No, I still don't understand. How do you 'force current' into an Opamp? You apply a voltage (within spec) and the Opamp takes whatever current it wishes. Am I missing something here?GLooP said:
Guys,
I keep coming back to this thread. It makes me smile when I need a smile most. There are not many topics that fill more space in the Amateur Audio pages than this one. From a home builders point of view Op-Amps are simpler and easier to work with than anything else that you can pick up. Here is a challenge; name a device with greater inherent negative feedback and PSRR, a device that cares less about the quality of the power supply than an Op-Amp.
Jfet’s are fun and if you want to build compensating voltage divider (buffer) power supplies that make a difference, have at it.
DT
I keep coming back to this thread. It makes me smile when I need a smile most. There are not many topics that fill more space in the Amateur Audio pages than this one. From a home builders point of view Op-Amps are simpler and easier to work with than anything else that you can pick up. Here is a challenge; name a device with greater inherent negative feedback and PSRR, a device that cares less about the quality of the power supply than an Op-Amp.
Jfet’s are fun and if you want to build compensating voltage divider (buffer) power supplies that make a difference, have at it.
DT
I do largely agree MB, though I don't see that the author's knowledge has much to do with the examination of such a simple device. Actually, it was another member who drew our attention, as a question and subsequently the author joined the thread. 'Not quite the same in terms of the informal protocol outlined by DF96, I think.
The effects generators I referred to, such as the DBX logarithnic companders were certainly well designed and built, being eventually distilled down to a single Ne572 IIRC. Some were not so and fly-by-night brands often did boil down to snake oil indeed, with little discernible effect of any description. Opening some up would reveal only a crude potted circuit of some unlikely cheap parts in a do-nothing circuit.
What I suggest though, is that whether Chris's circuit is designed to or was accidentally found to behave in the prescribed manner is irrelevant. It only comes into question on the grounds of reliable operation, as you say. He claims to have arrived at an operational specification for it, so beyond maintaining that in use, what quibbles are left, since his design is only for a DIL8 plug size module? Without samples, it's not likely we can examine this anyway.
I think we are just showing a disdain for simple psycho-acoustic tease devices which, oddly enough, is what many are quietly struggling to get into with our tubes and quirky 40 year old designs. We usually prefer to ignore where the special sound arises so as not to spoil the mystique or tarnish reputations, however. Some even call it "High-End" 😀
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What manner? Chris says "I included this emitter follower, and it improves the sound". It has been pointed out that it is not an emitter follower, and it is unlikely to affect the sound (unless the opamp has very poor PSRR, or the existing supply has HF resonances). Supporters of the circuit seem to be merely digging an ever deeper hole for it.Ian Finch said:
http://www.diyaudio.com/forums/solid-state/202003-powering-opamps-14.html
#136 - I am loath to quote this but the combination of this post with a string of similar statements by the author lead me to conclude that he has determined a range of suitable operating conditions, controllable by the selection of base resistors. I would call that prescribed - others may disagree that it is adequate or just with my conclusion.
Deeper Hole?..I think I've said I don't endorse it, will that do?
Post Script: #8 lays out the claims, in a manner.
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On the contrary, the statements by the OP in post 136 (and other posts) merely confirm that he doesn't understand his own circuit. Nowhere is there 15V across 2k4, as others have pointed out. He seems to have this strange notion that he can adjust the quiescent current of the opamp by varying the resistor (e.g. he mentions 10mA), yet the opamp supply voltage remains almost unchanged at around 14.3V for almost any sensible value of the BJT base resistor.
I don't think people have grasped how fundamental is the misunderstanding of basic electronics being displayed in this thread. In engineering terms the OP is talking simple nonsense. That is why those of us who do understand trivially simple BJT circuits find it all so silly. We are not arguing about esoteric debatable points, but elementary stuff.
I don't think people have grasped how fundamental is the misunderstanding of basic electronics being displayed in this thread. In engineering terms the OP is talking simple nonsense. That is why those of us who do understand trivially simple BJT circuits find it all so silly. We are not arguing about esoteric debatable points, but elementary stuff.
Yes, the author obviously lacks understanding of solid state electronics but I accept that he can adjust a desired quality(s) with some certainty by altering a resistance. I am still uncertain what measure he describes but a change that affects the desired result in this simple case, where we have simulated the operation with fixed resistances, is a sufficient start to me. It is like using any device we may not understand. We know that many licensed drivers, for example, go about their business with consummate skill but total ignorance of how their vehicle functions.
I understand that the informal process of examination requires a plausible explanation of the circuit's operation but I fail to see how an inability there should preclude its examination when, as you say, those who do understand such trivially simple BJT circuits and find it silly will understand what is going on at DC, at least. Since none other than cliffforest or Magic Box have expressed much curiosity with actual operation, there is probably no hope for a verification of the author's claims here though.
I understand that the informal process of examination requires a plausible explanation of the circuit's operation but I fail to see how an inability there should preclude its examination when, as you say, those who do understand such trivially simple BJT circuits and find it silly will understand what is going on at DC, at least. Since none other than cliffforest or Magic Box have expressed much curiosity with actual operation, there is probably no hope for a verification of the author's claims here though.
