Author 
Teach me more about transformers please! 
Monobass 
Thanks Graham... I'm looking forward to learning more about this once I get a bit further with this MIT course I'm doing.
So Babaluma have you ever come across any before and after type examples of audio transformers? 

Babaluma 
daverj wrote:  The concern in some modern studios with transformers is that if you go through a lot of them, the "color" they add is cumulative and can end up changing the signal quite a bit after running through a lot of them. 
Of course this could also be exactly what you are looking for, especially with music which has been made all ITB. It's the reason I went with all coloured pieces first, as I knew most of my clients would be 90% ITB. At some stage it would be nice to have a transparent EQ and compressor, as well as coloured ones, so you could use the best choice in any situation. 

Babaluma 
Monobass wrote:  So Babaluma have you ever come across any before and after type examples of audio transformers? 
Nope, but it would be an interesting A/B test! You'd need one of those transformer boxes, like the one Alan Farmelo built in the link above, then it would be easy to do a with and without transformer comparison.
Which MIT course are you doing? I'm looking for a distance learning Masters in audio, if anyone has any good leads.
Graham, thanks for all the great info. Indeed, my mic pre has a 1200/300 ohm, switch for the input impedance, so I am guessing it's transformer related. The tube circuits driving speakers via trannies is interesting too, I am presuming that's how something like a Fender Champ guitar amp works. There's another use of transformers that people talk a lot about, the different sounds of different output transformers in guitar amps... 

Graham Hinton 
Babaluma wrote:  The tube circuits driving speakers via trannies is interesting too, I am presuming that's how something like a Fender Champ guitar amp works. 
Yes, and if you noted my earlier post about transformers changing the impedance of what they are connected to that is why powering on a guitar amplifer without the speaker connected can damage the output valves. The low (16ohm or less) load of the loudspeaker through the output transformer is essential to provide the load the valves need.
There are not many books that I can recommend, but one that will give a good background and explanation to what people here are interested in without being academic is Music, Physics and Engineering by Harry F. Olson. If you don't know who he is and what he did shame on you!
Even though it was written in 1952 most of it is still relevant. This is a rare example of a book being written by someone who actually did it, rather than someone who copied it or didn't do it.
Monobass wrote:  I'm looking forward to learning more about this once I get a bit further with this MIT course I'm doing. 
Stick with it. The only prerequisite you need for understanding my posts is Ohm's Law. I'll try to add some diagrams to make it clearer. 

Monobass 

Babaluma 
Ah, thank you Monobass and Graham, once again!
Will hunt down that Olson book, have heard his name/that book mentioned before, but don't really know about him.
Have had Ohm's law explained to mae a few times, but I didn't manage to retain anything, so any simplified explanations would be very gratefully appreciated! 

Graham Hinton 
Babaluma wrote: 
Have had Ohm's law explained to mae a few times, but I didn't manage to retain anything, so any simplified explanations would be very gratefully appreciated! 
That is almost like saying "I've had the alphabet explained to me, can you recommend any good books on it?" . You will get millions of hits on Google, but the best simplified explanation I've seen for a while is this:
If you don't get it now, you probably never will. Or do you have to get it to see the wit? Anyway, it is absolutely fundamental to everything electrical and electronic so you won't really get the answers to the questions you are asking until you get a handle on it. It will just all seem like magic. Ohm's Law explains the very simple relationship between voltage and current in a metallic conductor and those have to be understood intuitively before their scientific definitions. Maybe that documentary will help more than just background interest? 

Babaluma 
Thanks, that makes a lot of sense. Yep, I remember an EE student friend at Essex Uni explaining it to me by using a water/river analogy (maybe volts the force pushing the water, ohms the width of the river, and I'm afraid I don't remember the amp analogy, and maybe the current being the speed of the flow?)
I get the Volt and Ohm but what is the Amp in that picture representing? He does look very poor indeed. Is Amp the same as current?
Got those three documentaries bookmarked, and watched the first one yesterday, so thanks for helping me out. Forgive the newbie questions, but I am genuinely interested to learn more about electronics. 

