Reading matterial and some questions :)

[Darkknigh_t]

Hey guys!
I can't seem to find that collection brian put up with all the pdf books if someone could link that please that would be great
I'm just reading the wampler books someone posted here which are amazing especially the first one with all the explanations of how the different circuits work.
I have a engineering degree its just different when it comes to instruments, the circuits I mean different goals are here.
I'm very interested in reading a bit about op amp circuits since my uni pretty much sucked at explaining op amps. It's very funny how they skip the explanations but when they have to give me a problem with tones of numbers then its okay.
I just can't seem to find good explanations about some things and if you guys could help that would be great
Here goes:
1. Since op amps (lets say a tl082) have a inverting and non inverting input, why would you ever want to invert your signal?
What do you achieve with inverting the input signal? I saw on some designs the input signal gets inverted and on some not :/

2. When using an op amp as an input buffer with Av=1 so no amplification, i know that the impedance of the op amp is very high and that that somehow effects the signal coming from the pickups but how? Is it maybe low input impedance of the circuit = easier to drive the signal? I really don't understand whats going on there :/

Sorry for my way of asking questions english isn't my first language xD
Thanks for your help in advance

[jimilee]

This should be it.
http://www.madbeanpedals.com/forum/index.php?topic=1232.0

[Darkknigh_t]

This should be it.
http://www.madbeanpedals.com/forum/index.php?topic=1232.0

thats it thank you very much

[RobA]

[]..
1. Since op amps (lets say a tl082) have a inverting and non inverting input, why would you ever want to invert your signal?
What do you achieve with inverting the input signal? I saw on some designs the input signal gets inverted and on some not :/

Sometimes, you do want to invert the signal, for something like phase correction, or maybe to go into a rectifier or a differential amplifier stage, but there are other reasons.

As you note below, the non-inverting amplifier tends to have a very high input impedance. That's not always a good thing. Circuits do better with matched impedances at interfaces. So, in some situations, the ability of the inverting amplifier to have a low input impedance is an advantage.

In mixer circuits, the inverting input sits near or at ground (or virtual ground), so it's a better place to mix the inputs than other topologies. The same thing can be true of different filter circuits. There are other reasons too.

2. When using an op amp as an input buffer with Av=1 so no amplification, i know that the impedance of the op amp is very high and that that somehow effects the signal coming from the pickups but how? Is it maybe low input impedance of the circuit = easier to drive the signal? I really don't understand whats going on there :/

It mainly has to do with impedance matching. A high impedance output trying to drive a low impedance input has poor power transfer. Cable's resistance and capacitance come into it too. It's harder for a high impedance output to drive the cable than it is for a low impedance source.
 

Sorry for my way of asking questions english isn't my first language xD
Thanks for your help in advance

Your English is perfectly fine and understandable. And, your questions are good too. Certainly, there's a lot more to things than I wrote above, but I hope it helps a bit.

[Darkknigh_t]

[]..
1. Since op amps (lets say a tl082) have a inverting and non inverting input, why would you ever want to invert your signal?
What do you achieve with inverting the input signal? I saw on some designs the input signal gets inverted and on some not :/

Sometimes, you do want to invert the signal, for something like phase correction, or maybe to go into a rectifier or a differential amplifier stage, but there are other reasons.

As you note below, the non-inverting amplifier tends to have a very high input impedance. That's not always a good thing. Circuits do better with matched impedances at interfaces. So, in some situations, the ability of the inverting amplifier to have a low input impedance is an advantage.

In mixer circuits, the inverting input sits near or at ground (or virtual ground), so it's a better place to mix the inputs than other topologies. The same thing can be true of different filter circuits. There are other reasons too.

2. When using an op amp as an input buffer with Av=1 so no amplification, i know that the impedance of the op amp is very high and that that somehow effects the signal coming from the pickups but how? Is it maybe low input impedance of the circuit = easier to drive the signal? I really don't understand whats going on there :/

It mainly has to do with impedance matching. A high impedance output trying to drive a low impedance input has poor power transfer. Cable's resistance and capacitance come into it too. It's harder for a high impedance output to drive the cable than it is for a low impedance source.
 

