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In Reply to: RE: This long thread just tells me what commercial SETs aren't.... posted by tube wrangler on September 03, 2017 at 03:40:55
"No fixed bias amp has ever reproduced music in a convincing fashion because the bias doesn't vary according to musical demand."
Please correct me if I'm wrong.
It sound like you think that the bias in a self-biased circuit does vary according to musical demand?
Dennis, let me ask you one simple question.
Does the "musical demand" (signal AC) flow through the cathode resistor in a self-biased circuit?
Dennis, this is a yes or no question.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Follow Ups:
Yes, it does, some of it. Some signal goes thru the resistor,
much of it through the capacitors.. The caps, of course
conduct mostly A.C. Any D.C. component through them is
due to capacitor leakage.The cathode resistor conducts both A.C.(signal) and D.C.,
and it generates artifacts concerning both. Not only does
the capacitor conduct signal, but it is also a filter in
that it shunts the resistor concerning the part of the
A.C. signal that is flowing thru the resistor.What you have here is two signal conducting devices--
the resistor and the caps-- the resistor conducts most
of the D.C., and plenty of A.C., and the caps conduct
nearly all A.C.It's a small composite SYSTEM.
Each component has a profound effect on the sound
qualities of the tube's plate and cathode signals.-Dennis-
Edits: 09/03/17 09/03/17
"Yes, it does, some of it. Some signal goes thru the resistor"Sure, some of it does.
let's say you have a 1000 ohm cathode resistor and a 100uf bypass cap.
What portion of a 1000Hz AC signal flows through the resistor?
Let's do the math.
The reactance of the cap at 1000Hz is 1.592 ohms.
So you have a 1000 ohm resistor shunted by a 1.592 ohm resistor.
Let's just pick .1 volts AC at the cathode,
62.814ma flowing through the cap1 / 1.592 = .062814 amps
And .1ma flowing through the resistor.
1 / 1000 = .0001 amps
"Each component has a profound effect on the sound qualities
of the tube's plate and cathode signals. "So you are saying that the cathode resistor that is conducting less than 1/628th of the total AC current at 1000Hz has a profound effect on what the 1000Hz AC signal will sound like? Get real Dennis.
Maybe at lower frequencies where the reactance of the cap is higher but the whole point of a bypass cap is to make it's value is such that the reactance at the lowest frequency of interest is a small fraction of the value of the cathode resistor.*
I'm sure in your design (where the cathode by pass cap is too small) the resistor does carry a lot of low frequency AC (a lot more than it should) and that resistor does make a profound effect on the sound but that's only because your design is flawed.
If you let too much (anything more than a tiny fraction) of the AC flow through the resistor instead of the cap then the bias will change.
That means you will have negative current feedback applied to your output tube and it's plate resistance will increase and the load line will rotate towards the vertical and that will cause an increase of the harmonic distortion as well as a loss of damping factor. (And none of that has anything to do with the sonic properties of the resistor used.)
but you knew all that, right Dennis?
* note, it's really the value of the cathode resistor in parallel with the impedance of the cathode but that discussion is for a different time.P.S. I hope everyone will excuse me for calling 1/628th "none". In my defense, it is very close to none.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 09/03/17 09/03/17
How about comparing that current( the nearly none )to the driver plate current. The percentage is now significant...LOL
All in all, I think *ALL* folks interested in a SE amp should buy one of Dennis-es amps. Wishing you a multitude of sales Dennis!!!
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
I like my flawed design.
It certainly has a way with music, it
almost never fails or suffers any kind of
breakdown, and some people consider it an
example of Industrial Art, and are collecting
them!
There is, of course, a certain hazard in
playing with this kind of equipment when
married: If you are listening to music
because you are enthralled by it, instead
of listening to the "Honey-Do" list--
especially-- then you may indeed see this
design as flawed, when marital distress
occurs!
I do like it, however. I'm proud of it!
-Dennis-
As Tre says: "honest"... and demonstrates a quiet strength absent in the strongly-worded machismo commonly posted here.
Despite my criticism of (your) absolutist posts/ stance and question your technical explanations at times, I respect your passion, uncompromising experimentation, and unwillingness to be boxed in by expert opinion and traditional methods. I'd like to meet you some day and listen to your system.
Take care.
Cheers,
91.
"Confusion of goals and perfection of means seems to characterise our age." Albert Einstein
Got a ticket to Denver?
RMAF 2017, Room 3017.
-Dennis-
Unfortunately not. The flight from Australia's East Coast is brutal.
Cheers,
91
"Confusion of goals and perfection of means seems to characterise our age." Albert Einstein
.
Have Fun and Enjoy the Music
"Still Working the Problem"
WHAT a MESS!
-Dennis-
Dennis, you only see what I posted as being a "MESS" because it's over your head (over your level of understanding).You didn't understand a thing I said.
Read a book. This stuff is not that complicated. You can learn to understand it if you try.
I believe this would help you in the long run.
You could build a circuit the right way (technically speaking) and if you don't like the way it sounds you could then "tweak" it to get the sound you like instead of just doing the whole thing experimentally.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 09/04/17
I wouldn't bother trying to argue his points. There's plenty of measurable evidence that contradicts several of his claims. Claiming that filament bias "injects distortion" is something that could easily be proven with a few hours of basic measurements, but why do that when you can just claim to be the omniscient SET authority!
I don't understand why the "Bored" puts up with him.
