chessrock said:
I just wanted to let some of you know that if someone starts a thread here that doesn't actually pertain to microphones . . .
. . . it is considered to be off-topic.
Much like spam or harassment threads, off-topic threads are generally dealt with by the moderators either by being removed or simply moved to the appropriate forum.
And speaking of harassment posts, please try and read between the lines of any new threads started in order to understand what the original intent was. If it appears that it's only intent was to stir . . . rouse or otherwise instigate others in to what we affectionately refer to as "pissing matches," . . .
. . . then chances are, it's a harassment post.
Another sure-fire sign is to look at the results of said thread. If it results in a pissing match, then chances are it was intended to be a pissing match, and therefore, a candidate for moderator involvement.
Anyhow, in the lower right hand corner of the post, you will notice, in blue letters, the words: "Report this post to a moderator. By clicking on these words, you will be promted further from there.
Thank you for your attention. Carry on, now.
Audio transformers can:
Step up (increase) or step down (decrease) a signal voltage.
Increase or decrease the impedance of a circuit.
Convert a circuit from unbalanced to balanced and vice versa.
Block DC current in a circuit while allowing AC current to flow.
Electrically isolate one audio device from another.
What is a transformer?
A transformer is an electrical device that allows an AC input signal (like audio) to produce a related AC output signal without the input and output being physically connected together. This is accomplished by having two (or more) coils of insulated wire wound around a magnetic metal core. These wire coils are called windings. When an AC signal passes through the input winding (the primary), a related AC signal appears on the output winding (the secondary) via a phenomenon called inductive coupling. By changing the number of wire turns in each winding, transformers can be manufactured to have specific input and output impedances. The ratio between the input and output impedances provides a gain or loss of signal level as the signal passes through the transformer. Transformers are bidirectional so that an input winding can become the output winding and an output can become an input. Because of a transformer's bidirectional nature, it can provide a gain in signal level when used in one direction or a loss when used in reverse.
Transformers can be manufactured with multiple primary or secondary windings. A winding can also have multiple connections or "taps". Multiple taps offer different impedances along with different gains/losses.
What types of audio transformers exist?
There are two basic types of audio transformers with each having multiple functions:
Step-up / Step-down transformers
Signal level compatibility or matching
Impedance compatibility or matching
Unity 1:1 transformers
DC blocking
Radio Frequency Interference (RFI) blocking
Ground lift and device isolation
Step-up / Step-down transformer
In a step-up / step-down transformer, the primary and secondary have a different number of windings, thus they have different impedances. Different impedances cause the signal level to change as it goes through the transformer. If the secondary has a higher impedance (more windings) than the primary, the signal level at the secondary will be a higher voltage than at the primary. A transformer with multiple taps provides access to multiple impedances and to different signal gains or losses. Many microphones have step up transformers at their output. For example, inside of every SM57 and SM58 microphone is a transformer that steps up the signal level and impedance before it exits the microphone.
Unity 1:1 transformer
Often called an isolation transformer, it has the same number of windings on each coil. As the impedance is identical for the primary and secondary, the signal level does not change. A unity transformer allows an audio signal to pass unmodified from the primary to the secondary while blocking DC voltage and radio frequency interference (RFI). Also, since the primary and secondary are insulated from each other, a unity transformer will electrically isolate different pieces of equipment. This can solve hum problems by isolating ("lifting") the grounds of different devices. Other unity transformer applications include providing multiple outputs from a single mic input by using multiple secondary windings, and changing balanced signals to unbalanced signals or vice-versa.
What are the limitations of audio transformers?
The first limitation is frequency response. By design, audio transformers only pass audio signals. Therefore, an audio transformer will block signals that are below or above the audio range of 20 - 20,000 Hz. This can be a limitation or a benefit depending on the situation. A second limitation is that audio transformers have a maximum input level that cannot be exceeded without causing a distorted signal. When the maximum level is exceeded, the transformer is said to be "saturated", i.e. it cannot hold any more signal. A third limitation is that audio transformers cannot step up a signal by more than about 25 dB when used in typical audio circuits. Because of this limitation, an audio transformer normally cannot be substituted for a microphone preamp. If more than 25 dB of gain is required, an active preamplifier must be used instead of a transformer.
What is the difference between an expensive transformer and an inexpensive transformer?
Most of the differences involve the limitations stated above. For example, an expensive transformer will have a flatter and broader frequency response. Often, a hotter input signal can be put through an expensive transformer without saturating it. Expensive transformers are also shielded better. Shielding reduces pickup of hum and interference from outside sources such as power supplies. Not only does the shielding keep unwanted signals out of the transformer, it also keeps the desired signal within the transformer. Many inexpensive transformers have no shielding while expensive transformers may have multiple shields.
Do's and Don'ts of Audio Transformers
Do use a transformer to match impedances.
Do use a transformer to increase or decrease signal level by up to 25 dB.
Do factor in load loss when determining total signal gain/loss.
Do use a 1:1 transformer to isolate problem components in an audio chain.
Do not use a transformer to increase signal level by more than 25 dB.
It took me 20 minuets to report this thread to a moderator because the too many users logged on thing
