The only "trick" that I can think of right now is the voltage doubler but that is only possible if the winding is specified for about 2x the current the filament is currently demanding. If not, you will get less or much less than 2x voltage depending on the specifications of the transformer.
The standard voltage regulation does not solve the intermodulation distortion issue. The Coleman's regulator is both current and voltage regulator with intrinsic soft start. You will need to use a dedicated toroidal with screen. The specifications and recommendations you can find them here:
https://www.lyrima.co.uk/dhtreg/dhtRegIntro.html
The standard voltage regulation does not solve the intermodulation distortion issue. The Coleman's regulator is both current and voltage regulator with intrinsic soft start. You will need to use a dedicated toroidal with screen. The specifications and recommendations you can find them here:
https://www.lyrima.co.uk/dhtreg/dhtRegIntro.html
Hello elac310,
I also have built such an amp with about the same configuration than yours, but as a push-pull version. Phase inversion is done by the input transformer (Sowter, 1:1+1), followed by a PCF200 - Triode input amplifier, Pentode voltage driver for the 211. Followed by a PL508 (former vertical deflection output in color TVs) adding the necessary current needed for operation into the positive grid range of the 211 (galvanic coupling), so I can use quite a low plate voltage of 750V. The PL508 do not only have a cathode resistor (820 Ohm), but also a choke formed by the 8kOhms primary winding of a small PP output transformer - to reduce the loss of AC driving power. Biasing of the 211 (actually on 70 mA) via the grid bias of the PL508. Output transformer 8 kOhm, 100W from Experience Electronics. I am using the Psvane 211 (the pair at ca. 300€) which have already about 3000 hours (counter) - and are still in perfect shape. Really good quality. Heating by two Meanwell switchmode supplies (adjustable) 12V 10A over thermistors and additional RF filter chains. The amp is dead silent, I mostly use it as home cinema amp due to its power and dynamics. Friends of mine love its smooth performance with classical music.
Salut de la Moselle, best regards 🙂
Uli
I also have built such an amp with about the same configuration than yours, but as a push-pull version. Phase inversion is done by the input transformer (Sowter, 1:1+1), followed by a PCF200 - Triode input amplifier, Pentode voltage driver for the 211. Followed by a PL508 (former vertical deflection output in color TVs) adding the necessary current needed for operation into the positive grid range of the 211 (galvanic coupling), so I can use quite a low plate voltage of 750V. The PL508 do not only have a cathode resistor (820 Ohm), but also a choke formed by the 8kOhms primary winding of a small PP output transformer - to reduce the loss of AC driving power. Biasing of the 211 (actually on 70 mA) via the grid bias of the PL508. Output transformer 8 kOhm, 100W from Experience Electronics. I am using the Psvane 211 (the pair at ca. 300€) which have already about 3000 hours (counter) - and are still in perfect shape. Really good quality. Heating by two Meanwell switchmode supplies (adjustable) 12V 10A over thermistors and additional RF filter chains. The amp is dead silent, I mostly use it as home cinema amp due to its power and dynamics. Friends of mine love its smooth performance with classical music.
Salut de la Moselle, best regards 🙂
Uli
Hi,
I would like to know what is the purpose of 150K and 20uF in series in the circuit? Is it considered as NFB for the amplifier?
Thanks.
I would like to know what is the purpose of 150K and 20uF in series in the circuit? Is it considered as NFB for the amplifier?
Thanks.
I get the sense that some of the arguments around things like that really derive from people stating that the circuit in question sounds bad when in fact it's just not the sound they were looking for.
You might look into what Bottlehead did years ago with their FC-1 filament choke. I don't recall exactly the details other than that it was a rectified voltage taken from a power transformer winding specified for the AC voltage of the filament . ie 2.5V for a 2a3/5V for a 300B , into a dual bay bifilar wound choke designed to have enough leakage inductance to do the job.
There's a post here that mentions it and in the attached schematic, another way.
The FC-1 was discontinued (though for the 211 you would have to have a different one custom wound anyway) but I don't know whether they decided it wasn't effective enough or whether perhaps it had something to do with their customers trying to squeeze them into a preordained form factor that was already pretty tight. You'd need to do some probing.
Yes. It's not a lot of feedback, but helps to overcome part-to-part variations in the driving stages, and slightly reduces the source impedance driving the output valves. This is actually a pretty well designed circuit.
All good fortune,
Chris
Thanks for your reply.
I was told that NFB is not good for SE tube amp in term of sound quality. However, from what I have studied in other schematic, the NFB is taken from the output transformer. Are these two methods differ? Which one is better? Thanks a lot.
