Thus, the voltage V R3 always equals V i , and the output voltage is then determined by the resistances of R 2 and R 3. Because the signal voltage is applied to the op-amp noninverting input terminal, the output always has the same polarity as the input. A positive-going input produces a positive-going output, and vice versa.
Thus, the input is not inverted at the output , and the circuit is identified as a noninverting amplifier. The voltage divider current I 2 is always selected to be very much larger than the operational amplifier input bias current, and. Figure shows a Non Inverting Amplifier Theory with a resistor R 1 connected in series with the noninverting input terminal.
As in the case of other op-amp circuits, this is done to equalize the resistor voltage drops produced by input bias current. The input and output impedances for a Non Inverting Amplifier Theory are easily determined from the negative feedback equations.
What is the relationship between input and output sine waves? This reveals crucial limitations of the inverting amplifier. We can model the op-amp as a voltage-controlled voltage source VCVS as we did in The Ideal Op-Amp and earlier op-amp sections solving the voltage buffer , voltage reference , and non-inverting amplifier to allow us to perform a more detailed analysis of how the inverting amplifier works:.
Is there a maximum gain we can get from an inverting amplifier? We can clean up that assumption a bit:. This tells us that our gain assumption holds only if one plus our design gain the resistor ratio k is much smaller than the open-loop gain of the op-amp. If we use an op-amp with finite open-loop gain, as all real-world op-amps have, then our ability to build an inverting amplifier is limited to approximately the negative open-loop gain of the op-amp. On the DC Sweep plot, what is the slope of the line for V out y-axis vs.
V in x-axis? If we truly needed this much gain, we need to either find an op-amp with higher open-loop gain, or split the amplification up into multiple stages. Something similar happened in the math for the non-inverting amplifier. No current flows into an op-amp input, so the input impedance of the non-inverting amplifier is infinite. However, one hugely significant difference between the inverting amplifier and the non-inverting amplifier is that the inverting amplifier has finite input impedance.
One way to avoid this is to add an op-amp voltage buffer just before the inverting amplifier. Observe the transition between two flat input impedances. What are the levels of the two flat sections? When does the transition start to happen? In this circuit, I1 is a test current source, set to 0 at DC but used as an AC signal source for small-signal frequency-domain analysis. We can look at the magnitude and phase of the resulting voltage at V in and this gives us a complex impedance for each frequency.
The most interesting trace to look at is V div. After the step, the op-amp observes a difference in its inputs and begins reducing its output voltage until the inputs are equal again. This does not happen instantaneously. As an exercise: replace the step voltage source V1 with a square wave source.
See what happens as you drive the inverting amplifier at various frequencies from 1 kHz to 1 MHz. If you are relying on a virtual ground, you have to be patient. Unlike a real ground, a virtual ground is only a low-impedance point when you move slowly. This expression includes the open-loop gain A OL which covers DC and low frequencies, and it includes a low-pass filter which drops off following the gain-bandwidth product GBW.
Following the same method we solved in detail in the previous section, the corner frequency can be found by determining where the imaginary part of the denominator is equal in magnitude to the real part. Review that section to see us work through the almost-identical math. Op-Amp Inverting Amplifier - Gain vs. Bandwidth Tradeoff. Try the frequency domain simulation.
Again, the gain-bandwidth product is not magic. Just as we discussed on the non-inverting amplifier , there is parasitic capacitance everywhere, and we have to be most concerned about it at high-impedance nodes like V div. How much parasitic capacitance does it take to start seeing overshoot in the step response? How about ringing? As the simulation demonstrates, it takes just picofarads of unintentional capacitance to cause serious overshoot or ringing.
As an exercise, add ,p to the end of the custom sweep list for C1. Increase the simulation stop time to 40u. What happens to the step response? This demonstrates why this issue is called instability , because the op-amp is very nearly unstable and prone to oscillating indefinitely. As another exercise, try making both resistors smaller by a factor of 0. Does this help or hurt? As discussed on non-inverting amplifiers , there are a few ways of mitigating this stability problem:.
Compensation means modifying the circuit slightly by adding components that counteract the undesired parasitic effects. We demonstrated feed-forward compensation in detail on the non-inverting amplifier. We can do something similar for the inverting amplifier, adding a capacitor C 2 in parallel with R f :. The simulator is set to try a range of different values for C2. Which value gives the best step response little ringing or overshoot? What happens if C2 is much larger or much smaller than that?
It depends on too many factors, including the resistances, the gain-bandwidth product, and the parasitic capacitance. If C2 is much larger than that, we eliminate ringing, but it also slows down the step response considerably. Somewhere around 0. It may even be present unintentionally due to parasitic capacitance in your physical circuit, simply from the PCB traces of the output and inverting input being in close proximity.
