The degree of feedback needed is dependent on speaker that is driving. You make a valid point. The designer purposefully built feedback into the amp.
I don't necessarily understand the article fully as my technical knowledge is limited, but I can recognize a well thought out article when I see it. I wanted start a discussion on this subject, and see what others had to say. Like I said, this seems to be the wrong forum. Many here are subjectivists and do not care about objective analysis. |
Mt, I'm sure your system sound awesome to you, but I've had my fill of single driver fostex speakers with low power tube amps which have significant drawbacks IMO. But you're getting off topic, and I do not see a reason to resort to personal attacks. Somehow you think you know more than I do and assume I am missing something important. Can you please stay on topic? |
Technically faithful reproduction can be measured, no? You compared the input signal to the output signal. |
Charles1dad and Viridian, did you read the entire article in the link? I think he raises valid points about nature of distortion and feedback in amplifiers. We can't all be complete subjectivists here. Afterall, it's mostly hard science and technology have produced these wonderful high end products we enjoy, with a little bit of snake oil sprinkled in of course :) |
""You compared the input signal to the output signal." Just how simplistic is this? So, I'll make this easy..."
Oh no you didn't. You didn't just try to dis me? ;) I don't think you are being condescending, so I'll give you benefit of the doubt and assume you are asking a genuine question. If that is the case, I thank you for your response.
"...if the two signals are exactly the same but one has 3% second harmonic distortion, and the other has .8% of the, more jarring, 7th harmonic distortion, which is the more "faithful"? Please answer my question."
Sure I'll answer. The result is the result and can't be disputed assuming you measured it correctly. What you're talking about is the INTERPRETATION of the result, which can be disputed. I do not know how a 3% 2nd harmonic distortion sounds relative to a 0.8% 7th harmonic distortion. But if the 7th harmonic distortion is say 80 dB down, I doubt I could ever hear it. Now 3% 2nd harmonic distortion may be audible, so I would consider that less faithful reproduction than a "jarring" 7th harmonic distortion I can't hear. Your interpretation may be entirely different than mine.
I can see how some might consider my input/output comparison simplistic. So let me explain. Why is it that a square wave is one of the industry standard of measurement of how an amplifier performs? Music does not contain square waves as far as I know. And I doubt if anyone considers a square wave a close facsimile of a music signal, which what an amplifier is suppose to reproduce. Wouldn't a more appropriate test signal be that of an instrument at certain frequency (eg, 1 kHz piano, guitar, or sax tone). Or even an instance of music containing many instruments. Is this technically too difficult to perform? I am relatively new at looking into the technical side of amplifier circuitry and performance, so my questions may seem naive to those who have years of technical experience. But this is one of the reasons why I started this thread. I would appreciate input from experienced individuals who would take the effort to be informative. As in any controversial thread, there will be individuals who will have nothing better to add other than dumb sarcastic or condescending comments. |
Hi Kijanki, thanks for your input. What do you think about the article I linked? |
Hi Elizabeth, what is a current fad or "catchphrase" is not important to me, but the finding the underlying reason for "catchphrase" or current fad is. If I did't think NFB or ZNFB made a difference in sound, I wouldn't have made this inquiry. |
Elizabeth, I have and owned amps that have adjustable NFB, and you can clearly hear a difference between different levels of feedback. IME, the higher feedback setting produced more realistic sound. So your contention feedback has little to do with how a product sounds is in direct contradiction to my experience. Do you have any amps with adjustable feedback? If you do, I would be surprised if you can't hear a difference. |
Kinjanki well said. That had been my experience with NFB as well.
I'm not looking for validation. I've been in this hobby for close to 30 years and I know what I like. I'm searching for technical explanation of why we hear what we hear.
