Hmmmmmmm
I don't see anything wrong with copying, it's a good place to start while I work up a reasonable tutorial beyond broad generalities. Not sure how deep to go, it just takes some composition time.
K-wood
I don't see anything wrong with copying, it's a good place to start while I work up a reasonable tutorial beyond broad generalities. Not sure how deep to go, it just takes some composition time.
K-wood
Whatever you decide to write, will be excellent. I'm a fan of choke loaded power differentials (my latest endeavor was at the BAF this year--the big fellow that took two people to lug to the listening table...
) and would enjoy learning more about employing the current/voltage controls you used in your design.Thanks for what you've shared so far.
Hmmmm
Well, a few things would be the same and a few would need to change. The differences between the 2SK60 and the LU1014D are significant in a couple of ways. The input capacitance of the LU part is 10 times the input capacitance of the Sony part, so the driving impedance would need to be significantly lower in order to maintain reasonable slew rate for fidelity. The reverse transfer capacitance Crss is also rather enormous for the LU part and it would seem to necessitate output cascoding to reduce that miller effect on bandwidth and phase distortion. the LU type parts are very different than the vertical grid channel devices built in the 70's and in the effort that I was involved with in the 90's. So, they just need a bit more gate drive energy and circuit finess over frequency to be truly transparent. And you're right, it would be an interesting experiment. One other configuration that I've done in the past used Supertex depletion mosfets which are kinder to the designer with regard to the critical capacitances.
K-wood
Well, a few things would be the same and a few would need to change. The differences between the 2SK60 and the LU1014D are significant in a couple of ways. The input capacitance of the LU part is 10 times the input capacitance of the Sony part, so the driving impedance would need to be significantly lower in order to maintain reasonable slew rate for fidelity. The reverse transfer capacitance Crss is also rather enormous for the LU part and it would seem to necessitate output cascoding to reduce that miller effect on bandwidth and phase distortion. the LU type parts are very different than the vertical grid channel devices built in the 70's and in the effort that I was involved with in the 90's. So, they just need a bit more gate drive energy and circuit finess over frequency to be truly transparent. And you're right, it would be an interesting experiment. One other configuration that I've done in the past used Supertex depletion mosfets which are kinder to the designer with regard to the critical capacitances.
K-wood
just for the sake of argument
Having a penchant for evolving tube circuits into silicon emulations of the same tends to make the signal path all majority carrier type devices,(N). So just to show that there is no prejudice here against minority carrier devices, (P), here is another watt sucking fireball amp made of 5 cent transistors and capable of >30watts. There is also the need to heatsink the face of every TO-92 to an aluminum plate which makes the mechanical layout interesting at best. The circuit is a self biased transistor array follower, modified to include gain by ratioing some negative feedback. Pretty clean and definitely cheap to build. The .01 caps are .01F or 10,000uF 35V each.
K-wood
Having a penchant for evolving tube circuits into silicon emulations of the same tends to make the signal path all majority carrier type devices,(N). So just to show that there is no prejudice here against minority carrier devices, (P), here is another watt sucking fireball amp made of 5 cent transistors and capable of >30watts. There is also the need to heatsink the face of every TO-92 to an aluminum plate which makes the mechanical layout interesting at best. The circuit is a self biased transistor array follower, modified to include gain by ratioing some negative feedback. Pretty clean and definitely cheap to build. The .01 caps are .01F or 10,000uF 35V each.
K-wood
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Yet another WSF or the Fun of it
This version of the WSF is the modern variation of the original design done 40 years ago in my parent's basement where a great deal of lernin' happened. This amp uses a MP5100 50 amp germanium transistor in series with a 4 ohm resistor as the collector load. 3.75 amps is the quiescent current for this output stage. The original had a finessed centering bias and a 5000uF coupling cap to the speaker, but still with the same results. I added the DC servo stuff on the later version because the feet just wont stay still. Though not terribly efficient, it has a remarkably clear response through the full spectrum. The drive is curiously booted to the output for bandwidth.
K-wood
This version of the WSF is the modern variation of the original design done 40 years ago in my parent's basement where a great deal of lernin' happened. This amp uses a MP5100 50 amp germanium transistor in series with a 4 ohm resistor as the collector load. 3.75 amps is the quiescent current for this output stage. The original had a finessed centering bias and a 5000uF coupling cap to the speaker, but still with the same results. I added the DC servo stuff on the later version because the feet just wont stay still. Though not terribly efficient, it has a remarkably clear response through the full spectrum. The drive is curiously booted to the output for bandwidth.
K-wood
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Majority and minority carriers can be either N or P. JFET's are always majority carrier devices be they N or P channel.
Semantics?