One reason that only a tiny capacitance is required here is because the two ends of the compensation capacitor are connected to voltages that are naturally moving in opposite directions: as V div rises, V out falls because of the op-amp. This means that even a small voltage change at the high-impedance side actually drives a large voltage change across the capacitor.
This is called the Miller effect. This can be hard to understand, but to a first order, we can think about the parasitic capacitance C 1 as adding charge stored at the inverting input node V div. It takes time for this charge storage to happen, which is what causes the ringing and oscillation in the first place. This is discussed in greater detail in the corresponding non-inverting amplifier section. To some degree, we can think of the compensation capacitor C 2 as trying to cancel out or remove that charge so that the circuit behaves overall more like the one without any parasitic capacitance.
This is the Miller multiplication effect at work!
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Warmer more valve like. Bass: Nichicon Muse KZ 2 x uf , connected —ve to -ve with Mundorf sio as bypass replace the mkp The bass is louder compared to before, though I would prefer a tighter bass. It sounds fine though. In closing I would like to thank Eric, Terry and the dozens of people from all over the world for so generously sharing their findings and knowledge.
Hi Frank, Glad to be of help and thank you for sharing the final results of your modification. Yeah, glad to be of some help, this is all so subjective that it is not easy to convey what things do in any specific way. Likewise I have a very specific sort of taste with what I want, I like the treble to be very extended and clean and clear, the bass is not as important to me. I just read another Capacitor Shootout that described that happening also.
I guess I was warned, that when I was considering the purchase, the break-in time to get them to sound good would be many many hours ? So that may be what it takes. I am going to remove them, and replace them with Audiocaps, or Jantzen Superior Z caps. The reviews are positive on those and not alot of break-in time needed. Thanks for the review! Pipe, the other users I've talked who have used the Mundorf Supreme Silver in Oil think that they sound very bright, due to a lot of high frequency information, and lightweight bass.
I have used the Mundorf Silver Supremes in several amps as coupling caps input, and between stages , and I get the same thing every time. Suppressed high range. Although the highs still sounds good just not as loud as before, and a pronounced midrange with more bloom. As coupling caps this seems to be a consistent finding of mine.
Now in other positions like power supplies, feedback loops, speaker crossovers, and some others I have not noticed this same sort of suppressed high frequencies. Sting, I don't think Clarity Caps are carried officially by anyone in Singapore.
You can try Liveacoustics at Chinatown. You can ask them to indent order the MR for you. Hi Friends, Capacitor is important device for electrical usage as it stores charge and energy, we provide highly efficient capacitor. Thanks for sharing. Well I looked at your site, your capacitors don't seem to apply to this application. I mean who needs a KV cap for audio applications. I am looking though for a good 10KV cap for a tube amplifier application though that doesn't break the bank.
This topic has inspired me for caps on my Apogee Centaur crossover. I now have Clarity Cap PX's as basic caps. The ESA's are a bit to aggressive for me, but maybe that's just me. Then I have Mundorf Supreme's as bypass. And finally the Ampohm Paper-in-oil Tin Foil as super-bypass.
The Supreme's are great and give the best separation and placement of instruments and voices. The AmpOhms add the sweet sound. They need a lot of break in time. If it wasn't for this blog I never would have known about them and tried them.
Thanks Eric! I would like to mention for the benefit of those reading and keeping up with this blog. The last six months I have been trying in many applications Russian teflon capacitors, and they are equal in my opinion to the V-caps which I would rate above all the caps in this comparison , at a fraction of the price.
Also we should start developing a plan to do another shootout with a completely different set of caps, like various audio grade electrolytics that are obtainable. I have had this idea of making an amplifier with five different coupling caps that are switchable with a rotary switch.
Then sending it out to for or five of my audio friends and have them rate them not knowing which caps were which. This way a blind test could be done completely without bias as to type, price, or brand. Then compare the findings of the five people to see how similar or dissimilar they are.
I actually have the V-Cap lying around, but the values are too small to be used in my test. Considering the size of the Ampohm caps and of the Mundorf Supreme caps I am thinking that the size is an important factor in the quality of the caps. By the way: Narendra Kumar's post on September 23, at PM only serves the purpose of advertizing spam.
Rick, it seems to be the case no pun intended. Perhaps the large size and bulk helps reduce microphony in the foil of the capacitor? Thought I would add some information again. Currently I am making my own Polypropylene film caps.
Because of this I can definitely say what adds to the size of the caps. Thicker dialectic material allows for greater voltage before failure which adds to the size. Thicker cathode and anode sections of the cap doesn't seem to do much, but larger area does increase capacitance.
