Perceived Localization
Hello TheGimp,
What I was thinking is this. If the Class A PP amp is operating at some low level, say less than one watt the 2nd harmonic will be reduced and the higher order harmonics may not become present until the power levels are higher. Put it another way, that first watt may be really clean.
I do not know this to be fact. It would be interesting to see on the FFT.
This is me thinking aloud about localization now. Much of sound reproduction is illusion or perception made up in our heads. Higher harmonics or for that matter any harmonics may disrupt, maybe add to, the illusion. I know 120 Hz hum distracts from my enjoyment of the music and the perception of being there. In the text books multiple frequencies interact and create, for lack of a better description coming to mind, intermodulation frequencies. This happens in amplifiers and the external real world as well. Unexpected IM may add to or ruin the illusion.
I recall one author discussing the perception of loudness. At high sounds levels our ears create higher order harmonics and possibly amplifier produced higher order harmonics could create the same perception of increased loudness.
I am going to try out Class A PP before I knock it.
DT
Hello TheGimp,
What I was thinking is this. If the Class A PP amp is operating at some low level, say less than one watt the 2nd harmonic will be reduced and the higher order harmonics may not become present until the power levels are higher. Put it another way, that first watt may be really clean.
I do not know this to be fact. It would be interesting to see on the FFT.
This is me thinking aloud about localization now. Much of sound reproduction is illusion or perception made up in our heads. Higher harmonics or for that matter any harmonics may disrupt, maybe add to, the illusion. I know 120 Hz hum distracts from my enjoyment of the music and the perception of being there. In the text books multiple frequencies interact and create, for lack of a better description coming to mind, intermodulation frequencies. This happens in amplifiers and the external real world as well. Unexpected IM may add to or ruin the illusion.
I recall one author discussing the perception of loudness. At high sounds levels our ears create higher order harmonics and possibly amplifier produced higher order harmonics could create the same perception of increased loudness.
I am going to try out Class A PP before I knock it.
DT
Hello SpreadSprectrum,
In my way of thinking 2nd and 3rd are lower order harmonics, 5th on up is higher order. Pick a spot for 4th.
DT
All just for Fun!
Funny you should mention the 4th harmonic. It's often conspicuously absent or at a relatively low level in the distortion spectrum of the tube amps I build. Not sure why that is, but I have recently played with MOSFETS in a tube circuit and got a significant amount of f4.
In fact, this may be of interest. I was going to make a silly quiz out of it but here it is. The first trace, Schadeode, is the circuit using a 6L6. The second trace, SSSchadeode, is the same circuit and op points but using a MOSFET or more precisely an IGBT, in place of the 6L6. The IGBT was degenerated to approximately the same gm as the 6L6.
The 6L6 version has a series of higher-order distortions going to f9 and perhaps beyond. The IGBT version has a big f4 peak and almost no higher order "grass". The sonic differences were hard to detect but I'd say the IGBT one was at least as pleasant to listen to as the 6L6 one; both sounded really nice. The reference level is one watt.
Now I'm interested in exploring this further but I suspect it has to do with the interaction of the driver nonlinearity with the output device nonlinearity and so-called distortion cancellation.
Oh yeah, I'd count f4 in with the low order because of it's tendency to mimic more common natural partials.
cheers,
michael
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Do you have schematic to post?
Could be instrumental error, but could be PIM as well. And indeed PIM sounds very nasty.
Ramblings
The ramblings here are the results of my thought experiments. Individual results may vary.
The primary purpose for using Class AB1 PP vs class B PP is to smooth the crossover notch or discontinuity in the Class B transfer function. In Class B PP each of the tubes in the PP pair is active for less than 180 degrees. In total the pair is inactive for a finite period of time. There is a hole in the transfer function that sounds very bad. There are exceptions to this sort of. Sigma Delta DAC’s are Class B with a lot of work by the IC team to close the gap then ample feedback is added to fill the cracks. If you need proof check out the reported THD numbers.
Class A PP amplifiers both devices are active all the time. That rough patch in the center of the transfer function is totally missing.
In Class AB1 the transfer function does not have a gap in the center. Both tubes are active or overlap to some degree in the center of the transfer function. The section of the curve where the devices overlap the composite mutual conductance is “double”. The slope of the transfer function is greater in this section of the curve.
My estimation is that the center portion of the Class AB1 curve will sound similar to Class A bias PP.
