tadgesualdo

rybitski, It is true you must understand basic electronic theory to understand how to utilized IC's in circuit, especially if you want to design with them. But even then you will not totally understand how or what is going on inside them fully. So I found it helpful to view them as black boxes, if you give the correct inputs, you should get the desired outputs. Therefore often times when you can't figure out why your circuit is not working properly, and you have checked that all required input information (supply voltages and input information) then you have not other choice but to assume that the black box (in this case an IC) is not working. The more complex the IC becomes, or the more pins it contains the more this way of thinking and trouble shooting is helpful I have found. IC's can really make electronics fun and a lot less work, but they come with limitations as well. Enjoy, TG :)

Hi all, Ok I have another question regarding op amp theory. What is the best way to make a op amp buffer? Most times you see two 10K resistors for this with a non-inverting input, but would not just a short between the output and the negative input work the same? What is the difference? Now with inverting inputs this seems to get more complex, because doesn't the input inpedance of the opamp have an effect on the feedback circuit, and needs to be taken into account? Thanks, TG :)

I found one thanks, I have been reading, this is what I needed, but to be quite honest you do need a little bit of background to grasp all of it. It would be nice to for things to be written in a bit more common language, I miss some of the detail stuff. TG :)

How do I open Ante's book, what program? TG :)

Audioguru, Why don't you tell us how you really feel, eh?

With regard to R3, R4, R11, and R12. The value you want depends on the other values you are using in the loop.

I thought this quote from a converstation I had with another designer might help others understand the reason for pursuing a design with resistors that bleed open loop gain in an op amp circuit. The idea is to allow the op amp to function in an area that it operates in a more stable condition. For some op amps noise may be a consideration that will not make this practical, for others like the OPA637 this is a viable solution that would otherwise make the op amp unable to work in a certain application. Some have found that most op amps, even those that are suposedly unity gain stable function better further from their oscillating point. I think most of my problems have been with not taking into consieration the differences between non-inverting op amp implimentation and inverting. The op amps become like different components. We will see as I try the schematic in my last post, with the new PCB's. "The implementation you show is correct enough, but keep in mind that using the resistors from (-) input to ground do not actually affect the output gain - they affect the feedback experienced by the op amp circuit, the op amp operates with less apparent feedback and is thus more stable that otherwise." Audioguru, I agree with all that you said with the phase shift of various components in most audio applications, but in my situation I am not so sure it applies. I have no crossovers in my power amp in the signal path, I have only a single capacitor in my speakers crossover and my tweeters are not reversed with the other driver in the two way speakers I have. The caps I put in the design were there in case the the preamp circuit has an unexceptable offset that I need to decouple it from other circuits. There are many reasons why things may sound different other than a difference in radio frequency extention. I feel that various circuits and components increase in distortion as frequency increases in the upper ranges of the audio band because of their gain bandwidth not being great enough. So the extention well abover human hearing is to make this distortion curve well out of audiable range. Would you not agree that the TL0x series sounds better than the NE5532 op amp in the audio band because of distortion? If this is so would that not be because of the gain bandwidth differences? I am curious if others have experimented with op amp circuit design and found other interesting effects of circuit design on them. Like I said I like inverting input better than non-inverting, but I hope it wasn't because the circuit I used in each case was not what made the precieved differences. Keeping an open mind is the beginging of understanding. TG :)

I really like the idea of I2C contol of audio and home theater components. A lot of IC's use the Philips I2C standard to control a IC volume control, input selection, bass/treble controls, and anything else that we use to control with pots and switches on from pannels. Does anyone know of a controller that you could put in a front pannel of a home made home theater preamp with a few switches and knobs that could you program to contol various audio chips that use the I2C format. I know of a few guys that use the I2C interface in robotics, but don't know any DIY guys in audio that use it. TG :)

Well I haven't gotten the "noise-gain" resistor design implimented to "hear" it yet.

The reason for the two op amps is that the second corrects the phase back to where it was in the begining.

