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straylight

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straylight last won the day on March 1 2023

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  1. Hi Ed, Kirk and Russ and spouses planning to attend (cabin 11). Called Chelsea for reservation dates but she was out of the office today. Will update when I hear back from her.
  2. Grace Potter and Joe Satriani 'kill' 'Cortez the Killer'...
  3. Hi Ed, Russ and Kirk (and wives) plan to stay in cabin 11 and really look forward to seeing everyone again for CF 2023. We all had a blast last year and it was really great to meet everyone. We will most likely stay for most if not all of the scheduled dates but will let you know if that changes.
  4. @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.
  5. 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.
  6. 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!
  7. 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?
  8. @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.
  9. @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.
  10. 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.
  11. 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.
  12. 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.
  13. Another important innovation of Bob's that turned out to be a very significant step forward in modern vacuum tube amplifier design is the incorporation of the 6AL5 tube in the circuit or the 'DC restorer' as Bob referred to it at the time of invention. This tube is found in all his 180 vacuum tube amps and includes even the higher power Cherry and Black vacuum tube amp versions. I went back to the original auction page he used when he held the amp auctions on ebay (circa 2008-2009) and in Bob's own words here is how he describes the function of this innovative circuit, which keeps the grids of the KT-88 power tubes from going into non-linear operation and restores stability during dynamic music passages. The end result is much cleaner sound even at high volume levels : "Every vacuum tube amp in the world suffers from shifting DC operating points and this unfortunately has remained a functional limitation and maddening sore point for amplifiers designers ever since the very beginning of vacuum tubes. Consequently I had to invent a DC restorer circuit using an 6AL5 / 5726 tube; it eliminates every last vestige of DC shift, while simultaneously reducing distortion three-fold and vacuum tube idle power by the same." Whoever writes his book I hope they include this picture of Bob. Although Bob is a very humble individual I think he should be recognized for his many outstanding accomplishments that have changed the direction of audio design in the USA and around the world! If there can be an embodiment of the "humble maverick" I think Bob is it...
  14. There are so many examples of Bob's maverick designs that it is hard to believe that anyone could be in any doubt about his innovations. I have been fortunate enough to have owned a few really excellent examples of Bob's work and each of these examples are designs with truly exceptional abilities and in many ways each pushes the limits of conventional design by a wide margin. When I bought my Rootbeer 180s from Bob over ten years ago he told me that the idle current on the KT-88s was so low that the tubes would last for decades. I was a bit skeptical at first but that was in 2009 and now, in 2022, after 13 years of operation I have never had to replace a single power tube and both mono amps continue to operate superbly on the same tubes. Bob has been true to his word! The other example I would like to share involves his CARVER VACUUM TUBE REFERENCE Model-1 Preamp. I have owned a turntable for many years that has an extremely low-output phono cartridge mounted on it. We are talking about .1 to .2 mv output. This is the Ortofon MC2000 phono cartridge from the 1980s. It was an excellent performer and was J Gordon Holt's (editor of Stereophile magazine) favorite cartridge back in the day. Well I was never able to use it with ANY preamp on the market because any preamp I tried would either have too low of gain or would have too much hum in the output. Never got it to work with anything. I recently got it out to see if it would work with Bob's VACCUM TUBE REFERENCE preamp and I was surprised and very amazed with how well it sounded and also the fact that I could not hear ANY hum from the output even at full volume! Here is a picture of the perfect match up of that SOTA turntable, Souther linear arm with the very finicky Ortofon MC2000 cartridge. Now, after many years of frustration, I can actually put this excellent cartridge to work. These are but two examples and I'm sure members have many more stories to tell about Bob innovations. Although I have talked with Bob over the phone many times I have never met him in person....but I am really looking forward to finally meeting him at CARVERFEST this year. Have to agree with Ar9Jim...CARVER designs are truly exceptional!
  15. Warren Haynes - backs up band with "killer" lead
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