I was told that NFB is not good for SE tube amp in term of sound quality. However, from what I have studied in other schematic, the NFB is taken from the output transformer. Are these two methods differ? Which one is better? Thanks a lot.
I would suggest that those seeking knowledge begin by ignoring the pronouncements of Gurus and other self-proclaimed Experts who try to reduce a complex discussion to some cookbook formula.
Real cooking is a process, not just a list of ingredients, and so is a technical design. Seeking knowledge, we must begin somewhere, but we must not be distracted by shortcuts that substitute questionable simplifications for real knowledge. "Feedback is bad" is a modern example of poor understanding amplified by the echo chamber of modern discussion group thinking. Question all assumptions, and as you progress question the assumptions beneath those.
If this comes across as harsh or uncharitable to Gurus and Experts, please forgive me, but it's been a dark night in America.
Always good fortune,
Chris
Real cooking is a process, not just a list of ingredients, and so is a technical design. Seeking knowledge, we must begin somewhere, but we must not be distracted by shortcuts that substitute questionable simplifications for real knowledge. "Feedback is bad" is a modern example of poor understanding amplified by the echo chamber of modern discussion group thinking. Question all assumptions, and as you progress question the assumptions beneath those.
If this comes across as harsh or uncharitable to Gurus and Experts, please forgive me, but it's been a dark night in America.
Always good fortune,
Chris
A friend of mine with a long experience in tube amp construction has built the Uesugi 211 1971 for me. The heating of the 211 was changed to vdc but for the rest we sticked to the original schematic. With the exception of a very slight hum it’s a very lively and high resolution amp which surprised me for its ability to deal with a pretty complex load (2x15” bass each channel, comp drivers for mid and high, with variable impedance). Even the bass is surprising and my reference is a Crown 1Kw+ transistor amp…. The slight hum could be caused by some stress on the power supply: although we used toroid transformers the HT amperage in the schematic is somewhat underrated as the 2x211 alone already consume 100-120 mA
Hi Chris, couldn't agree more.
Unfortunately, it appears to be an uphill battle.
It is always easier to believe the gurus instead of educating yourself; that's hard work so is seldom undertaken.
Jan
Amplifiers:
There will always be discussions about every kind of circuit topology, and how good, or how bad, it "sounds".
There are some things that affect the "sound" of any given topology:
1. How well that particular topology is designed (details count, not just the general topology).
2. How well that particular topology is implemented, including the layout, parts quality, etc.
3. What other products are in the sound system: signal source, loudspeakers, room, etc.
4. . . . And finally the "sound" is judged in the ears of each listener.
5. Not all listeners like the same kind of "sound".
Example:
One person says cathode followers sound bad.
Another person says cathode followers sound good.
Take each statement with a grain of salt, and then refer to 1, 2, 3, 4, and 5 above.
The discussions and judgements of bad, OK, and good, will continue;
But hopefully there will not be any arguments.
There will always be discussions about every kind of circuit topology, and how good, or how bad, it "sounds".
There are some things that affect the "sound" of any given topology:
1. How well that particular topology is designed (details count, not just the general topology).
2. How well that particular topology is implemented, including the layout, parts quality, etc.
3. What other products are in the sound system: signal source, loudspeakers, room, etc.
4. . . . And finally the "sound" is judged in the ears of each listener.
5. Not all listeners like the same kind of "sound".
Example:
One person says cathode followers sound bad.
Another person says cathode followers sound good.
Take each statement with a grain of salt, and then refer to 1, 2, 3, 4, and 5 above.
The discussions and judgements of bad, OK, and good, will continue;
But hopefully there will not be any arguments.
People search always something to believe, it makes them less anxious.
There are amplifiers that measure perfectly and sound good.
And there are amplifiers that measure mediocre but are all singing and all dancing.
How do you explain this difference objectively?
Nobody is crazy enough to write a book about psichoacustics vs. amplifier topologies.
There are amplifiers that measure perfectly and sound good.
And there are amplifiers that measure mediocre but are all singing and all dancing.
How do you explain this difference objectively?
Nobody is crazy enough to write a book about psichoacustics vs. amplifier topologies.
If so, then we're not measuring the right thing(s). One thing that we notoriously don't measure (because it's historically difficult) is distortion at low output levels, where the amplifier is actually operating with music signals. Until recently this was difficult to distinguish from noise, so was swept under the rug.