Sorry for my way of asking questions english isn't my first language xD
Thanks for your help in advance

Your English is perfectly fine and understandable. And, your questions are good too. Certainly, there's a lot more to things than I wrote above, but I hope it helps a bit.

Thank you very much
This is perfect, I get it i remember matching impedance's means full power transmission ideally no loss, that's like with antennas and receivers/transmitters.
Hmmm the thing is in some schematics (very simple 1 op amp pre amps) lets say the input signal is entering the inverting input, now sometimes the non inverting input is grounded and sometimes there is a power source connected to it. I get that with a voltage divider they are trying to create a voltage drop on the non inverting input, but for what reason, i mean these are two completely different things, being grounded or having a couple of volts there. Is it maybe to achieve a certain voltage difference between the inverting and non inverting input? But then having the other input grounded would also create a big voltage difference :/
I know my questions sound pretty vague and there are a lot of factors why are things the way they are and they are not easily answered :/ i need a proper book like " this a op amp pre amp, this is here cause of this and that is there cause it needs to be there" xD
damn you OP amp and your black magic xD

[RobA]

Here's a list of useful application notes from TI. I usually try to link from the source, TI in this case, but TI seems to have many of their application notes totally screwed up. You should probably download these and save them, since some of them seem to be disappearing from the TI site. In general, TI and National have tons of application notes that are very helpful.

The original doc on op amps, pretty good source and fun to read.
http://www.ti.com/lit/an/sboa092a/sboa092a.pdf
This one is pretty much a standard on the whys of Op-Amps. It's been expanded and turned into a book I think. The book's probably a good source, but I haven't read it.
http://seniordesignlab.com/sd_docs/Links/Op_Amps_For_Everyone.pdf
Since most guitar circuits tend to be single power rail designs, this is a really good doc to read. It explains the why and the how of single-supply design.
http://www.eng.yale.edu/ee-labs/morse/compo/sloa058.pdf

If you want to go full on engineering style and get into the development of the equations , this one goes through the derivation from the ideal op-amp assumptions,
http://www.ti.com/lit/an/slaa068a/slaa068a.pdf

There are more, some of them like the series on audio applications from TI's Analog Applications Journal are really good for specific topics. These will usually pop up when you do a search on a topic, and if they do, I usually go to them first when I'm trying to figure something out.

[RobA]

[...]
Hmmm the thing is in some schematics (very simple 1 op amp pre amps) lets say the input signal is entering the inverting input, now sometimes the non inverting input is grounded and sometimes there is a power source connected to it.

I'm guessing that what you are seeing here is in single-rail designs. In a split-rail design, the non-inverting input is connected to ground, usually through a resistor that helps eliminate voltage offset, but for a single-rail design, the signal is biased up to near half-supply and the op-amp circuit needs to be adjusted to handle this. There are different ways to handle this depending on the specific circuit involved. The single-supply design doc I listed above goes into lots of detail.

...
I know my questions sound pretty vague and there are a lot of factors why are things the way they are and they are not easily answered :/ i need a proper book like " this a op amp pre amp, this is here cause of this and that is there cause it needs to be there" xD
damn you OP amp and your black magic xD

Yeah, I know what you mean here. The op-amp black magic bugged me for a long time, and still does some times. I have a hard time with doing things in a way that doesn't derive obviously from first principles. But, here's a couple of things that help me. Op-amps are designed, at least to first order, to match the ideal op-amp equations as well as possible. So, for design purposes, you really can treat the beginning of the design or understanding of the circuit based on the ideal op-amp equations. The specific implementation stuff, like how big your input resistors can be or why there is a resistor to ground from the non-inverting pin, is second order and depends on how the op-amp is actually constructed. That stuff is usually in the docs for the specific device or the application notes for working with that type of device. Stuff like JFET inputs versus BJT inputs or something similar.

The second thing that helped me, and the thing that really turned on the light bulb, was the realization that the two transistor long-tailed pair, differential amplifier, is pretty much the whole thing with op-amps. Read up on the long-tailed pair and you get a better understanding of what's going on in an op-amp. To a large degree, the rest of the op-amp is just there to clean up the output from the long-tailed pair to make the op-amp match the ideal op-amp equations better.

