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straylight last won the day on July 22

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Power Diode

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  1. Proving an inferior product seems like it may be very difficult...hey everyone has their own idea of what may be inferior...there is no concensus really. Much easier to prove misrepresentation. I also think they were sold a superior product, but the digiphobes among them will probably never admit it.
  2. Perhaps the lawsuit will serve two purposes: 1) Provide a refund path for customers who are dissatisfied with the product 2) Enable Mo-Fi to continue to make recordings and preserve their craft The judge should throw out the emotional-damage-claim bunk and only award a reasonable penalty as required Other countries have criticized our free society and rule of law, but many in this country also believe that although we live in an imperfect union it is a least better than those who have no such courts or system of laws to settle disputes in an equitable manner.
  3. All good points. Should the penalty of this law suit be so severe as to choke off the source of those delicious sounding recordings...perhaps only a jury can decide that. But there are others out there making good recordings if you look. MoFi is not alone in this endeavor. And if they explain their preservation steps as a necessary digital manipulation then at least they are being honest about their process and the marketing of said process. The only claim in the lawsuit that does not hold water is that the digital conversion that was done for preservation has somehow compromised the dynamic range of these analog ecordings. That's absurd. Even the best Studer recorders of the 60s and 70s had at best 90 db or 95 db of dynamic range. DSD and other modern PCM digital recording formats are on the order of 120 db. So if you use a digital capture format with greater dynamic range than the analog original you DO NOT degrade it, you preserve it. But at this point you can no longer claim your product is still analog...it is not, even if you make an analog LP pressing from it. Back in the day of early CDs they were all labeled definitely with three coded letters like AAD or ADD or DDD to tell you that the 1) source, 2) mixing and 3) mastering were done in either analog or digital domains.
  4. After listening to the posted thread of actual law suit it seems to hit the highlights pretty well. The Mo-Fi response from their president doesn't address the main issue. Every day the analog masters sit in their vaults and collect dust they also degrade. Computer magnetic tape has, over the years, suffered the same exact fate. If you wait long enough the bleed-through from where each of the wound layers touches the inside adjacent layer will also 'print through' and eventually begin to 'pollute' other portions of the tape. That's why you must exercise mag tapes or you will lose them. These master tapes are all going to continue to shed particles for a long time and eventually they will sound like mush. They are turning to dust in the long run and Mo-Fi has known that for a very long time. The Mo-Fi president is right in believing that making noisy analog copies of noisy, aging analog tapes is folly. I agree, he is absolutely right, but this is not about proper archival methods. Its about what people thought they purchased and how that was communicated (or not) to the masses. Although I don't agree with the emotional-damage-claim woo that's stated in this suit, there is much to be said about unjust enrichment of millions of dollars going to corporations that have employed deceptive or misleading advertising.
  5. Agree. Anybody with a little bit of common sense should know that the all-analog days have been over for many years. Technology marches on. Before retirement I spent many years in project management and one of the most important things I learned was not to let wrong or inaccurate assumptions go unchallenged. If they knew this was happening but didn't do anything about it then... its on them. Nothing kills reputations, team moral or multi-million dollar projects faster than false assumptions. I've bought and traded a lot of Mo-Fi over the years. They have done some incredible recordings in their time but seeing their reputation waver like this is just sad.
  6. @Ar9Jim and Viet, Fascinating! Thank you for follow up on the question, much appreciated. Whether or not there really is any more detail in the music or not the positive phased 2nd harmonic (relative to the main signal) when present persuades the human ear into thinking that the music is closer and more detailed whereas the negative phased 2nd harmonic lets the listen believe its embedded in a deeper soundstage farther away from the listener. Wow, that's amazing. The phase difference makes some sense because I think a doppler effect tricks the human ear in a very similar way - perceiving either rising tones or decreasing tones, depending on the direction of movement of the sound source relative to the listener. But we all know the tone pitch never changes...it is only the ear that is tricked into thinking there is a change. It's a trick. As Bob was once famously quoted as saying, "Its all trickery" This concept also seems to relate directly to my perception/experience of hearing different levels of soundstage depth on the different speaker taps (2, 8 and 16 ohm) of the Rootbeer 180 mono amps. I am aware that each tap results in measurably different distortion levels and harmonics on each tap. If this also results in a substantially different amount of phase shift (plus or minus 180 degrees) for the 2nd order harmonic than this could explain it! I can measure the different levels of 2nd order on each impedance tap but determining the phase shift would be something that I would not know how to detect with my existing equipment. Nonetheless this is really interesting and goes beyond just circuit topology. It begins to approach the borders of the ear/brain interface and how it all works together with electronic circuits to actually perceive sound.
