Please review the following threads to familiarize yourself with exactly what Scott i
""As for the confusion of the C7, and the variations with other Aleph amplifiers, besides the Aleph 2, I asked Nelson Pass, and got this response:
"The value of the npn compensation cap pretty much depends on the placment. .001 for CB or .01 for CE."
This means that it does not matter if you put it from the collector to base, or from the collector to emitter, as long as you use the right value. ""
This is the bottom line for all BrianGT Aleph board users on my cap observation. I missed the post but saw the possible ambiguity when looking at amplifier oscillations thread. I reccomend down loading all the aleph schematics and you can get an idea of simularities and differences between the versions and insight on the evolution of the circuit. A free two semester course in amplifier design and some ideas on frequency compensation for the aleph type circuits!
Ren
""As for the confusion of the C7, and the variations with other Aleph amplifiers, besides the Aleph 2, I asked Nelson Pass, and got this response:
"The value of the npn compensation cap pretty much depends on the placment. .001 for CB or .01 for CE."
This means that it does not matter if you put it from the collector to base, or from the collector to emitter, as long as you use the right value. ""
This is the bottom line for all BrianGT Aleph board users on my cap observation. I missed the post but saw the possible ambiguity when looking at amplifier oscillations thread. I reccomend down loading all the aleph schematics and you can get an idea of simularities and differences between the versions and insight on the evolution of the circuit. A free two semester course in amplifier design and some ideas on frequency compensation for the aleph type circuits!
Ren
Meditations upon an amplifier design
It is said that once upon a time a general went to the Oracle and asked if he would be victorious in battle. The Oracle's response was that a great army would fall that day. Secure in the knowledge that he would win, he marched forth to war. He was utterly defeated.
You see, in his pride, he ignored the fact that the Oracle hadn't specified <i>which</i> great army would fall that day. He simply assumed that it was that of his opponent.
There is a quote by Einstein that is bandied about quite frequently to the effect that things should be made as simple as possible, but not simpler.
One wonders whether the man found his true calling in physics.
Most folks around these parts have seen Nelson Pass's minimalist DIY projects, and many have looked over the schematics that he has made available for his older commercial product. Some of these designs push the limits of 'simple.'
On the other hand, I've seen people--with a perfectly straight face--use the same quote to justify designs with seventy-'leven transistors, double differentials, current sources, current mirrors, current events, and folding paper dolls.
How can this be?
Easy.
Just divide Einstein's quote at the comma and focus on the half that suits your personal views. Like the Oracle's pronouncement, it means whatever you want it to mean.
Nelson, all things being equal, chooses to hang his hat on the first portion; the one that says,"as simple as possible." Others, for reasons which seem sufficient to them, point at the second part, which says,"but not simpler."
It's all in the interpretation.
I'm tempted to suggest that we need a second oracle to interpret the sayings of the first, but the second one's answer would probably be just as ambiguous as the first and we'd need a third oracle...then a fourth...
That way madness lies.
So I, and this is me speaking, not Jam or Harry or Nelson or Sonny...just me, I choose to whip out my Gordian sword (I hope all these old ghosts don't mind being thrown together for a few moments) and slice the knot rather than spend time trying to unravel it. I choose simplicity. I will focus on the first half of Einstein's words.
Why?
Well, part of it is esthetics. To me a simple circuit is pleasing to the eye. Another part of it is my hard-won experience, both when I was selling gear and as a listener, that specs don't count for much when the stylus hits the groove. And part of it is an inchoate suspicion that adding more parts is a darkly seductive addiction; it starts with one part, then two, and a little later three, and before you know it, you've rationalized adding twenty-seven more resistors, five capacitors, two tubes, and eleven FETs, each time saying,"Thus far, but no further..." Best not to begin. "Once you start down that path, forever will it dominate your destiny."
(Might as well drag Yoda into this...)
"But, Grey, a cascode is a single gain stage, just like a differential," someone calls out.
Let's take a look at that term: Single gain stage. Somehow, in peoples' minds, that has come to mean that a group of transistors is equivalent to one transistor; that a cascode, for example, is in some mysterious way reduced to equivalency with an ordinary grounded Source MOSFET, for instance. It ain't so, folks. A cascode still means that the signal travels through at least two transistors. The term 'single gain stage' is a semantic convenience for describing a set of devices that perform one particular function. Sort of a black box with a label on the side that says GAIN. But do not blind yourself to the fact that if you take the time to open that box, there will be all kinds of parts in there, and the more parts you add, the further the balance tips from the first half of Einstein's statement to the second. Just because you can call a group of transistors a cascode does not mean that there's only one transistor. It means that there's only one <i>function</i> and that's an entirely different can of worms.
Now, when I started trying to visualize this circuit over a year ago I had everything but the kitchen sink. But since the Aleph output stage has voltage gain, I didn't need the extra gain that would result from using a cascode. The thing about gain is that you've got to get rid of all that you don't need. You can't just put it in a box on the shelf until you need some on a rainy day. The near-universal way to get rid of gain is to burn it off as feedback. To those who think that specs are adequate to describe the sound of a piece of gear, this seems good. But my experience as a listener tells me that feedback is a double-edged sword--it giveth, and it taketh away. It's that taketh away part that bothers me.
