Back EMF
Hello All,
I run a Hk CIT II with early kT-90's.
I have run a few different preamps & sources; I have a HeathKit SP2 & have used other cit solid state preamps; the obviously 2nd harmonic rich Sp2 always won the listening time. Being an optical physicist I wanted the "clean" preamp to win but it simply didn't in front of the CITII. I still am looking to clean up the sound without losing whatever brings that dynamic alive, I hear it on the trailing edge of male vocals, close mike snare & in the"air" around tenor sax and trumpet lines.
But I digress, my main point was I just recently pulled some early Johnzer sealed 12 inch threee way's for some rectlinear III's which I am modding ( blown mid on one) with a modified focal7k011DB/tc90 pair. (previously used in a homemade 3 order x-over sub system)
The difference in performance from the CIT II under the vented woofer load was stunning. Now I really have to fix the preamp as it is coloring strongly past "raised voice talking level " 80-90dB.
I have heard quite few systems since my Uncle's AR3a/Marantz receiver set of the 1960's, I am always surprised none of them 30 dollars ->15000 ( within the limits of recording media) can reproduce the sound of live acoustic; Play a sax or bang an upright piano and surely any of you can hear delta.
What that delta is still not clear to me, but first order crossovers compared to third order crossovers seem to have a similar difference with first order more lifelike.
Hello All,
I run a Hk CIT II with early kT-90's.
I have run a few different preamps & sources; I have a HeathKit SP2 & have used other cit solid state preamps; the obviously 2nd harmonic rich Sp2 always won the listening time. Being an optical physicist I wanted the "clean" preamp to win but it simply didn't in front of the CITII. I still am looking to clean up the sound without losing whatever brings that dynamic alive, I hear it on the trailing edge of male vocals, close mike snare & in the"air" around tenor sax and trumpet lines.
But I digress, my main point was I just recently pulled some early Johnzer sealed 12 inch threee way's for some rectlinear III's which I am modding ( blown mid on one) with a modified focal7k011DB/tc90 pair. (previously used in a homemade 3 order x-over sub system)
The difference in performance from the CIT II under the vented woofer load was stunning. Now I really have to fix the preamp as it is coloring strongly past "raised voice talking level " 80-90dB.
I have heard quite few systems since my Uncle's AR3a/Marantz receiver set of the 1960's, I am always surprised none of them 30 dollars ->15000 ( within the limits of recording media) can reproduce the sound of live acoustic; Play a sax or bang an upright piano and surely any of you can hear delta.
What that delta is still not clear to me, but first order crossovers compared to third order crossovers seem to have a similar difference with first order more lifelike.
vanderpol, your conclusions are interesting, but they are not very complete. 2'nd harmonic is tolerable, but real high fidelity reproduction does not add it deliberately. However, I suspect that less than 0.05% harmonic would be almost impossible to detect in normal listening. Every one of my designs is completely complementary push-pull, BUT I have heard some single ended systems that sounded pretty darn good, almost to to point of sounding like 'live acoustic'. You just can't judge without listening.
Depends on how you define "traditional measurements." That sort of thing shows up as sidebands in spectral analysis (which is both common and trivial to do these days).
SY, just how are we supposed to measure the sideband deviations with traditional spectral analysis? Do you imply that we could evaluate FM distortion this way? If so, please give me your procedure. Also, just because it may not be visible on a screen, does not mean that it could not be audible. It might be the limitation of the FFT resolution or the test equipment, I should think. AM distortion certainly is audible below what we see on an oscilloscope, normally, as a comparison.
Hi fidelity
Hi John,
Yes I suppose one can say we never add harmonics on purpose but the truth is we may hear relative amplitude of odd/even harmonics and be senstive to this. That is what I think I am aiming for a "musical balance" down close to the noise floor, and perhaps under it...
Has anyone ever composed a table of the 1-4 odd and 1-4 even harmonics for say 10 amps/preamps? To me that would an interesting figure of merit.
I think another interesting measurement would a white/pink noise measurement; a fourier transform that transfer function, F(Noise out/Noise in)
might be very telling.
I think everyone would also agree that a single channel source is very different "sounding" then stereo. I suspect that the phase relationship of the odd order harmonics is what gives space to reproduced music; perhaps this why mono is "easy" to listen for long periods of time, again a straight forward measurement might be F(L+R Noise In/ Nout),in phase and F(L+R Noise In/ Nout), out of phase
Using these metrics I would be willing to bet a direct mapping of 70's transistor, 90's FET's, 50's push pull and modern amp designs would be differentable.
In closing check out
Brass instrument (lip reed) acoustics: an introduction
the mute/no mute is very interesting; wonder if a THD/IMD measurement would show any measurement of the non harmonic envelope under the harmonic structure
Lou
Hi John,
Yes I suppose one can say we never add harmonics on purpose but the truth is we may hear relative amplitude of odd/even harmonics and be senstive to this. That is what I think I am aiming for a "musical balance" down close to the noise floor, and perhaps under it...
Has anyone ever composed a table of the 1-4 odd and 1-4 even harmonics for say 10 amps/preamps? To me that would an interesting figure of merit.
