Rotate your "normal" schematic by 90 degrees and it gets scary. Who are your ancestors, John?
I am serious, by the way.
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Here's an alternative to mirroring that maintains power supply immunity. Cascoding of the VAS is required for best performance.
Thanks,
Chris
Thanks,
Chris
Because that circuit will work, sound good, measure well and still work in 15 years. Plus if the parts are Toshibas it will go up in value.
Few days ago John mentioned importance of resistors used at NFB chain.
I did impedance measurements of some different type resistors, impedance behaviour above 100kHz is very specific for every individual resistor, and even below 100kHz some fluctuations of impedance modulus is observed (I'll post it late on). Another side of the story, what materials resistors are made of, and how "pure" manufacturing technology is.
I did impedance measurements of some different type resistors, impedance behaviour above 100kHz is very specific for every individual resistor, and even below 100kHz some fluctuations of impedance modulus is observed (I'll post it late on). Another side of the story, what materials resistors are made of, and how "pure" manufacturing technology is.
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Here is the relative variation of the impedance modulus of various resistors with frequency. The vertical axis is |Z(f)| / |Z(200Hz)|, total span of the axis is +-2%.
Even at medium frequencies there are some ripples of impedance (possibly some electrostrictive deformation).
These results are taken at the same 1V RMS test sine signal. Impedance will also vary by the test signal amplitude variation. I am afraid to imagine what goes on with a given resistor when unstable schematics usually oscillate (10...100MHz).
Even at medium frequencies there are some ripples of impedance (possibly some electrostrictive deformation).
These results are taken at the same 1V RMS test sine signal. Impedance will also vary by the test signal amplitude variation. I am afraid to imagine what goes on with a given resistor when unstable schematics usually oscillate (10...100MHz).
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Interesting - but fairly meaningless without details of the test set-up and equipment used.
I use mass produced immitance meter
IMMITANCE (RLC) METERS E7-20
•Immitance (RLC) Meter Å7-20
•25 Hz - 1 MHz, ±0.1%
•Wide frequency range 25 Hz–1 MHz
•Capacitance 10**(-15) to 1 F
•Inductance 10**(-11) to 10**4 H
•Resistance 10**(-5) to 10**9 Ohm
•Conductance (10**(-11) – 10) S
•Complex impedance module (10**(-5) – 10**9) Ohm
•Reactance (10**(-5) – 10**9) Ohm
This is a manufacturer's site
????? | IMMITANCE (RLC) METERS E7-20
I just realized there's no need to upset the resistor network; here's another way to set the bias....
(Idea swiped from the Musical Fidelity A1, which also uses split feedback to set bias.)
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Nothing in particular. I was just looking for ways to stabilize the bias for that sort of topology. MOSFETs would work too, but JFETs would be a bit awkward.
Still would benefit from cascode in output. These circuits get so linear that the Vas non-linear Ccb can add even up to 20dB to the thirds at 10kHz
BTW the avatar is "woman ball player", the Mayan version of "ball" had unfortunate consequences for the loser.
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Musical Fidelity A1 does not use current mirror loads, hence they don't have the same bias problem: http://www.tcaas.btinternet.co.uk/mf-a1.gif
Your bias solution doesn't seem to be good enough. In this configuration, assuming all bipolars and jfets identical and perfectly matched, Q7 and Q10 are saturated (Vcb=0).
Adding degeneration to the Q6 and Q7 emitters may help here. Though I am not sure if such a setup will conserve much of the maximum/ideal differential loop gain.
No doubt. The simple circuits were to show the idea, while (hopefully) avoiding "can't see the wood for the trees" syndrome.
Dunno about that. I remember Olivier trying to follow Edmond's advise in this thread. After nearly a year, he still hadn't got it to work. My opinion at the time:
Edit: Huh? Where did Bonsai's post go? 😕
P.S. Yes, I know Edmond came back later.
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I don't agree Godfrey. I also followed the above thread. I think Olivier was simply not ready to tackle a fully comp current mirror loaded LTP design.
Note, in my post I also referenced RC and SW who also provided solutions to this problem.
Note, in my post I also referenced RC and SW who also provided solutions to this problem.
No, but it does have _a_ bias problem, and uses split feedback to fix it.
They'll work with Vcb=0, but it would be better to put something (diodes/LEDs/other) between the emitters of Q6 and Q9 and the rails to provide some extra voltage drop. Especially if the mirror is degenerated, as it should be.
Sorry, I don't follow. Where is gain being lost?
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