As a purely technical exercise, I'm certain that it's possible to put the full X front end as shown on the patent in front of an Aleph output and make it work. But I just didn't need it.
If you folks want to take a whack at it, be my guest. The only person you might want to check with is Nelson. They're his patents. Since he gave the go-ahead to this project (he saw a half-dozen versions of this schematic as the circuit developed), I don't think he'd mind, but it's not my place to put words into his mouth.
And so we come to the circuit as it stands today. There are recognizable portions in it; the Aleph is particularly easy to see, the X a little less obvious, perhaps, but there is a schematic at the beginning of this thread that shows a bunch of parts strung together in a manner that will amplify a signal.
Then the emotional stuff came into play.
I foresaw this--they won't let you be a science fiction author if you can't see at least a little ways into the future. That's not to say that I <i>like</i> it, but I knew that it would happen, given the dynamic that we're faced with here at the DIY site at this time.
Sure enough, things have gotten, shall we say, polarized. People are taking sides over whether this circuit will actually amplify a signal without smoking itself or a speaker that's attached to the outputs. The question that must be asked is whether this emotional outburst is due to the circuit or to other issues.
Clearly, Harry feels that I've been singling him out for ill treatment. He feels that he's been unjustifiably picked on. From his point of view, he's just a normal guy with a sense of humor and wants to have fun.
The flip side of this is that there are others who don't appreciate how Harry behaves towards others. I hear from them because I'm the moderator. They e-mail me; five last night, alone. Sometimes they want grievances addressed. Sometimes, and this is the more tragic message, they're writing to say good-bye. They just don't feel that the atmosphere of the board is condusive to learning and having fun.
Unfortunately, Harry has gone so far as to imply that I'm lying about this. I wish I were.
Guys, try to keep in mind that, as moderator, I have to keep the health of the site in mind at all times. And my view of things is that we need a level playing field where <i>no one</i> feels intimidated. Ever. Period. This is not open to a vote. The only person who can gainsay me on this matter is Jason. It's his site. If you can talk him into it, then I will yield. Not only will I yield, but I will depart. I will not be a member of a site that allows that kind of behavior as a matter of policy. It's shameful enough that it goes on now.
We have now reached a point where the issue of Harry (and others of like mind) has become intertwined with the question of whether the amplifier will work properly in the real world. That clouds the matter. To some people (possibly including Harry, himself) it appears that Harry is demanding that I put in a cap, and that I, out of pride or stubbornness, am refusing to put it in.
I don't know whether I haven't been expressing myself clearly, or whether people simply don't read the posts carefully.
Here is my position: I'll be glad to put in any number of caps, even change the topology of the amp, in order to ensure that it will behave properly. However, I will not do so just because someone tells me to. I want to see any parts added <i>earn</i> their right to be there.
The thing that seems to have escaped some peoples' attention is that this is an actual prototype. It's not a thought experiment, it's not a what-if, it's not a simulation, it's an honest-to-goodness functioning circuit on my bench.
And it's not oscillating.
Why, I don't know.
Harry feels, on theoretical grounds, and perhaps also from simulations, that the amplifier should oscillate. We've got any number of simulations going out there now, and some people have said that the simulations indicate instability.
That's cool.
But it's still not oscillating.
I'd like to ask for two things:
1) Suggestions for ways to <i>make</i> this circuit break into oscillation if it is, indeed, prone to doing so. No, I haven't put a cap across the output yet. I've got other things that I'm doing in my life besides this, but I promise you that I will try things as soon as I can get to them. (As long as they don't cost a lot of money--no gots dinero.)
2) I'd like to ask that someone else breadboard this thing and see whether their amp acts up or not. Maybe I've just got some accidental stray capacitance that's keeping the thing from breaking into oscillation. Stranger things have happened.
I left the caps out because they didn't earn their right to be in the Mini-A (which I breadboarded on these same push boards, incidentally). I simply didn't need them. This circuit is derived from the Mini-A and, for whatever reason, it doesn't seem to need compensation above and beyond what I've got in there now.
I intend to keep this thing as simple as possible.
But not simpler.
Grey
It is said that once upon a time a general went to the Oracle and asked if he would be victorious in battle. The Oracle's response was that a great army would fall that day. Secure in the knowledge that he would win, he marched forth to war. He was utterly defeated.
You see, in his pride, he ignored the fact that the Oracle hadn't specified <i>which</i> great army would fall that day. He simply assumed that it was that of his opponent.
There is a quote by Einstein that is bandied about quite frequently to the effect that things should be made as simple as possible, but not simpler.
One wonders whether the man found his true calling in physics.
Most folks around these parts have seen Nelson Pass's minimalist DIY projects, and many have looked over the schematics that he has made available for his older commercial product. Some of these designs push the limits of 'simple.'
On the other hand, I've seen people--with a perfectly straight face--use the same quote to justify designs with seventy-'leven transistors, double differentials, current sources, current mirrors, current events, and folding paper dolls.
How can this be?
Easy.
Just divide Einstein's quote at the comma and focus on the half that suits your personal views. Like the Oracle's pronouncement, it means whatever you want it to mean.