With modern ADCs and free software (REW, etc.) we have no excuse to pretend that distortion always decreases montonically with signal level, because we can actually measure it. The "mystery" of folks' strange preferences for Class A amplifiers, even SETs with their OPT penalties and other impracticalities, makes some sense if we measure amplifiers at output levels where they're actually used, say -60dBVU to -10dBVU, or for most folk the output required for 25dB SPL to 75dB SPL at listening position. This assumes 0VU to be "mastering level" of 85dB SPL, very loud to me. Any crossover distortion at all is inherently non-monotonic.
All good fortune,
Chris
With modern ADCs and free software (REW, etc.) we have no excuse to pretend that distortion always decreases montonically with signal level, because we can actually measure it. The "mystery" of folks' strange preferences for Class A amplifiers, even SETs with their OPT penalties and other impracticalities, makes some sense if we measure amplifiers at output levels where they're actually used, say -60dBVU to -10dBVU, or for most folk the output required for 25dB SPL to 75dB SPL at listening position. This assumes 0VU to be "mastering level" of 85dB SPL, very loud to me. Any crossover distortion at all is inherently non-monotonic.
All good fortune,
Chris
Chris,
I like your comment about the low level signal distortion.
I also like your use of the term non-monotonic.
When using vacuum tubes and an output transformer . . .
i suspect that it is easier to design and build a single ended monotonic amplifier, than it is to build a push pull monotonic amplifier.
And the same goes for crossover distortion.
I once took two single ended amplifiers, drove one of the inputs out of phase versus the other input, and then swapped the common and 8 Ohm leads on one of the two amplifiers.
Then I connected the two commons together, and tied the two 8 Ohms together.
I thought I had done something unusual, and then discovered the French had already tried that.
In one of the recent threads I mentioned the Southwest Technical Products "Little Tiger" solid state amplifier.
I had a Teak Tape recorder, and the line output had a volume control. I listened to about 90 prerecorded tapes.
I had been using a Harmon Kardon kit stereo tube amp, with output tubes that were similar to 6V6s,
I was so hopeful for some good sound from the Little Tiger Amp.
What a disapointment . . . it sounded very "Grungy".
Then I put a sine wave through it, and you could see the crossover distortion on a scope that was half way across the room.
What an education!
I was able to use a JFET Op Amp to make a global negative feedback loop, the sound and scope trace were both 100% better.
But the idea of straight-forward and simple was destroyed.
I like your comment about the low level signal distortion.
I also like your use of the term non-monotonic.
When using vacuum tubes and an output transformer . . .
i suspect that it is easier to design and build a single ended monotonic amplifier, than it is to build a push pull monotonic amplifier.
And the same goes for crossover distortion.
I once took two single ended amplifiers, drove one of the inputs out of phase versus the other input, and then swapped the common and 8 Ohm leads on one of the two amplifiers.
Then I connected the two commons together, and tied the two 8 Ohms together.
I thought I had done something unusual, and then discovered the French had already tried that.
In one of the recent threads I mentioned the Southwest Technical Products "Little Tiger" solid state amplifier.
I had a Teak Tape recorder, and the line output had a volume control. I listened to about 90 prerecorded tapes.
I had been using a Harmon Kardon kit stereo tube amp, with output tubes that were similar to 6V6s,
I was so hopeful for some good sound from the Little Tiger Amp.
What a disapointment . . . it sounded very "Grungy".
Then I put a sine wave through it, and you could see the crossover distortion on a scope that was half way across the room.
What an education!
I was able to use a JFET Op Amp to make a global negative feedback loop, the sound and scope trace were both 100% better.
But the idea of straight-forward and simple was destroyed.
That seems to be a law of nature.
If you want to improve something, it needs more effort, more parts, more expensive parts, more complex system, etc.
I suspect it is a collorary of the 2nd Law of Thermodynamics.
This is not necessarily the case, there are many factors that determine that.
Jan
If you want to improve something, it needs more effort, more parts, more expensive parts, more complex system, etc.
I suspect it is a collorary of the 2nd Law of Thermodynamics.
I assume with 'monotonic amplifier' you actually mean an amplifier with monotonically falling harmonic distortion levels.
This is not necessarily the case, there are many factors that determine that.
Jan
jan.didden,
No, I was not even considering the fall rates of harmonic distortion products as the signal amplitude is reduced.
I probably should not have used the word: "Monotonic".
There are too many definitions in electronics for that word.
One example:
With a sine wave test tone, look on a scope display. Given a crossover wiggle that you can see, I consider it to be non-monotonic.
Now, send a square wave, and look again. There could be a dribble-up on the rise and/or fall sections (not a straight line).
And, there might be a very small overshoot, followed by a very small divot, before settling to a flat top, until the next fall comes.
