I used transformer because I needed to sense current through speaker driven by a pair of bridged amps. Otherwise one resistor to the ground would be simpler and better.
The same voltage to the same motor will deliver the "same energy profile", unless there is long term energy storage. I make no assumptions about the angle between voltage and current. Think of the amp as a voltage generator with a low but non-negligible output impedance - the impedance can even be non-linear. How it achieves this internally is irrelevant. Think of the speaker as a complex impedance, including short term energy storage. Now you could in principle have different amps producing the same voltage at the junction (=output terminals) by having different open circuit voltages but also different output impedances so the two changes exactly cancel, but then the same voltage is delivered to the load so the same sound will come out. In essence you have a potential divider, with the amp o/p Z at the top and the transducer at the bottom. If the voltage at the middle is the same then the current is the same, because it is flowing through the same lower impedance.tvrgeek said:
I think there is a confusion here, but I can't quite work out what it is. Always difficult to see inside someone else's head!
Folks,
Allow me to pose a few question, quite simple.
Given is:
1) An AP2 testset
2) A Resistor Load 4R
3) A Speaker Simulator Load as used by JA in stereophile
4) A Amplifier (DUT in the following)
The DUT is tested using the AP2 with any of the standard tests (THD&N, IMD, FR) and the tests show that the amplifiers output voltage is essentially an amplified replica of it's input with no measurable (by AP2) distortion and noise added and with a passband sufficiently wide to eliminate issues (phase, amplitude) in the audio band and is not affected by the loads used to test (listed above).
Questions:
please provide reasoning as to why the answer is as you answer, even though the questions themselves are simple are simple yes/no(/pass) type
1) With the AP2 Measurements as given above, do you consider this DUT to be "as near to perfect as possible"?
2) Do you feel any measurements not listed above, that is other than noise, harmonic distortion, intermodulation distortion, frequency response and load tolerance (damping factor); are required to make the determination in Question 1 and if yes, what are they?
3) Do the AP2 Measurements as given above inform us about about the actual performance of this amplifier when inserted into a real audio system?
4) Do the AP2 Measurements as given above inform us if the DUT when inserted into a HiFi Audio System will produce what is perceived by the majority of the potential customers "good sound" and would lead to a purchase of the DUT?
Ciao T
Allow me to pose a few question, quite simple.
Given is:
1) An AP2 testset
2) A Resistor Load 4R
3) A Speaker Simulator Load as used by JA in stereophile
4) A Amplifier (DUT in the following)
The DUT is tested using the AP2 with any of the standard tests (THD&N, IMD, FR) and the tests show that the amplifiers output voltage is essentially an amplified replica of it's input with no measurable (by AP2) distortion and noise added and with a passband sufficiently wide to eliminate issues (phase, amplitude) in the audio band and is not affected by the loads used to test (listed above).
Questions:
please provide reasoning as to why the answer is as you answer, even though the questions themselves are simple are simple yes/no(/pass) type
1) With the AP2 Measurements as given above, do you consider this DUT to be "as near to perfect as possible"?
2) Do you feel any measurements not listed above, that is other than noise, harmonic distortion, intermodulation distortion, frequency response and load tolerance (damping factor); are required to make the determination in Question 1 and if yes, what are they?
3) Do the AP2 Measurements as given above inform us about about the actual performance of this amplifier when inserted into a real audio system?
4) Do the AP2 Measurements as given above inform us if the DUT when inserted into a HiFi Audio System will produce what is perceived by the majority of the potential customers "good sound" and would lead to a purchase of the DUT?
Ciao T
Maybe time for me to come out
No. It will always be possible to design an amp with is 'more perfect' than the latest one. Matter of spending enough effort and money.
Yes. As said, it will always be possible engineering wise to build a 'better' amp and I expect that other measurements may be required to proof that one amp is better than another, but I have no specific answer as to which measurements this might be.
Yes. Since the measurements inform us about how faithfull and transparant the DUT amplifies the input signal, that has a direct bearing on its performance in an audio system. The amp doesn't change when taken from a testbench into a system.
No. The perception of 'good sound' and eventual purchase decisions are based on a myriad of factors like physical shape and form, price, brand, marketing, reputation and several others, of which the actual, objective sound quality is just one. The diversity of the market of actual purchases, from Halcro though Parasound to Bose is proof of that.
hope this contributes,
jan
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Jan,
Just to be clear, my point was when tested using AP2 test the DUT does not add any HD or IMD the AP2 can measure and does not change it's bahviour using the specified loads.
So this Amp is at least as good as the AP2 or better. If you make a better amplifier how will you know?
Hmm, so you position COULD be rendered as: "The listed measurements are insufficient, but I do not know in what way and what needs to be measured in addition to them"?
Jan, I included this question on purpose and I would suggest it actually bears some import and is worth reconsidering your answer. To focus this a little, sure, the amplifier does not change, but could it be perchance that it's environment change in ways that would influence the measured performance of the amplifier?
Okay, let us de-link "good sound" and "purchase decision", though I had good reasons to include it, as it in many ways at least in the audiophile context the ultimate arbiter, "will I trade what I have for this new gizmo at a financial loss to me".