Nelson, all things being equal, chooses to hang his hat on the first portion; the one that says,"as simple as possible." Others, for reasons which seem sufficient to them, point at the second part, which says,"but not simpler."
It's all in the interpretation.
I'm tempted to suggest that we need a second oracle to interpret the sayings of the first, but the second one's answer would probably be just as ambiguous as the first and we'd need a third oracle...then a fourth...
That way madness lies.
So I, and this is me speaking, not Jam or Harry or Nelson or Sonny...just me, I choose to whip out my Gordian sword (I hope all these old ghosts don't mind being thrown together for a few moments) and slice the knot rather than spend time trying to unravel it. I choose simplicity. I will focus on the first half of Einstein's words.
Why?
Well, part of it is esthetics. To me a simple circuit is pleasing to the eye. Another part of it is my hard-won experience, both when I was selling gear and as a listener, that specs don't count for much when the stylus hits the groove. And part of it is an inchoate suspicion that adding more parts is a darkly seductive addiction; it starts with one part, then two, and a little later three, and before you know it, you've rationalized adding twenty-seven more resistors, five capacitors, two tubes, and eleven FETs, each time saying,"Thus far, but no further..." Best not to begin. "Once you start down that path, forever will it dominate your destiny."
(Might as well drag Yoda into this...)
"But, Grey, a cascode is a single gain stage, just like a differential," someone calls out.
Let's take a look at that term: Single gain stage. Somehow, in peoples' minds, that has come to mean that a group of transistors is equivalent to one transistor; that a cascode, for example, is in some mysterious way reduced to equivalency with an ordinary grounded Source MOSFET, for instance. It ain't so, folks. A cascode still means that the signal travels through at least two transistors. The term 'single gain stage' is a semantic convenience for describing a set of devices that perform one particular function. Sort of a black box with a label on the side that says GAIN. But do not blind yourself to the fact that if you take the time to open that box, there will be all kinds of parts in there, and the more parts you add, the further the balance tips from the first half of Einstein's statement to the second. Just because you can call a group of transistors a cascode does not mean that there's only one transistor. It means that there's only one <i>function</i> and that's an entirely different can of worms.
Now, when I started trying to visualize this circuit over a year ago I had everything but the kitchen sink. But since the Aleph output stage has voltage gain, I didn't need the extra gain that would result from using a cascode. The thing about gain is that you've got to get rid of all that you don't need. You can't just put it in a box on the shelf until you need some on a rainy day. The near-universal way to get rid of gain is to burn it off as feedback. To those who think that specs are adequate to describe the sound of a piece of gear, this seems good. But my experience as a listener tells me that feedback is a double-edged sword--it giveth, and it taketh away. It's that taketh away part that bothers me.
As a purely technical exercise, I'm certain that it's possible to put the full X front end as shown on the patent in front of an Aleph output and make it work. But I just didn't need it.
If you folks want to take a whack at it, be my guest. The only person you might want to check with is Nelson. They're his patents. Since he gave the go-ahead to this project (he saw a half-dozen versions of this schematic as the circuit developed), I don't think he'd mind, but it's not my place to put words into his mouth.
And so we come to the circuit as it stands today. There are recognizable portions in it; the Aleph is particularly easy to see, the X a little less obvious, perhaps, but there is a schematic at the beginning of this thread that shows a bunch of parts strung together in a manner that will amplify a signal.
Then the emotional stuff came into play.
I foresaw this--they won't let you be a science fiction author if you can't see at least a little ways into the future. That's not to say that I <i>like</i> it, but I knew that it would happen, given the dynamic that we're faced with here at the DIY site at this time.
Sure enough, things have gotten, shall we say, polarized. People are taking sides over whether this circuit will actually amplify a signal without smoking itself or a speaker that's attached to the outputs. The question that must be asked is whether this emotional outburst is due to the circuit or to other issues.
Clearly, Harry feels that I've been singling him out for ill treatment. He feels that he's been unjustifiably picked on. From his point of view, he's just a normal guy with a sense of humor and wants to have fun.
The flip side of this is that there are others who don't appreciate how Harry behaves towards others. I hear from them because I'm the moderator. They e-mail me; five last night, alone. Sometimes they want grievances addressed. Sometimes, and this is the more tragic message, they're writing to say good-bye. They just don't feel that the atmosphere of the board is condusive to learning and having fun.
Unfortunately, Harry has gone so far as to imply that I'm lying about this. I wish I were.
Guys, try to keep in mind that, as moderator, I have to keep the health of the site in mind at all times. And my view of things is that we need a level playing field where <i>no one</i> feels intimidated. Ever. Period. This is not open to a vote. The only person who can gainsay me on this matter is Jason. It's his site. If you can talk him into it, then I will yield. Not only will I yield, but I will depart. I will not be a member of a site that allows that kind of behavior as a matter of policy. It's shameful enough that it goes on now.
We have now reached a point where the issue of Harry (and others of like mind) has become intertwined with the question of whether the amplifier will work properly in the real world. That clouds the matter. To some people (possibly including Harry, himself) it appears that Harry is demanding that I put in a cap, and that I, out of pride or stubbornness, am refusing to put it in.
