Bob, you are not making a commercial amplifier. You do not do what we must do to make the amplifier have the gain and the flexibility that it must have to be a commercial product.
On another tact, what is the noise contibution of your active loads? .1dB, 1dB, or do you even know?
On another tact, what is the noise contibution of your active loads? .1dB, 1dB, or do you even know?
Ipanema said:
It's not likely to be significant at all. That's why John's assertion that my circuit has a noise injection problem is a complete red herring. The icing on the cake is that if John's JC-1, with an 88 dB S/N is good enough on noise, my circuit with an S/N of 108 dB can't possibly have a noise problem in any reasonable power amplifier application.
Cheers,
Bob
What is the sound of device noise e.g. 1/f noise, shot noise? Are we able to hear it even with the noisest amp (all other noises negligible) with our audio system?
Thanks.
Thanks.
PMA, an OP AMP is an amplifying stage with a defined high input impedance, direct coupled internally, high gain, defined single dominant pole and a low output impedance. What is your definition of an OP-AMP? the 741?
JC, I am not interested in your patronizing. Which succesful commercial opamp have you designed? What is your definition of opamp, uA709 or AD829?
PMA, the term OP-AMP is a generic term for a certain KIND of design, not a product made just for servos or analog computers. Please look up the definition of an OP-AMP and understand what I am saying. Why this question has come up is a surprise to me.
If you look at the phono stage of the original JC-2, you will see a classical example of an OP-AMP. Amazingly, it looks like the same basic topology used by Bob Cordell in his amplifier design. I did not invent this topology, I just put fets on the input and the output of this op-amp circuit.
If you look at the phono stage of the original JC-2, you will see a classical example of an OP-AMP. Amazingly, it looks like the same basic topology used by Bob Cordell in his amplifier design. I did not invent this topology, I just put fets on the input and the output of this op-amp circuit.
What I meant is that technology level influenced circuit design of monolithic IC opamps. Their designer did not have that "free hands" as a designer of discrete circuits. On the other hand, he could benefit from perfect thermal coupling. I am surprised that this was not obvious from my posts.
PMA, after all, you wrote "Which opamp, namely, have you designed?" to John Curl. I agree with John, an opamp is not necessarily one piece of silicon inside some 8 pin DIP or SOIC or whatever. I think John gave a good description of the opamp. BTW his modules in the original Levinson preamps are opamps as good as any. + and - high impedance inputs, a low impednce output, and +/- voltage pins. Cast in epoxy. Built with discrete transistors inside. As John also briefly explained.
Sorry to interrupt your discussion, but I guess you both know all this. So boys, please come back into serious mode
Sorry to interrupt your discussion, but I guess you both know all this. So boys, please come back into serious mode
R-K Rønningstad said:PMA, after all, you wrote "Which opamp, namely, have you designed?" to John Curl. I agree with John, an opamp is not necessarily one piece of silicon inside some 8 pin DIP or SOIC or whatever. I think John gave a good description of the opamp. BTW his modules in the original Levinson preamps are opamps as good as any. + and - high impedance inputs, a low impednce output, and +/- voltage pins. Cast in epoxy. Built with discrete transistors inside. As John also briefly explained.
Sorry to interrupt your discussion, but I guess you both know all this. So boys, please come back into serious mode
I assume we all know what is an opamp and I find it silly to recommend to find definition in the text book. Thanks, I have university degree in EE and I have known what is an opamp for several decades.
I intentionally asked JC what commercially succesfull opamp he has designed. It is the same kind of question he used to give to Bob Cordell about power amplifiers, and IMHO is UNFAIR, not the case. So I emphasized it.
PMA said:
Yes, OK, I can agree with you on this. I understand why you did it this way.
Well, better to bow out of this. Bye!
BTW: I guessed you knew about opamps, yes. I checked your (nice) homepage before I posted.
regds
😎
john curl said:
If you are referring to the balanced inputs, only a very poor design approach to achieving balanced inputs would penalize the S/N by 20 dB.
I guess "we" does not include Boulder, Bryston, et al, as they do not seem to suffer this problem. You seem to be pretty loose with the word "we".
Bob
Hi John,john curl said:
are you saying that active loads whether current mirror in lieu of collector loads or CCS for the tail resistor, are noisier or quieter than pure resistive loads?
Then, by how much for a typical power amp front end with typical source resistance/impedance?
If the source is DC blocked, then the input sees resistance//capacitor as source impedance. What effect does the DC block have on the noise contribution?
Bob, only a CHEAP design approach would add extra noise. It is a good, and PURE design approach. I just don't like to add extra active devices to my circuits.
By the way, Parasound never got any complaints about noise. Maybe it is quiet enough for the job at hand.
I might remind you that I am a low noise expert, and have some idea of the situation.
By the way, Parasound never got any complaints about noise. Maybe it is quiet enough for the job at hand.
I might remind you that I am a low noise expert, and have some idea of the situation.
john curl said:
I thought you were blaming the higher noise of the JC-1 on the need for balanced inputs in your last post. If they are not the cause of the increased noise, as you seem to assert here, then it must be the amplifier architecture itself.
I'm sure the JC-1's noise is low enough. The point is, you shouldn't be in the position of criticizing the noise of another circuit when that circuit is 20 dB better than yours.
I checked the noise results for my circuit by SPICE simulation for three cases, so there would be a reasonable apples-apples answer to the question of the role that the active current source load plays in overall circuit noise.
1) The circuit as originally designed
2) The active current sources replaced with appropriate load resistors, but with the emitter followers retained.
3) The active current sources replaced with appropriate load resistors and the signals routed directly to the second differential pair, without the emitter follower buffers.
Here are the input-referred noise voltages for the three cases:
1) 4.4 nV per root Hz
2) 4.3 nV per root Hz
3) 4.7 nV per root Hz
Thus the use of the active loads increases noise by 0.1 nV per root Hz, or by about 0.2 dB, over the resistively-loaded and EF-buffered case. I think that answers your question.
BTW, 4.4 nV per root Hz input referred noise for a power amplifier is very, very good. Halcro brags about achieving input-referred noise of 5 nV per root Hz.
Note that the third case suffers increased noise due to the omission of the emitter followers. What is happening here is that noise from the VAS is beginning to come into the picture.
Cheers,
Bob
4.4 nV per root Hz is better than sole OPA134. