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#101 |
diyAudio Member
Join Date: Oct 2003
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For Joachim's circuit in post #99, THD is 0.0016% in Spice.
- Without 4x 370R loading resistor, THD is improved to 0.0012% for lesser voltage swing at input FET drains. - Without the 4 helper BJT, THD is increased to 0.003%. - Without 2x 50k feedback resistor is THD is 0.0021%. So plenty of choices, whether to go for simplicity or the last few dBs THD. We'll stay with the Wilson mirror for now. I think I had a thinking error with Calvin's circuit. I think I get it now about the biasing. My apologies to Calvin. Still, my prejudice remains against exponential devices. But I guess the real test is a listening test. See if I have time to put a proto board together, using 3 separate supplies. Patrick |
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#102 |
diyAudio Member
Join Date: Mar 2009
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Thanks for simulating. I only have simple math in my toolbox. I studied electronics in the 70th where even a pocket calculator was forbidden. I failed my promise by a factor of two. Could it be that noise performance could be compromised without the loading resistors ?
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#103 |
diyAudio Member
Join Date: Oct 2003
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Joachim,
A member of my team did the sim, not me .... ![]() I think it is just simple Spice with perfect resistors, so noise is not taken into account. If you want to know more, please send me a email via the forum. I'll get you in touch with him directly so that you don't have to talk via me. Of course I want to be on the copy list to know what is going on ... ![]() Shall be travelling tomorrow, so no email then. Patrick |
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#104 |
diyAudio Member
Join Date: Oct 2003
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Noise plot of Joachim's circuit.
Upper trace, without load resistors. Lower trace, with load resistors. Joachim is right of course. Noise performance is much better with load resistors. Patrick |
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#105 |
diyAudio Member
Join Date: Mar 2009
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This outcome may surprise some. Adding resistors lowers noise, but thats the way constant current sources and mirrors work.
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#106 |
diyAudio Member
Join Date: May 2005
Location: Denmark
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Euvl ..
could I ask you to post the LTspice circuit...in a zipped folder.. would like to play a little with that and Joachim's RIAA...based on the same Idea... Thanks |
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#107 |
diyAudio Member
Join Date: Jan 2003
Location: Netherlands
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Just for the fun, a(nother) BJT version.
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#108 |
diyAudio Member
Join Date: Oct 2003
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> could I ask you to post the LTspice circuit
You mean you want our asc files ? |
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#109 |
diyAudio Member
Join Date: Oct 2003
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Some more noise simulations for the original SEN & CEN.
Hard to beat a pair of FETs on their own. Patrick |
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#110 |
diyAudio Member
Join Date: May 2005
Location: Denmark
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Yes.. I can see you have the models for the small transistors.. I have already modeled the circuit, but have some trouble with the balance.. would like to see how that changes with your small transistor models...
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