Not to be pedantic about it, that was a slight of hand comment for color but even the device designers will often call out in term, this: "A device in which the current is conducted by the charges dominant in the lattice is called a majority carrier device (e.g., electrons in n-type material, or holes in p-type material if the current is conducted by charges not dominant in the lattice, the resulting device is called a minority carrier device " (IRC) Though this is most often used in the description of channel devices like FET's, where current flow is conducted through a single type of semiconducting material and not passing through any junctions, the slight of hand was extending this to include "bipolar" junction devices for polarity sake. In the case of initial implied reference to WSF No.4, the entire signal path is N-channel devices and might be said, tongue in cheek, to be a majority carrier amplifier. Die sizes for "complimentary" devices are a good illustration of the difference. The P channel die compliment to it's N equivalent will be three times as large for the same doping regime to have "complimentary" characteristics. There will always be finessed parameters involving doping concentration and area to make the conductivity, capacitance and depletion efficiency match up, so areas can vary from 1.5 to 3 times in ratio when trade-offs are managed. Always will be the argument that there is no such thing as a truly complimentary device structure, and it's a good argument to engage when a Speyside single malt scotch is employed to refine the details therein, but a forum on this subject would turn into a full time job, and I have one of those. So thank you for the correction, I'll try to restrain my loose cannon for a more outrageous subject later.
K-wood
Not to be pedantic about it, that was a slight of hand comment for color but even the device designers will often call out in term, this: "A device in which the current is conducted by the charges dominant in the lattice is called a majority carrier device (e.g., electrons in n-type material, or holes in p-type material if the current is conducted by charges not dominant in the lattice, the resulting device is called a minority carrier device " (IRC) Though this is most often used in the description of channel devices like FET's, where current flow is conducted through a single type of semiconducting material and not passing through any junctions, the slight of hand was extending this to include "bipolar" junction devices for polarity sake. In the case of initial implied reference to WSF No.4, the entire signal path is N-channel devices and might be said, tongue in cheek, to be a majority carrier amplifier. Die sizes for "complimentary" devices are a good illustration of the difference. The P channel die compliment to it's N equivalent will be three times as large for the same doping regime to have "complimentary" characteristics. There will always be finessed parameters involving doping concentration and area to make the conductivity, capacitance and depletion efficiency match up, so areas can vary from 1.5 to 3 times in ratio when trade-offs are managed. Always will be the argument that there is no such thing as a truly complimentary device structure, and it's a good argument to engage when a Speyside single malt scotch is employed to refine the details therein, but a forum on this subject would turn into a full time job, and I have one of those. So thank you for the correction, I'll try to restrain my loose cannon for a more outrageous subject later.
K-wood
The chance is nil, but I do turn up in San Jose on occasion. I will send advanced notice next time.
As another funny coincidence, I live 2 blocks from the former Teledyne Crystalonics JFET fab on Sherman St.
Not sure the purpose of your resistors in series with the
caps that bridge your split tail pairs in the 1st schematic?
I assume the intent was folding a cascode both ways to
make a theoretically perfect differential?
See you like the Wilson Mirror! Ever tried Blumlein's Garter
in that application? This was kinda my thought process how
to autobias a pair of tubes accurately enough for a toroid
OPT... I don't know how well it'd work under a JFET input
circuit like yours.
Drawing #1 is the pair of CCS shown in Drawing #2.
caps that bridge your split tail pairs in the 1st schematic?
I assume the intent was folding a cascode both ways to
make a theoretically perfect differential?
See you like the Wilson Mirror! Ever tried Blumlein's Garter
in that application? This was kinda my thought process how
to autobias a pair of tubes accurately enough for a toroid
OPT... I don't know how well it'd work under a JFET input
circuit like yours.
Drawing #1 is the pair of CCS shown in Drawing #2.