It's one thing for a person to have an opinion on how this or that circuit sounds but Dennis has made so many proclamations on technical matters that are patently false.
I can't decide if he is really that ignorant or if he's just playing a game for financial gain.
Thanks for the input CB.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Maybe the Bored would like to answer your inquiry?
the ac does not flow through the cathode resistor.It flow through the bypass cap that has a very low reactance to all frequencies of interest if it's the right uf value.
Therefore the bias DOES NOT vary "according to musical demand".
What did you think the bypass cap was for other than holding the bias steady?
That is the sole purpose of a cathode bypass cap.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 09/03/17
That's PART of the story-- the caps certainly steady
the voltage.That's not all there is to it by a long shot!
You have to get an amplifier to accurately track music.
In order to do that, you have to think outside the box
on many areas of concern.You're firmly grounded inside the BOX!
Things must be very comfortable in there...
Theories are changed as performance increases-- in
all areas of human endeavor.I use, invent, or learn what I need to get that
performance. I DISCARD any theory that
doesn't deliver the goods.-Dennis
Edits: 09/03/17
"the caps certainly steady
the voltage."
I thought you said that in a self-biased the bias varies according to musical demand.
When you said "No fixed bias amp has ever reproduced music in a convincing fashion because the bias doesn't vary according to musical demand." is that not the same as saying that in a self-biased circuit the bias does vary with the musical demand?
Which is it Dennis?
Does the bias stay steady or does the bias vary in a self-biased design?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Things that happen simultaneously in degrees aren't
well explained with absolutist calculations.
As usual, I will be going by actual performance.
Theory does come in, but ONLY when IT CONTRIBUTES.
-Dennis-
"Things that happen simultaneously in degrees aren't
well explained with absolutist calculations."Yes they are.
As the frequency falls the reactance of the capacitor increases and more of the total current flows through the resistor.
If we want 20Hz to flow only through the cap (and not cause current feedback to be applied to the tube) then we design the filter so that it's -3db point is a decade below 20Hz.
With a -3db point of 2Hz the phase and amplitude will be back to flat by 20Hz and virtually no AC will be flowing through the resistor.
What is the -3db point of the filter created by the (cathode resistor in parallel with the cathode impedance) and the value you picked for your cathode bypass cap.
If you give me the numbers I can show you how much of the AC is going through the resistor at any frequency you're interested in.
I can even tell you how much negative current feedback you are applying to the output tube at any frequency you're interested in and how much that increased the output tube's plate resistance and what that does to the damping factor of the amplifier.
All of these complex situations are easily explained with absolutist calculations.
BTW whether you know it or not it's that local current feedback that gives you the sound you are looking for. Your circuit design is technically wrong but you won't admit that. The fact is you're just building for a sound, an effect.
That's OK, we probably all do but most of us admit to it.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 09/04/17 09/04/17
as it is clearly better than the others...and by a long chalk.
Was LMAO a bit, we now have Energy Conservation being abused along with Transfer Efficiency...:)
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
speaking of Transfer eff, its a real phenomenon in that a tube driver uses a IT and good transfer eff is VERY important.
you could also apply this to the output transformer too :)
Lawrence
I understand your faith in being able to
calculate anything you want.
I don't tweak, period. I listen to the best
recordings available on the best equipment available.
I have owned movie theatres, and have designed and built
many a Stadium Theatre. Most theatres have bad sound--
but not very bad-- if the owners keep up with maintenance.
I have, over the years, enjoyed hearing and measuring
and observing in theatres, what it takes to totally
involve people in the presentation, and take the sound
system out of the equation-- make it so good that no one
notices it-- just what is happening.
My standard for HOME playback is the sound that is
factory encoded on L.P.'s, CD's, and on-line
Hi-Resolution downloads.
This is compared to studio master recordings, and
also to the systems that competitors have at audio
shows, and to people's own home systems.
I ask an amplifier to play back any and all of
these sources with verbatim accuracy-- at the point
that counts-- the speaker or headphone interface to
the listener..
I have found over the years, several solid state
amplifiers that will do this very well.
In order to have vacuum tubes do the same thing
well, the tube amp had to be condensed into a form
that would do this simply because all the other
tube amps I have applied, or heard-- have fallen
woefully short.
I haven't mentioned this lately on a forum, so
I'll just repeat it here: I NEVER build anything
unless I HAVE TO. I MUCH prefer to BUY it.
In the case of vacuum tube amplifiers, the
existing technology and construction methods
were absolutely hopeless. So, I FIXED that
problem. And, FIXED it is!
It's too bad that it's so controversial with you.
Actually, all it is is energy conservation applied
at every level, and superior layout and construction
methods, coupled with the use of really good parts.
Circuit operating values are super conservative
because I don't like the sound of stressed vacuum
tubes that every other tube amp I ever heard displays,
if played on large radiating area, point-source,
speakers that are over 100db/watt efficiency. The
GOOD amps-- including a few over 200 watt solid state
models, will play well on such speakers.
Nearly all tube amps that have been, or are being
built fall short in many ways.
If you're a modifier, you can rescue some older tube
amps by lowering voltages and currents, using better
parts, mounting iron on brass standoffs, and re-wiring
the whole thing..
If you do that, you're still coming up a bit short--
but much better--, so why not just start over and
design something that is sure to work?
It does!
-Dennis-
I think it depends on whether the foil hat is on or off.
.
Have Fun and Enjoy the Music
"Still Working the Problem"
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