That sounds like an interesting circuit. Is there a schematic posted somewhere? I tried local output stage feedback on my Citations, and my circuit didn't work. It made things worse.
Sure, I've posted and explained it here several times. Also, there were at least couple of threads here just yesterday, about local feedbacks across output tubes.
One: http://www.diyaudio.com/forums/showthread.php?t=149195
Another: http://www.diyaudio.com/forums/showthread.php?t=149674
And, finally, my driver: http://wavebourn.com/forum/download.php?id=119&f=7 -- resistors from plates of GU-50 tubes to plates of 6P15P tubes are 220K 2W both.
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i strive for high fidelity but i am open to interpretation as far as what that exactly is.
for example i question notions such as "bass below 80 hz cannot be localized" or "stuff below 20hz does not matter" or "phase distortion is not audible"
i prefer to investigate these questions rather than just pick a side and proclaim everybody else a heretic.
i have discovered that in general, not just in audio, people tend to take many things for granted without asking for much evidence. quite often the stuff taken for granted ends up being wrong.
Maybe he came from here: Audiophile Invasion.
LOL! MullardEL34's comment about Audio Asylum is spot on 🙂.
its an honest question. i never owned tube amps. i only heard a tube amp once ( some big-a$$ McIntosh driving Sonus Faber Amati speakers with SACD source ). it sounded very liquid and beautiful but there was no treble and bass sounded sloppy. i don't know if that was the speakers or the amp. i would give that setup 5 stars for midrange, 3 stars for treble and 2 stars for bass.
I'm honestly kind of surprised DIY made the list 😛
Tweaks forum on AA would be my first stop, though
So, wrong forum, huh? We have some forums dedicated to speakers.
You could start the thread, "What causes low star ratings for bass and treble in speakers"? 😀
Sounds like an MC275. They are well-built, last forever, measure well from 20 to 20K, but are lacking in accuracy at the ends of the spectrum. I suspect the 100% local NFB to the output cathodes and the need to supply positive feedback to the driver to help generate the very high drive voltages is the culprit. You get a low-distortion output stage, but the driver stage becomes a big problem.
I've never heard Sonus Fabers, so I can't comment.
One thing I've noticed is the amps I like cover a wide frequency spectrum. Since I can't hear these extreme frequencies when presented from an oscillator, I have to assume that waveshape and phase are audible in complex sounds. For instance, if the amp quits at 20,000 Hz, it can't produce anything but a sine wave above 10,000 Hz, and it can't do an accurate square wave above 2,000 Hz or so. Bass likewise. If response extends into the infra-sonic, it creates a sense of ease and image solidity.
When someone maintains that a particular thing is inaudible, it is often the case that the observation is based on untrained listeners, who don't hear the effect simply because they don't know what it sounds like. Take the early digital recordings, for example. They were pronounced "perfect" because they didn't have tics and pops or wow and flutter. As people became familiar with CDs, they began to hear deficiencies. Digital compression is likewise sold as "inaudible", but it's clearly not as any cell phone call will show.
You have the right idea to check things out for yourself. My ears and my experience are not yours. We differ. But we learn from each other. Many times somebody's pointed out something I haven't noticed, and I wonder how I could have missed it.
Right on the spot!
There was no proof presented, ever, that our perceptions does Fourier analysis, while measurements based on it suppose to show all audible errors.
that is certainly true, but i dont know if it has anything to do with phase.
all i know is now that my sub puts out flat to about 16 hz music sounds much better than when it was only to about 25 hz ( same sub, just different equalization )
i dont know what it is really. maybe its because i went from 48db/oct subsonic filter to 18db/oct or maybe its the very small amount of energy that is actually present in that extra 10 hz.
but the interesting thing for me is how changing very low bass makes the entire music sound different. it doesnt sound like same music plus or minus that extra deep bass but just sounds different.
because the brain doesn't go through a checklist ( 30hz check, 25hz check etc ) but rather performs some sort of math that we have not the slightest clue about and changes we make to the system affect this math in strange ways.
i think there is something special about bass as far as importance to the brain. we are taught that 1 khz it the *center * of the music but i have a strong feeling that 60 hz is the real center. the craving for bass was always there ( pipe organ ) but for the rest of us the audio world is only beginning to catch up with that craving just now. sounds between about 16 and 30 hz sound so awesome ! people must have been INSANE to filter them out. MAD ! high passing at 30 hz is almost like low passing at 4 khz.
of course by the time you buy your CD everything below 30 hz is already gone. but this practice is turning around slowly i believe.
