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Started by Koreth, February 09, 2010, 04:16:59 AM
Quote from: Joe on February 11, 2010, 09:24:24 PMPushed output transformers are definately part of the "tube sound". This really shows up in professional tube amplifiers. The SVT Classic comes to mind, as well as a dimed JCM800. Raising the volume to 10 brings out a monster that wasn't there on 3.Just some random thoughts...
QuoteIt's good to find all this information. Today I've been reading the paper of Dimitri Danyuk "On triode Emulation", doing some math and trying to get the same graphics shown on the paper. (here is a link to the paper). I don't understand the last part, when Dimitri differentiates the double logarithm if the normaliced transfer function in order to obtain the exponent.The paper talks about using a resistance on the Source of the FET as a negative feedback in order to change the transfer function from a power 2 to something very similar to a power 1.5 . Basically, he tries to find the Rs that gets closer to that power 1.5 . He finds that the best match is Rs= 0.83*Vp/Idss . Well, I run some plots in matlab and I get that the best match in order to minimize the difference is Rs = 0.64* Vp/Idss as show on this figure: ....
Quote from: rowdy_riemer on February 12, 2010, 06:34:36 PMThis sounds like the theory behind the Fetzer Valve article on runoffgroove.com.I might play with the Fetzer Valve design using your figures for calculating Rs.
Quote from: rowdy_riemer on February 12, 2010, 06:34:36 PM BTW, JFETs are more like triodes than Enhancement MOSFET's, but not more triode like than depletion mode MOSFETs, which can be pushed into enhancement mode.
Quote from: Koreth on February 12, 2010, 02:58:55 PM I know Teemu's book talks about some early SS designs that employed transformers, but that is largely unnecessary know, since SS devices have such an incredibly low output impedance. The impedance matching function an transformer serves in a valve design isn't needed to drive the speakers in a SS design. I wonder if one could work some transformer magic with an appropriately built 1:1 transformer between the output device(s) and the speaker. Another thing to add to the (growing ever longer) list of things to research and experiment with, I guess.
QuoteMy guess,,To even come close to approxamating a valve design output implies that you need to run the OT off the Collector/Drain,, not the emitter/Source.