  7. The scope plots below should help members to visualize and understand what the harmonic distortion products are and how they actually look on an oscilloscope. We are showing a test signal of 50 Hz (bass frequency). and so the higher order harmonic distortions are easily calculated as follows: H2 = 50 x 2 = 100 Hz H3 = 50 x 3 = 150 Hz H4 = 50 x 4 = 200 Hz H5 = 50 x 5 = 250 Hz H6 = 50 x 6 = 300 Hz The first plot is of my HP 3580A Spectrum Analyzer shows a clean 50 Hz peak without any measurable distortion. Notice how clean it looks to right of the scope display. A perfect amplifier without any distortion would look like this when reproducing a 50 Hz wave. Of course this is just the test signal on the scope…no amplifier would look this clean in real life. The second plot shows my Acrosound-330 EL-34 project amps that Bob helped me with at 1 watt into an 8 ohm load. We were also working on how much negative feedback to feed the circuit to clean up the sound. This plot shows the amp with -6db of negative feedback at 1 watt into 8 ohm load. This is the feedback level I finally decided to use in the circuit. Notice the evenly spaced peaks AFTER the first 50 Hz fundamental tone peak on the left…each successive peak is a higher order harmonic going from left to right on the display. The small peaks in between the first few harmonics are probably power supply related and therefore are not associated with the EL-34 output tube distortion tones produced. Notice how the distortion products get progressively smaller as you go to the right. This is a natural state of how tubes distort in many circuit topologies. The more offensive sounding fifth, sixth and seventh harmonics (H5 H6 H7) can be seen in the second band of peaks above 250 Hz about mid-scope. According to research by consultants in postings above, H5, H6 and H7 and higher order harmonic peaks are much more objectionable to the human ear and should be suppressed by the amplification circuit in order to get a more pleasing musical sound from the amp. By contract H2 and H3 can be present in much higher proportions without sounding harsh or offensive to the listener.
  8. Sounds like a solid approach...and it should actually work for most designs too...vacuum tube, solid state even Mosfet or whatever. The fifth, sixth, and higher order harmonics are the 'meanies' and should be avoided at all costs for pleasing, musical sound. I would call this "combing the distortions"...just like straightening your hair to get kinks out!
  9. Degree designations of -70 or -90 usually means phase shift or phase distortion produced within the circuit topology itself. You are correct to point out that it is not explained but if it is phase differences (which are a type of distortion too) I have always been told that no phase shift is best (0 degrees) situation since you always want accurate phase for accurate sound and dynamics. But the designers may know something we don't and phase anomalies may be perceived as a difference in depth of soundstage. Never heard this before, so yes very intriguing, unless we are interpreting this incorrectly? @Ar9Jim....can you comment about what the -70 degrees for 2nd order harmonic is? Is this phase shift or something else they are referring to?
  10. @Ar9Jim This is quite a bit of a download of information on the Crimson but should be welcomed by all since it gives meaningful information about circuit topology, distortion levels and real-world performance that old-school static specifications cannot and do not address. I have a few questions and some comments. Q: Is the spec of 80 watts into 8 ohms an average wattage for all frequencies from 20 Hz to 20kHz or is it a simple 1 KHz frequency power test? Not stated. Comment: The use of stated percentages of harmonic distortions is very welcome as it drives home some new ideas of the type of distortions that we perceive. Amp designer Nelson Pass (of Threshold fame) also discovered that H2,H3,H4 are not all perceived the same as far as how objectionable we perceived them. His Threshold amplifier designs, although bi-fet transistor in nature, also favored the lower harmonics like H2, H3 and he found that these could be tolerated in much higher amounts. He also obtained his hand selected bi-fets directly from Motorola based on matching up the ones with similar distortion characteristics. The legendary designer John Curl also plays very close attention to the distortion-quality (harmonic content) of the parts he puts into his amp designs too. As the H2, H3 and H4 approach -80 db levels, however, it is rather doubtful that they would be audible to the human ear to make much of a difference. So the much lower db level harmonics are probably not contributing much to the perceived sound. The other comment I'd like to make is that most tube amplifiers are somewhat deficient at delivering power at the frequency extremes. My EL-34 Acrosound amps, Tube Dynaco amps of the 50s and many modern tubes designs all lose power at the bass end and at high frequencies. A simple power test at the frequency extremes (for example using an Audio Precision tester at low frequency sweep) will show a pronounced drop in power between 20 Hz and 100 Hz and also a drop at the high frequency extremes (15kHz - 20kHz). The fact that the Crimson has only -2.7db drop at 20kHz in amazingly good performance for any tube amplifier of any power level to achieve. Also the use of Fast Fourier transform for your tests is a great idea as the amplifiers performance can change significantly during the several second scan time necessary for frequency swept testing methods. Thanks for posting this great information. Its food for thought about amp design that you don't normally see shared.