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I assume you are talking about HiFi amps. Guitar amps are many times designed with very high THD on purpose.
Back to your question: You have to think like an engineer. An engineer's job is never to build the "best" product. It is always to build a product to meets specific numerical specifications for lowest price. The key words here are "numerical specifications".
But this just runs backwards. How do you get those specs? This is the reason the SS and tube amps have different specs. If you want to sell amps they have to sound good so you pick specs that result in good sound. It just turns out that a tube amp can sound good with THD specs that are much higher than a transistor amp.
Why? Why can a tube amp with high THD sound as good as a SS amp with lower THD? The answer is the "T" in "THD". It stands for "Total". The THD spec lumps all distortion products into just one number. An interesting "thought experiment" would would be to think about the sound you would hear if you had a 1% THD amp and could remove 99% of the sound and listen to only the distortion and not the music. What would it sound like? The distortion products of a SS amp sound like someone's fingernails on a chaulkboard. The sound is anything but "soft on the ears". It's just horrible noise. But the main distortion product of a tube amp is the second harmonic of the music. Most musical instruments already produce much energy in the second harmonic. Traditional acoustic instruments use "mechanical amplification" (sound boards inside pianos, violins and the like) The distortion products of vacuum tubes mimic this sound and are not objectionable to the listener. Because SS amps product a kind of distortion this is very objectionable the THD must be very low.
It continues to roll backwords, Why are tube's distortion products different" The real reason is that tubes are non-linear devices and SS is very much more linear. Seems at first counter intuitive that a non-linear system should produce better sounding distortion. I could explain it mathematically but maybe the easy way to see it is to think about the natural world, your ears, the way wood, cat gut and steels strings vibrate and even the musical scale (frequency doubles with each octave, is non-linear) nothing in the natural world is linear, Linearity is man-made. It is not surprising that we like the sound of non-linear systems. We can tolerate higher THDs in tube amps than in perfectly linear SS amps. You can do all kinds of math and so on but the bottom line is "it's just the way human hearing works." Our hearing is "designed" to work in the natural world.
Oh I don't think so. My best shot at a large output driver swung 160 Vrms into 50kohm with about 0.05% predominantly second harmonic distortion with no inter-stage feedback. Try that with two transistors.
Again, SS permits much more cheap gain and feedback than tubes. Measure the distortion spectra with frequency of a popular SS device such as the LM3875. A long string of harmonics blast out of the noise floor at ~1 kHz, suggesting device gain is falling rapidly.
borat................. how do you rate valve sound if you have only listened to one amp ever.
after all the real test is how they sound
after all the real test is how they sound
Ummm... both tubes and transistors are non-linear. They have different distortions, though. Driving 160V into 50K with a pair of transistors would be silly. (Not without a transformer to turn current into voltage.) Likewise, you wouldn't try driving 10 Amps into 4 Ohms with a pair of tubes. (Not without a transformer to turn voltage into current.)
If you compare a tube amp of similar gain and power output (not just a single tube) to an LM3875, you'll find it has issues as well. Harmonics may not "blast out of the noise floor" because the floor is higher. The harmonic distribution will be different as well. Remember a chip amp is a whole amplifier of many stages on a single hunk of sand. If you look at "device gain" of a complete tube amplifier, it falls pretty rapidly too.
Apples and oranges. 🙂
I have to admit I'm pleasantly surprised at the sound of my new Chip amps. The equivalent circuit in National's data sheets doesn't look all that special. Final opinion reserved until I've lived with them for 6 months or so.
