On the subject of cascoding...
Okay, let's set aside bandwidth, capacitance, distortion, and whatever else you can say for cascodes. There's one point that I never see mentioned, which is that cascoding runs 180 degrees opposed to the "run 'em hot" school of thought. High rail voltages (tubes, anyone?) and high bias currents lead to better specs and better sound. Split that by cascoding and you'll end up with an anemic cousin of the original circuit. Yes, you gain this, that, and the other thing, but...
Just thought I'd toss that in the mix.
Grey
P.S.: Yes, you can jack the rails even higher, then run both devices hot, but that's another topic for another day.
Okay, let's set aside bandwidth, capacitance, distortion, and whatever else you can say for cascodes. There's one point that I never see mentioned, which is that cascoding runs 180 degrees opposed to the "run 'em hot" school of thought. High rail voltages (tubes, anyone?) and high bias currents lead to better specs and better sound. Split that by cascoding and you'll end up with an anemic cousin of the original circuit. Yes, you gain this, that, and the other thing, but...
Just thought I'd toss that in the mix.
Grey
P.S.: Yes, you can jack the rails even higher, then run both devices hot, but that's another topic for another day.
Maybe reading this thread again would be in order:? http://www.diyaudio.com/forums/showthread.php?s=&threadid=3398&highlight=sound+of+cascade
On the subject of cascoding...
Seems to me that cascoding allows one to run devices at a higher current for a given device dissapation. Higher curent gives greater transconductance and one can use lower value drain, plate or collecter resistors for the same gain as the devices run at lower current with bigger load resistors. Inverted cascodes
even allow more DC current through the gain device than the load resistor lower rail voltage requirements for a given value load resistor. Distortion due to voltage varations across the gain device are reduced by cascoding to a much greater degree than increasing the DC voltage across gain device.
It seems to me that the "run 'em hot" school of thought makes a very good case for cascoding rather than against it.
Setting aside bandwidth, capacitance, distortion, and whatever else you can say for cascodes when disscusing them seems a bit strange since those are the very reasons that cascodes are used to begin with. I don't think you can have a useful disscussion on an approach by ignoring its merits.
Not running a bit hot,
Fred
P.S. I am glad to see you back as well and can't imagine you would stay gone for this long. I save my real conStErnation for a certain SomeonE who SEems to thrive on it....
Seems to me that cascoding allows one to run devices at a higher current for a given device dissapation. Higher curent gives greater transconductance and one can use lower value drain, plate or collecter resistors for the same gain as the devices run at lower current with bigger load resistors. Inverted cascodes
even allow more DC current through the gain device than the load resistor lower rail voltage requirements for a given value load resistor. Distortion due to voltage varations across the gain device are reduced by cascoding to a much greater degree than increasing the DC voltage across gain device.
It seems to me that the "run 'em hot" school of thought makes a very good case for cascoding rather than against it.
Setting aside bandwidth, capacitance, distortion, and whatever else you can say for cascodes when disscusing them seems a bit strange since those are the very reasons that cascodes are used to begin with. I don't think you can have a useful disscussion on an approach by ignoring its merits.
Not running a bit hot,
Fred
P.S. I am glad to see you back as well and can't imagine you would stay gone for this long. I save my real conStErnation for a certain SomeonE who SEems to thrive on it....
What argument .......
Maybe the same reason that moderators allow post like that below:
http://www.diyaudio.com/forums/showthread.php?postid=231743#post231743
Maybe the same reason that moderators allow post like that below:
http://www.diyaudio.com/forums/showthread.php?postid=231743#post231743
Fred Dieckmann said:
Steve Eddy said:
I already got in trouble once, for trying to implement more relaxed ways of running things around here. So my comments will be really short and not exactly what I want to say.
But, IMHO, moderators here are not for the reasons to watch what members say to each other, but only to protect them from incoming conflicts and emotional arguments.
It seems to me that you were the first to start the argument, with SE, with your subtle, yet apparent remark. Now, SE just replied to you the best he could. Again, personally, not as a moderator but as a member, I can't blame him for that.