Looking at the long-tailed pair can also brighten the picture when trying to understand the OTA, which seems like even deeper and darker magic than the standard op-amp. It's a good place to start I think.

[Darkknigh_t]

[...]
Hmmm the thing is in some schematics (very simple 1 op amp pre amps) lets say the input signal is entering the inverting input, now sometimes the non inverting input is grounded and sometimes there is a power source connected to it.

I'm guessing that what you are seeing here is in single-rail designs. In a split-rail design, the non-inverting input is connected to ground, usually through a resistor that helps eliminate voltage offset, but for a single-rail design, the signal is biased up to near half-supply and the op-amp circuit needs to be adjusted to handle this. There are different ways to handle this depending on the specific circuit involved. The single-supply design doc I listed above goes into lots of detail.

...
I know my questions sound pretty vague and there are a lot of factors why are things the way they are and they are not easily answered :/ i need a proper book like " this a op amp pre amp, this is here cause of this and that is there cause it needs to be there" xD
damn you OP amp and your black magic xD

Yeah, I know what you mean here. The op-amp black magic bugged me for a long time, and still does some times. I have a hard time with doing things in a way that doesn't derive obviously from first principles. But, here's a couple of things that help me. Op-amps are designed, at least to first order, to match the ideal op-amp equations as well as possible. So, for design purposes, you really can treat the beginning of the design or understanding of the circuit based on the ideal op-amp equations. The specific implementation stuff, like how big your input resistors can be or why there is a resistor to ground from the non-inverting pin, is second order and depends on how the op-amp is actually constructed. That stuff is usually in the docs for the specific device or the application notes for working with that type of device. Stuff like JFET inputs versus BJT inputs or something similar.

The second thing that helped me, and the thing that really turned on the light bulb, was the realization that the two transistor long-tailed pair, differential amplifier, is pretty much the whole thing with op-amps. Read up on the long-tailed pair and you get a better understanding of what's going on in an op-amp. To a large degree, the rest of the op-amp is just there to clean up the output from the long-tailed pair to make the op-amp match the ideal op-amp equations better.

Looking at the long-tailed pair can also brighten the picture when trying to understand the OTA, which seems like even deeper and darker magic than the standard op-amp. It's a good place to start I think.

Here's a list of useful application notes from TI. I usually try to link from the source, TI in this case, but TI seems to have many of their application notes totally screwed up. You should probably download these and save them, since some of them seem to be disappearing from the TI site. In general, TI and National have tons of application notes that are very helpful.

The original doc on op amps, pretty good source and fun to read.
http://www.ti.com/lit/an/sboa092a/sboa092a.pdf
This one is pretty much a standard on the whys of Op-Amps. It's been expanded and turned into a book I think. The book's probably a good source, but I haven't read it.
http://seniordesignlab.com/sd_docs/Links/Op_Amps_For_Everyone.pdf
Since most guitar circuits tend to be single power rail designs, this is a really good doc to read. It explains the why and the how of single-supply design.
http://www.eng.yale.edu/ee-labs/morse/compo/sloa058.pdf

If you want to go full on engineering style and get into the development of the equations , this one goes through the derivation from the ideal op-amp assumptions,
http://www.ti.com/lit/an/slaa068a/slaa068a.pdf

There are more, some of them like the series on audio applications from TI's Analog Applications Journal are really good for specific topics. These will usually pop up when you do a search on a topic, and if they do, I usually go to them first when I'm trying to figure something out.

Thank you very much this is exactly what I was looking for this is what I mean, single rail and split rail designs, I mean sometimes you don't even know what to google for. Just with a couple of posts you made things a hell of a lot clearer to me and now I have the means to learn more.
I always say to myself if i managed to study and learn so many things about electronics these specific things won't be a problem, you just need to find that single thing that turns your light bulb on and say "ahaaaaa that's it now i get it", and with that step everything else is just a matter of time till you understand it.
Thank you again I will start my research and study straight away and if you don't mind i will post again here if I don't understand something
Thank you very much for your time and help this has been of amazing help to me!

[RobA]

I'm glad I could help some. It really can be confusing just to figure out where to start looking. If you run in to other questions, there's almost always someone around here that can help.