If you compare a tube amp of similar gain and power output (not just a single tube) to an LM3875, you'll find it has issues as well. Harmonics may not "blast out of the noise floor" because the floor is higher. The harmonic distribution will be different as well. Remember a chip amp is a whole amplifier of many stages on a single hunk of sand. If you look at "device gain" of a complete tube amplifier, it falls pretty rapidly too.
Apples and oranges. 🙂
I have to admit I'm pleasantly surprised at the sound of my new Chip amps. The equivalent circuit in National's data sheets doesn't look all that special. Final opinion reserved until I've lived with them for 6 months or so.
No I would not try that with transistors. An engineer when assigned the task of driving a 4 to 8 ohm loudspeaker would almost certainly spec some mosfets and run them at a more reasonable voltage.
It is actually easy to find counter examples to what I said but
when I said "linear" or "non-linear" I should have added "as typically used in most amps". The best example of a non-linear device, the rectifier diode, is solid state. My comment applied to typical audio gain stages
The more accurate way to say it might be that most SS components used in typical amps are designed to work within their linear region. But tubes are always non-linear and because more and more so in a gradual way as they are driven harder.
All of the above was secondary to my main point which was that the real reason why THD can be higher in tube amps is because "T" stands for "Total" and the kind of "HD" in each amp is different. So that when you compare "Tube-THD" with "SS-THD" it is an apples to oranges comparison.
Sources of distortion in amplifiers.
3 elements of sound, amplitude, ie loudness, frequency, (pitch) and tone
thus amplitude distortion, frequency distortion, and phase distortion.
amplitude distortion is what we normally refer to.
Even harmonic and odd harmonic.
Intermodulation distortion.
Transient distortions.
eg. slew distortion, note very controversial.
distortion comes from the valve characteristic, ie graph, tube curves, the grid lines.
magnetic distortion, eg overloading a iron core gives 3rd harmonic distortion, triodes produce much 2nd harmonic.
pentodes 3 rd harmonic.
2nd harmonic is cancelled by push pull, balanced, symettrical circuits.
all distortion is reduced by feedback.
Class A amplifiers produce more distortion than class B, as they are run with less feedback generally.
push pull amplifers as 2nd harmonic is cancelled is more prevalent in odd harmonic distortion
type speaker distortion into google to see the causes of that, very interesting, voice coil coming out of the magnet field, , inductance modulation, ie varying.
single ended triodes typically 5-10% 2nd harmonic, oldies use 5% 2nd and 1% 3rd as design guidelines any more is considered bad.
it was a race to get distortion below 0.1% then as low as poss, odd harmonics are sharper, high order are nasty. crossover distortion caused by to low bias current in push pull
is very nasty, hi order odd.
Class A sounding better is absolute garbage, as you can see, it distorts more to start with, I have heard class B amps waste class A ones, eg pioneer a-09 was bettered by naim nap250 and michell alecto transistors by the way.....
all single ended amplifiers are class A. just means they don't turn off, all small stages of transistor amplifiers are class A.
more but I have forgotton most of it.....
engineers concentrate on what is added, but I suspect more is taken away somehow.
read doug selfs ;amp book for definitive sources of distortion in transistors. he deserves an oscar for it, very least a doctorate
3 elements of sound, amplitude, ie loudness, frequency, (pitch) and tone
thus amplitude distortion, frequency distortion, and phase distortion.
amplitude distortion is what we normally refer to.
Even harmonic and odd harmonic.
Intermodulation distortion.
Transient distortions.
eg. slew distortion, note very controversial.
distortion comes from the valve characteristic, ie graph, tube curves, the grid lines.
magnetic distortion, eg overloading a iron core gives 3rd harmonic distortion, triodes produce much 2nd harmonic.
pentodes 3 rd harmonic.
2nd harmonic is cancelled by push pull, balanced, symettrical circuits.
all distortion is reduced by feedback.
Class A amplifiers produce more distortion than class B, as they are run with less feedback generally.
push pull amplifers as 2nd harmonic is cancelled is more prevalent in odd harmonic distortion
type speaker distortion into google to see the causes of that, very interesting, voice coil coming out of the magnet field, , inductance modulation, ie varying.
single ended triodes typically 5-10% 2nd harmonic, oldies use 5% 2nd and 1% 3rd as design guidelines any more is considered bad.
it was a race to get distortion below 0.1% then as low as poss, odd harmonics are sharper, high order are nasty. crossover distortion caused by to low bias current in push pull
is very nasty, hi order odd.