Monobass 
yeah that drawing is great. Ohms law seems very simple of paper... I still have moments where I really go round in circles with it in practice though.. it's due to getting confused about what the primary 'agent' is, voltage or current. I think that's a flawed way of approaching it.
Maybe it's because I studied fluid dynamics a little, the analogy between that and electricity is very limited. 

Graham Hinton 
Monobass wrote:  I still have moments where I really go round in circles with it in practice though.. it's due to getting confused about what the primary 'agent' is, voltage or current. I think that's a flawed way of approaching it. 
Yes that might be a stumbling block, neither is primary, they are linked by Ohm's Law. A voltage across a resistor will drive a current through it, but equally a current going through a resistor will develop a voltage across it and the ratio of the voltage and current is the resistance (or the admittance, depending which way you look at it). If you know any two you can find the other. The graph of V against I for a resistor is a straight line going through zero, which means you can't have one without the other and they are always proportional.
You have to become totally conversant and happy with it before you can move on to larger networks, first just combinations of resistors to get familiar with how currents divide and the scale of things. You need to be able to glance at a 4k7 resistor across a 15V power supply and just feel that's about 3mA flowing through it. Then add capacitors, then diodes and so on. You have to do the exercises at first to help it become second nature, but practical exercise helps more. If you sit down with a battery and a handful of resistors and a meter (or two) they will do the same thing for you as they do for me. It's easier than learning about gravity by falling off a log and like gravity nobody has a monopoly on it. 

daverj 
Babaluma wrote:  Is Amp the same as current? 
Yup. Amp, as in "Ampere" (not amplifier). Current is measured in amps.
Monobass wrote:  yeah that drawing is great. Ohms law seems very simple of paper... I still have moments where I really go round in circles with it in practice though.. it's due to getting confused about what the primary 'agent' is, voltage or current. I think that's a flawed way of approaching it.

The deal with Ohm's law is that if you know two of the three parameters, you can calculate the other one. They are all interdependent. None is the "primary" value.
 If you know the voltage across a resistor, and the value of the resistor, you can calculate the current flowing through it.
 If you know the voltage across a resistor and the current flowing through it, you can calculate the resistance.
 If you know the resistance and the current flowing through it, you can calculate the voltage across it.
The way to remember it is using the little triangle symbol. And just remember that if any corner changes, the others change.
When I learned it, they used "E" for the voltage symbol (E = Electromotive force). These days they seem to simply use V for Volts. The "I" used for current is an old symbol standing for Intensity of current (measured in Amps). And of course, the R stands for Resistance (measured in Ohms).


Graham Hinton 
A diagram, as promised:
An AC voltage, Vp, drives a current, Ip, into the transformer primary. This current generates a magnetic field which is picked up by the secondary winding which causes a current, Is, to flow through an external resistive load, RL, and develops a voltage across it.
Each winding in the transformer has a number of turns in the ratio 1:n, where n may be = 1, >1 for step up or <1 for step down. If there are double the number of turns on the secondary the voltage is doubled and the current halved. Note the dots on the transformer symbol, this indicates which end of the windings are in phase. Sometimes schematics change the dot end to avoid crossing lines so be observant of this detail.
Zin is the input impedance of the transformer as it appears to whatever is driving it. Impedance is like resistance in that it is the ratio of voltage to current and has units of Ohms, but resistance is only defined for a metallic conductor (even though many resistors and pots are made of carbon). The important difference of an impedance is that it may change, eg at different frequencies, and it is notated as Z instead of R to show that distinction. If you measure the resistance of a winding with a meter you will see the dc resistance of the copper wire, impedance is what happens when it is in use.
In the case of a valve amplifier output RL would then be a loudspeaker impedance of 8 or 16 ohms and the transformer would be a step down type so n <1. This multiplies the loudspeaker impedance to make it seem higher to the valve driving it, this also means that the current flowing through the valve is less than that going through the loudspeaker.
Does all this make sense? 

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