I don't know whether I haven't been expressing myself clearly, or whether people simply don't read the posts carefully.
Here is my position: I'll be glad to put in any number of caps, even change the topology of the amp, in order to ensure that it will behave properly. However, I will not do so just because someone tells me to. I want to see any parts added <i>earn</i> their right to be there.
The thing that seems to have escaped some peoples' attention is that this is an actual prototype. It's not a thought experiment, it's not a what-if, it's not a simulation, it's an honest-to-goodness functioning circuit on my bench.
And it's not oscillating.
Why, I don't know.
Harry feels, on theoretical grounds, and perhaps also from simulations, that the amplifier should oscillate. We've got any number of simulations going out there now, and some people have said that the simulations indicate instability.
That's cool.
But it's still not oscillating.
I'd like to ask for two things:
1) Suggestions for ways to <i>make</i> this circuit break into oscillation if it is, indeed, prone to doing so. No, I haven't put a cap across the output yet. I've got other things that I'm doing in my life besides this, but I promise you that I will try things as soon as I can get to them. (As long as they don't cost a lot of money--no gots dinero.)
2) I'd like to ask that someone else breadboard this thing and see whether their amp acts up or not. Maybe I've just got some accidental stray capacitance that's keeping the thing from breaking into oscillation. Stranger things have happened.
I left the caps out because they didn't earn their right to be in the Mini-A (which I breadboarded on these same push boards, incidentally). I simply didn't need them. This circuit is derived from the Mini-A and, for whatever reason, it doesn't seem to need compensation above and beyond what I've got in there now.
I intend to keep this thing as simple as possible.
But not simpler.
Grey
The trouble with Harry
"We have now reached a point where the issue of Harry (and others of like mind) has become intertwined with the question of whether the amplifier will work properly in the real world. That clouds the matter."
Uncloud it! Several people have asked to get back to the subject of the Aleph X. I and others are most likely tired of hearing how we all have to get along and the threat to democracy and world peace that Herr Haller poses. Why not talk about amplifier design and leave all the emotional hand wringing for another time and thread? Throw Harry off the forum and press on to other things. You are the moderator aren't you? Since you seem to be on good terms with Mr. Pass, and surely he knows more about it than the rest of us put together, why not pose the frequency compensation question to him in Email or on the forum? This sounds like a no brainer to me. I am sure people are much more interested in amplifier stability than Harry's stability. I know I am.
Ren
"We have now reached a point where the issue of Harry (and others of like mind) has become intertwined with the question of whether the amplifier will work properly in the real world. That clouds the matter."
Uncloud it! Several people have asked to get back to the subject of the Aleph X. I and others are most likely tired of hearing how we all have to get along and the threat to democracy and world peace that Herr Haller poses. Why not talk about amplifier design and leave all the emotional hand wringing for another time and thread? Throw Harry off the forum and press on to other things. You are the moderator aren't you? Since you seem to be on good terms with Mr. Pass, and surely he knows more about it than the rest of us put together, why not pose the frequency compensation question to him in Email or on the forum? This sounds like a no brainer to me. I am sure people are much more interested in amplifier stability than Harry's stability. I know I am.
Ren
Some stable feedback ....
Grey,
a design published on a forum such as this is bound to be scrutinized - especially one that is more contemporary than the the Alephs. Peer review can be an important aspect of circuit design but it falls to the designer to use relevant comments constructively and answer directly.
Asking how a feedback amplifier design is compensated is a pretty obvious thing to do - particularly if the compensation is not obvious. The short answer appears to be that you never use a compensation cap but the prototype does not oscillate with a given list of loads.
Then discussions could lead in a number of directions - how to esitmate stability margins before you breadboard, how to fully test the stability of the built design, etc. (Thankfully) we're dealing with the quantifiable aspects of DIY audio design on this board so the answers should be quick, easy and angst free.
I think you do HH a disservice in this thread. I do not see any condescension in his posts, maybe they are not addressed at the layman but then is publishing a design with unknown stability margin suitable for the layman either? Also, if someone is alienating members then I suggest you make an overture off-line with that person to try and ameliorate things. The way you raised the subject in this case could be interpreted as sour grapes over criticism of your design.
I hope you find this feedback constructive (and stable)
Regards
13th Duke of Wymbourne
Grey,
a design published on a forum such as this is bound to be scrutinized - especially one that is more contemporary than the the Alephs. Peer review can be an important aspect of circuit design but it falls to the designer to use relevant comments constructively and answer directly.
Asking how a feedback amplifier design is compensated is a pretty obvious thing to do - particularly if the compensation is not obvious. The short answer appears to be that you never use a compensation cap but the prototype does not oscillate with a given list of loads.
Then discussions could lead in a number of directions - how to esitmate stability margins before you breadboard, how to fully test the stability of the built design, etc. (Thankfully) we're dealing with the quantifiable aspects of DIY audio design on this board so the answers should be quick, easy and angst free.
