LarryC Posted September 13, 2020 Share Posted September 13, 2020 Very interesting, Backfire! What db output would be generated by a couple of watts into Class A? I don't believe any schematics are available for a Joule OTL, which makes them very difficult to repair. I use Rich Brckich of Signature Sound in Liverpool, NY, the one who worked with Jud for many years. Yes, they do sound superb. -- Larry Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted September 13, 2020 Share Posted September 13, 2020 47 minutes ago, Backfire said: All of which is a long-winded way of saying that I think it is almost certainly running in class AB, and not class A. At low powers, up to a couple of watts, it will effectively be running in class A, but transitioning to AB at higher powers. Nothing at all wrong with that, though! It's just a little bit naughty, I think, when manufacturers make overstated claims about class A operation. (Joule-Electra would not be the only one!) Class AB refers to a specific set of operating conditions which are usually somewhere between class A and class B. So unless the amp has provision to change that, it is running in AB at idle through its maximum power output. It combines the advantages of both classes while minimizing their respective disadvantages. Maynard Quote Link to comment Share on other sites More sharing options...
LarryC Posted September 13, 2020 Share Posted September 13, 2020 Very interesting and good to hear. No, no provision to change the class. What wattage output at 8 ohms do you estimate for mine? What do you think might be the sound difference between A's and mine? - Larry Quote Link to comment Share on other sites More sharing options...
Backfire Posted September 13, 2020 Share Posted September 13, 2020 22 minutes ago, tube fanatic said: Class AB refers to a specific set of operating conditions which are usually somewhere between class A and class B. So unless the amp has provision to change that, it is running in AB at idle through its maximum power output. It combines the advantages of both classes while minimizing their respective disadvantages. Maynard Yes, I was speaking a bit loosely. People sometimes speak of a class AB amplifier as "operating in class A up to X watts," where X is the maximum power it can put out before the tubes essentially stop conducting at the bottom half of the audio cycle. It can give a useful characterisation of how much power it takes before the tubes go into cutoff. Quote Link to comment Share on other sites More sharing options...
Coytee Posted September 16, 2020 Author Share Posted September 16, 2020 On 9/14/2020 at 1:37 PM, Jeffrey D. Medwin said: What caused you to sell your four SE-OTLS ?? Power or more accurately, lack of. If they would have had say, 30 or more watts, I'd kept them forever. As it is/was, they just couldn't keep up with how I turned things up (especially while working in other parts of house when system was pounding..... this was on Khorns) Edited to add: I only had two amps, not four. Quote Link to comment Share on other sites More sharing options...
babadono Posted September 16, 2020 Share Posted September 16, 2020 What is the cathode bypass capacitor in the circuit for? What is it therefore? Quote Link to comment Share on other sites More sharing options...
Coytee Posted September 16, 2020 Author Share Posted September 16, 2020 All this time I thought it was my wife giving me NFB.... Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted September 16, 2020 Share Posted September 16, 2020 4 minutes ago, Coytee said: All this time I thought it was my wife giving me NFB.... For you Richard. https://hometheaterhifi.com/editorial/negative-feedback-fact-and-fantasy/ Quote Link to comment Share on other sites More sharing options...
Moderators Travis In Austin Posted September 16, 2020 Moderators Share Posted September 16, 2020 1 hour ago, CECAA850 said: For you Richard. https://hometheaterhifi.com/editorial/negative-feedback-fact-and-fantasy/ Haven't read yet, I will. @mikebse2a3 is very knowledgeable on this subject and messed around with it a lot, he has a clear preference (cannot recall what), but to the point that if someone can tell him what their preference is he can advise/warn a particular amp may not be to their likeing because of that one parameter alone. I assume that article is going to tell me it's a preference thing, not a signal compromise. I'm going to also guess the fantasy part come is because of how things are recorded, and so you are fooling yourself if you think there is some advantage to having, or not having it, for sound reproduction at home. Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted September 16, 2020 Share Posted September 16, 2020 1 minute ago, dwilawyer said: I assume that article is going to tell me it's a preference thing Then we'll wait for you to read it. It's informative and not that long. They didn't use too many big words that I didn't understand. Quote Link to comment Share on other sites More sharing options...
babadono Posted September 16, 2020 Share Posted September 16, 2020 I'm an electronics tech with 40+ years manufacturing/ test engineering experience.(oh and I enjoy Klipsch horn loaded speakers). The way I understand it is All AMPLIFIERS have some degenerative element(s) otherwise they would have too much gain. I know with simple tube amplifiers it is possible to control the gain with cathode or grid degeneration and no output to input global feedback. But with high gain operational amplifiers this is not possible. The only available method to control the amplifier is NFB. Without it the only circuits you could make would be comparators or oscillators. Quote Link to comment Share on other sites More sharing options...
Moderators Travis In Austin Posted September 17, 2020 Moderators Share Posted September 17, 2020 4 hours ago, CECAA850 said: Then we'll wait for you to read it. It's informative and not that long. They didn't use too many big words that I didn't understand. Great article, I was totally wrong on what I thought it would say. Explains NFB very well, and also problems without if not compensated for correctly. Quote Link to comment Share on other sites More sharing options...
mikebse2a3 Posted September 17, 2020 Share Posted September 17, 2020 7 hours ago, babadono said: What is the cathode bypass capacitor in the circuit for? What is it therefore? It affects gain, frequency response, distortion reduces degenerative/local negative feedback. 1 Quote Link to comment Share on other sites More sharing options...
mikebse2a3 Posted September 17, 2020 Share Posted September 17, 2020 This might help some to understand how the cathode bypass capacitor affects performance of the gain stage whether in a preamp or amplifier output stage. 1 Quote Link to comment Share on other sites More sharing options...
mikebse2a3 Posted September 17, 2020 Share Posted September 17, 2020 Very good papers by Nelson Pass about feedback and the complexity of amplifier design choices that some may like to read. Especially about degenerated feedback use and non-use. art_dist_fdbk.pdf art_the_square_law.pdf art_se_classa.pdf miketn 1 Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted September 17, 2020 Share Posted September 17, 2020 There are 2 ways to reduce distortion in SEP amps. One is to use it at a fraction of its maximum output power, and the other is to use nfb. I prefer the latter (as voltage fb) as it reduces the typically high output impedance as well as increasing the bandwidth. If applied within reason, it does not ruin the resultant sound in my experience. In fact, it can provide a very triode like experience in some systems. Maynard Quote Link to comment Share on other sites More sharing options...
mikebse2a3 Posted September 18, 2020 Share Posted September 18, 2020 On 9/16/2020 at 10:54 PM, Jeffrey D. Medwin said: How do you like to usually bypass a 2A3's Rk ?? usually a film type. I also like to use fixed bias to eliminate the need for the RK/Bypass Cap. Quote Link to comment Share on other sites More sharing options...
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