Peter,
Loved that link to the thread on cascodes above and it certainly was graced by the finest minds on the forum including Mr Pass and Hugh Dean who needs know introduction but is a true master of communication with technical literature on the Web.
I think Hugh sums up the difficulties of debating on forums perfectly well.
Ian
QUOTE
" You feel too intently, and maybe you think too much about these relatively unimportant things. Your post listing the dos and don'ts makes good common sense, but it is prescriptive, and best left unsaid."
" Rules can create resentment, and I wouldn't like to have all my posts put through those rules to check correctness. I have no wish to start a flame war, and never will (although I like to stir occasionally!) but believe me, if it happens, I'm outa here. I have survived many flame wars on joenet only by remaining silent; flames are fanned only by emotional responses. The brain damage is much worse if you respond; humans are often incensed by disagreement, yet they are drawn to it like moths to a flame. Leave the email unanswered if you don't agree with it; this works every time, as time dilutes everything."
"Now, may I return to my hobby horse, that pesky cascode? I am like a dog with a bone on this one, I love a friendly debate, and since I've built it and measured it, I know its performance, and the gain is huge. This is in sharp contrast to the diff pair, whose gain is trivial by comparison. "
I recall there is a ample coverage of cascodes also in the A75 article by Norman Thagard & Neslon Pass. This is an excellent read and clearly outlines the application of cascode and their variants
http://www.passdiy.com/pdf/A75p1.pdf
Loved that link to the thread on cascodes above and it certainly was graced by the finest minds on the forum including Mr Pass and Hugh Dean who needs know introduction but is a true master of communication with technical literature on the Web.
I think Hugh sums up the difficulties of debating on forums perfectly well.
Ian
QUOTE
" You feel too intently, and maybe you think too much about these relatively unimportant things. Your post listing the dos and don'ts makes good common sense, but it is prescriptive, and best left unsaid."
" Rules can create resentment, and I wouldn't like to have all my posts put through those rules to check correctness. I have no wish to start a flame war, and never will (although I like to stir occasionally!) but believe me, if it happens, I'm outa here. I have survived many flame wars on joenet only by remaining silent; flames are fanned only by emotional responses. The brain damage is much worse if you respond; humans are often incensed by disagreement, yet they are drawn to it like moths to a flame. Leave the email unanswered if you don't agree with it; this works every time, as time dilutes everything."
"Now, may I return to my hobby horse, that pesky cascode? I am like a dog with a bone on this one, I love a friendly debate, and since I've built it and measured it, I know its performance, and the gain is huge. This is in sharp contrast to the diff pair, whose gain is trivial by comparison. "
I recall there is a ample coverage of cascodes also in the A75 article by Norman Thagard & Neslon Pass. This is an excellent read and clearly outlines the application of cascode and their variants
http://www.passdiy.com/pdf/A75p1.pdf
Can we go back to the thread subject, PLEASE?
Before certain users intervention people were slowly getting somewhere, now we are getting nowhere fast. (I have the distinct impression someone used this before)
Fred I have learned how cascodes really work from this site thank to Nelson, you, and a few others I can't remember right now.
Can you seriously tell me you don't understand what Grey is saying?
Peter why are you wasting time posting here about another thread that went to crap because you didn't do anything about it? How many more disposable threads do you need?
Before certain users intervention people were slowly getting somewhere, now we are getting nowhere fast. (I have the distinct impression someone used this before)
Fred I have learned how cascodes really work from this site thank to Nelson, you, and a few others I can't remember right now.
Can you seriously tell me you don't understand what Grey is saying?
Peter why are you wasting time posting here about another thread that went to crap because you didn't do anything about it? How many more disposable threads do you need?
Cascode
I understand what he is saying. I just don't agree with it. Hot means power. Power is voltage times current For given device power limit increasing the quiesent current will give higher transconductance and greater linearity than increasing the voltage at the expense of bias current. Cascoding does not prevent one from running devices "hot" The real reason for using cascodes is not to limit dissapation was the one of the points I was trying to make.