Crank up either the AB1 or A pairs into the tails of the Transfer function there begins to be some soft rounding of both peaks of the output. That is the definition of even harmonic canceling and prominence of 3rd and higher harmonics. SE Class transfer function does not have a shoulder or rounding at the top of the curve. This lack of symmetry is what causes the prominent 2nd harmonic.
The center 2/3 of the Class A PP transfer function interests me. Stay off the tails of the curve.
In Class AB1 PP the sweet spot is smaller but there are more total watts.
Michael
Tuning the interaction between the drivers and output tubes could be intresting.
Running the FFT's at various power outputs I bet the sonic signatures will change at differing levels on the transfer function. I also bet that the IGBT transfer functions are a funny shape.
DT
All Just for fun!
The ramblings here are the results of my thought experiments. Individual results may vary.
The primary purpose for using Class AB1 PP vs class B PP is to smooth the crossover notch or discontinuity in the Class B transfer function. In Class B PP each of the tubes in the PP pair is active for less than 180 degrees. In total the pair is inactive for a finite period of time. There is a hole in the transfer function that sounds very bad. There are exceptions to this sort of. Sigma Delta DAC’s are Class B with a lot of work by the IC team to close the gap then ample feedback is added to fill the cracks. If you need proof check out the reported THD numbers.
Class A PP amplifiers both devices are active all the time. That rough patch in the center of the transfer function is totally missing.
In Class AB1 the transfer function does not have a gap in the center. Both tubes are active or overlap to some degree in the center of the transfer function. The section of the curve where the devices overlap the composite mutual conductance is “double”. The slope of the transfer function is greater in this section of the curve.
My estimation is that the center portion of the Class AB1 curve will sound similar to Class A bias PP.
Crank up either the AB1 or A pairs into the tails of the Transfer function there begins to be some soft rounding of both peaks of the output. That is the definition of even harmonic canceling and prominence of 3rd and higher harmonics. SE Class transfer function does not have a shoulder or rounding at the top of the curve. This lack of symmetry is what causes the prominent 2nd harmonic.
The center 2/3 of the Class A PP transfer function interests me. Stay off the tails of the curve.
In Class AB1 PP the sweet spot is smaller but there are more total watts.
Michael
Tuning the interaction between the drivers and output tubes could be intresting.
Running the FFT's at various power outputs I bet the sonic signatures will change at differing levels on the transfer function. I also bet that the IGBT transfer functions are a funny shape.
DT
All Just for fun!
SE amp not necessary generates high 2'nd order harmonics. It depends on selected tube and it's regime.
Try GU-50 with Shade feedback, with 400V cathode to anode voltage, +250V stable on G2, 160 Ohm of cathode bias, 1K load, and you will get a nice symmetrical curve.
Class B in tube amps is not the same as class B in solid state amps, since "cut-off" region is less steep. If to use transformer for a phase splitter blocking distortions don't appear. However, when capacitive coupling become the norm higher idle currents become usual for P-P amps.
For example, 6N7 tube could give 8W with 250V anode voltage, with about 15 mA of idle current, with less then 4% of THD. Idle current was much higher than zero, but it was still called class B. Tubes for push-pull amps were designed such a way they did not require negative bias, so no cathode resistors nor shunting caps were needed.
Try GU-50 with Shade feedback, with 400V cathode to anode voltage, +250V stable on G2, 160 Ohm of cathode bias, 1K load, and you will get a nice symmetrical curve.
Class B in tube amps is not the same as class B in solid state amps, since "cut-off" region is less steep. If to use transformer for a phase splitter blocking distortions don't appear. However, when capacitive coupling become the norm higher idle currents become usual for P-P amps.
For example, 6N7 tube could give 8W with 250V anode voltage, with about 15 mA of idle current, with less then 4% of THD. Idle current was much higher than zero, but it was still called class B. Tubes for push-pull amps were designed such a way they did not require negative bias, so no cathode resistors nor shunting caps were needed.
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THD was reduced to a meaningless number, not distortion.
As you know distortions are not all harmonic in nature and they are very audibly not all equal
. In fact for some music it's difficult to classify 2nd harmonic even as distortion.I do not think you can generalize about the type, except in efficiency terms where the traditional C/B/AB/A classification holds true.
I've played with some really out-there SET-Hybrid headphone amps, where the load on the tube was practically nothing so I am listening to just pure SET tube with the most efficient speakers made (Grados) and you know what affects the sound more than anything? Capacitors, frinkin capacitors. Not just coupling caps but power supply caps, cathode bypass caps.
