Relevant idea for topic: Transformers

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chessrock

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I just thought of an idea for a thread topic.

Why don't some of the more accomplished electrical/techie types enlighten the rest of us on the topic of transformers.

This is what I know, or at least THINK I know:

* They are often used in microphones, preamps and other rack equipment.

* They impart somewhat of a sonic "stamp" if you will.

* In mic preamps, they can help prevent hard clipping (?)

* They are a very important component of sound: Bad ones will tend to sound harsh, and good ones can sweeten the sound.

* Jensen is kind of the most respected manufacturer of them.

* They are cool action figures and cartoons.

* I don't have a freakin' clue as to what exactly they do, from an electronic standpoint. My question is do they all perform the same function? Is the transformer in my mic performing the same tasks as the transformer in a preamp?

How about the ones in a D.I. box?

How about the impedence-matching transformer in my adapter I use to convert a balanced signal to an unbalanced input? Do those perform a similar function?

Thanks in advance for the discussion.
 
Chess,

> This is what I know, or at least THINK I know: <

Those are a lot of half-truths.

> * They are often used in microphones, preamps and other rack equipment. <

Yes, and the main two purposes are to avoid ground loops and match impedance.

> * They impart somewhat of a sonic "stamp" if you will. <

Yes, but they're not supposed to!

> * In mic preamps, they can help prevent hard clipping (?) <

No.

> * They are a very important component of sound: Bad ones will tend to sound harsh, and good ones can sweeten the sound. <

I wouldn't count on a transformer to sweeten anything. The best you can hope for is for it to be transparent.

> * I don't have a freakin' clue as to what exactly they do, from an electronic standpoint. My question is do they all perform the same function? Is the transformer in my mic performing the same tasks as the transformer in a preamp? <

You might be interested in my "Hardware Tutor" mini-book. Go to my Articles page:

www.ethanwiner.com/articles.html

Then look for the Hardware Tutor about 1/4 way down the page.

--Ethan
 
Thanks Ethan. I'll be sure to check that out. I hope it includes a dictionary on terms, as I am quite clueless . . . but hey, at least I'm man enough to admit it.

That was my bad on the tranformer promoting soft-clipping. I believe it was single-ended tube and transistor circuits that soft-clip. See, I'm getting better at this stuff already. :) Gee I mutht be thmart.
 
Chess,

> I hope it includes a dictionary on terms <

Not so much as simple explanations of electronic concepts and components. But that's why I'm here every day. Ask away.

> That was my bad on the tranformer promoting soft-clipping. <

Not really. Transfomers do soft clip, I suppose. But the real issue is that competant engineers don't drive any of their gear into clipping! It is a huge myth that distortion is a good thing, unless you're trying to fuzz out an electric guitar part. :)

--Ethan
 
*the real issue is that competant engineers don't drive any of their gear into clipping!*

The competent engineer may not, but sometimes the overly-aggressive drumer, screamer or finger-picker who forgot to take their ritalyn might. :)

*It is a huge myth that distortion is a good thing*

One guys warm is another man's dirty. It's a matter of taste.
 
chessrock,
you might want to go here to learn about some basic concepts of transformers
http://www.epanorama.net/links/componentinfo.html#transformers

BTW a transformer in a mic and a mic pre is mainly used to balance/unbalance the signal. A side effect is that it also decouples the signal from ground. The ideal transformer would not add any color while doing this.
There are quite a few mics and mic pres out there that are electronically balanced and don't have any trannies in them. Examples are schoeps, the neumann tlm series, the AKG 414TL, the octava mc012 and many others. Many mic pres that are considered to be very clean don't have transformers, if remember right the millenia, the studio technologies, DACS, earthworks, mindprint. It is always a compromise: If you avoid trannies, you have caps in the signal path.
Apart from Jensen there is another manufacturer of high end audio transformers called Lundahl.
 
Man, lots of good info. here. I bookmarked both of the links.

So it's main function is to balance or unbalance a signal, and it should do it with minimum color of the signal. Excellent.