I understand what he is saying. I just don't agree with it. Hot means power. Power is voltage times current For given device power limit increasing the quiesent current will give higher transconductance and greater linearity than increasing the voltage at the expense of bias current. Cascoding does not prevent one from running devices "hot" The real reason for using cascodes is not to limit dissapation was the one of the points I was trying to make.
In an uncertain world, it's good to see that some things remain constant: The sun rises in the east, gravity pulls things downwards, and Fred still hasn't learned manners & civilized public behavior. I was making bets with myself as to how long it would take him to show up. The only question was how long it would take him to start trying to pick a fight. To do so in a single post is a marvel of efficiency.
For those who believe that Fred's attitude towards me is based on anything as mundane as facts, I trust that his post above--wherein he carefully disregards the benefits of higher voltage simply to start an argument--will enlighten them.
Reminds me of the advice given to aspiring lawyers. If the facts are against you, argue the law. If the law is against you, argue the facts. In Fred's case, perhaps we could amend this to argue the current if the voltage is against you.
Case in point. I had the Aleph-X on the bench hooked to a distortion meter. Ran the rail voltage up--distortion dropped. Dropped it back--distortion rose. The current was held constant for all devices due to the current sources. For that matter, you can raise and lower current independent of voltage with the three pots I designed into the circuit (sneaky of me, eh?), and that has clear benefits, too.
But to argue the current in isolation? Sad. And the guy claims to be an EE.
The defense rests.
No doubt the prosecution will go on for quite some time...
Grey
For those who believe that Fred's attitude towards me is based on anything as mundane as facts, I trust that his post above--wherein he carefully disregards the benefits of higher voltage simply to start an argument--will enlighten them.
Reminds me of the advice given to aspiring lawyers. If the facts are against you, argue the law. If the law is against you, argue the facts. In Fred's case, perhaps we could amend this to argue the current if the voltage is against you.
Case in point. I had the Aleph-X on the bench hooked to a distortion meter. Ran the rail voltage up--distortion dropped. Dropped it back--distortion rose. The current was held constant for all devices due to the current sources. For that matter, you can raise and lower current independent of voltage with the three pots I designed into the circuit (sneaky of me, eh?), and that has clear benefits, too.
But to argue the current in isolation? Sad. And the guy claims to be an EE.
The defense rests.
No doubt the prosecution will go on for quite some time...
Grey
Grey,
I would like to welcome back and hopefully to see you here for a long time and have a productive stay in the process.
Fred could be better but could be a lot worse, he's just part of the characters ensamble that make up this site. I think you can accept that and get on with the program. I think he likes both you and SE though he will never admit it. He finds your post worthy, I don't think he would argue with you otherwise.
I would like to welcome back and hopefully to see you here for a long time and have a productive stay in the process.
Fred could be better but could be a lot worse, he's just part of the characters ensamble that make up this site. I think you can accept that and get on with the program. I think he likes both you and SE though he will never admit it. He finds your post worthy, I don't think he would argue with you otherwise.
Is is just me, or is this tendency for threads to spawn, willy-nilly, other threads troublesome to other folks as well? I did not actually start this thread, though my name is attached to it. Presumably some moderator decided that it needed independent life, but that rather leaves readers coming in on the middle of a discussion that has been taken out of context. The culprit (I believe I know who it was) chose not to explain what's going on or why he did what he did.
Ah, well.
At the risk of flogging an issue better left alone, there is a post from Nelson that says something along the lines of what I was originally saying before Fred chose to misinterpret what I wrote. Try for post #2371 in the Aleph-X thread. I'd quote it here, but the method for quoting seems to have changed since the last time I used the function and I can't seem to make the system bring it up here.
Grey
Ah, well.
At the risk of flogging an issue better left alone, there is a post from Nelson that says something along the lines of what I was originally saying before Fred chose to misinterpret what I wrote. Try for post #2371 in the Aleph-X thread. I'd quote it here, but the method for quoting seems to have changed since the last time I used the function and I can't seem to make the system bring it up here.