I think you do HH a disservice in this thread. I do not see any condescension in his posts, maybe they are not addressed at the layman but then is publishing a design with unknown stability margin suitable for the layman either? Also, if someone is alienating members then I suggest you make an overture off-line with that person to try and ameliorate things. The way you raised the subject in this case could be interpreted as sour grapes over criticism of your design.
I hope you find this feedback constructive (and stable)
Regards
13th Duke of Wymbourne
Okay i will try be a little constructive too.
Run a squarewave signal into the input. Watch for overshoot on the rising edge. This will give you a indication of phasemargin. I would say max. 5 - 10%
Try place a cap between the drains of Q5 and Q7 of ~ 47pf- 1nF and watch the squarewave.
You could also compensate by placing the cap across Q4 and Q9 (two caps same size)... Both way should work... I do not have the parts right know so i can not build it. I would like too.
Sonny
Run a squarewave signal into the input. Watch for overshoot on the rising edge. This will give you a indication of phasemargin. I would say max. 5 - 10%
Try place a cap between the drains of Q5 and Q7 of ~ 47pf- 1nF and watch the squarewave.
You could also compensate by placing the cap across Q4 and Q9 (two caps same size)... Both way should work... I do not have the parts right know so i can not build it. I would like too.
Sonny
rtirion,
I just reread one of my earlier posts--the one I believe you might have interpreted as anger towards you--and I feel that I should apologize. I did not express myself clearly. My fault.
Duke,
Peer review is fine. The problem is that Harry, Ren, and sundry simulation programs are saying that it's unstable, yet I have been absolutely unable to replicate same here with the actual circuit. It's a bit frustrating. Don't get me wrong...I don't <i>want</i> the circuit to be unstable, but if it is I want to know, obviously. This may be a case where the simulations fail (as far as I know, all anyone's done so far are thought experiments and simulations). That's why I requested that someone build an actual circuit somewhere other than here and report. I'm getting a little weary of people stridently insisting that the circuit isn't working. It is--at least on the bench.
ritirion & all who are simulating,
I just tossed a 1uF cap across the output (in parallel with the 8 ohm load resistor) and...nothing happened. It didn't even twitch.
Oh, very important, forgot to mention earlier: Phase shift is zilch. On the order of a degree or two at all frequencies under 100kHz. Very consistent. I gather from an earlier post (rtirion?) that someone was simulating major phase shift as early as 1-2kHz. I'm not getting it here.
Like I said, if someone can give me some ideas to try to make this thing do what theory says it should, then I'm game. I don't want my tweeters roasted any more than you guys do, but so far the thing just keeps smiling, no matter what I throw at it.
There are other posts that I need to respond to. Apologies to all, but I've got to get some sleep. Hopefully tomorrow.
Grey
I just reread one of my earlier posts--the one I believe you might have interpreted as anger towards you--and I feel that I should apologize. I did not express myself clearly. My fault.
Duke,
Peer review is fine. The problem is that Harry, Ren, and sundry simulation programs are saying that it's unstable, yet I have been absolutely unable to replicate same here with the actual circuit. It's a bit frustrating. Don't get me wrong...I don't <i>want</i> the circuit to be unstable, but if it is I want to know, obviously. This may be a case where the simulations fail (as far as I know, all anyone's done so far are thought experiments and simulations). That's why I requested that someone build an actual circuit somewhere other than here and report. I'm getting a little weary of people stridently insisting that the circuit isn't working. It is--at least on the bench.
ritirion & all who are simulating,
I just tossed a 1uF cap across the output (in parallel with the 8 ohm load resistor) and...nothing happened. It didn't even twitch.
Oh, very important, forgot to mention earlier: Phase shift is zilch. On the order of a degree or two at all frequencies under 100kHz. Very consistent. I gather from an earlier post (rtirion?) that someone was simulating major phase shift as early as 1-2kHz. I'm not getting it here.
Like I said, if someone can give me some ideas to try to make this thing do what theory says it should, then I'm game. I don't want my tweeters roasted any more than you guys do, but so far the thing just keeps smiling, no matter what I throw at it.
There are other posts that I need to respond to. Apologies to all, but I've got to get some sleep. Hopefully tomorrow.
Grey
Aleph-X
Don't know whether this helps any, but my simulations of Grey's circuit do not indicate instability. There is a small amount of lift at 50KHz or so, but this is kept under control by C2 and C4 - presumably as intended. Maybe it depends on the simulator one uses: I get good results from PSpice but rather less reliable results from CircuitMaker (for example). Curious since they all seem to be based on the same underlying engine but a fact nonetheless. I do have some observations on the sensitivity of the current source setting, but I will leave the details until I am a little more sure of my facts.
Don't know whether this helps any, but my simulations of Grey's circuit do not indicate instability. There is a small amount of lift at 50KHz or so, but this is kept under control by C2 and C4 - presumably as intended. Maybe it depends on the simulator one uses: I get good results from PSpice but rather less reliable results from CircuitMaker (for example). Curious since they all seem to be based on the same underlying engine but a fact nonetheless. I do have some observations on the sensitivity of the current source setting, but I will leave the details until I am a little more sure of my facts.
The Alpeh - X
Grey,
Enough huming and harring, time for some hands of effort.
I am on leave as of Friday for a week to complete another project (Aleph 2) and would delighted at buildup the Aleph X as is on a breadboard as requested.