Audioguru, R3, R4, R9, R10, were inserted in this design based on the design notes below, see the subtitle "noise gain manipulation".

Ok I am going to try to post the schematic in this post. TG :)

Audioguru, While I figure out how to post a schematic perhaps you could answer a few more questions. Are these supply caps your talking about in series with the supply, or between the positive and ground of the supply? What starts to happen the further from the supply pins of the op amp you start getting with these caps? I make my own PCBs (toner transfer method) so I make my traces as wide as possible, I imagine this helps. Is there any other thing I can do to reduce inductance in working with the PCB? Also if this helps I use a +/-15v supply on the opamps. It doesn't appear at this point that I am losing anything in the audible range, but it wouldn't hurt to play it safe. What effect would this inductance make regarding the likelihood of my opamps oscillating? If might be helpful for me to post a pic of the PCB layout as I don't have the power traces on the schematic, they are so simple I just put them in on the second side of the PCB. TG :)

Audioguru, Currently the circuit I am tweaking and experimenting with is a two stage inverting opamp configuration. I really like the idea of stages and components not effecting each other, so i try to issolate and buffer them as much as possible. For instance on my first opamp stage I use the ratios of resistors that present a higher circuit impedance to the source circuits, and I use up some circuit gain by issolating the two stages with a law faked volume pot. The second stage then I have complete flexibility to do the most radical things, as this section will not effect other circuits nearlly as much. I also use a 100 ohm resistor on its output so that the decoupling cap I have on the output will not effect the second stage as much, we all know opamps don't like to drive capacitive loads. I don't mind using inverting inputs as long as I have an even number of opamp stages so that my output would be as if I were using non-inverting inputs. Could you expand on the reasons for this? What capacitor values do you use? What benefits does this have with the opamps performance? I guess since opamps leave you with mostly the buffering and feedback to worry about, it becomes much easier to focus on these parts of the circuit. So far my experiments in this area have had satisfying benefits. I am very impressed with how good you can make opamp circuits, they perform much better than I ever would have imagined TG ;D.

I had higher hopes for this thread, not that some of you haven't delivered, but I was hoping this would go in the direction of some experiences some of you had in developing circuits with opamps.

Indulis, I wish you could come over and I could have you listen to this little preamp that I made for the purpose of checking out opamps. I don't know why but the AD843 sounds much cleaner than say a TL072. I don't know enough about these specification to understand what is over kill, this is one thing I am trying to understand. I do know 250v slew rate is better than say 60v, but I don't know what is over kill and if you can have such. The AD843 is inexpensive enough that even if it were overkill it wouldn't matter all that much. So lets talk about bandwidth and slew rates. Most opamp have bandwidth way above human hearing, does that matter as long as it is ABOVE human hearing. What I mean is who cares as long as it is not and issue? With slew rates, at what point is this specification addiquate for audio? What part of the transient response equation is slew rate, recovery time, or diviation? What i am trying to figure out is how are these specifications related to what I am hearing, in other words how can I make these specifications more practical, by understanding them? BTW, there are a few papers out that mention that in a sense humans can hear above 20K Hz. We localise sound by a combination of two things, amplitude and phase. So we precieve phase difference of frequencies above our own human hearing range, even though we can't detect those frequencies. So saying NOTHING above 20K Hz has no use, is like throwing out the baby with the bath water. Perhaps these frequencies add very little to our listening experience, but if your listening to stereo images, then they must add some spacial properties, otherwise why don't we just listen to mono. Can we start on the most basic level like saying that an amp with 8v slew rate will sound dull, because it can't respond even to a 15K hz sine tone? I just want to understand how things relate to others. What I would like to do is be able to listen to two different opamp and then after picking which one I like, look at teh specification and understand the measured differences that could be contributing to what i am hearing. I have no clue. Then again perhaps I am better off in ignorance as it is more honest this way. It sounds good but I don't know why, not because I thought it would because of a spec, but because it just does. TG :)

Well for the last several months I have been reading everything on the net, and in some books about opamps.