Grey
When all else fails, do it the old-fashioned way. This is post #2371 from the Aleph-X thread. I just cut-'n-pasted the blasted thing...
Nelson Pass:
---BEGIN QUOTE---
Very good questions.
In general, after you get more than 2 volts or so Drain to Source, the device pretty much acts like a voltage controlled current source. As the voltage increases, this tends to be even more the case, with a higher transconductance number. The linearity of the transistor has similar behaviours in the case of bias and voltage. First off, the transconductance increases with current (up to a rather high point, anyway) and so you find that the distortion due to variations in current decreases, but of course it is also true that your signal current will also likely be a smaller proportion of the bias current. Both these effects will lower the distortion, keeping in mind that higher chip temperature does lower the transconductance. With voltage, the transconductance increases with voltage, and all the junction capacitances will decrease with increased Drain-Source voltage (this is good for bandwidth), and once again, the when the output signal swing is small compared the DC "bias", the distortion is less. So basically this means that for maximum linearity, we want to run our devices at high current and high bias. Unfortunately the dissipation involved can cut our activity short, so it always comes down to some sort of compromise. It's different for each device, but a little experimentation can get you the information you want. In the case of the newly published
ZV5, we see that for a given load impedance and desired wattage, there is a bias voltage and current beyond which you get diminishing returns. Check out Figures 4, 5, and 6 of that article at www.passdiy.com
---END QUOTE---
I'm afraid I've changed the formatting a bit, meaning where he had paragraphs and such, as the paste didn't quite follow his original. I trust that those with good intentions will be able to follow the thrust of his reasoning anyway. If something is still unclear, consult his original post. Perhaps proper formatting will make it clearer.
I once ran across a site where they were talking about mods to the front end of the Atma-Sphere OTL amps. (Tube cascoded current sources, and other concatenations of buzz words. [Stacked 6SN7s...cool.]It was interesting reading.) The writer was extolling the virtues of high current, even at the expense of going to a lower voltage. Well...yes, but no. I wanted to reach though the screen, tap the person on the shoulder and say,"It's not that simple." Simply running up the bias current will bring benefits. But so will increasing the voltage. The trick is to do both in good measure (with an eye cocked towards device dissipation).
To blindly run up current, whether the circuit is a cascode or any other circuit, ignores a whole 'nother possibility. Either approach is valid in its time and place. Better still to do both at the same time.
I'm not sure when/how "high current uber alles" became Holy Writ. Obviously, Fred is a True Believer. But he's not alone. In some mysterious manner, it became 'common knowledge.' Perhaps it's a pendulum thing and the copy writers of tomorrow's gear ads will cry,"High rail voltages!" Audiophiles everywhere will nod wisely and compare circuit X (with 100V rails) to circuit Y (blessed with 125V rails) and annoint Y with the circuit of the month badge. Current? That's passe, man. Today's circuits depend on voltage to achieve their magic.
And they will be just as wrong as the current guys are today.
grataku,
I'd rather that people who liked me showed it in more conventional ways. Just a personality quirk on my part.
Grey
Nelson Pass:
---BEGIN QUOTE---
Very good questions.
In general, after you get more than 2 volts or so Drain to Source, the device pretty much acts like a voltage controlled current source. As the voltage increases, this tends to be even more the case, with a higher transconductance number. The linearity of the transistor has similar behaviours in the case of bias and voltage. First off, the transconductance increases with current (up to a rather high point, anyway) and so you find that the distortion due to variations in current decreases, but of course it is also true that your signal current will also likely be a smaller proportion of the bias current. Both these effects will lower the distortion, keeping in mind that higher chip temperature does lower the transconductance. With voltage, the transconductance increases with voltage, and all the junction capacitances will decrease with increased Drain-Source voltage (this is good for bandwidth), and once again, the when the output signal swing is small compared the DC "bias", the distortion is less. So basically this means that for maximum linearity, we want to run our devices at high current and high bias. Unfortunately the dissipation involved can cut our activity short, so it always comes down to some sort of compromise. It's different for each device, but a little experimentation can get you the information you want. In the case of the newly published
ZV5, we see that for a given load impedance and desired wattage, there is a bias voltage and current beyond which you get diminishing returns. Check out Figures 4, 5, and 6 of that article at www.passdiy.com
---END QUOTE---
I'm afraid I've changed the formatting a bit, meaning where he had paragraphs and such, as the paste didn't quite follow his original. I trust that those with good intentions will be able to follow the thrust of his reasoning anyway. If something is still unclear, consult his original post. Perhaps proper formatting will make it clearer.
