Could I get some schooling on impedance and transformers?

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carboncomp

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Hello, I started down the rabbit hole of Di/Reamping boxes and could really do with some help understanding some principles. Right now my understanding of impedance is minimal and maybe even wrong. I understand it as AC current resistance that varies at different frequencies. is that wrong as a very basic statement?

When I look at Di & reaping boxes most seem to use a transformer to setup up or down a signal and in turn change the input/output resistance. I am interested in trying to get my head around the qualities you want for a transformer in this application, is it purely the ratio of primary and secondary?

I feel that's not the case, as I assume the Resistance, Capacitance, Henry and Frequency of the coil affect the impedance (based on looking at online impedance calculators rather than an inherent understanding)
So, I guess I'm asking how can I tell what transformers to get to play with these projects so I can understand why, and not just grab ones on schematics and not understand why that one is being used.

(feel free to explain things to me like I'm a small child, as that is how I feel regards this topic).
 

JohnRoberts

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don't have enough time to do that but a few simple basic relationships.

"Transformers" do more than just step up/step down voltage based on windings turns ratios. They also transform the impedance seen by inputs/outputs. For example a 8:1 step down transformer, transforms the impedance by the voltage ratio squared. So 8:1 voltage ratio delivers a 64:1 impedance ratio. This makes sense if you keep in mind that transformers do not consume power just scale input and output power to be the same.

For a passive DI box the 8:1 ratio knocks down the voltage to make it more compatible with a mic preamp, while simultaneously converting the mic preamp's nominal 2K input impedance up to look like 128k at the DI input.

JR

caveat: I just picked the 8:1 ratio as an example not a design suggestion.
 

carboncomp

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So 8:1 voltage ratio delivers a 64:1 impedance ratio. This makes sense if you keep in mind that transformers do not consume power just scale input and output power to be the same.

For a passive DI box the 8:1 ratio knocks down the voltage to make it more compatible with a mic preamp, while simultaneously converting the mic preamp's nominal 2K input impedance up to look like 128k at the DI input.
Thank you so much, that really helped me get a grasp of what is going on. Time to work on my maths skills and grasp that formula!
 

Bo Deadly

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Impedance is the key to understanding E. If you don't understand impedance just stop whatever you're doing and go figure it out because you're not going to get very far without it.

Every net (a junction of two or more component leads) in a circuit has an impedance which is defined by the resistance, inductance and capacitance of all the components. The impedance of the resistance is just the resistance. The impedance of an inductance depends on frequency - the higher the frequency, the higher the impedance. The impedance of a capacitance depends on frequency - the higher the frequency, the lower the impedance. The DC resistance of an inductor is theoretically zero but in practice the wire has DC resistance (known as DCR in transformer speak). The DC resistance of a capacitor is theoretically infinate but in practice there is some leakage current. This is the basic explanation of the difference between inductance and resistance.

For re-amping, you don't need transformers. A transformer is great for ground isolation which is almost always very important to preventing noise and hum when trying to connect a bunch of unbalanced gear like guitar pedals and amps to your recording rig (especially computers like USB audio interfaces). Without ground isolation, you will get currents between the grounds induced by magnetic fields and small differences in ground potentials.

But if you use the right cables, you can connect earth grounded unbalanced gear to balanced inputs of something like a USB audio interface such that the earth grounds are not connected and not get noise and hum.

Otherwise, most guitar stuff is high impedance (like 1M) and so the impedance of the source device shouldn't matter much. There is a lot of BS on the Internet that is contrary to this. Some folks think they need to match the impedance of the guitar to the amp. Someone just posted something about a "reamp" box that apparently steps up to match the complex impedance of the guitar source (which is about 30K but changes w/ frequency and w/ controls) but whatever it is is going to be low compared to 1M so there should be very little attenuation at various frequencies and so matching is usually not important.

I just posted something about this a few days ago. Look at my profile and content to find it.

You don't need fancy transformers. You just need the right cables and to experiment a bit.
 

carboncomp

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I just posted something about this a few days ago. Look at my profile and content to find it.
Thank you for taking the time to write that all out for me, it is sincerely appreciated. I will certainly go check out your other post on the topic.

Once again Thank you.
but what is impedance? ;)
I'm getting closer to understanding. Well, that is a lie, I now understand more about how much I don't know! 😀
 

CJ

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Impede

To interfere with or slow the progress of,

In electronics sometimes we interfere with or slow the progress of electrons , we are impeding them,

My electronics teacher explained impedance as the transmission of a car, matching the load of the road to the power of the engine ,
Crotchety old man, john McCollum, that's troublemaker Steve jobs on the right,
1659681717117.png
 
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JohnRoberts

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Impede

To interfere with or slow the progress of,

In electronics sometimes we interfere with or slow the progress of electrons , we are impeding them,

My electronics teacher explained impedance as the transmission of a car, matching the load of the road to the power of the engine ,
an auto transmission is a fair analogy for a transformer

JR
 
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