Sorry to quote myself, but thought I should clarify. This is relative to the ability of the amplifier to damp or control speaker resonances. It doesn't apply to the ability of the amplifier to keep its output constant into varying load impedances, which can matter a lot with most speaker impedances varying more than 10:1 in magnitude!
Watch out for those homopolar generators. His name was never uttered in any context while I was at MIT even though he was still involved in the community AFAIK. Another victim of substance abuse I'm afraid. For those that don't know he is/was Brian dePalma's brother. Interesting to note Brian was interested in science and physics before film even had a high school science project, "An Analog Computer to Solve Differential Equations". must have been an interesting family. Anyone else remember "Greetings", I had just turned 18 so I could see "X" rated films?
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Looks like 20 grand and your all set with amps and speakers, this guy is way too cheap.
I did say 'so far'. Wolcott is a new one on me. But anyone who claims 'unmeasurable' for a parameter starts on the back foot as he clearly needs to rent a better test rig, if only for a day.
His approach seems interesting but why does he have to wrap it in so much marketing guff if its patented? Still trying to find if the patent number is anywhere so I can look it up.
But he both claims that his feedforward design makes the amp a perfect voltage source then offers a damping control. Curious.
EDIT: He has a white paper explaining his patented design, but charges $5 for it. Joy
His approach seems interesting but why does he have to wrap it in so much marketing guff if its patented? Still trying to find if the patent number is anywhere so I can look it up.
But he both claims that his feedforward design makes the amp a perfect voltage source then offers a damping control. Curious.
EDIT: He has a white paper explaining his patented design, but charges $5 for it. Joy
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I suspect that US3111630 is the patent, and if so, the need for the marketing guff should be pretty evident.
Well I re-read the 2 part critical damping article and didn't change my view that it was a 50s solution to a 50s problem. But as I had never really given current drive a second thought but know that Nelson Pass has decided to see what he had written and found http://www.firstwatt.com/pdf/art_cs_amps.pdf . I have to take my hat off to NP. Whilst his is not writing for academic publication, he does manage to get the gist of the technical discussion over in an easy to digest and accurate format. And he confirmed its a 50s solution to a 50s problem.
Nothing invalid if you love fostex / lowther/ big old hoofing 27" field coils.
But one throwaway comment from NP. He did mention that he had found some success with current drive of ribbons. Now that DOES interest me and will warrant more research.
Nothing invalid if you love fostex / lowther/ big old hoofing 27" field coils.
But one throwaway comment from NP. He did mention that he had found some success with current drive of ribbons. Now that DOES interest me and will warrant more research.
I am the proud owner of one of Hugh's amps, a Naksa 125
Wary always of subjectivist obfuscation, I offer this :
"warmth" generally means perceptibly distorted
"engagement" translates as "wow I like that track"
Imaging is always accomplished by a flat phase response.
Harold Black invented feedback to maintain accurate gain as the tubes in undersea repeaters aged.
Open loop amps and SETs just get quieter over time. And they distort like crazy.
Not my cup of tea thanks.
i want a straight wire with gain. And all the good ol feedback in the mixing desks that made all your Cds accomplish this. Feedback is good. You hear the results every day.
Wary always of subjectivist obfuscation, I offer this :
"warmth" generally means perceptibly distorted
"engagement" translates as "wow I like that track"
Imaging is always accomplished by a flat phase response.
Harold Black invented feedback to maintain accurate gain as the tubes in undersea repeaters aged.
Open loop amps and SETs just get quieter over time. And they distort like crazy.
Not my cup of tea thanks.
i want a straight wire with gain. And all the good ol feedback in the mixing desks that made all your Cds accomplish this. Feedback is good. You hear the results every day.
In spite of controversy about DePalma's competence, his subjective preference for fully symetrical circuit can be confirmed by this John Linsley Hood quote:
"There are difficulties in relying on one's own or on other listeners' ears for quality assessments in audio circuitry. However, it is possible to form opinions on the nature of circuit structures which lead to favourable audience responses, and of these the most readily defined is that of symmetry in the circuit architecture.
Of course, one must accept that true symmetry, as between NPN and PNP devices, or between those of N-channel or P-channel construction, is not really practicable, simply because of mobility of electrons and holes is so dissimilar. Nevertheless, at low frequencies, some measure of mirror-image symmetry is feasible, and this seems sometimes to be preferred by listeners when two otherwise similar circuit structures are compared.
