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Looking at SE DC 2A3 finals in ARTA Steps.The effect of reduced current biasing of 2A3 finals.
Vp-k = 245VDC @ 43maDC 1W power output.
The top graph is with a 2.5K plate load.
Bottom graph is with 5K plate load.
The THD and all harmonic % are broken down.
The low Hz performance is actually a bit better with the 2.5K plate load/reduced current biasing.
But at 1KHz, the 3rd harmonic seems to be much more prominent.
dt 667
Edits: 04/21/14Follow Ups:
nt
The 2A3 plate is loaded with a typical air-gapped SE OPT primary winding.
The OPT secondary is loaded with an 8 ohm power resistor.
A 10:1 test probe is placed across the 8 ohm resistor.
That sends an AC signal into the soundcard input to be measured.
The results are displayed on ARTA graphs for analysis.
The OPT likely does not have enough inductance to support lowest frequencies. The tube is thus loaded with lower impedance at the low frequencies resulting in higher distortion.
Yes, the graphs clearly show that, but that's a separate issue.
The stated THD is at 1kHz where the inductance (or lack of) is not an issue.
3.37% vs. 1.57% clearly shows that a 2a3 running 240vdc at 43ma. is much happier with the higher impedance load.
It would be interesting to see a comparison of the 1kHz THD with the tube running 250vdc at 60ma into both the 2.5k and 5k ohms loads.
Thanks for doing this DT.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
yes thanks DT!
The 2A3 DHT, in particular, can run ANYTHING happily, 1.5K to 5 K Ohms NO problemo dudes and dudessses.
Maybe one day people will learn that, some have !! Horrors, its not spelled out that way in RDH-4, so what ??
Build it, listen, and come to RMAF 2014 .....later this year. :-)
Jeff Medwin
DT, for Tony's sake, I will add that your Hammond 125ESE SE OPT has a primary that can be 10k, 5k or 2.5k depending on how the secondary is loaded/connected.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Here is the signal circuit.
It is a breadboard experiment, so I am not telling anyone to build this.
dt 667
But...can you hear the differences? And if so, in what frequency ranges is the distortion more prominent at the different plate loadings?
It looks very ambiguous, but what does it sound like?
Observe, before you think. Think before you open your yap. Act on the basis of experience.
You need to look at the graph a bit more.
Each harmonic and THD% is plotted vs. frequency.
Notice the distortion level markers on the left side of the graph.
Frequency is marked on the bottom of the graph.
It might not be easy enough to see, but study the ARTA downloads for STEPS on their website and it will be easier to understand.
As far as the subjective sound, how far below the fundamental does something need to measure in dB or % before it is not detected by the ear?
I need to figure out what things in the measurement will have any impact on what I am hearing, then go from there.
is the only odd harmonic that the ear regards as musical to the fundamental... at least according to Ralph.
Interesting, though it would not be enough to prevent me from wanting a higher load.
Cheers.
“As long as we have any intention to be right… we should be wary. So long as words have the slightest ego attachment, they are dishonest.” Charlotte Joko Beck
I've no idea who Ralph is, but just for the record it is the EVEN harmonics that are "musical" to the ear. For instance, A is 110Hz; the second harmonic is 220Hz which is also an A; the fourth is 440Hz also an A; the sixth...
You guessed it: 880Hz, A.
is the only odd harmonic that the ear regards as musical to the fundamental... at least according to Ralph.
I thought that the odd order harmonic distortions were subjectively dissonant sounding to the human ear.
The more linear load line seems to diminish the 3rd order harmonics.
don't have a clue - something to look into though.I was just suggesting that what Ralph had claimed on another forum could help explain the sonics of amps using a low load. I have no idea whether the 3rd harmonic is musical or not.
Although I have not experimented with loads personally, my inclination is to load high, per Thorsten's and many others' recommendations. But if someone can convince me otherwise... In the end, for me it is about the musical presentation.
Cheers.
“As long as we have any intention to be right… we should be wary. So long as words have the slightest ego attachment, they are dishonest.” Charlotte Joko Beck
Edits: 04/24/14
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