I once ran across a site where they were talking about mods to the front end of the Atma-Sphere OTL amps. (Tube cascoded current sources, and other concatenations of buzz words. [Stacked 6SN7s...cool.]It was interesting reading.) The writer was extolling the virtues of high current, even at the expense of going to a lower voltage. Well...yes, but no. I wanted to reach though the screen, tap the person on the shoulder and say,"It's not that simple." Simply running up the bias current will bring benefits. But so will increasing the voltage. The trick is to do both in good measure (with an eye cocked towards device dissipation).
To blindly run up current, whether the circuit is a cascode or any other circuit, ignores a whole 'nother possibility. Either approach is valid in its time and place. Better still to do both at the same time.
I'm not sure when/how "high current uber alles" became Holy Writ. Obviously, Fred is a True Believer. But he's not alone. In some mysterious manner, it became 'common knowledge.' Perhaps it's a pendulum thing and the copy writers of tomorrow's gear ads will cry,"High rail voltages!" Audiophiles everywhere will nod wisely and compare circuit X (with 100V rails) to circuit Y (blessed with 125V rails) and annoint Y with the circuit of the month badge. Current? That's passe, man. Today's circuits depend on voltage to achieve their magic.
And they will be just as wrong as the current guys are today.
grataku,
I'd rather that people who liked me showed it in more conventional ways. Just a personality quirk on my part.
Grey
Re: Cascode
Fred, to keep it short:
are you telling us that for the same power dissipation, transistors work better with high current and "low" voltage, than with normal voltage and current, or even high voltage and low current?
But, ie with a SE Class A amp, with a cascode and high current biasing. You'll end up with a high output current capability, but low output voltage swing.
Compared to the same amp without the cascode (but the same dissipation), you'll have less output power in the same load (but more in lower impedance loads)
By lowering the voltage swing, and increasing the current; you're modifying the impedance in which the amp will give it's maximum power (when both U and I are max)
Fred Dieckmann said:
Fred, to keep it short:
are you telling us that for the same power dissipation, transistors work better with high current and "low" voltage, than with normal voltage and current, or even high voltage and low current?
But, ie with a SE Class A amp, with a cascode and high current biasing. You'll end up with a high output current capability, but low output voltage swing.
Compared to the same amp without the cascode (but the same dissipation), you'll have less output power in the same load (but more in lower impedance loads)
By lowering the voltage swing, and increasing the current; you're modifying the impedance in which the amp will give it's maximum power (when both U and I are max)
Re: Re: Cascode
Hi,
unfortunately the issue is not that simple. There are too many
grey steps between black and white to generalize it to
a) as much current as possible
b) as much voltage as possible
The truth is, that every gain device (BJT, MOSFET, JFET, TUBE)
has it´s own special AREA where it behaves near optimum.
The art of designing a circuit is to keep devices in the desired
AREAS.
Uli
Bricolo said:
Hi,
unfortunately the issue is not that simple. There are too many
grey steps between black and white to generalize it to
a) as much current as possible
b) as much voltage as possible
The truth is, that every gain device (BJT, MOSFET, JFET, TUBE)
has it´s own special AREA where it behaves near optimum.
The art of designing a circuit is to keep devices in the desired
AREAS.
Uli
Grey,
how high in voltage did you go on the A-X?
In my prototype I went to 23-0-23 with a single pair of irfp044.
What kind of distortion figures did you get?
One thing I can say for sure is that if I can choose conditions of lower distortion on the same circuit it will definitely produce better sound.
how high in voltage did you go on the A-X?