Another non-monotonic curve.
Consider a DAC where the analog output changes at the expected level: 1 lsb, 1 more lsb, 1 more lsb, etc.
Now, Consider a DAC where the analog output changes at this rate: 1 lsb, 0.5 lsb, 1.5 lsb, 1 lsb, etc. I would call that non-monotonic.
Let us go back to your good question/observation about harmonic levels versus signal levels, and the word monotonic:
1. Single Device HD:
Most linear single devices have smooth changes of harmonic levels, and follow the 2nd order intercept, and 3rd order intercept rules.
Of course, the intercepts are never reached, no matter what the signal amplitudes are.
But, it is important to note that in the linear regions, the 2nd HD and 3rd HD levels do change monotonically versus the fundamental frequency's signal amplitude.
That is called the "well behaved region". Below that we get in the noise region, where it is harder to track the harmonic levels, but it is expected that they also are monotonic there too.
It is when we get near the 1dB compression point, and/or fairly close to the 2nd and 3rd intercept amplitudes, that we have problems with a single device (no longer well behaved).
Suppose you increase the signal level by 3 dB, the 2nd HD will increase by 3 dB, and the 3rd HD will increase by 6dB. This is considered well behaved, it has the slope of the intercept curves (slope before the 1dB compression point, and slope far before the intercept point).
2. Multi-devices: Serially Cascaded device pairs:
Use a test sine wave . . .
There can be some serial 2nd order HD cancellation.
If the devices are near to their 1dB compression points, one in the positive alternation, and the other device in the negative alternation, we have 3rd HD.
Now, suppose as the sine wave amplitude is varied, that one device gets near its 1dB compression, before the other device gets near its 1dB compression, we are not there until the sine wave amplitude is raised even more.
This is likely to make the rates of 2nd HD and 3rd HD not increase at the well behaved rate of a single device, Instead the 2 devices are interacting with each other, versus the signal, that is now a non-well behaved result.
I sometimes see this effect when doing live FFTs, and changing the signal amplitude.
It can be Very apparent.
Thanks!
You have pointed out a Very good test for me to add to my regular battery of tests I do on my designs;
before I ever connect a loudspeaker and play a music CD.
Hopefully that is helpful, and not to confusing.
No, I was not even considering the fall rates of harmonic distortion products as the signal amplitude is reduced.
I probably should not have used the word: "Monotonic".
There are too many definitions in electronics for that word.
One example:
With a sine wave test tone, look on a scope display. Given a crossover wiggle that you can see, I consider it to be non-monotonic.
Now, send a square wave, and look again. There could be a dribble-up on the rise and/or fall sections (not a straight line).
And, there might be a very small overshoot, followed by a very small divot, before settling to a flat top, until the next fall comes.
Another non-monotonic curve.
Consider a DAC where the analog output changes at the expected level: 1 lsb, 1 more lsb, 1 more lsb, etc.
Now, Consider a DAC where the analog output changes at this rate: 1 lsb, 0.5 lsb, 1.5 lsb, 1 lsb, etc. I would call that non-monotonic.
Let us go back to your good question/observation about harmonic levels versus signal levels, and the word monotonic:
1. Single Device HD:
Most linear single devices have smooth changes of harmonic levels, and follow the 2nd order intercept, and 3rd order intercept rules.
Of course, the intercepts are never reached, no matter what the signal amplitudes are.
But, it is important to note that in the linear regions, the 2nd HD and 3rd HD levels do change monotonically versus the fundamental frequency's signal amplitude.
That is called the "well behaved region". Below that we get in the noise region, where it is harder to track the harmonic levels, but it is expected that they also are monotonic there too.
It is when we get near the 1dB compression point, and/or fairly close to the 2nd and 3rd intercept amplitudes, that we have problems with a single device (no longer well behaved).
Suppose you increase the signal level by 3 dB, the 2nd HD will increase by 3 dB, and the 3rd HD will increase by 6dB. This is considered well behaved, it has the slope of the intercept curves (slope before the 1dB compression point, and slope far before the intercept point).
2. Multi-devices: Serially Cascaded device pairs:
Use a test sine wave . . .
There can be some serial 2nd order HD cancellation.
If the devices are near to their 1dB compression points, one in the positive alternation, and the other device in the negative alternation, we have 3rd HD.
Now, suppose as the sine wave amplitude is varied, that one device gets near its 1dB compression, before the other device gets near its 1dB compression, we are not there until the sine wave amplitude is raised even more.
This is likely to make the rates of 2nd HD and 3rd HD not increase at the well behaved rate of a single device, Instead the 2 devices are interacting with each other, versus the signal, that is now a non-well behaved result.