Since I am not using the metalized method my caps are quite large, but I have full control over every aspect of them. I am silver and gold plating my copper plates for my caps currently to find what sonic differences this makes. Also with these Russian Teflon caps I have here they are rated at VDC so low voltage values don't seem to be an issue. But capacitance values have all been below 1uF that I have seen. For coupling capacitors I have not found better at any price.
Hello Eric I like reading your blog very much. Are you referring to bypassing a coupling cap, another plastic cap in a power supply, or an electrolytic cap? For electrolytic caps in the power supply, I got excellent results bypassing them with very small values e.
But usually alternate crossover does not have 4. If I want to try new cap, should I get cap based on a nearest value to 4. Hi Peter, You can parallel two or more caps to get the right value. However, I wouldn't sweat it and just get the nearest right value. So, your original 4 uF cap would be unlikely to spot on in value. Regards Eric.
Hi, Thank you for the cap test, my only problem in your test is that you used caps with different values therefore different "sound" may appear because of the difference in the caps values. Great article, thank you. I hear good things about Auricap XO Capacitors.
Have you tried them? I've only tried the Auricap XO in crossover applications. Auricaps are quite close to neutral and good performance capacitors in my view. Hi Eric Thank you for this excellent review of caps. Its highly educational and impressive.
With your vast experience, I hope to seek your advise. The stock coupling caps come with 2 x Obbligato Gold 2. May i ask what would be the sonic signature of the upgraded version. Do you think its worth the investment in your opinion? As I would be making my purchase soon, I would very much appreciate your thoughts. Thank you Ram. Hi Ram, How coincidental. It's a really great preamp for the money.
The sonic signature of both the capacitors are listed on this post, have a read and see which one you prefer. Whether it is worth it depends on how good your upstream equipment is. If the rest of the partnering equipment is modest, I think the Mundorf is overkill. Personally I would just go with the stock capacitors which are already quite good , and get used to the sound first before deciding which direction you want to tweak the sound. Also, if your power amp has a high enough input impedance, you can save a bit of money and go for a smaller sized coupling capacitor.
Since fitting in new capacitors on the Musical Paradise is so easy, there is no real downside to taking this approach. Hi Eric What a coincidence! I finally found someone local who has this amp. This is a rare coincidence. I was looking for reviews for this preamp but it was hard to come by.
How do you find the sonic signature of the amp? Heard some rare good reviews from other sites. Great if you could share your impressions. I hope its not too warm till it supresses details. I like it neutral, some sense of warmth is fine but overly warm can be too much especially me being used to solid state kind of neutral detailed music. Guess it comes at a better price point. My speakers are Klipsch f RP which are pretty easy to drive at 96db. This is the first time I am actually venturing into a preamp and that too tubes.
Never used tubes before. Right now with my solid state i enjoy the clarity, details and tight bass. My system has decent soundstage. Am hoping with the MP Mark II preamp with tubes, I am able to get a holographic feel; kind of enveloping sound with a wider soundstage without losing the clarity, details and bass reproduction which I currently enjoy.
Guess the sound am hoping for is better musicality. My system upstream is certainly not high end. Its mid or reasonable range. I have read your cap reviews. Very informational. I guess I wont be losing much as your review finds the Obligatto musical as well. I really dont have much experience changing caps myself so will just go with their stock Obligatto Gold caps 2.
Thanks for your advise. Really helped clear things up for me and save bucks. I am likely going to use the stock tubes before I learn to tube roll. I would love to hear your impressions of the Mark II preamp though. Thanks once again for your great work and reaching out to me.
Really appreciate your views. Best regards Ram. Hi Ram, The is quite open and transparent, you won't find it mushy or rolled off at all. As your power amp has high power and you are using very sensitive speakers, try out the preamp on it's lowest gain settings. The is designed to allow easy tube rolling. No soldering is required as the capacitors are connected using binding posts.
I'll post a full review when I have some time. My stock tubes were a bit noisy, but I have plenty of tubes on hand and a new set fixed that. To sum it up, the is a great preamp and a bargain at the price. Hi Eric Thank your for your insightful views. Glad to hear the Mark II is a quality preamp and is open and transparent. Coming from a seasoned audiophile like you, it really means something. Its reassuring that I made the right choice.
Will be purchasing the amp today. I will take your advice and stick with the stock caps and upgrade if need be in due time. What you have said makes a lot of sense to me. Looking forward to your review of the amp, and hopefully some tube recommendations when you have the time.