I think another interesting measurement would a white/pink noise measurement; a fourier transform that transfer function, F(Noise out/Noise in)
might be very telling.
I think everyone would also agree that a single channel source is very different "sounding" then stereo. I suspect that the phase relationship of the odd order harmonics is what gives space to reproduced music; perhaps this why mono is "easy" to listen for long periods of time, again a straight forward measurement might be F(L+R Noise In/ Nout),in phase and F(L+R Noise In/ Nout), out of phase
Using these metrics I would be willing to bet a direct mapping of 70's transistor, 90's FET's, 50's push pull and modern amp designs would be differentable.
In closing check out
Brass instrument (lip reed) acoustics: an introduction
the mute/no mute is very interesting; wonder if a THD/IMD measurement would show any measurement of the non harmonic envelope under the harmonic structure
Lou
Spectral resolution is pretty straightforward- with a typical computer setup, better than 1Hz is easy. The sidebands that result from FM or plain old amplitude distortion are pretty characteristic. $200 gets you nearly 100 kHz of bandwidth, better than -150dB noise floor, and better than 1Hz resolution.
This capability cost six figures when I was at Nicolet. I am still totally amazed at how easy and reliable modern implementations are.
This capability cost six figures when I was at Nicolet. I am still totally amazed at how easy and reliable modern implementations are.
Vanderpol, what do you think that we do as audio designers? First of all, NOT ALL harmonics are the same in effect or annoyance. This has been stated in the 'Radiotron Designers Handbook' for more than 70 years, and their original estimates are amazingly similar to what we find today, especially in relative amplitudes, as to what we can detect and what to avoid when designing audio electronics.
Stick a negative feedback and bias knob on the front panel, with good tweaking one could get ,
1. Class-a sound
2. Class-d sound ( dial back the bias, wack out the NFB)
3. Toob sound ( resistor box for damping control, dial back feedback/up bias )
4. Class-a/ab sound
An amp for everyone ...........
1. Class-a sound
2. Class-d sound ( dial back the bias, wack out the NFB)
3. Toob sound ( resistor box for damping control, dial back feedback/up bias )
4. Class-a/ab sound
An amp for everyone ...........
Traditional means static measurements using sinewave generators, notch filters, AC voltmeters. However, spectrum analyzer is the way to observe dynamic behavior, but you can't name and calibrate all possible dynamic flaws of all possible topologies, to define a new tradition of measurements.
And even if you do, how many would agree with your new standards? At least, Stereophile always has own opinions, independent on engineers'.
Thanks for the great info chaps, sorry i could not get back here earlier. now to pull the discussion back to thermal stability:
Tubes by their nature stay pretty warm, even in class AB. How much will the dynamic peaks of music change that temperature? And what differences will thermal stability make?
Yes John, that pretty much what I was trying to express. Since Class-A runs a such at high idle current and idle temperature, just how much will short term bursts of music change that point? I.E., if the dynamic peaks are only equal to the idle current, the change in current flow won't be high in relation to idle current. Temperature should not change much. Thorsten seems to say that it will, but I ask how much as compared to a low bias amp?
Tubes by their nature stay pretty warm, even in class AB. How much will the dynamic peaks of music change that temperature? And what differences will thermal stability make?
If the total measured THD of an audio chain (to the amplifier output posts) is below 0.05% there is no point in splitting the hair into odd-even harmonics. That level is low enough not to be a problem.
Limited bandwidth of a 44.1kHz sources is clearly audible on the sounds like in the original post. I found out that DSD or PCM 96kHz are needed for a "life-like" sound. Bandwidth and step/impuls response is clearly measurable.
Now, the speakers will never be in that range. I was amazed how much difference is between my speakers and a pair of decent headphones.
Measuring speaker's THD is a little more "delicate" to do because of their nature (pressure devices) and nelinear dependence of the actual level of electrical (input) signal.
As for thermal on tubes - anodes will heat up based on the current is flowing thru them (number of electrons hitting the anode). That will affect efficiency, noise...
Limited bandwidth of a 44.1kHz sources is clearly audible on the sounds like in the original post. I found out that DSD or PCM 96kHz are needed for a "life-like" sound. Bandwidth and step/impuls response is clearly measurable.
Now, the speakers will never be in that range. I was amazed how much difference is between my speakers and a pair of decent headphones.
Measuring speaker's THD is a little more "delicate" to do because of their nature (pressure devices) and nelinear dependence of the actual level of electrical (input) signal.
As for thermal on tubes - anodes will heat up based on the current is flowing thru them (number of electrons hitting the anode). That will affect efficiency, noise...
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agree................ and my original point !!!
You should get better speakers, when correctly voiced they should sound pretty close to the headphones.
Traditional means static measurements using sinewave generators, notch filters, AC voltmeters. However, spectrum analyzer is the way to observe dynamic behavior, but you can't name and calibrate all possible dynamic flaws of all possible topologies, to define a new tradition of measurements.
And even if you do, how many would agree with your new standards? At least, Stereophile always has own opinions, independent on engineers'.
Can't edit: I can use signal generator, DVM, oscilloscope, CD player, to observe behavior of the amp I design and to find potential flaws and directions where to go, but I would not call it traditional measurement. I would rather call it a specialized, topology - dependent test.