And say what you want but no RMAA can show the extent of the change that swapping same valued but different construction capacitors has on the sound signature.
So I look at THD and anything we can measure with a grain of salt. As an engineer I say "You can't Measure Perception." No one knows what is at the interface of the brain to the ear. Measurements can weed out problems if you have bad hearing, other than that I think they are highly over rated.
And say what you want but no RMAA can show the extent of the change that swapping same valued but different construction capacitors has on the sound signature.
So I look at THD and anything we can measure with a grain of salt. As an engineer I say "You can't Measure Perception." No one knows what is at the interface of the brain to the ear. Measurements can weed out problems if you have bad hearing, other than that I think they are highly over rated.
X2 MKTs (polyester) work great for de-coupling. I'm using 1uF 275V ones on 300V supplies in addition to the Al Electrolytics.
I just found the spec sheet on them (B81133) and I've been limiting the use to less than 390V as I figured 275*1.414 = 388.8, well the data sheet states
"Permissible continuous dc voltage 630V"
"DC Test voltage 1700V, 2s"
Yikes!
Looks like they are good for anything I'll build.
I just found the spec sheet on them (B81133) and I've been limiting the use to less than 390V as I figured 275*1.414 = 388.8, well the data sheet states
"Permissible continuous dc voltage 630V"
"DC Test voltage 1700V, 2s"
Yikes!
Looks like they are good for anything I'll build.
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Is it real or illusion? Can’t tell? That is the goal. The pieces parts of the amplifier are secondary to the perception. Many of us engineer types let the pride of designing and building the machine get in the way. It is the human that counts.
I think that it is too late to apply for this job. Still take a look at what is done in a psychoacoustics lab.
[visionlist] Off topic: PhD position (auditory psychophysics)
They do study human auditory perception even if we do not.
DT
All just for fun!
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Yes Yes Yes, I am an Engineer but all my electives were in science and philosophy. Perception digs deep into the core of scientific structure, quantum mechanics is a bit of an example but consciousness plays a huge role in perception and therefore audio. Engineers who didn't get a broad education shrug things off as placebo or "psychology", but there is much more to it.
For my gear I go for what I call realism, putting the performer in the room with me, not a hi-def picture perfect copy.
And I think that means using the recording as a tool or means to an end, not "let's reproduce the recording as accurately as possible", how about lets reproduce the performance with our amp/transport/DAC ? Microphones and ADC's are imperfect, so the playback has to compensate. Its pretty logical when you think about it.
Wavebourn,
I will PM you since it seems off topic here.
regal,
You have to admit, thought, that when you spend a bunch of money on something the result is that you will really want it to be good. That can affect your perception. What's the big harm if someone thinks that something sounds better when it is really the same or worse(compared to if that same person had to choose in a blind test)? Nothing. It just angers me to see the snake oil salesman getting rich.
I agree, Thats why I like DIY, keeps the fun it the hobby. There are a lot of charlatans in the audio biz.
Realism is good. I prefer Illusion.
To reproduce the music or to produce primal fear with the sounds of the stalking animal creeping through the grass followed by the growl of the final lunge, these Illusions require realistic sound intensity levels.
To stay on topic with this thread, is insufficient sound pressure level a distortion that bursts the bubble of illusion?
Push Pull may have the edge here.
Will the absence of a paper in oil capacitor and the inclusion of a $1.71 Vishay-Roderstein MKP-1837 capacitor destroy the effect?
DT
All just for fun!
Realism is good. I prefer Illusion.
To reproduce the music or to produce primal fear with the sounds of the stalking animal creeping through the grass followed by the growl of the final lunge, these Illusions require realistic sound intensity levels.
To stay on topic with this thread, is insufficient sound pressure level a distortion that bursts the bubble of illusion?
Push Pull may have the edge here.
Will the absence of a paper in oil capacitor and the inclusion of a $1.71 Vishay-Roderstein MKP-1837 capacitor destroy the effect?
DT
All just for fun!
neuroscience, audiology, neurochemistry, cranial nerve biology, sensory biology, consciousness science... I guess if someone has all the answers they can explain a working model of the brain and consciousness.
Its laughable to me as an engineer to see people run a few ruimentary RMAA tests and think they have all the answers to the unexplored core of science.
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