Thank you for the very helpful advise. Keep up the great work! Hi Eric As my MP amp. You mentioned your stock tubes were noisy. May I know what you replaced these with. Can the MP take in tubes other than 12AU7. Would this be a good set to get? Others with some good reviews seem to be Sylvania, Mullord Nos and the 83C replicate types. Is it also better to change the rectifier tube too. Amywhere in sg where I can go tube shopping? Appreciate your advise. Hi Ram, It may be more helpful to open a new thread on this.
I will put up a post as a placeholder for the MP preamp, and if you could re-post your comment, we will discuss that there. Thanks in advance. I just thought I would weigh in on a couple of things about tubes, since I am an amplifier builder. If so there is a list of tubes that can be used in the amp on their website.
Regarding tubes there are a few factors that determine how noisy a tube can be. Obviously the more it amplifies the more noise it can have, but also the types of resistors used can create more noise then others. For example carbon composition resistors are known to be very noisy. Buy specifically dealing with tubes, tubes with less transconductance and higher Gm are the least noisy.
From manufacture to manufacture there is some variance. As far as specific manufactures to some degree that depends on the tube. Generally Svetlana are generally fairly low noise but some tubes they have made are more noisey then other brands. Mullards have always been good tubes in my experience. Also for some reason cryo treating tubes seems to lower their noise so the JJ brand from Cryoset are very nice tubes, but JJ in general makes good tubes.
I haven't had a poor quality tube from them yet. All this may or may not help, I know as a builder I deal with noise differently as I just start changing the circuit in some fashion, but all most folks can do is change the tubes. Not to mention there are different types of noise, power supply noise, device noise, circuit noise, and they are all different and manifest differently.
Hi Terry Thanks for you detailed views. Thanks for highlighting the point about resistors and their impact on noise. Not being as technically competent or experienced as you, I belong to the category of people just changing tubes to manage sonic quality. Good to hear the JJs are a good option. Mullards are well known as you have shared. Appreciate your thoughts.
Hi, I am recapping my Accuphase tuner T and I have to cause some bipolar's for the small places on the audio board. Hi Eric, Firstly, thank you for posting this shootout. I think it is very helpful with all the dizzy options available out there. I have a couple of questions and will like your insights in helping me decide on best use of caps in my tube preamp. I am looking the following values to swap out in my RIAA phono section below: 2x 0. Listening to me built-in phono stage on my tube preamp and comparing against the Schiit Mani Phono Preamp, the Schiit Mani is the obvious winner.
The easily audible difference was the Schiit Mani had a clearly more resolving top end. More decay and sparkle. Overall, I found the Schiit Mani had more spatial details and wider soundstage and more air. In the 0. Given I am running tubes distortion , I wonder if that will smooth out any form of grain or edge in replacement caps. The Vishay and GAD-viva are similarly priced just a few cents difference. Hi Nimo, It could be a fun experiment but I personally have doubts whether changing a few capacitors would result in a massive improvement in your phono stage.
Why not just use the Schitt, or get an even better phono stage? Between the capacitors you mention, I would go with the Vishay HQ. Hi Eric, Thanks for coming back. I hear you about changing just a few caps and using the Schiit instead. Was more of an experiment, try and see if it changes anything. The frequency response of a RC coupled amplifier is as shown in the following graph.
From the above graph, it is understood that the frequency rolls off or decreases for the frequencies below 50Hz and for the frequencies above 20 KHz. The capacitive reactance is inversely proportional to the frequency. At low frequencies, the reactance is quite high.
The reactance of input capacitor C in and the coupling capacitor C C are so high that only small part of the input signal is allowed. The reactance of the emitter by pass capacitor C E is also very high during low frequencies. Hence it cannot shunt the emitter resistance effectively. With all these factors, the voltage gain rolls off at low frequencies. Again considering the same point, we know that the capacitive reactance is low at high frequencies.
So, a capacitor behaves as a short circuit, at high frequencies. As a result of this, the loading effect of the next stage increases, which reduces the voltage gain. Hence the voltage gain rolls off at high frequencies. The voltage gain of the capacitors is maintained constant in this range of frequencies, as shown in figure. If the frequency increases, the reactance of the capacitor C C decreases which tends to increase the gain. But this lower capacitance reactive increases the loading effect of the next stage by which there is a reduction in gain.
The frequency response of RC amplifier provides constant gain over a wide frequency range, hence most suitable for audio applications. The circuit is simple and has lower cost because it employs resistors and capacitors which are cheap. Teach with us. RC Coupling Amplifier Advertisements. Previous Page.
Capacitor-Coupled Inverting Amplifier: Apart from the selection of R. When a noninverting amplifier is to have a signal capacitor-coupled to its input, the op-amp noninverting input terminal must be grounded via a resistor to. A capacitor-coupled inverting amplifier is the figure. In this case, bias current to the op-amp inverting input terminal flows via resistor R2, so coupling.