One last question here: In my recording setup, I have an awful lot of balanced signals I am feeding to some unbalanced inputs. Right now, I'm using some el-cheapo Hotwire impedence-matching transformers. Should I re-invest in something of higher quality, do you suppose?

To my ears, the audio I am inputing sounds quite good, so I don't suppose the cheapo transformers are doing any harm.

Thoughts?
 
Chessrock,

> One last question here: In my recording setup, I have an awful lot of balanced signals I am feeding to some unbalanced inputs. <

As long as you don't have any hum, you're okay doing that.

> Right now, I'm using some el-cheapo Hotwire impedence-matching transformers. Should I re-invest in something of higher quality, do you suppose? <

Cheap transformers can affect the sound. But if you don't hear any degradation, there's no good reason to spend more money.

--Ethan
 
Alright, this is going to be a dumb question again, but still very relevant to a lot of other people who might also be more of the musician-type than the engineer-type:

If the transformer's main function is to balance and unbalance a signal . . . then I assume the "tranny" output on a mic is balancing the mic's output signal to be sent down the TRS wire. That makes sense. But then why do so many preamps have a transformer input? Most preamps I am aware of have balanced ins and balanced outs. Where is the additional conversion taking place?

Does the preamp have to transform the balanced signal to an unbalanced one again in order to amplify it?

Thanks for all of your patience. You guys are troopers.
 
Chessrock,

My limited knowlege about transformers in general was in a radiologic technology (ie medical X-ray etc) physics class. From what I remember anything that "tranforms" electrical energy from one form to another qualifies as a tranformer.

I may be wrong on this but I don't believe that because a piece of musical equipment has a transformer that it automatically implies a conversion of unbalanced to balanced signal. From my limited readings transformers are more geared toward stepping up or stepping down the power to meet the needs of the equipment. Your guitar and bass amps will have power transformers in association with the power amp and none of these are typically balanced signals. The transformers used in X-ray physics are used to improve efficiency and get more bang for the buck from the electrical power supply coming in from your power lines.

Also of interest there used to be an article at Pats Tube Schematics website about the importance of quality tranformers and the illusion of tubes adding "warmth" to the signal. While Pat is an avid tube enthusiast he believed the "warmth" assocated with tube equipment from the 60's had more to do with the transformers used and he had some solid state preamps designs/kits that he said were as "warm" as any tube gear. He also recomended the Lundhal tranformers for studio preamps etc.

I tried to find the direct link but I can't find the article now at his site but the site is at www.nanaimo.ark.com/~pat I do think it is an interesting topic and perhaps if no one else offers their expertise Harvey in the microphone forum could enlighten us.
 
It sounds like this is an issue that could envoke a lot of debate.

Ethan seems to assert that the transformer shouldn't impart any sort of sonic effects, and the best you can hope for is that it will remain neutral.

I've heard that from others before, so before this turns in to "one of those" debates, let's just try to keep this on the subject of what "function" the tranny performs. I like Ethan's transmission analogy. It seems to make a lot of sense. So what you're saying is the transformer not only balances/unbalances signals, it transforms the voltage/audio signal in other ways (maximizes/distributes it's energy more efficiently?).
 
Scooter B said:
Chessrock,

I may be wrong on this but I don't believe that because a piece of musical equipment has a transformer that it automatically implies a conversion of unbalanced to balanced signal.
Click to expand...

not necesarily, but the transformers used in MICROPHONES and on the in and outs of PREAMPS serve only this purpose (well, and provide a bit of gain and impedance matching)
If you look at the schematics of a neve 1073 you will see that the whole signal is unbalanced behind the input trannie and before the output.
(Today you can do this conversion with a pair of chips, BB drv134 and INA107, if I remember right).
There are also designs that work completely as differential amplifier, ie the signal is never converted to unbalanced but stays balanced the whole way trough the preamp.
One big advantage of transformer designs (as far as i understand it) is, that the trannies also decouple dc (the powersupply) from ac (the signal). Without (audio-) transformers you need capacitors to perform this task, which can also degrade the signal. The capacitors that where available 30 or 40 years ago have been of much lower quality than even todays cheapest caps, this might be tha reason why older designs seem to favor transformers.
 