Think like you have a beefy cap connected. When the power source is disconnected from the circuit, the cap will try to keep voltage constant. Because of this, the circuit will react with current flowing until the cap is discharged. Now imagine your cap is a big tank, filled with water and you try to stop it flowing with a hand. If the pressure (capacitance) is too high, you may have a hard time doing so.
Class B integrated circuits have never sounded better with added capacitance, just the opposite. This is my attempt to figure out the cause for this.
It is always hard to see inside someone else's head, but I suspect you are confusing capacitance (or charge?) and voltage. Until you are clear on this any attempt to optimise Class B is likely to end in tears.GLooP said:
I'm not trying to optimize anything.
Current is the reaction of closed circuit when voltage is applied. Current flows, voltage does not, but current flows because the voltage applied. Don't regard an OpAmp as a resistor, behaving like constant current source. Also, even on open loop, OpAmps have their idle current.
Surely, you might be right, actually. But I had always the impression that adding unneeded capacitance will result in "forcing" more power in.
Some say that capacitance influences integrated Class B negatively. Others say that inductance from large caps is to be blamed. Another one will tell you that this is non sense, Electrolytic caps are not that big source of inductance that some people claim. You can read or hear people clam added resistors just before the OpAmp power pins will result in better sound by rejecting some HF noise (but also means higher PSU DCR). Other people say that the same result can be achieved by emitter follower or pass transisors, discussed here (they lead to lower PSU DCR, right?).
Seems like the truth is subject to (mis)interpretation.
Current is the reaction of closed circuit when voltage is applied. Current flows, voltage does not, but current flows because the voltage applied. Don't regard an OpAmp as a resistor, behaving like constant current source. Also, even on open loop, OpAmps have their idle current.
Surely, you might be right, actually. But I had always the impression that adding unneeded capacitance will result in "forcing" more power in.
Some say that capacitance influences integrated Class B negatively. Others say that inductance from large caps is to be blamed. Another one will tell you that this is non sense, Electrolytic caps are not that big source of inductance that some people claim. You can read or hear people clam added resistors just before the OpAmp power pins will result in better sound by rejecting some HF noise (but also means higher PSU DCR). Other people say that the same result can be achieved by emitter follower or pass transisors, discussed here (they lead to lower PSU DCR, right?).
Seems like the truth is subject to (mis)interpretation.
True, except inductors make it more complicated than that.GLooP said:
No. Voltage determines current. Extra capacitance may mean that the current can flow for longer, but that is usually what you want from a PSU anyway (except possibly for a guitar amp).
Most likely cause of this is LC resonance in PSU, poor grounding, or inductive coupling of charging pulses. A cap which is too big can create problems, for perfectly sound engineering reasons. Nothing to do with 'forcing current'.
Not much complicated, actually. The inductor will try to keep the current constant, hence "inducing" voltage. Just the opposite to the cap.
Your point about "forcing current" seems quite logical, but my mind still struggles for some reason. If you are right, what is the problem of having pass transistors set for current larger than 6 mA as people say beyound that a deterioration is SQ is percepted?
Caps that are bigger generally have a lower ESR and can be more demanding on the PSU especially if regulated, on large-delta transient handling.
Meaningless statement. The voltage drop across the BJT is around 0.7V for any reasonable value of Rb, so the opamp gets 14.3V. Therefore its current demand does not change. You can drop the current somewhat by a significant increase in Rb, but you can't increase it - even a short circuit for Rb will not change anything much as you will still get 0.6-0.7V across the base-emitter junction.GLooP said:
Big caps after a regulator can create problems, as they make life very hard for regulator loop stability. Big caps should not be needed after a regulator, anyway. A good regulator does not need big caps after it. Many regulators may misbehave with big caps after them. A few small caps to keep HF under control is all that should be necessary, and these may need to be isolated by small inductors.MagicBox said:
Adding big caps after a regulator can be a sign that the designer does not understand what he is doing.
Hi,
This is untrue. The problem is created by low value, very low ESR capacitors (e.g. Film 1uF Film), not large value low ESR Capacitors (e.g. 3,300uF Electrolytic).
That depends on the regulator. Standard 3-Pin stuff generally needs big cap's to avoid measurable and audible problems.
For example an LM317 with adjust cap may be seen as 20mOhm Resistance in series with a virtual inductor of around 4uH, so it becomes inductive above around 1KHz.
To offset this we need a capacitor on the output of the LM317 with around 20mOhm ESR and around 4000uF capacitance. Then not only is the regulator stable, but also the output impedance is flat resistive...
On the contrary. If they are after 78XX/79XX or LM317/LM337 style regulators they are generally an indication that designers knows what he does only too well.
I would however say that anyone who issues blanket declarations like "Adding big caps after a regulator can be a sign that the designer does not understand what he is doing." show limited understanding and faulty logic...
Ciao T
This is untrue. The problem is created by low value, very low ESR capacitors (e.g. Film 1uF Film), not large value low ESR Capacitors (e.g. 3,300uF Electrolytic).