Pending what eventuates I may be able to stick it on an analyser (Liberty Audio) for some real measurements.
best regards
macka
Grey,
Enough huming and harring, time for some hands of effort.
I am on leave as of Friday for a week to complete another project (Aleph 2) and would delighted at buildup the Aleph X as is on a breadboard as requested.
Pending what eventuates I may be able to stick it on an analyser (Liberty Audio) for some real measurements.
best regards
macka
I find it odd that so many are so quick to point out the difference between simulations and the "real world", yet are so quick to criticize this prototyped design based on what their simulations are saying! I wonder why that is...
If Grey responded in a way that seemed on the defensive, it was only because of the accusatory tone directed at the design. Yes, it is good to give a design critical analysis. It is totally something else when it is picked apart based on someone's ideas (which aren't even based on actually building and testing the circuit). Whatever happened to critical thinking when it comes to theory applied to real world situations? I have a feeling that some here want nothing more than to find a problem with the design. If they were really serious, they would be prototyping instead of typing. Wouldn't it be amazing if there was something about this new technology that made it inherently stable?
My point is that theory is great, only when it is backed up by real-world testing. If we were all so narrow as to define our reality only through what we know from books and past experience, we could very easily miss out on something that is a major step forward. Dosen't leave a lot of room to grow, does it? Then again, for some people that is safer. They are the absolute masters of what they know- just ask them.
When I have the money, I will build it, just to see what is what. Until you build it, your speculation is only just that.
Grey, How does the circuit sound?
Steve
If Grey responded in a way that seemed on the defensive, it was only because of the accusatory tone directed at the design. Yes, it is good to give a design critical analysis. It is totally something else when it is picked apart based on someone's ideas (which aren't even based on actually building and testing the circuit). Whatever happened to critical thinking when it comes to theory applied to real world situations? I have a feeling that some here want nothing more than to find a problem with the design. If they were really serious, they would be prototyping instead of typing. Wouldn't it be amazing if there was something about this new technology that made it inherently stable?
My point is that theory is great, only when it is backed up by real-world testing. If we were all so narrow as to define our reality only through what we know from books and past experience, we could very easily miss out on something that is a major step forward. Dosen't leave a lot of room to grow, does it? Then again, for some people that is safer. They are the absolute masters of what they know- just ask them.
When I have the money, I will build it, just to see what is what. Until you build it, your speculation is only just that.
Grey, How does the circuit sound?
Steve
Simulate This! &%#$
Simulations are a tool and a very questionable one at that. That is why I don't use them. Why create questions or answers that don't exist in the real world. I am not saying that simulations are not useful they have their place. A lot of what we do is an art form and no simulation is going to tell us what something sounds like.
Guys, Grey built the thing, it works in the real world and he was kind enough to share his hard work with you. What annoys me is that there are some of you that insist that it won't work and you haven't built the damm thing.
Does Mr.Pass use simulations?
Grey,
I still want to know what it sounds like?
Jam
Simulations are a tool and a very questionable one at that. That is why I don't use them. Why create questions or answers that don't exist in the real world. I am not saying that simulations are not useful they have their place. A lot of what we do is an art form and no simulation is going to tell us what something sounds like.
Guys, Grey built the thing, it works in the real world and he was kind enough to share his hard work with you. What annoys me is that there are some of you that insist that it won't work and you haven't built the damm thing.
Does Mr.Pass use simulations?
Grey,
I still want to know what it sounds like?
Jam
Does Mr.Pass use simulations?
Maybe he does, maybe he doesn't. He does seem to use compensation caps in his designs and I will bet money he knows what constitutes good phase margin. I guess all one would have to do is actually measure the phase margin for this design to shed
some light on the matter. Spice modeling is really a pretty good tool for tweaking this and measurements can be done very easily with a function generator and a 25 Mhz or faster scope. I don't think the only issue is rather the thing will oscillate but also how it will sound. My experience is that getting this right has great sonic dividends I encourage anyone to build this circuit and play with simular approaches to what Mr.Pass has done for the compensation and report back on measured and sonic results. There may be much to learn and isn't that the whole point of this forum?
Ren
Maybe he does, maybe he doesn't. He does seem to use compensation caps in his designs and I will bet money he knows what constitutes good phase margin. I guess all one would have to do is actually measure the phase margin for this design to shed
some light on the matter. Spice modeling is really a pretty good tool for tweaking this and measurements can be done very easily with a function generator and a 25 Mhz or faster scope. I don't think the only issue is rather the thing will oscillate but also how it will sound. My experience is that getting this right has great sonic dividends I encourage anyone to build this circuit and play with simular approaches to what Mr.Pass has done for the compensation and report back on measured and sonic results. There may be much to learn and isn't that the whole point of this forum?
Ren
Ren,
I see your point but for the most part Grey's achievement seems to have been missed.
I works!
I am more intrested in knowing
a) What it sounds like
b) Will we face any problems when it is scaled for higher powers
c) Stability into weird loads
e) Ideas on improving it's performance
f) If someone is going to design a board for it
and a few more...
Jam
I see your point but for the most part Grey's achievement seems to have been missed.
