = so=20 weak? Transformers, baby. A step-up transformer, = =20 to be exact.

The voltage induced by the ribbon in the magnet field has to = be=20 transmitted through cables, wires, etc. for it to be = any=20 use to us. More importantly, the A.C. needs to be in an = impedance=20 that is compatible to most mixing consoles. = What=20 good is a mic that you can't use with your favorite Preamp?

The ribbon material itself has very = little=20 resistance. Mine has a resistance of .6 Ohms. = =20 POINT 6. almost none. Basically about as close to a = straight=20 wire as possible. But by manipulating the current = =20 and resistance of any circuit, you can change the voltage. = If Ohm's=20 law popped in your head, then you are on the right = =20 track.

The tranformer I used (and most = ribbons use)=20 is a step up of 1:12 ratio. It steps the = voltage up=20 12 time for every 1 that you put in.

Step up transformers are not rare, = but ones=20 for use in AUDIO applications are. The quality = of=20 the transformer is extremely important for the quality of the = audio. =20 Noise rejection, output, and frequency = response all=20 rely on the transformer. So you can see, I cannot stress = enough how=20 important it is for quality in a ribbon = mic.

Other concerns for selecting a=20 transformer...

Input and output impedence, = distortion,=20 noise, and frequency response.

There are quite a few manufacturers = for=20 audio quality step-up transformers. The only problem = =20 is that they are expensive, and usually not just a little. = If you=20 are familiar with phonographs, then you should know = that=20 there is a subculture of audiophiles that spend years creating the = best=20 possible phonographs and amplifiers possible. = As it=20 turns out, phonograph transformers for moving coil needles = (pick-ups,=20 stylus, etc.) are very similar to what we need = for ribbon=20 mics. Since there are many high quality moving coil = tranducers that=20 have very low resistance, there are many choices = for a=20 transformer.

It would take some math to explain, but the input = impedance=20 doesn't have to be .6 ohms. In fact, the =20 transformer I use has an input impedance of 46 Ohms, and looks for = a=20 source impedence of up to 5 Ohms, and it still = =20 works great. The effect, I believe, is on the frequency = response of=20 the transformer (correct me if I'm wrong). = Since my=20 transformer has a frequency response of -3 dB from .3 Hz to 200 = kHz with=20 an source of 5 Ohms, the response is not that = affected=20 (at least not in the audible range). I've got a lot of room = to=20 play.

There are a lot of other factors that I'm not going to go = into=20 here. If you have a question, let me know. = =20 I'm NOT a transformer guru, and I am just now getting into = transformer=20 design and physics (after years of working on tube = =20 amps. Yeah, they kinda scared me, but not anymore). = I'll try=20 to let you know an answer, or at least put you in = touch=20 with someone who can help.

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Again, here is the schematic I used to wire up the=20 transformer. It is really for a phonograph, but = it=20 works for ribbon microphones just as = well.

The address is (again):

http://www.comtran.com/as/as067.pdf = =20

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Some of=20 the manufacturers are floating around the internet. Look=20 around. see if you can find a used one for = a decent=20 price. But BE CAREFUL. There is no telling what people = have=20 done to them.

My suggestion is to buy one new. I got mine as a = gracious=20 donation from JENSEN (THE name in transformers) for this = =20 project. Its the JT-346-AX. Please do NOT contact them = asking=20 for a transformer. You will succeed in only = pissing=20 them off and making them mad at me. Other wise, it would = cost over=20 $200.00. I cannot thank them enough, and = will be=20 giving them all my business from now on, because this thing sounds = incredible, and the specs are fantastic for every = area=20 that counts. Use my link to check them out. Also, check out = the PDF=20 in the schematic section for the adaptation of = the=20 transformer to ribbon mic use.

There are other companys, such as Sowter and whatnot, but I = have not=20 tried their transformers. You will probably = have to=20 get in touch with them to custom make you a transformer for this=20 purpose. It'll cost you, but if everything = is done=20 right, you will be well rewarded with a great sounding microphone = that you=20 built completely with your own two hands.

Another suggestion if you want to make a mic just for the = hell of=20 it. If you are doing it purely out of curiosity = ,=20 use a phonograph preamp. The RIAA curve is a little = annoying, but it=20 still works. It won't sound good by = any means=20 and will be noisy as HELL, but it will let you hear the sound of = your own=20 voice. This was a suggestion of Larry = Killip (see=20 the links) from early on in the project, and it worked like a = champ.=20

Since then, Erik (from = Buellton) has=20 let me know of a transformer for 44 American dollars = (if=20 you Guys knew how many over-seas people I had emailing me, the you = would=20 understand the "American Dollars" thing). = Try a=20 Google search of Cinemag XFMR and see = what you=20 come up with. Thanks Erik! =20

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