That depends on the regulator. Standard 3-Pin stuff generally needs big cap's to avoid measurable and audible problems.
For example an LM317 with adjust cap may be seen as 20mOhm Resistance in series with a virtual inductor of around 4uH, so it becomes inductive above around 1KHz.
To offset this we need a capacitor on the output of the LM317 with around 20mOhm ESR and around 4000uF capacitance. Then not only is the regulator stable, but also the output impedance is flat resistive...
On the contrary. If they are after 78XX/79XX or LM317/LM337 style regulators they are generally an indication that designers knows what he does only too well.
I would however say that anyone who issues blanket declarations like "Adding big caps after a regulator can be a sign that the designer does not understand what he is doing." show limited understanding and faulty logic...
Ciao T
My understanding may be limited, but I can't see any flaw in my logic.
Nowadays 3000uF might look small to some people. My main point is that any caps are there to sort out HF, not simply patch up a poor regulator. The reg should deal with syllabic frequencies, ripple, and low audio. Simply whacking on a big cap (many 10 000uF) is not the answer.
Nowadays 3000uF might look small to some people. My main point is that any caps are there to sort out HF, not simply patch up a poor regulator. The reg should deal with syllabic frequencies, ripple, and low audio. Simply whacking on a big cap (many 10 000uF) is not the answer.
Hi,
It is. In one of my designs I use 33,000uF after the regulator (but there is a good reason for that).
In the case of the common garden 3-pin regulators the cap's emphatically do not deal with HF, but AF.
One might say that these 3-Pins are poor regulators and that the big cap after it is a patch. Then again, these regulators, like all others that operate closed loop have requirements of loop stability, which limits the improvements.
Surely if it is the answer or not depends on the question. And I can see questions where this is (one of the) possible answers.
My point is that just because someone has a big capacitor after a regulator they are not necessarily stupid, uneducated or otherwise challenged.
To me whacking a big cap after a 3-Pin reg is a valid engineering solution (especially as the cap does need any serious ripple current specs etc. so it can be quite cheap) over designing an extensive discrete regulator that does not in the end does much better anyway...
Of course I'd probably instead take a small cap enough to make the reg stable and add a resistor before the big cap (or bootstrap the reg to act as AC current source) to get more for my money, but that, as they, is another story.
Ciao T
It is. In one of my designs I use 33,000uF after the regulator (but there is a good reason for that).
In the case of the common garden 3-pin regulators the cap's emphatically do not deal with HF, but AF.
One might say that these 3-Pins are poor regulators and that the big cap after it is a patch. Then again, these regulators, like all others that operate closed loop have requirements of loop stability, which limits the improvements.
Surely if it is the answer or not depends on the question. And I can see questions where this is (one of the) possible answers.
My point is that just because someone has a big capacitor after a regulator they are not necessarily stupid, uneducated or otherwise challenged.
To me whacking a big cap after a 3-Pin reg is a valid engineering solution (especially as the cap does need any serious ripple current specs etc. so it can be quite cheap) over designing an extensive discrete regulator that does not in the end does much better anyway...
Of course I'd probably instead take a small cap enough to make the reg stable and add a resistor before the big cap (or bootstrap the reg to act as AC current source) to get more for my money, but that, as they, is another story.
Ciao T
Your words, not mine. My statement "can be a sign that the designer does not understand what he is doing" is more measured, as I accept that sometimes this could be the right thing to do.ThorstenL said:
I should have been clearer. By 'HF' I didn't mean just RF but also the higher end of AF. I realise that the output impedance of a regulator can rise within the audio range.
Hi,
And the fun thing is that normally the lower the output impedance at DC the lower will be the frequency at which the regulator impedance begins to rise and the larger value and lower ESR our output capacitor needs to be...
So, the paradoxical part is that the only regulators that work okay with fairly low value output capacitors are fairly high impedance ones, where I'd probably hang a big cap of the end of it to get that Z down...
So, if wanted to be persenicky we may actually conclude that if we see a low output impedance regulator with a small value capacitor following, that in fact the designer did not REALLY understand what he was doing, but simply put his faith into some folksy "traditional wisdom" without actually analysing the circuit properly, or that he was more interested in other parameters (size/weight/cost) than performance...
Ciao T
And the fun thing is that normally the lower the output impedance at DC the lower will be the frequency at which the regulator impedance begins to rise and the larger value and lower ESR our output capacitor needs to be...
So, the paradoxical part is that the only regulators that work okay with fairly low value output capacitors are fairly high impedance ones, where I'd probably hang a big cap of the end of it to get that Z down...
So, if wanted to be persenicky we may actually conclude that if we see a low output impedance regulator with a small value capacitor following, that in fact the designer did not REALLY understand what he was doing, but simply put his faith into some folksy "traditional wisdom" without actually analysing the circuit properly, or that he was more interested in other parameters (size/weight/cost) than performance...
Ciao T
So I guess some people will call for regulator open loop bandwidth to cover the audio range.
This thread seems to have wandered a long way from the original BJT+resistor "emitter follower" for feeding power to an opamp.
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