Chessrock,

I know what you mean about "one of those" debates especially about preamp etc that are prefferred by some to be "neutral as possible" the proverbial wire with gain knob versus one that imparts a sonic character or flavor.

It was just interesting to me in light of Ethans comment that a dedicated tube guy would comment on the ability or possibility of a transformer to "warm" up a signal. I don't wish to start another debate about wether that is a good or bad thing.

Also I seem to remember several products (direct boxes for one) that converted unbalanced to balanced with out transformers and I was not aware that they were using microchips to do this.

I thought the transformer info I learned in the X-ray physics class would be somewhat applicable as the production of X-rays still depend on tube technology. The premise if I remeber it right was that tubes needed DC power not AC but I forget why. So the first step used was to "block out" the AC curent in the sine wave that dropped below neutral
but that left you with half of the electrical current to use. Transformers were developed on this field to use various forms of "rectification" that would produce a constant level of non alternating DC current.

If we are only going to discuss the "what function" the tranny performs in mirophones and preamps it sound like you have you awnser; if I undestand Ethan and HKuhn correctly.

1. Converts unbalanced to balanced signal and this is its primary purpose.

2. Decouples DC from the AC wich sounds like what I was describing with the rectification.

3. Provides a little bit of gain.

My question is if #1 is true why do microphones and mic cables start out with a balanced line. If they are already balalanced to begin with then they would not need a transformer so to speak only a way to adjust and increase the gain without the transformer. Lets take you basic SM-57 for example. It has no built in chips, circuits or transformers but generates a signal (or more correctly converts a sound wave into an electrical signal) that is sent throught a balanaced line. Would this mean that without a transformer in the signal path (or IC chips etc) that the signal coming out of the mic cord would be unbalanced?

If #2 is an important factor then again what benefit is a transformer if you are using a battery powered mic or active guitar/bass preamp as batteries are already DC and do not need to be decoupled from AC?

While I understand the benefits of keeping everything balanced - maintaining signal strength, preventing electrical noise from entering the signal etc etc I am in budget 4-track cassette land and my Yamaha 4-track has no balanced line inputs. So at this point in time the balanced line issue is of little interest to me. It does come into play as I buy rack based effects and pre's etc and I want to buy things that will still be usefull when I can upgrade to a system with balanced line capability.

Thanks for your input Ethan and HKhun, I only have a little knowledge in this area and a little knowledge can be dangerous but not as dangerous as total ignorance he he he.
 
look what i found

from http://www.proav.cc/data/linetransformer.html

"Audio Line Transformers

A transformer is a device that converts a voltage to a magnetic field and then back to a voltage again. It produces a related AC output signal without the input and output being physically connected together.
Transformers are AC only devices (operation depends on a changing magnetic field) and can be designed to operate at frequencies from about 0.01 Hz to many GHz. Generally those operating under about 1 MHz use multiple windings or turns of wire around the core of magnetic material to confine and concentrate the magnetic field. They are used to perform a variety of functions, like phase reversal, balanced to unbalanced coupling, impedance transformation and hybrid functions.
An isolation transformer connected between two pieces of audio equipment will prevent the flow of circulating earth currents, because there is no electrical connection between the input and output of the transformer (the audio signal is coupled only magnetically).
The physical size of audio transformers is dependent upon the lowest frequency and the power available at that frequency.
Transformers can be manufactured with multiple primary or secondary windings.
The input winding is called the primary side and the output (or load) winding is called the secondary side of the transformer. The input and output windings are electrically insulated from each other.
To prevent external magnetic fields from generating unwanted signals into the transformer, a magnetic shield around the transformer itself is also required. "

and later:

"Distortion: The distortion of a transformer is due to the hysteresis of the magnetic material. It is caused by irregularities in the inner structure of the magnetic material. Distortion is not obviously a problem in power transformers, in audio line transformers it can make all the difference.
Low distortion and high performance transformers are made by using special core materials with a very uniform crystalline structure.