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In the course of acoustic events
The Real Goal
In the grand scheme of things we strive to record and play back for all time to recall, a sound, like the smell of something that brings back a memory, reproduced the way we remember, the moment. There are certain phenomenon in audio reproduction that, when eyes are closed, will reveal that what is heard is real or reproduced. Much of that “false” image in reproduction is an intermodulation, fabricating non-original artifacts. What would be great is a holographic reproduction system. One that flawlessly reconstructs the entire field of acoustic influence from all angles, delays, environmentally influenced spectral convolutions, and most of all, true fidelity from copy to projection. Bringing this discussion out of the ethereal and making the bold assumption that a Louther, Manger, NHT, Magnaplane, Tanoy or the like will truly move air the way that it should be, an amplifier working in harmony with that load should be able to drive an electrical current with enough voltage compliance to satisfy uniform consumption of that energy but to do it without accelerating the load beyond it’s compliance limits. A perfect amplifier would have zero intermodulation distortion, constant output impedance, not zero or infinite, and if driven to a point of creating harmonic distortion, that it be compliant to the ear’s own asymmetric compliance limits and therefore acoustically invisible. A speaker system can be as guilty of hidden distortions as anything in the chain. Often unnoticed are non uniform speaker input impedances causing spectral notches in energy transfer through to the air. A speaker crossover should not only equalize the transfer function between radiating elements but also present a constant load to the amplifier allowing linear power transfer through its entire range. In radio frequency applications we call this broadband impedance matching, often not a trivial task. A filter will pass what it will and the remaining energy must go somewhere other than back down the throat of the amplifier. Though not efficient, adjacent filter dummy loads and attenuators are employed to feed off excess energy not transferred to the air and equalize the impedances throughout. When not, amplifiers having bipolar follower output stages will reflect an image of the load backward through beta demagnification to the base drive and so on, this is a loop gain shifter and it does have an effect. Reverse transfer capacitance, GM shifting drain to source V/I swings, Beta shift with collector current, Source and emitter resistance changes with current, all contribute to a series of complex interactive quantities that interfere with perfect linear transfer gain. As Time allows I’d like to illustrate some simple concepts toward that goal. An effort to keep this discussion on a conceptual basis first is to hold the “Concept” as primary, details of implementation may then have a stable framework for construction. Years ago at KRL’s Vudu Lab we observed subjectively that a perfectly clean audio source could be heard through a mix of other sources far better than the same source through a dirtier amp. When a clean source is heard, the perception is unmuddled by artifacts and can be said to have a high signal to noise ratio. The same source through a dirtier amp needs to be turned up in order to have the same perception of the source material being heard. In a constant noise field the clean source will be more easily perceived because all of its structure is a fixed power above the noise where the more distorted amp contributes noise to the listening field and must be turned up to compensate. I think this may explain why really distorted music is often played louder than should be humanly tolerated to say nothing about the attendant fatigue, and clean sources tend to be more comfortably level adjusted. So, the cleaner the source, the lower the volume and hearing damage. Not that I have an opinion, but it seems to me that poor tradeoffs have been made over time in favor of convenience and we may be loosing the perceptual ability to discern what is real and what is not. More later, after you cut this prattle to shreds…………………………
K-wood
The Real Goal
In the grand scheme of things we strive to record and play back for all time to recall, a sound, like the smell of something that brings back a memory, reproduced the way we remember, the moment. There are certain phenomenon in audio reproduction that, when eyes are closed, will reveal that what is heard is real or reproduced. Much of that “false” image in reproduction is an intermodulation, fabricating non-original artifacts. What would be great is a holographic reproduction system. One that flawlessly reconstructs the entire field of acoustic influence from all angles, delays, environmentally influenced spectral convolutions, and most of all, true fidelity from copy to projection. Bringing this discussion out of the ethereal and making the bold assumption that a Louther, Manger, NHT, Magnaplane, Tanoy or the like will truly move air the way that it should be, an amplifier working in harmony with that load should be able to drive an electrical current with enough voltage compliance to satisfy uniform consumption of that energy but to do it without accelerating the load beyond it’s compliance limits. A perfect amplifier would have zero intermodulation distortion, constant output impedance, not zero or infinite, and if driven to a point of creating harmonic distortion, that it be compliant to the ear’s own asymmetric compliance limits and therefore acoustically invisible. A speaker system can be as guilty of hidden distortions as anything in the chain. Often unnoticed are non uniform speaker input impedances causing spectral notches in energy transfer through to the air. A speaker crossover should not only equalize the transfer function between radiating elements but also present a constant load to the amplifier allowing linear power transfer through its entire range. In radio frequency applications we call this broadband impedance matching, often not a trivial task. A filter will pass what it will and the remaining energy must go somewhere other than back down the throat of the amplifier. Though not efficient, adjacent filter dummy loads and attenuators are employed to feed off excess energy not transferred to the air and equalize the impedances throughout. When not, amplifiers having bipolar follower output stages will reflect an image of the load backward through beta demagnification to the base drive and so on, this is a loop gain shifter and it does have an effect. Reverse transfer capacitance, GM shifting drain to source V/I swings, Beta shift with collector current, Source and emitter resistance changes with current, all contribute to a series of complex interactive quantities that interfere with perfect linear transfer gain. As Time allows