In that case, however, let us remove the purchase decision and focus on "will it sound good?"
Ciao T
Maybe time for me to come out
No. It will always be possible to design an amp with is 'more perfect' than the latest one. Matter of spending enough effort and money.
Just to be clear, my point was when tested using AP2 test the DUT does not add any HD or IMD the AP2 can measure and does not change it's bahviour using the specified loads.
So this Amp is at least as good as the AP2 or better. If you make a better amplifier how will you know?
Hmm, so you position COULD be rendered as: "The listed measurements are insufficient, but I do not know in what way and what needs to be measured in addition to them"?
Jan, I included this question on purpose and I would suggest it actually bears some import and is worth reconsidering your answer. To focus this a little, sure, the amplifier does not change, but could it be perchance that it's environment change in ways that would influence the measured performance of the amplifier?
Okay, let us de-link "good sound" and "purchase decision", though I had good reasons to include it, as it in many ways at least in the audiophile context the ultimate arbiter, "will I trade what I have for this new gizmo at a financial loss to me".
In that case, however, let us remove the purchase decision and focus on "will it sound good?"
Ciao T
That is intellectual slight of hand...
Any wise engineer would also make environement testing , i.e , checking
stability and current capabilities for exemple , so your exemple is quite
irrelevant as it implies that the tester didnt check all necessary parameters
enough to make certainity that the amp is environment variation proof..
Indeed , there s a direct relation between how an amplifier measure
and how it sound , and in this respect , most amps , if not used
close to clipping , sound the same provided minimal care has been
done in the design and building.
I don't understand what you mean in detail.
My amp hasn't caps between input and output stage,
but maybe it's possible that a FET typically produces
even order harmonics when driving a partially capacitive load compared to BJT ?
Ignoring seems to be the most basic function of the brain (anyone can do that, but for ex. hiding interest is not so easy).
And the evolution of my hearing is even one step further
by being optimized for music (singers only count as instruments, apart from the content). Not serious.
Ok, thanks! Shurly interesting.
Sry for not writing the details of my amp.
I'm sure you found the right components for yours.
I'd like to stay with the FET-input because overshoot and
settling time are less than with bipolar input.
With BJT the distortion suddenly explodes when clipping
and there exhibit strong sidebands around the harmonics, whereas measuring with the FET input at clipping level just shows, that also odd order harmonics came up and the
harmonics havn't sidebands around.
Answers to Thorsten's questions.
The showroom might have a taxi firm next door flooding everything with RF. If obvious this will be dealt with by using filters, sending rude letters etc. If not obvious it will be lived with, but may affect the sound for good or ill.
Possibly, but not necessarily.
Close spacing IMD (i.e. sub-Hz). Variation of output impedance with frequency. Rejection of radiated and conducted interference. Rejection of input signal fast spikes and other out-of-spec inputs. There may be others I have not thought of.
Inform us, yes. Guarantee good performance, no.
No. Some people prefer distortion and wobbly frequency response. Some people may prefer some noise. Some people buy on appearance or price, not performance. Some people may need the amp to compensate for a transducer or room problem e.g. dull amp with bright speakers.
The showroom might have a taxi firm next door flooding everything with RF. If obvious this will be dealt with by using filters, sending rude letters etc. If not obvious it will be lived with, but may affect the sound for good or ill.
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It's a while since I used a taxi, but I suspect that PMR is still widely used in the UK. The pub next door might have a wireless mike for karaoke evenings.
The shop salesman probably has a cell phone in his pocket, and being indoors and partially screened it will be operating at highish power.
My general point is that there is lots of RF about, both from transmitters and poorly suppressed SMPS. In theory an amp would need to have good EMC performance in order to get a legal CE sticker, but I doubt if audio EMC is a high priority for trading standards officers.
The shop salesman probably has a cell phone in his pocket, and being indoors and partially screened it will be operating at highish power.
My general point is that there is lots of RF about, both from transmitters and poorly suppressed SMPS. In theory an amp would need to have good EMC performance in order to get a legal CE sticker, but I doubt if audio EMC is a high priority for trading standards officers.
Wasn't faulting the RF question, where you are completely correct, just pointing out the anachronism (or soon to be one in some places) in the canonical example. I see "taxis" used quite often as a proxy for the general run of RF sources, yet I can't ever remember getting breakthroughs of taxi transmissions in a hifi system, nor have most people I've asked about it. Maybe it was a problem in 1957? The few people who have ever responded positively said that it happened once or twice, maybe 20-30 years ago when they were living in Manhattan. Other RF sources, sure.
I see "taxis" used quite often as a proxy for the general run of RF sources, yet I can't ever remember getting breakthroughs of taxi transmissions in a hifi system, nor have most people I've asked about it. Maybe it was a problem in 1957? The few people who have ever responded positively said that it happened once or twice, maybe 20-30 years ago when they were living in Manhattan. Other RF sources, sure.
Gainesville Florida, 1966. Church. Taxis over the wireless mic system at mass. System quickly dropped! And that's not fair, it was a wireless mic.
Since then I've had audio gear pick up everything from cell phone noise to CB radio to FM broadcast in various places around the country. The air is an RF soup! Have also had RF from Class-D amps cause problems.
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