I works!
I am more intrested in knowing
a) What it sounds like
b) Will we face any problems when it is scaled for higher powers
c) Stability into weird loads
e) Ideas on improving it's performance
f) If someone is going to design a board for it
and a few more...
Jam
And I call myself a writer...
<i>Fooey.</i>
Folks, this time I <i>know</i> I've failed to express myself clearly. I haven't given sufficient details. The only excuse I can make (and it's a poor one) is that most of my posts have been made during slow times at work when, by definition, I don't have the circuit with me. I generally don't even have my notes with me. I'm also guilty of not always taking notes.
Sonny, I have failed you by not specifying that I have already used square waves many times, generally at 1kHz and at 10kHz. I'd be glad to try other frequencies, if someone thinks there's a sharply defined area of instability.
What do I see?
If I set the output for 1W sine 1kHz into an 8 ohm purely resistive load, then switch to square wave (roughly 4.5V P-P), I have a slightly overdamped leading edge. There's no overshoot at all; the leading edge is ever so slightly rounded off. 10kHz, ditto, except slightly more rounded. This is no surprise, given that the closer we get to the upper response of this amp the more high frequencies we lose, hence sharpness on the corners of the square wave. Normal Fourier analysis.
-3 dB circa 130kHz at full power, which is a smidgen lower than you would think from calculating 10pf against 100k, but that is going to be due to capacitance on the MOSFETs, plus possibly stray capacitance (maybe...jury's still out on that). Note that lots of amps lose bandwidth at full power (standard Bode plot stuff, da?), but this one's still going strong right up to clipping.
Clipping is symmetrical, by the way, and very clean--no spurious nasties. For those who are taking a deep breath prior to telling me that Alephs clip asymmetrically, remember that this is two Alephs, back to back, each going opposite directions, and that one will be clipping on one half cycle, then the other on the other half cycle. Result: symmetry. Neat, huh?
If I put a 1uF cap across the 8 ohm load with a 1kHz square wave, I get a half cycle of overshoot to the upside, followed by a retrace of about half that. It decays rapidly. Looks to me to be sufficiently damped. If anyone feels otherwise, say so. I can never remember what the "standard" torture test load is, but I regard 1uF as fairly brutal. A 10kHz square wave is more drawn out, proportionately, across the top of the square wave, but shows essentially the same thing; a half cycle to the upside, followed by a retrace downwards of about half that amplitude. It still damps quickly.
To those who are asking about sound quality: I can't build two of these at the moment. Not enough push boards. Not enough heat sinks. Ideally, I'd like to use air cooling on this one because I've got a funny feeling that a lot of my buddies are going to want to hear this thing in their systems, and water-cooled stuff isn't exactly portable. On the other hand, water-cooled does a really good job. Clearly, I've got some decisions to make as to packaging.
(I still like Nelson's form-follows-function design for the Alephs, but I'll have to work with whatever heatsinking I can get my hands on--the usual problem we face--unless I go water-cooled, in which case I have more control over the outcome.)
Oh, Sonny, sorry...caps across the Aleph NPNs have virtually no effect at all on square wave testing. I said this earlier, but not as clearly as I should have. My apologies to all for not being clearer.
Yes, Harry, you too.
Anyone got anything else they want me to look at? In hindsight, I should have made this post back on the first or second page, but I didn't. Mea culpa. I need to be painting and working on the tomatoes today, but I'd also like to get this resolved to everyone's satisfaction so that I can go back to laying out a circuit board and working on a fancy power supply.
Grey
<i>Fooey.</i>
Folks, this time I <i>know</i> I've failed to express myself clearly. I haven't given sufficient details. The only excuse I can make (and it's a poor one) is that most of my posts have been made during slow times at work when, by definition, I don't have the circuit with me. I generally don't even have my notes with me. I'm also guilty of not always taking notes.
Sonny, I have failed you by not specifying that I have already used square waves many times, generally at 1kHz and at 10kHz. I'd be glad to try other frequencies, if someone thinks there's a sharply defined area of instability.
What do I see?
If I set the output for 1W sine 1kHz into an 8 ohm purely resistive load, then switch to square wave (roughly 4.5V P-P), I have a slightly overdamped leading edge. There's no overshoot at all; the leading edge is ever so slightly rounded off. 10kHz, ditto, except slightly more rounded. This is no surprise, given that the closer we get to the upper response of this amp the more high frequencies we lose, hence sharpness on the corners of the square wave. Normal Fourier analysis.
-3 dB circa 130kHz at full power, which is a smidgen lower than you would think from calculating 10pf against 100k, but that is going to be due to capacitance on the MOSFETs, plus possibly stray capacitance (maybe...jury's still out on that). Note that lots of amps lose bandwidth at full power (standard Bode plot stuff, da?), but this one's still going strong right up to clipping.
Clipping is symmetrical, by the way, and very clean--no spurious nasties. For those who are taking a deep breath prior to telling me that Alephs clip asymmetrically, remember that this is two Alephs, back to back, each going opposite directions, and that one will be clipping on one half cycle, then the other on the other half cycle. Result: symmetry. Neat, huh?