In contemplating this observation, it is tempting to rationalize this preference as a consequence of the sensitivity of the ear to any slew-rate limiting effects, since it can be argued that in a truly symmetrical structure the inevitable stray load capacitances will be driven in both polarity directions and will, in consequence, have betters slewing characteristics than a single-ended driver system". (Electronics and Wireless World, January 1985, 31-34)
"There are difficulties in relying on one's own or on other listeners' ears for quality assessments in audio circuitry. However, it is possible to form opinions on the nature of circuit structures which lead to favourable audience responses, and of these the most readily defined is that of symmetry in the circuit architecture.
Of course, one must accept that true symmetry, as between NPN and PNP devices, or between those of N-channel or P-channel construction, is not really practicable, simply because of mobility of electrons and holes is so dissimilar. Nevertheless, at low frequencies, some measure of mirror-image symmetry is feasible, and this seems sometimes to be preferred by listeners when two otherwise similar circuit structures are compared.
In contemplating this observation, it is tempting to rationalize this preference as a consequence of the sensitivity of the ear to any slew-rate limiting effects, since it can be argued that in a truly symmetrical structure the inevitable stray load capacitances will be driven in both polarity directions and will, in consequence, have betters slewing characteristics than a single-ended driver system". (Electronics and Wireless World, January 1985, 31-34)
Yo cannot measure or 'experience' output impedance unless the amp delivers some power. Your insistence to make a difference in this context between your made-up 'power paradigm' and 'voltage paradigm' is confusing and suggests a limited understanding of the issue.
Also, your continued linking of output impedance and output current or power capability does the same. You can have high Zout and high current capability, or high Zout and low output current capability;you can have low Zout and high current capability, or low Zout and low output current capability . All combinations are possible precisely because Zout and output current or power capability have nothing to do with each other.
I have owned a transconductance amp with a Zout of more than 10 kOhms yet able to deliver 20A RMS - on the other side of the spectrum you have the lowly opamp follower with 0.1 Ohms Zout yet running out of steam above 10mA.
Jan
The effect on loudspeaker response and output impedance is quite obvious, speaker are designed to be driven by voltage, but runs on the current it pulls at various frequencies. When the speaker has a resonance it responds with an impedance rise an thus pull less current here. A sort of self balancing system that in most cases results in a fairly even power response
(big resonances and the corresponding peaks are often too much for the amplifier/speaker system to handle as the balance between applied force (current) and the resonant will power to continue the swinging motion of resonance is too weak)
A slightly negative amplifier output impedance would improve a spekers in room power response. I believe that can be made by taking the feedback between an small power resistor and the load.
(big resonances and the corresponding peaks are often too much for the amplifier/speaker system to handle as the balance between applied force (current) and the resonant will power to continue the swinging motion of resonance is too weak)
A slightly negative amplifier output impedance would improve a spekers in room power response. I believe that can be made by taking the feedback between an small power resistor and the load.
Thank you belatedly and kindly for these comments John.
I found that there was definitely a sweet spot past which too much degeneration started to make things worse again, and also prefer the sound of amps I've tried that use the complementary diff pair input stage. I'm honoured to know I'm in such esteemed company with this 🙂
Curl/Owdeo, why not push this ewen further an have a gain of one heavy feed back OPS and then make the voltage gain totally free from feedback. Would that not reduce/prevent TIM
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Hi All, and my dear friend Hugh 🙂.
I am a devout believer in my favorite form of amplification of a voltage gain stage followed by an open loop buffer to drive a pair of speakers. Of course Negative feedback is somewhat a necessity, though zero loop feedback designs have been done, I tend to prefer this at the preamp level. My thoughts are that negative feedback is not bad at all, even gnfb, but it's application has been critical to these ears. The best use of gnfb bar none to the most natural sound has been a constant level of gnfb within the audible band, which implies open loop should reach at least 10khz. Why have 60db of feedback at 50 hz with 5db at. 20khz?, in that case I've always found 5db across the whole audio band better than this. It takes work to acheive, but the ears and sense of music have always been richly rewarded.
Colin
I am a devout believer in my favorite form of amplification of a voltage gain stage followed by an open loop buffer to drive a pair of speakers. Of course Negative feedback is somewhat a necessity, though zero loop feedback designs have been done, I tend to prefer this at the preamp level. My thoughts are that negative feedback is not bad at all, even gnfb, but it's application has been critical to these ears. The best use of gnfb bar none to the most natural sound has been a constant level of gnfb within the audible band, which implies open loop should reach at least 10khz. Why have 60db of feedback at 50 hz with 5db at. 20khz?, in that case I've always found 5db across the whole audio band better than this. It takes work to acheive, but the ears and sense of music have always been richly rewarded.
Colin
It could be even better (subjectively!) if you could reduce complexity to some 30% of the original. "Less is more" principle works for audio circuits as Mr. Pass may confirm.