RC filter between impedance of the feedback and parasitic capacitance of the emitter that receive feedback voltage (or current) and its phases consequences when you subtract feedback signal from original one..
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Is it better or worse when that capacitance is voltage modulated than when the cob of a VFA feedback transistor is..? My initial feeling with CFA is that they must be good as you take a device capacitance out ,and thus reduce phase shift of the feedback signal.
But as you also voltage modulate the feedback node it's not really removed just changed.
Then this is maybe not even close to what simulations show, only some realty work will show.
But as you also voltage modulate the feedback node it's not really removed just changed.
Then this is maybe not even close to what simulations show, only some realty work will show.
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The law is the same. But in a LTP, we need (not to loose benefits of the symetry) to have feedback impedance equal to the one of the signal input, while we don't care to make feedback impedance as low as we want in a CFA, rejecting the pole far out of the band.
A second point is the base/emitter junctions of the two input transistors in a LTP have to deal with the full level of the signals (input and feedback) while it is only their difference in a CFA. Reason of the 'current on demand' or 'expansive' behavior of the CFAs.
Makes sende, yet simulation show quite a difference in how multi tone signals are handled, I still believe it's because the emitters are voltage modulated at the feedback node, where VFA only sees current from the device IV. Understanding mixed mode is far more complex than dealing with a current difference.
MiiB, could-you provide the two schematics you used for your simulations ? I stay surprised by your results.
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I wil send them to you, but it will take a few weeks as I am traveling and don't have acces to my work files. I too was suprised, but as earlier said my investigations came after not getting the results I expected from my CFAs. I actually built three different CFA before trying a VFA IPS in the same amplifier.
Not exactly. It is exactly the same than for a VFA.
www.esperado.fr - VSSA with Diamond input and DC servo
First schematic: the R36/R6 or R40/R15 bridge. (for AC, because C6 & C4)
Second schematic (Diamond) : R12/R6.
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i just want you to know that we are numerous to be shocked by what happened to the people of Greece and its dignity. I cannot enter in political comments, here, but, really, something need to be changed in the way the all world is turning since decades.Now we can buy nothing outside the Greece:
All projects stop
Esperado +1
Kindhornman yes we can still receive packages but we can't pay with PayPal not using credit cards outside of the Greece.
Evan, Thanks.....for another time.
Thank you all guys!
Continue on Symetri IPS.
I have only one par of mosfets for now (on order a few pairs), double bootstrapped mosfet OPS swings nicely nearly to rail.
No changes at all made at the IPS board (same as for BJT version). Looks stable on the scope. I will do some more tests next few days after I will get more parts.
Basicly very nice IPS board from bimo factory. Sounds nice, clips nice, speed is nice and looks nice
Regards
I have only one par of mosfets for now (on order a few pairs), double bootstrapped mosfet OPS swings nicely nearly to rail.
No changes at all made at the IPS board (same as for BJT version). Looks stable on the scope. I will do some more tests next few days after I will get more parts.
Basicly very nice IPS board from bimo factory. Sounds nice, clips nice, speed is nice and looks nice
Regards
Attachments
I'm not Borys, but they appear to be screen shots from a Rigol 1000Z series scope.
That Rigol scope is very popular right now, up till recently there was nothing on the market with as many features in the same price range.
Only very recently have the other lower end companies have come out with comparable models. Such as the Instek 1000B series and the Siglent SDS1000X series.