I sometimes see this effect when doing live FFTs, and changing the signal amplitude.
It can be Very apparent.
Thanks!
You have pointed out a Very good test for me to add to my regular battery of tests I do on my designs;
before I ever connect a loudspeaker and play a music CD.
Hopefully that is helpful, and not to confusing.
Last edited:
I understand your use of the word, but it is never used that way. A square wave with a 'wiggle' has ripple but is never called non-monotonic.
I am aware of the use in the relative levels of harmonics, and the monotonicity (or lack thereof) in ADCs and DACs, but I'm sure there are more I'm not aware of.
If you introduce new ideas (because maybe you're not familiar with the existing lingo?) the danger is that nobody knows what the hell you're on about 😎
Your discussion of the harmonics is to the point; interesting thinking.
Jan
I am aware of the use in the relative levels of harmonics, and the monotonicity (or lack thereof) in ADCs and DACs, but I'm sure there are more I'm not aware of.
If you introduce new ideas (because maybe you're not familiar with the existing lingo?) the danger is that nobody knows what the hell you're on about 😎
Your discussion of the harmonics is to the point; interesting thinking.
Jan
jan.didden,
Thanks!
Yes, I perverted the term monotonic as applying to a single "ring" of a square wave.
1. Another characteristic of some square waves is a zig-zag of the rise, and/or a zig-zag of the fall (if it is there, it is at about 50% of the rise or fall) . . .
That is called Dribble-Up. I first saw this in 1968, and do not remember seeing it since, and so I do not remember any more details about it.
I guess I opened a bucket of worms with my abuse of the word monotonic.
But I am not the first to pervert a word.
2. Many know that I do not like the name: Beam Power Tetrode.
Pentode was patented (Suppressor Grid) 5 elements (filament, or filament + cathode, counted as one element).
Beam Power was developed, and "circumvented" the Pentode patent (Beam Power had Beam Formers, instead of a Suppressor Grid)
5 elements (filament, or filament + cathode, counted as one element).
The Tetrode has Only 4 elements (filament, or filament + cathode, counted as one element).
. . . If you add Beam Formers to a Tetrode, it is Not a Tetrode anymore.
Having said that, here comes the perverted name:
Beam Power Tetrode, No! (They did Not remove the Screen and replace it with Beam Formers).
i will not be the last to mis-use a term, definition, or word.
3. I am hoping to re-test one of my new amplifiers today.
I do plan on watching the rise and fall rates of the 2nd and 3rds harmonic distortions, as the signal level is increased and decreased.
(looking to see if it is monotonic, or non-monotonic).
Thanks!
Yes, I perverted the term monotonic as applying to a single "ring" of a square wave.
1. Another characteristic of some square waves is a zig-zag of the rise, and/or a zig-zag of the fall (if it is there, it is at about 50% of the rise or fall) . . .
That is called Dribble-Up. I first saw this in 1968, and do not remember seeing it since, and so I do not remember any more details about it.
I guess I opened a bucket of worms with my abuse of the word monotonic.
But I am not the first to pervert a word.
2. Many know that I do not like the name: Beam Power Tetrode.
Pentode was patented (Suppressor Grid) 5 elements (filament, or filament + cathode, counted as one element).
Beam Power was developed, and "circumvented" the Pentode patent (Beam Power had Beam Formers, instead of a Suppressor Grid)
5 elements (filament, or filament + cathode, counted as one element).
The Tetrode has Only 4 elements (filament, or filament + cathode, counted as one element).
. . . If you add Beam Formers to a Tetrode, it is Not a Tetrode anymore.
Having said that, here comes the perverted name:
Beam Power Tetrode, No! (They did Not remove the Screen and replace it with Beam Formers).
i will not be the last to mis-use a term, definition, or word.
3. I am hoping to re-test one of my new amplifiers today.
I do plan on watching the rise and fall rates of the 2nd and 3rds harmonic distortions, as the signal level is increased and decreased.
(looking to see if it is monotonic, or non-monotonic).
jan.didden,
I do remember that the Dribble Up I saw, did not have to do either with negative feedback, or with a circuit that was on the edge of oscillation.
I wish I could remember more about the effect.
I do remember that the Dribble Up I saw, did not have to do either with negative feedback, or with a circuit that was on the edge of oscillation.
I wish I could remember more about the effect.
In SE stages, the dribble up appears when leakage inductance resonates with parasitic capacitance in output transformer. Good quality transformers have upper frequency fall at this resonating frequency (the two coincides).
Just a thought.
Just a thought.