To guaranty good lo-frequency response requirements, the primary inductance of the transformer must be enormously high. It can require wire turns of many thousands with a very small wire diameter. Primary inductance of more than 1000 Henries are common. The downside is, that the small wire diameter and the large number of turns necessary for an excellent lo-frequency response reduces the high frequency response (higher capacitance). A perfect transformer is a compromize of both obtained by special layering and interleaving windings.


A theory: "Basically a transformer slows down upper frequencies and allow the low frequencies to pass first, creating what we perceive as a "fat/warm" tone." ??


1:1 transformer: Called an isolation transformer, it has the same number of windings on the primary and the secondary side. The signal level does not change because of the same impedance for the primary and secondary.

Balanced center tapped transformer: A balanced line consists of three conductors with one at ground and two signals identical but 180 degrees out of phase with each other. Any external induced noises will be equally carried by both signal wires and canceled because they are 180 degrees out of phase. "
 
Ah! All this theory explains one thing to me. The transformer decouples the circuit from DC ground. I saw a practical world demonstration of this. A friend had a TV connected to his cable line and was getting some nasty hum. He got an isolation transformer for the cable line and the hum went away completely. Because there is not physical connection to ground, the hum vanished. I can see the practical application of this in a preamp circuit. It makes it not hum!
 
Chess,

> Ethan seems to assert that the transformer shouldn't impart any sort of sonic effects, and the best you can hope for is that it will remain neutral. <

Damn straight! :) This is why audio transformers generally recognized as being very good - like those from Jensen - cost so much. It takes a lot of good design work and manufacturing talent to make a transformer that has both a good frequency response and also low distortion. These have always been the primary design goals.

> I like Ethan's transmission analogy. <

Yes, the primary purpose of a transformer is to manipulate the voltage and current - impedance matching, really - although the total amount of power always stays the same. For example, with a tube audio power amp, the output is a high voltage with low current capability. So the audio output transformer converts that to the low voltage with high current capability that's needed to drive an 8 Ohm loudspeaker.

Another use of a transformer is to convert from balanced to unbalanced or vice versa, though this is less common. With older audio gear, the transformers provide a balanced connection to avoid hum-causing ground loops by not requiring the grounds of the two devices to be connected. These days a lot of gear uses op-amps to provide a balanced input.

Another use of a transformer is for isolation. Years ago I worked for a company that makes very high voltage equipment. One of their devices was a tube tester. But unlike the ones you may have seen at Radio Shack 20+ years ago, these were for testing the tubes in 50 KW broadcast transmitters! We used enormous transformers that were made of a wooden frame the size and shape of an automobile tire. The wire was wound such that one winding was a foot away from the other. Even though only 115 volts AC (normal US power) was passed through the transformer, the two winding could have 100 KV difference between them.

--Ethan
 
Chess, take a look over at the guitar amp board Ampage:

http://www.firebottle.com/ampage/

While the interest there seldom wanders away from power and output iron, there are a couple of guys over there that have a fearsome amount of knowledge about the things.

Monty
 
Thanks h kuhn,

I never knew the part about audio line transformers electronically "interupt" the signal and passes the signal only through magnetic means.

RE: the balanced line - I understand the three wire concept with the signal being 180 degrees out of phase and the noise cancelling out when the signal is brought back in phase. I was not aware this required a transformer or op chips to accomplish this...if this is true that would mean that all your bass DI's for instance that send out a balanced signal would have to have a tranformer or op chips in them. Maybe the active SansAmps have op chips but I don't think the passive ones would have them (Coutryman DI).

I suppose this veers off the original subject of transformers but the balanced line conversion requiring a tranny or chips still has me confused as I thought there were many passive DI boxes and balanced line inputs into recorders that have neither op chips or tranny's.
 
Scooter B said:
Thanks h kuhn,

I suppose this veers off the original subject of transformers but the balanced line conversion requiring a tranny or chips still has me confused as I thought there were many passive DI boxes and balanced line inputs into recorders that have neither op chips or tranny's.
Click to expand...

AFAIK the only possibility to achieve galvanic insulation of an audio signal from ground is a transformer. Every DI box i know works that way. It is called active when it has a gain stage.
Go to the Jensen site to learn more about DI box designs!
 
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