|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
27.96.218.1
In Reply to: RE: musical loadlines posted by dave slagle on July 20, 2015 at 09:54:35
At 20Hz the loadline is more vertical as expected, caused by the lower than ideal inductance. At the higher frequencies of the audio signal the loadline is more ideal but still elliptical caused by the limitations of the transformer (leakage C & L) at high and low frequency extremes.
I was more interested in what happened in your earlier example where the music was played simultaneously with the LF tones. As expected the music rode on the LF waveform which could aid to premature clipping as Paul pointed out.
However I believe that at any single point along the non ideal LF loadline the more ideal loadline for the higher audio frequencies is preserved. Thus lower distortion at mid frequencies as opposed to frequencies at the extremes.
The width of the the loadline at LF is concerning but perhaps just serves to highlight the limitations of transformers?
Naz
Follow Ups:
In the presents of both HF and LF.......when a large HF signal is at the lower part of the large ellipse, caused by the LF, the HF will run out of current early.
The only way to prevent this is to either increase the inductance or limit the low frequencies.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
In the presents of both HF and LF.......when a large HF signal is at the lower part of the large ellipse, caused by the LF, the HF will run out of current early.
I disagree. Everything is held constant in this but the load where green is 2K5 and blue is 10K.
It seems clear to me that the situation where current is going to become the issue is with the heavier load. Now lets look at the case of a plate choke. Green is 2K5 load and blue is 1 meg.
Now if the "width of the loop" is really a major concern, one would expect a plate choke to be far less than optimal and a CCS to be the ideal, yet I have yet to hear a CCS better a plate choke. The natural response to this from the "ccs camp" is I simply must enjoy distortion. For me, as long as the lines are closer to horizontal and keep away from the current extremes, I don't lose much sleep over it. I could really go out on a limb and say that for a given voltage swing, the larger the load, the more inductance you need to avoid traversing the nonlinear parts of the curves.
dave
Just do a sim with 20Hz and 1000Hz at the same time with both being large signals.Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 07/22/15
OK... well they can't both be "large signals" since they will clip if the values sum to more than the bias voltage so I did 22.5V+22.5V. The above was for 5 "loops" and the width of the loop isn't as wide as it appears since it takes a cycle or two to "settle" at the bias point. Below is a single loop and the actual loop width is about 2/3 of what shows up.
" well they can't both be "large signals" since they will clip if the values sum to more than the bias voltage so I did 22.5V+22.5V. "
I see what you mean.
But isn't there still a problem with the 1kHz operating at different points as it follows the ellipse? When it's at the lower right vs the upper left?
Won't that lead to some form of IMD?
What does the above sim look like mixing 1kHz with 200Hz instead of 20Hz?
Thanks.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
But isn't there still a problem with the 1kHz operating at different points as it follows the ellipse? When it's at the lower right vs the upper left?
If the lines were all parallel and evenly spaced I would say no but as you get to the knee, i would expect distortion.
Won't that lead to some form of IMD?
yes and i would expect the distortion of the 2K5 load to be worse since it traverses a more nonlinear part of the curves.
What does the above sim look like mixing 1kHz with 200Hz instead of 20Hz?
for anyone still interested here is another set of plots where i changed the inductance and the load.
I guess the point I am trying to get to is the actual width of the ellipse may not be as important as its slope.
dave
Thank you Dave.
Keeping the low frequency out of the picture keeps the ellipse from being so large (wide) that it drives the signal into the more extremely non-linear parts of the tube's curves, as shown in the green and red of your second graph.
In the end, I think that was all I was trying to say. I also think that is what Voltsecond was saying.
All I know for sure is when I limited the LF going to my SET amp (I already have woofers, driven by a SS amp, handling the bass and my mids don't play bass anyway) the sound of the mids and highs got much better.
I believe the graph above, vs. the other graph you show, is the reason for this.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
I guess then the questions become....How do you filter? and is the cure worse than the sickness?
The image above represents a nearly full scale 20hz signal which seldom happens in real music and if it does happen it is not cyclical for any period of time. Below is a 10 second section of the 1812 with the cannon fires. 25hy 2K5 and 10K loads.
The question that needs to still be answered is which is worse, the narrower green envelope that spans 110ma of the curves or the wider blue envelope that spans 55ma? To me the blue remains in the more linear part of the curves and keeps with my building / listening experience. FWIW, the flat line in the lower right of the curves is hard clipping of the .wav file.
dave
It would be interesting to me to see what sim would look like for a midrange amp, say 400hz and 6000hz.
---------------------------------------------------
Big speakers and little amps blew my mind!
"I guess then the questions become....How do you filter? and is the cure worse than the sickness?"
That is clearly up for debate.
Not just the single series filter cap but the fact that's the rest of the frequencies are being played by a SS amp.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: