John Curl's Blowtorch preamplifier part II - Page 3584 - diyAudio
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Old 25th February 2013, 04:03 PM   #35831
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Yes, we're busy staring at the ground and drooling.
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Old 25th February 2013, 04:04 PM   #35832
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Kindhornman, it is the LOW SLEW RATE of the Phase Linear power amp that made it show distortion. The same for the Audio Research, and while not shown, would be the same for a Crown power amp of the time. The test signal TIM(100) is one of the most stringent test signals ever devised for audio, and in many cases, it might be somewhat more than really needed for many practical situations, but it is still a useful tool to show TIM.
Your question about the Blowtorch shows a complete lack of understanding as to what the CTC Blowtorch is or what would make it distort. It would be the same for the Hirata test. You would not measure anything useful, BECAUSE the Blowtorch is UN-SLEWRATE-ABLE, and you would only get risetime limiting.
I'm sorry guys, but think before you ask.
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Old 25th February 2013, 04:19 PM   #35833
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As I said, it is difficult to get into a really useful discussion here, because we have two sorts of 'critics'. People much more educated than most audio designers, who think that they know 'everything' already and are impatient with people like me, when I try to go back to basics, in order to get people not as familiar with audio design to get some added understanding of some audio problem.
On the other hand, I have a number of 'critics' who are essentially 'roadies' with a lot of practical knowledge with audio equipment, but don't really know how they operate at the design level. Both groups have strong personal opinions: One individual might insist that 2V/us is OK for a preamp, another might insist that 1000V/us is necessary for best sound quality. Why is this discrepancy so large? It appears to be because neither individual fundamentally understands the nature of slew rate limiting. If both of them read the Solomon article that I put forth relatively recently, there would be no 'criticism' especially of what I design. But 'you can bring a horse to water, but you can't make him drink'. And so it goes... '-)

Last edited by john curl; 25th February 2013 at 04:37 PM.
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Old 25th February 2013, 04:33 PM   #35834
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Kindhornman, let me follow up that I too have used Phase Linear power amps. I know both designers as well. I have heard them in use with the Pink Floyd, in 1972, where Kelsey and Morris (London) had racks of them, and with a California based PA used it for the woofer-midrange amp in their design, with some success. And finally, Mark Levinson, in 1973 had a Phase Linear 700 driving a pair of Dayton-Wright electrostatic speakers, with some success, except that his mother complained that it gave her a headache. Mark had used tubes previously, so she knew the difference. In any case, I pretty much know the 'goods' and the 'bads' of the Phase Linear series, much like you do.
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Old 25th February 2013, 04:37 PM   #35835
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As I said, it is difficult to get into a really useful discussion here, because we have two sorts of 'critics'.
Are both wrong simply because they disagree with you?
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Old 25th February 2013, 04:40 PM   #35836
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Pano, people have a perfect right to disagree with me.
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Old 25th February 2013, 05:04 PM   #35837
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John,
Yes they were the Phase Linear 700 amplifiers. If I remember correctly I think that we were one of the very first to use some of these amplifiers at the time and I don't remember the designer's name but think that he was involved with what we were doing somehow. The same with the Spectra Sonics at the time.

I know that your blowtorch is a preamplifier but am wondering why you would not test a pre for the same types of distortion as a power amplifier? And I do not follow why even a super fast slew rate would make this test a non issue?
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Old 25th February 2013, 05:05 PM   #35838
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It is amazing how quiet it is when we put up work that we did over 1/3 century ago. '-)
I suspect this is because the technical level of many of my critics is not quite up to it.
BS!

It was completely by chance that I saw this message, I don't follow this thread anymore, this (and other threads that could be interesting) is so full of meaningless nonsense that I have given up long ago.

I'll ask Jason to delete my account.

Have fun.

Cheers
Stein
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Old 25th February 2013, 05:07 PM   #35839
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John,
Yes they were the Phase Linear 700 amplifiers. If I remember correctly I think that we were one of the very first to use some of these amplifiers at the time and I don't remember the designer's name...
Reputedly, Bob Carver. They're still a cult item, fetch lots of money on resale if you can find one that hasn't blown up.
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Old 25th February 2013, 05:18 PM   #35840
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Sy,
Thank you for that information, it was so long ago. It probably didn't help the type of speakers we were using at the time, Altec, JBL and even some old RCA W-bass bins. Another factor was that many times we were doing shows outdoors and the power to drive the system was sometimes portable generators driving the system! I would supposed we put the equipment under the toughest load requirements and if it was going to fail it was going to be under these types of conditions.
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