I have listened to SET amps paired with high efficiency speakers. There's no denying the beautification of the midrange which can sound glorious and involving. But in the long run I know it's the way things sound in real life. And I do understand why some gravitate to this type of sound. |
Meant to say its NOT the way things sound in real life. |
Phaelon, you may be thinking of Rethem speakers which have powered subwoofer drivers with a wide bander taking care of the rest of the freq. they are coming out with low power ZNFB amp for their speakers. I think with powered subwoofers the low freq limitation of most ZNFB amps is negated while preserving the upper range qualities some people seek. |
Mt, please start making sense. Start your own thread to vent whatever frustrations you have. You're just trolling here. You'll get no more response from me. |
Mapman, I understand those who say just enjoy your gear, there is no best. I'm not looking for the best. And I am not looking for validation, nor am i unhappywith my gear. Some on this thread mistakenly make these assumptions about the intent of my thread. But that is not the point of this thread. I perceive NFB to be more realistic than ZNFB more often than not and I'm looking for a techical explanation. Perhaps I posted this in the wrong forum. Many have posted without reading the link which I think is pretty comprihensive on the subject. Tech Talk may be the more appropriate forum. |
Edwyun, I have an amp with adjustable feedback, so you can change feedback while keeping every other parameter constant. In this case, feedback can have a significant, if not drastic, effect on the sound. So stating feedback alone has little effect does not hold true in this case. |
Kinjanki, I think the Hyperion 938 is truly one of the great speakers in high end. I regret selling them to a friend. You can get 938s at bargain prices now. I am thinking of getting another pair. |
"Mapman, the question here is if NFB makes reproduction MORE faithful. Some answered that there is no faithful reproduction, which doesn't answer this question, while others stated they prefer sound of ZNFB which doesn't answer this question either. The truth is, that there is no SS amp (and very few tube amps) with zero feedback. SS amp by nature is a voltage source, and as such needs some form of negative feedback, at least for the output stage. The question is how much and that might depend on the load, your preference etc. It is undisputed fact, that even small amount of NFB widens bandwidth, lowers output impedance and reduces THD/IMD distortions. Does it make reproduction more faithful on average? I think it might. What sound you like has nothing to do with original question."
Kijanki, you seem to be the only one who understand the intent of my original post. Thank you for putting into words better than I.
I find it amusing some found my OP to be an attack on their equipment and taste in music, which was not my intent at all. If some of you were offended, sorry. |
Atmasphere, I've seen you write about how bad odd order harmonics can sound (ie, subjectively bright and hard) even at very low levels. Can you please specify at what level are odd order harmonics perceived as unpleasant? I don't recall you ever giving an actual number.
I have owned your M60 amp which I think uses a 2 dB of NFB and compared to a pentode, class AB, tube amp with 20 dB of NFB. Everything else in my system was constant. The volume level was as close to even as I can get them with SPL meter, and the volume ranged between 85 to 90 dB max during the comparison. The speaker had minimum narrow impedance band of 5.8 ohms and was 90 dB efficient. By your own words, 20 dB of NFB is considered excessive. However, I did not hear any excessive hardness or brightness in either amp. Both were very smooth in the midrange and treble regions. How do you explain that? |
Atmasphere, could you please clarify a statement you made on another related thread?
"Marqmike, unfortunately all amplifiers make odd ordered harmonics. It is the 5th, 7th and 9th that we are concerned about (the 3rd is considered musical to the human ear). When you add negative feedback to any amplifier design, the result will always be an enhancement of odd orders, even if the feedback is successful in removing most of the open loop distortions ('open loop' means the amp operating without feedback).
The reason this is so has to do with the fixed amount of time it takes a signal to move through a circuit. This time is called 'propagation delay'. The issue is that a low frequencies feedback works pretty good, but as frequency is increased, the propagation delay means that the feedback signal is arriving later and later to correct the circuit. In fact a designer has to be careful with feedback because this effect means that at some frequency the feedback as actually positive rather than negative. This is entirely due to the propagation delay in the amp."
I find your statement misleading. You state that NFB "enhances" odd order harmonics. According to the article I cited, NFB does not enhance (ie, increase) or add odd order harmonics. NFB reveals the odd order harmonics already produced by the amplifier before NFB is applied; this is a result of NFB greatly reducing other distortion components that mask the odd order harmonics. And NFB can reduce those higher order odd harmonics to below 110 dB from the fundamental. Can one hear distortion that low? You've claimed that we are very sensitive to odd order harmonic distortion, but could you provide a study that shows we can detect distortion this low?
As for propagation delay, an amplifier operated in its linear range will have delay in nanosecond range as far as audio frequency is concerned, including frequencies at the limit of human hearing. This is also explained in the link. Nano second range delay seems pretty negligible to me.
I, obviously, do not have more technical knowledge in amplifier design than you, but your claims seem to be directly at odds with the article I cited. |