Class A sounding better is absolute garbage, as you can see, it distorts more to start with, I have heard class B amps waste class A ones, eg pioneer a-09 was bettered by naim nap250 and michell alecto transistors by the way.....
all single ended amplifiers are class A. just means they don't turn off, all small stages of transistor amplifiers are class A.
more but I have forgotton most of it.....
engineers concentrate on what is added, but I suspect more is taken away somehow.
read doug selfs ;amp book for definitive sources of distortion in transistors. he deserves an oscar for it, very least a doctorate
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No.
No.
No.
It is not about sources of distortions in transistor amps. It is about source of distortions in the single topology chosen by Douglas Self for his Blameless Amp.
If to examine sources of distortions of slightly different amp the new whole book needs to be written. Too many books are needed to cover all sources of distortions in transistor amps.
Much-much less of books are needed to learn how to design properly...
afriad you are wrong, look at distortion of commercial class A vs b class A produce more distorion on the whole as they do not have xover distortion so do not use as much feedback to reduce.
therefore class B amplifiers having more feedback, have less distortion. I am talking commercial measurements here. as in real amplifiers.
scientific and measurement fact. read it in context. it is correct
self's book does indeed give the sources of distortions, ie that a diff pair will cancel even harmonics, I agree about the nature it is all about his amplifier, but nevertheless his analysis of the classic 3 stage and distortion reduction is valid.
self's amp uses 'devices' commonlly used in all design, eg mirrors, his analysis of loading effects on distortion is valid irrespective of his own topology
what self did was take the std 3 stage voltage feedback amplifer, used in about 95% of commercial amplifier designs, and simply optimised if for harmonic distorion
I agree totally that its very very narrow and needs much more elaboration, but simply adding an active load to the diff pair, and a few buffers and followers driving stages,
its pretty generic
we probably agree in liew of contexts....
you are probably a knowledgeable engineer...
disprove my points by data please, if you can't.....
prove class A sounds better....there are many better sounding B class than A class I have listened extensively, 100s
or simply turn an A class amp down into verge of xover distortion, just above, and prove the garbage that's spoken
I am willing to be proven wrong on class A sound, its my opinion, its marketing horse.XXX
therefore class B amplifiers having more feedback, have less distortion. I am talking commercial measurements here. as in real amplifiers.
scientific and measurement fact. read it in context. it is correct
self's book does indeed give the sources of distortions, ie that a diff pair will cancel even harmonics, I agree about the nature it is all about his amplifier, but nevertheless his analysis of the classic 3 stage and distortion reduction is valid.
self's amp uses 'devices' commonlly used in all design, eg mirrors, his analysis of loading effects on distortion is valid irrespective of his own topology
what self did was take the std 3 stage voltage feedback amplifer, used in about 95% of commercial amplifier designs, and simply optimised if for harmonic distorion
I agree totally that its very very narrow and needs much more elaboration, but simply adding an active load to the diff pair, and a few buffers and followers driving stages,
its pretty generic
we probably agree in liew of contexts....
you are probably a knowledgeable engineer...
disprove my points by data please, if you can't.....
prove class A sounds better....there are many better sounding B class than A class I have listened extensively, 100s
or simply turn an A class amp down into verge of xover distortion, just above, and prove the garbage that's spoken
I am willing to be proven wrong on class A sound, its my opinion, its marketing horse.XXX
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Sure. It's what I am doing in this thread, again and again: http://www.diyaudio.com/forums/showthread.php?t=147916
You can't turn my class A amps into verge of xover distortions. It is impossible by definition. There are also commercial models on the market that were born to be class A amps. What you are referring to, is again and again a typical OpAmp that can be class A biased, but can be not... It is not a class A amp. it is an OpAmp.
Like the Universe is not limited by a bedroom, amps are not limited by OpAmp topology.
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