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Condemnation Without Examination Is Prejudice, Or Words of Wisdom, by John Curl

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Condemnation Without Examination Is Prejudice, Or Words of Wisdom, by John Curl Condemnation without Examination is Prejudice, or Words of Wisdom, by John Curl May 2006 John Curl at CES 2001 John Curl at CES 2002. John Curl at CES 2006 2 “I am always giving stuff away for free. It is not in my best interest, and I am continually reminded of this by my associates. It is so easy! I already know it. Yet, when someone tries to patent your suggestion, without your knowledge, trust me, it is a wakeup call.” “By the way, I only developed some of the topologies that you folks use, but I am familiar with all of them. Who do you think first developed most of the circuits that you make here on DIY audio? Do you have any idea?” J. Curl 1 About myself I am an audio design consultant, have been for more than 30 years, and I design several new or improved products every year. I KNOW HOW to develop the topology and get the basic performance from audio circuits. However, this is NOT enough, IF I want to make something other than a mid-fi product. I have proven this to myself by allowing others, in the past, to make the 'minor decisions' such as connectors, layout, wiring, etc and have paid the price of poor sales, and a diminishment of my design reputation. I could NOT MEASURE any problems, with previous decisions, just lost sales and less enthusiastic reviews. I did some of my best work when I worked at AMPEX, as well. What a place! A wonderful technical library. I virtually zeroxed it for the audio info. Still have many obscure zeroxes going back to the '30's. I worked in Instrumentation, Audio, and Research/video, when I was there. We even had a digital audio recorder: 12 bits/50kHz clock. I independently invented the complementary differential input stage and learned low noise design while working there. In 1969, I developed a complementary differential, balanced bridge, 2000W power amp with current controlled output (high Z) for a motor drive application, while working in the Research Dept. Those were the days! I worked at Ampex in the years 1967-1969. I did not work with Watkinson. 33 years ago, I started working with the Grateful Dead. I learned what worked and what didn't work by testing them in live music performance. I tried all kinds of things, transformers, open loop circuits, quality IC's, all kinds of stuff. I learned how to make successful audio designs, that stand up today, sonically, before I ever worked with Mark Levinson. Mark was a good craftsman, but I had to show him the direction to go, which I had previously tested with live music. I am in the business of serving the audio public. The only 'entertainment' that I provide is being laughed at by others who are not as successful in making audio products. I usually 3 get along fine with my competitors, who are on this website, as we respect each other, even if we do not agree on every detail. What I try to do is to make circuits that give people extra pleasure, much like homemade ice cream or a good tasting wine, compared to the cheapest variety of either. Midfi gives you the 'cost effective' store bought variety. I was always told that: "Contempt, without examination, is PREJUDICE" I believe that not trying something, not attempting to make actual measurements, and showing contempt of anything outside ones own paradigm is effectively, prejudice 2 Psychoacoustics Human hearing In fact, someone could make a sine-square comparison at 20KHz or even 10KHz, and 'prove' that it is inaudible. Still, I made a test about 20 years ago with three people. I used a Pioneer ribbon tweeter with a measured response of more than 45KHz, with an Electrocompaniet, Otala based power amp, and a function generator. As I remember, I set the function generator with a 5KHz square wave and deliberately limited the risetime to 3.5us, which is about a 100K response, with a quality film polystyrene cap to ground. The function generator had a buffered 50 ohm output. Then, during the test, I added another polystyrene cap in parallel to ground to change the effective risetime to 10us, or 35KHz. We all could hear the difference. It was fairly easy to, as well. Why? I don't know, but we seem to be sensitive to rate-of-change, more than actual frequency response. I did the best that I could to keep everything in check, BUT there are always tiny differences. Harmonic perception I don't know of any definitive info that demands a series of harmonics in a certain way, EXCEPT that higher order odd components are very bad. This includes 7th,9th, etc. However, I agree with the right to state the opinion that the large 2nd harmonics makes a good sounding amp. In earlier years, I used to go all out and manually balance out any residual even order harmonics, in order to get the distortion as low as possible. Today, I leave a little to a lot of even order harmonics in the final output, because this hypothesis has some merit. Let me help with this even-odd topic: 'Science and Music' Sir James Jeans 1937 p. 87 This book is available through Dover. "... The seventh harmonic, however, introduces an element of discord; if the fundamental note is c', its pitch is approximately b (flat) , which forms a dissonace with c. The same is true of the ninth, eleventh, thirteenth, and all higher ODD-numbered harmonics; these add dissonance as well as shrillness to the fundamental tone, and so introduce a roughness or harshness into the composite sound. The resultant quality of tone is often described as METALLIC" 4 Well folks what do you think that this means? This is not the first time that I have quoted this passage over the years, but it just gets ignored by those who would not learn from it. Still, I hope that you can understand that higher order ODD harmonics are sonically problematic. Even harmonics, if extended beyond the 10th or so, might also be a problem as well, but they are difficult to generate in any significant amounts to be very important. It can be debated whether 2'nd harmonic is really necessary to make good sounding audio reproduction. Analog tape, for example, has virtually no 2'nd harmonic distortion, just 3rd and sometimes 5th harmonic, yet can be very pleasant to listen to, without adding 2'nd harmonic to the mix. Transistor sound First of all, 3'rd harmonic is actually almost as acceptable as 2'nd harmonic. How do we know? Because 3'rd harmonic is the only distortion normally measurable on analog magnetic tape, and its value is usually between .1% and 10% depending on output level. How is it that we can, or could listen to analog tapes without crying out in pain? It is the HIGHER ORDER ODD HARMONICS that are the big problem. For example, 7th and 9th harmonic. 8th harmonic should be OK, within reason. Transistors generate much more higher order distortion than do tubes. This is because of the curvature of their transfer function, due to very nonlinear Gm. Tubes also have some nonlinearity in gain, but they work on a different principle and change less over current, and usually have less distortion, and it will be of lower order in general. There is a big difference between amplifier bandwidth and high frequency amplifier performance (slew rate, non-linear capacitance, xover distortion, etc). Amplifier bandwidth is usually determined by the amount of negative feedback available. With tubes, this is usually limited by the LOW FREQUENCY oscillation called 'motorboating', not just by high frequency techniques. This usually limits the max feedback in the tube amps to about 20dB. With IC's and discrete power amps, you can have 80+ dB of feedback, because you can direct couple the stages and have no low frequency problems. Also, you can avoid transformers in the output stage. This gives you bandwidth, but not necessarily better performance at high frequencies. When you put RF into a tube amp, you should just get a rolloff in level, without slew rate limiting. However, with a solid state power amp, you will usually get slew rate limiting somewhere, or else you have deliberately rolled off the high frequencies at the input. This is an important difference between normal tube designs, and NORMAL solid state designs I have found that simple is usually better, unless complication can make a better throughpath. Sometimes it does, sometimes it doesn't. Generally, I personally would avoid the complication for my own audio designs. 5 Distortion compensation Asymmetric distortion, that is normally spoken of as even order, WILL CANCEL, if you mix it with an inverted signal of the same magnitude. This is normally called push-pull design. All active components normally create lots of even order distortion, because the voltage gain of all individual active components normally increases with increasing current. Analog magnetic tape creates [compressive] odd order distortion (S-curve), because away from 0 level, the output loses [gain] in both directions. This cannot be fixed by push-pull operation. However, you can create a different form of 3'rd harmonic [expansive] or inverted S curve from the input signal, and mixing it with the compressive signal distortion, will cancel it out. This is rarely done, because often, the residue created by the process has even more higher order distortion, which is MUCH worse sounding than third harmonic, in almost any amount.
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