  11. @jjptkd There is one correction that I should make on the above. Some notes were taken on the 180s when I first installed them and after checking my written notes I realized that it was not the bias but the 2 ohm, 8 ohm or 16 ohm taps that made THE BIGGEST difference in the depth of field. At 2 ohms the soundstage was very wide but not that deep. At 16 ohm the soudstage had inverted and had great depth but was not as wide. This was an interesting result and is what I shared with Bob. The soundstage geometry was changed by which impedance tap was used for the speakers. Just wanted to make that correction. Although I did change the bias it did not seem to be associated with any soundstage characteristics.
  12. There are a few tube circuit designs that will reduce even order harmonics but I don't think they can easily be totally eliminated because this is the native state for tubes. They prefer to distort at even order harmonics. The late Bascom King had a design that significantly reduces even order harmonics. My guess is that it may give a more analytical type presentation, more like a Mosfet than a tube but not as analytical as some transistors sound. Depth of image or depth of soundstage may, in fact, be a bit more complex and actaully be a result of several different parameters. For example tube brands, bias setting and circuit topology may ALL play a part. Bob told me how to change the bias voltage on the 180 mono amps and it also shortened the depth of the soundstage....Bob was fascinated by this result as it was quite surprising to both of us. This was using the 180s with Apogee ribbon speakers which are pretty good at depth of field presentation. However not everyone may perceive this depth of soundstage the same way.
  13. I've listened to both transistor and tube amps over the years It has always been my perception that the distortions produced by tubes are primarily even order harmonics. In the same proportion vacuum tube distortions seem to be much less objectionable than the odd order harmonics present in most transistor designs. That is why tube amps with one percent distortion at rated power often sound much better than transistor amps with .1 % distortion. Agree with what's been said by Ar9Jim and Bob. Delivering enough power at the frequency extremes is more of a problem than distortion is for tube amps designs. The 180 amps I have sound better on the less negative feedback setting than on the higher feedback setting even though technically you will have slightly more distortion. Less complex tube circuits tend to sound better and are more stable than complex designs...there is less to go wrong when driving real-world speaker loads.
  14. In 2009 I acquired my Rootbeer 180 mono amps from an auction that Bob was running on ebay. After that we had a number of lengthy phone calls together and I happen to mention that I was also at that time building a pair of EL-34 mono amps and that I had this weird anomaly going on when measuring the output from the amp. Each amp had an Acro-330 output transformer mounted, one of the best sounding transformers by Herb Keros and the famed David Halfer. I wanted this build to be perfect but it was not. Bob asked me over the phone what the anomaly was exactly and I described that with no input connected I was measuring a weird 20 kHz oscillation on the scope. When I shorted the RCA inputs the oscillation would decrease but never go away. He said hey, why don't you send a few pics of the inside and I'll call you back shortly. Eventually Bob reviewed my schematics in detail and spent time on the phone with me in front of the scope making great suggetions to trouble shoot this issue. Finally he called and said you need a 'star ground' and then all your problems will likely vanish. Picture of Acrosound-330 EL-34v Mono Amp build project that Bob helped me with... In soldering the amp I had gotten lazy and had several ground points that were not needed or recommended and Bob insisted that I use only a single ground "star connection" for all ground paths. After eliminating the serval grounds and consolidating all of then into one I called Bob back and let him know that the problem has disappeared. No more oscillations and the output was extremely quiet and noise-free form the point on. Bob helped me to understand that my amplifier circuit with multiple grounds was acting as an open loop antenna and causing the oscillation anomaly. I told him that my mistake seemed really foolish but his response was immediate....don't feel bad we all make design mistakes....even I've made these kinds of mistakes at one time or another. I still have the amps and although they don't quite sound like the Rootbeer 180 monos I still am very proud of building them and very thankful that Bob would take time and effort to give me the guidance necessary to make that project the best it could be. Thanks Bob!
  15. So much can happen in less than a millisecond inside an amplifier when driving real world speaker loads that unless you measuring for it and look for it while it is occurring the conventional standard measurement (like static distortion vs. freq. or wattage) is all but meaningless. This is were Bob gets it. He is aware of things happening in real time with real speaker loads and uses unconventional means to to monitor and correct these anomalies. Also his knowledge of human perception and how we actually hear things I think also plays a key role in his grasp and mastery of what may go wrong within amplification circuity and how we perceive it. His approach to research is always novel, therefore his designs are too.
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