If I put a 1uF cap across the 8 ohm load with a 1kHz square wave, I get a half cycle of overshoot to the upside, followed by a retrace of about half that. It decays rapidly. Looks to me to be sufficiently damped. If anyone feels otherwise, say so. I can never remember what the "standard" torture test load is, but I regard 1uF as fairly brutal. A 10kHz square wave is more drawn out, proportionately, across the top of the square wave, but shows essentially the same thing; a half cycle to the upside, followed by a retrace downwards of about half that amplitude. It still damps quickly.
To those who are asking about sound quality: I can't build two of these at the moment. Not enough push boards. Not enough heat sinks. Ideally, I'd like to use air cooling on this one because I've got a funny feeling that a lot of my buddies are going to want to hear this thing in their systems, and water-cooled stuff isn't exactly portable. On the other hand, water-cooled does a really good job. Clearly, I've got some decisions to make as to packaging.
(I still like Nelson's form-follows-function design for the Alephs, but I'll have to work with whatever heatsinking I can get my hands on--the usual problem we face--unless I go water-cooled, in which case I have more control over the outcome.)
Oh, Sonny, sorry...caps across the Aleph NPNs have virtually no effect at all on square wave testing. I said this earlier, but not as clearly as I should have. My apologies to all for not being clearer.
Yes, Harry, you too.
Anyone got anything else they want me to look at? In hindsight, I should have made this post back on the first or second page, but I didn't. Mea culpa. I need to be painting and working on the tomatoes today, but I'd also like to get this resolved to everyone's satisfaction so that I can go back to laying out a circuit board and working on a fancy power supply.
Grey
I am more intrested in knowing
It's a fairly simple circuit, go build one! Can someone really tell you what something sounds like anyway?
"If someone is going to design a board for it"? Guys we treading a very fine line here. If Mr. Pass considers this his newest and topology, and money starts changing hands on people building knock offs there are going to be long term issues with Mr. Pass's cooperation with this forum. Grey has been very cautious thus far and I for one appreciate that. This could easily get out of hand as we have seen several "incidents" along these lines before concerning current Pass Labs products. Let's not bite the hand that feeds us as they say.
Ren
It's a fairly simple circuit, go build one! Can someone really tell you what something sounds like anyway?
"If someone is going to design a board for it"? Guys we treading a very fine line here. If Mr. Pass considers this his newest and topology, and money starts changing hands on people building knock offs there are going to be long term issues with Mr. Pass's cooperation with this forum. Grey has been very cautious thus far and I for one appreciate that. This could easily get out of hand as we have seen several "incidents" along these lines before concerning current Pass Labs products. Let's not bite the hand that feeds us as they say.
Ren
GRollins said:
Grey ... I do not know how to xpress my self right now... But it was not meant to be nasty on you..
From what you tell you circuit should have a fine phase margin.
For the 1uF load you tell us about the circuit this is fine too....
So their should not be anything to complain about ... My first post regarding Harry's post have nothing to doo with your circuit...
What i have understand from reading this thread is that you haven't thought of checking phasemargin... That was the reason for my last posting regarding phasemargin... I think your circuit is neat really neat!!
Sonny
Ren makes a good point in that we need to respect Nelson's wishes, and closely adhere to any regulations of usage he attaches to his designs. It would be a tragedy to lose his trust. On the other hand, as Grey has been in close contact with him, he is at least somewhat aware that this is going on. His designs seem to be marketed at consumers who have a little deeper pockets than the average DIY'er. Even so, we should make sure that Nelson approves of any "DIY kit" type of situations that may come into being on this board.
As far as someone being able to describe the sound of an amplifier- I think a lot can be said to define the general character of an amplifier. It would at least give us an idea. I can think of quite a few adjectives that could be used, both negative and positive.
Grey,
you aren't holding back on the description of sound for any reason we should be aware of, are you? Did it meet your expectations? Any impressions you could give about dynamics, warmth (or lack of), inner detail, etc. would be greatly appreciated. I don't know about the rest of you, but I am not really inclined to give up money on something that is not going to fit (read: I am <B>cheap</B>!).
steve
As far as someone being able to describe the sound of an amplifier- I think a lot can be said to define the general character of an amplifier. It would at least give us an idea. I can think of quite a few adjectives that could be used, both negative and positive.
Grey,
you aren't holding back on the description of sound for any reason we should be aware of, are you? Did it meet your expectations? Any impressions you could give about dynamics, warmth (or lack of), inner detail, etc. would be greatly appreciated. I don't know about the rest of you, but I am not really inclined to give up money on something that is not going to fit (read: I am <B>cheap</B>!).
steve
Re: Meditations upon an amplifier design
Hello,
can this circuit be build with IRFP240's? As I have plenty of them and IRF9610 and ZTX's to build a prototype as well! I love to build one as a 'novice' to give it a 'novice' seal of approval! When something blows up I do not really mind...
Let me know,
Edwin
Hello,
can this circuit be build with IRFP240's? As I have plenty of them and IRF9610 and ZTX's to build a prototype as well! I love to build one as a 'novice' to give it a 'novice' seal of approval! When something blows up I do not really mind...
Let me know,
Edwin