In my prototype I went to 23-0-23 with a single pair of irfp044.
What kind of distortion figures did you get?
One thing I can say for sure is that if I can choose conditions of lower distortion on the same circuit it will definitely produce better sound.
It's been several months since I tested the Aleph-X for distortion, so I don't remember what the distortion figures were. I think I wrote them down, but I'll have to hunt up my notes. For what it's worth, I had one of my tube amps on the bench about two weeks ago and it measured .11% distortion. Not bad for an "obsolete" technology that's only using 10 dB of negative feedback.
Bear in mind that I'm pushing my pair of Aleph-Xs way out to the edge of the envelope in regards to the voltage/current ratio because I'm driving a 2.5 ohm load or thereabouts. That's why I went with comparatively low rails and high current. For a more normal load, I'd have gone for more voltage and less current. Other people--who probably built the Aleph-X as I posted it, or possibly with even higher rails still--will have different distortion figures.
Remind me to look for distortion numbers if I forget. Right now I gotta go feed the baby.
Grey
Bear in mind that I'm pushing my pair of Aleph-Xs way out to the edge of the envelope in regards to the voltage/current ratio because I'm driving a 2.5 ohm load or thereabouts. That's why I went with comparatively low rails and high current. For a more normal load, I'd have gone for more voltage and less current. Other people--who probably built the Aleph-X as I posted it, or possibly with even higher rails still--will have different distortion figures.
Remind me to look for distortion numbers if I forget. Right now I gotta go feed the baby.
Grey
things haven't changed..........
I believe that the point was origionally made was that transistors work better when hotter and to cascode them was often a compromise for this design goal.
Cascoding reducing voltage distortion and running a device at a lower voltage and higher current FOR A GIVEN DEVICE DISAPATION (which is limited by what the device can handle) will result in greater linearity than increased voltage for a given bias current and a larger voltage. There are obviously other parameters involved in the circuit like how large a power supply rail one uses. CASCODE CIRCUITS DO NOT PRECLUDE RUNNING DEVICES HOT AND A GREATER BIAS CURRENT AND LESSER VOLTAGE WILL LIKELY GIVE GREATER LINEARTY AND LOWER DISTORTION SINCE THE CASCODE IS VERY EFFECTIVE IN MINIMIZING VOLTAGE DISTORTION.
This was about technical question. I made my points from an engineering standpoint. Why you want to turn this into a personality issue is a mystery to me, but I don't think too many people are going to buy it. If you feel you have a real issue take it to the moderators. That's what they are there for......
Thanks,
Fred
I believe that the point was origionally made was that transistors work better when hotter and to cascode them was often a compromise for this design goal.
Cascoding reducing voltage distortion and running a device at a lower voltage and higher current FOR A GIVEN DEVICE DISAPATION (which is limited by what the device can handle) will result in greater linearity than increased voltage for a given bias current and a larger voltage. There are obviously other parameters involved in the circuit like how large a power supply rail one uses. CASCODE CIRCUITS DO NOT PRECLUDE RUNNING DEVICES HOT AND A GREATER BIAS CURRENT AND LESSER VOLTAGE WILL LIKELY GIVE GREATER LINEARTY AND LOWER DISTORTION SINCE THE CASCODE IS VERY EFFECTIVE IN MINIMIZING VOLTAGE DISTORTION.
This was about technical question. I made my points from an engineering standpoint. Why you want to turn this into a personality issue is a mystery to me, but I don't think too many people are going to buy it. If you feel you have a real issue take it to the moderators. That's what they are there for......
Thanks,
Fred
grataku said:
Grataku, what exactly do you want from me here?
I posted the link because the subject is about cascoding and some people are glad to read more useful info than old arguments. Here's one example: (unless you are talking about post #5, but in this case Fred brought it to my attention)
macka said:
Fred, I hope you are aware that this thread was not started by Grey, but is a part of a different one and other moderator decided to split it this way. BTW, you kinda remind me mikek with your last post. Sorry if I'm mistaken. BTW, it's nice to see you posting again.
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