I’d like to illustrate some simple concepts toward that goal. An effort to keep this discussion on a conceptual basis first is to hold the “Concept” as primary, details of implementation may then have a stable framework for construction. Years ago at KRL’s Vudu Lab we observed subjectively that a perfectly clean audio source could be heard through a mix of other sources far better than the same source through a dirtier amp. When a clean source is heard, the perception is unmuddled by artifacts and can be said to have a high signal to noise ratio. The same source through a dirtier amp needs to be turned up in order to have the same perception of the source material being heard. In a constant noise field the clean source will be more easily perceived because all of its structure is a fixed power above the noise where the more distorted amp contributes noise to the listening field and must be turned up to compensate. I think this may explain why really distorted music is often played louder than should be humanly tolerated to say nothing about the attendant fatigue, and clean sources tend to be more comfortably level adjusted. So, the cleaner the source, the lower the volume and hearing damage. Not that I have an opinion, but it seems to me that poor tradeoffs have been made over time in favor of convenience and we may be loosing the perceptual ability to discern what is real and what is not. More later, after you cut this prattle to shreds…………………………
K-wood
Another thought
Transformer outputs are a wail of tradeoffs. If you want a Single ended drive the leakage reactance will be high so as to accommodate DC bias plus the differential swing about that point. In the P-P amp leakage reactance is managed depending on how much the tube quiescent current can be tolerated. Sloppier builds with more open window area in the core means the sloppier the tube balance can be. But little can be done with toroids accept balance, balance, balance. Low leakage, good coupling and high permeability tend to saturate toroid cores with little imbalance. It's a tight path to acoustic coupling efficiency as long as DC balances are corralled. There is a toroid tape winding technique available from Stangennes Industries in Palo Alto that spaces the permeable steel a bit with a dielectric coating. This provides some leakage in the core and makes a more forgiving toroid transformer. General Radio built a number of toroid transformers for audio, the 942-A comes to mind. it was used in the Gotham recording amplifiers some time back and driven with 811's I think. They used a winding technique called astatic winding which tended to reduce the imbalance issue by increasing some of the leakage and reducing distributed capacitance by this winding and isolated primaries. The isolated primaries were useful, allowing them to operate in parallel in a totem pole output stage developed by Donald Sinclair in 1952. This lowered the input impedance by 4 and effective distributed capacitance consequently upping the frequency range and uniformity of coupling coefficient to the speaker. The Sinclair P-P output stage is what I use almost exclusively in all the amps I do weather they are OTL or not. But then balance is always a good thing to do any way for other subtle influences in symmetry.
Prattling on....................K-wood
Transformer outputs are a wail of tradeoffs. If you want a Single ended drive the leakage reactance will be high so as to accommodate DC bias plus the differential swing about that point. In the P-P amp leakage reactance is managed depending on how much the tube quiescent current can be tolerated. Sloppier builds with more open window area in the core means the sloppier the tube balance can be. But little can be done with toroids accept balance, balance, balance. Low leakage, good coupling and high permeability tend to saturate toroid cores with little imbalance. It's a tight path to acoustic coupling efficiency as long as DC balances are corralled. There is a toroid tape winding technique available from Stangennes Industries in Palo Alto that spaces the permeable steel a bit with a dielectric coating. This provides some leakage in the core and makes a more forgiving toroid transformer. General Radio built a number of toroid transformers for audio, the 942-A comes to mind. it was used in the Gotham recording amplifiers some time back and driven with 811's I think. They used a winding technique called astatic winding which tended to reduce the imbalance issue by increasing some of the leakage and reducing distributed capacitance by this winding and isolated primaries. The isolated primaries were useful, allowing them to operate in parallel in a totem pole output stage developed by Donald Sinclair in 1952. This lowered the input impedance by 4 and effective distributed capacitance consequently upping the frequency range and uniformity of coupling coefficient to the speaker. The Sinclair P-P output stage is what I use almost exclusively in all the amps I do weather they are OTL or not. But then balance is always a good thing to do any way for other subtle influences in symmetry.
Prattling on....................K-wood
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Just a bit more
This is an example of a Sinclair-Peterson type push pull totem pole amplifier from the Oct. 1951 GR Experimenter publication. It puts both output tubes across the voltage rail to ground, cancels the magnetizing current as in a normal push pull and couples both primaries in parallel capacitively so the sending impedance is 1650 ohms instead of the usual 6600 ohm P-P. Of note is the fact that both output tubes are driven grid to cathode and the gain transfer function of both are identical as in the normal P-P configuration. Some stacked tube amps are driven so as to have the lower tube with transfer gain and the upper tube used as a unity gain follower with upper-lower drive correction through feedback. The Sinclair-Peterson architecture is a symetric drive impedance particularly when using triodes and requires little feedback.
This is an example of a Sinclair-Peterson type push pull totem pole amplifier from the Oct. 1951 GR Experimenter publication. It puts both output tubes across the voltage rail to ground, cancels the magnetizing current as in a normal push pull and couples both primaries in parallel capacitively so the sending impedance is 1650 ohms instead of the usual 6600 ohm P-P. Of note is the fact that both output tubes are driven grid to cathode and the gain transfer function of both are identical as in the normal P-P configuration. Some stacked tube amps are driven so as to have the lower tube with transfer gain and the upper tube used as a unity gain follower with upper-lower drive correction through feedback. The Sinclair-Peterson architecture is a symetric drive impedance particularly when using triodes and requires little feedback.
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