Gee, I thought you meant temperature stability we usually go 0 to 70C min. Even my Hafler DH220 was only a few mV off after a year with a pot across two diodes for trim (at room temp).
I don't really relate to these standards of performance, if you have some need to flog your circuit go for it.
Enough about you -
Not really. Comments trigger thought and so i write them down. I dont sell any IC's or have any stake in IC or opamps or any other topology. btw - I have already commented on its temp stability range as well..... there hasnt been shown any change in the short term and now shown in the long term drift, either.
Or, do you mean --- Enough About You. Let's talk About Me. ?
Not really. Comments trigger thought and so i write them down. I dont sell any IC's or have any stake in IC or opamps or any other topology. btw - I have already commented on its temp stability range as well..... there hasnt been shown any change in the short term and now shown in the long term drift, either.
Or, do you mean --- Enough About You. Let's talk About Me. ?
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Never say never
I think the Ayre KX-R is based on the same concept.
L.
How can you claim no feedback when you used Diamond buffers with 100% negative feedbacks?
Being a student I got a bottle of cognac by making an amp on emitter followers only, with auto-transformer in the middle. 100% feedback, unity-gain stages.
[The Hafler DH220 is cap coupled in the feedback via 470mfd bipolar. It also isnt jFET on the input; Much easier to be dc stable with bipolar]
How can you claim no feedback when you used Diamond buffers with 100% negative feedbacks?
Being a student I got a bottle of cognac by making an amp on emitter followers only, with auto-transformer in the middle. 100% feedback, unity-gain stages.
I meant no * global * feedback. But tons of local feedback, of course; and Sziklai pairs in the output diamond, too
- actually I have nothing against Harold Black, but the performances of the CF architecture I did mention (which is more or less the standard one - you can see it in an awful lot of monolithic CFAs) are quite amazing.L.
CFA
Can you give examples of good discrete CFA designs/schematics with the output stage similar to your idea?
I meant no * global * feedback. But tons of local feedback, of course; and Sziklai pairs in the output diamond, too
L.
Can you give examples of good discrete CFA designs/schematics with the output stage similar to your idea?
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Not really. Comments trigger thought and so i write them down. I dont sell any IC's or have any stake in IC or opamps or any other topology. btw - I have already commented on its temp stability range as well..... there hasnt been shown any change in the short term and now shown in the long term drift, either.
Or, do you mean --- Enough About You. Let's talk About Me. ?
Folks here know me well enough I have nothing to sell and could care less what you think of me. The truth is you do have something to sell unless your web site is just for show.
Here you go, from this thread several pages ago:
Here is one more topology that can be used in custom discrete opamp as an output stage. Actually, it is complementary symmetric opamp with 100% feedback. As drawn, it works in class AB, but output devices do not go through cut-off. If to remove diode-resistor shortening networks in tails and decrease values of resistors in tails it works in class A.
Diodes in current mirrors can be replaced by transistors. But not diodes in right sides of diffpairs: transistors have low base-emitter breakdown voltage, and when the amp goes from voltage follower mode to current amplifier mode (shortened output, or too low load impedance) transistors would be fried.
Resistors in tails instead of current sources are there on purpose: max current depends on output signal level.
For line level current mirrors better to be more balanced: R5 and R6 decreased, R9 and R10 increased. And transistors in places of D1 and D6.
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I dont have a web site. Those products are long ago gone and company dissolved. The brand name (MARSH) is still used by Asian company (Magnet Technology) who made them originally. They have my blessing to sell the designs with my name in Asia. I havent recieved any money in years. And, they are not making or selling headphone amps that i know of. -RNM
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Also highly unlikely, since e sub n from the 1k feedback divider alone will produce 13.4nV/sqrtHz at the output, which if flat with frequency will amount to 1.89uV rms. For 135dB S/N the signal will need to be 10.65V rms, more than 12V rails will permit. Hence my question.
I think a few of you guys need to take the tone down a notch or two...
So are we to suppose that you calculated the closed loop noise from the open loop noise, rather than measuring it? I can't reconcile the stated results of 135dB S/N closed loop, especially if referred to 1V rms, with the analyzed, and as well, simulated behavior of the circuit.
Again, at best, the 1k feedback divider resistor alone limits S/N referred to 1V to a far smaller value than 135dB. I get at least 13.2nV/sqrtHz at the output, in a 30kHz BW, thus 2.29uV rms, which below 1V is an S/N 112.8dB. Not shabby and would trouble no one, but not the stupendous 135dB. And this is ignoring the JFET noise, and the noise of the feedback R, and the noise of the load resistors in the JFET drains, etc.
If one does herculean efforts with much quieter JFETs (including the nearly unobtainable 2SJ74) with higher gm, higher transconductances, a much smaller inter-source resistance trim, and a much lower impedance divider, it is feasible to push the S/N ratio up a lot. But it is not trivial, and "costs" a lot of voltage and (if operating the output stage in class A) a lot of power.
EDIT: OK I see where, as a computation , and based on the measurement of output noise of -85dBV, with an open-loop gain of 62dB and supposing an open-loop bandwidth of 25kHz, you could approximate the noise with closed-loop gain of 12dB as 135dB below 1V. However, this cannot be reconciled with the noise as described above. Etwas ist nicht in Ordnung
A free pdf of the Chaldean numerological correspondence for the alphabet for the first person to satisfactorily explain the discrepancy
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I read and reread bcarso's comments on the theoretical snr of the RN Marsh discrete op-amp and after thinking about it worked the same analysis, and conclude he got it correct - this is at least the way I analyze my own designs when not being too lazy... I understand the argument, but the actual feedback components are not improved by feedback so adding the feedback margin to the calculated open loop noise performance doesn't look right to me either. Scaling the resistor values in a downward direction which looks possible and reasonable here would help a little, ultimately I suspect the device source resistance, external source resistors and balance pot contribute significantly as well, the actual noise is probably a couple of dB higher than calculated.
IMO the SNR is probably more than good enough, and I don't get me wrong I think this is a pretty cool design.
I understand the argument, but the actual feedback components are not improved by feedback so adding the feedback margin to the calculated open loop noise performance doesn't look right to me either. Scaling the resistor values in a downward direction which looks possible and reasonable here would help a little, ultimately I suspect the device source resistance, external source resistors and balance pot contribute significantly as well, the actual noise is probably a couple of dB higher than calculated.IMO the SNR is probably more than good enough, and I don't get me wrong I think this is a pretty cool design.