M-Audio 192 card in a cheap HP PC, which allows both balanced and unbalanced I/O as well as SPDIF I/O. Street price is ~$150. Bought it on Amazon. AudioTester, REW, Rightmark, HOLM, Soundeasy software. AT was about $40, the others were free.
Two interface boxes, one is Pete Millett's, the other is my own design (BUF03s, noisy but superbly low distortion and source Z). My box is set up to use standard (1x, 10x) scope probes.
I have conventional gear as well for backup and verification, but that seems to get used less and less. I'd love to have an AP2, but with a little elbow grease and one-off jigs, I can get just about all the measurements that an AP2 is capable of with the PCI card.
IOW, using your grandpa's gear.
A tacit point that you've made is that the ability to determine which measurement to make, what the error sources are, and how to interpret the measurement is thousands of times more important than the brand of equipment.
Figure of Merit
John,
I am sure you balance steady state harmonics perfectly, given the topology and noise constraints.
What I pointed out was that given time series of "pink noise" will have a fourier transform; after amplification that fourier transform will be modified; against known human preception of that harmonic content of the transform S(w)amp/S(w)o there may be a measurable FOM that sorts ampifiers by their percieved quality.
In summary The point is pretty simple; why can't there be an accepted measurable quantity that can be used to gauge audible "fidelity"? If I look at THD and IMD S/N for:
a 1970's yamaha reciever
a 1970's kenwood 40WpC integrated amp
a 1960 HK Cit II
a Carver"the receiver"
a 1990's denon pre-amp
a pioneer super tuner car radio
A pair of PP monoblocks
Any modern amplifier "high" or "low" end
I can't "see" what I hear or have heard over the years . Further the feedback topology of the HK CITII suggests you can't "hear" the tubes, however I certainly know when the splitter pentode is aging, ( not sure if there is a measurable THD IMD with this though).
I also know a single ended triode preamp sound is recognizable, as this is DYI audio what I really want to know is ( so I clean up my preamp!):
a) why does a high NFB class A preamp sound "sterile" what measurement is sterile to musical?
b) what do I measure and minimize in the triode class A preamp to have my cake and eat it to?; that is a musical combination and no syrup colorations.
Do I move the B+ up? drop the 12AU7 stage? move the S.E. 12Ax7 final stage to SRPP? Do I take gain and feedback? How much? How do I know? What do I measure? What figure of Merit do I use?
What if I wanted to switch preamp? what FOM do I look for? That one I know: there is no published marketing info that tells me, not slew rate, not THD, not IMD. It is all word of mouth and audio trial and error.
c) Does a different topology change the sound/noise e.g. if I totem pole either the 12au7 or the 12ax7 stage will I "improve" the amplifier fidelity?
That is what I am looking for, a measurable way to gauge my amplifier mod or review known topologies and compare the fidelity of each.
Lou
John,
I am sure you balance steady state harmonics perfectly, given the topology and noise constraints.
What I pointed out was that given time series of "pink noise" will have a fourier transform; after amplification that fourier transform will be modified; against known human preception of that harmonic content of the transform S(w)amp/S(w)o there may be a measurable FOM that sorts ampifiers by their percieved quality.
In summary The point is pretty simple; why can't there be an accepted measurable quantity that can be used to gauge audible "fidelity"? If I look at THD and IMD S/N for:
a 1970's yamaha reciever
a 1970's kenwood 40WpC integrated amp
a 1960 HK Cit II
a Carver"the receiver"
a 1990's denon pre-amp
a pioneer super tuner car radio
A pair of PP monoblocks
Any modern amplifier "high" or "low" end
I can't "see" what I hear or have heard over the years . Further the feedback topology of the HK CITII suggests you can't "hear" the tubes, however I certainly know when the splitter pentode is aging, ( not sure if there is a measurable THD IMD with this though).
I also know a single ended triode preamp sound is recognizable, as this is DYI audio what I really want to know is ( so I clean up my preamp!):
a) why does a high NFB class A preamp sound "sterile" what measurement is sterile to musical?
b) what do I measure and minimize in the triode class A preamp to have my cake and eat it to?; that is a musical combination and no syrup colorations.
Do I move the B+ up? drop the 12AU7 stage? move the S.E. 12Ax7 final stage to SRPP? Do I take gain and feedback? How much? How do I know? What do I measure? What figure of Merit do I use?
What if I wanted to switch preamp? what FOM do I look for? That one I know: there is no published marketing info that tells me, not slew rate, not THD, not IMD. It is all word of mouth and audio trial and error.
c) Does a different topology change the sound/noise e.g. if I totem pole either the 12au7 or the 12ax7 stage will I "improve" the amplifier fidelity?
That is what I am looking for, a measurable way to gauge my amplifier mod or review known topologies and compare the fidelity of each.
Lou
IOW, using your grandpa's gear.
A tacit point that you've made is that the ability to determine which measurement to make, what the error sources are, and how to interpret the measurement is thousands of times more important than the brand of equipment.
Exactly. But we still read here about THD and DF comparisons
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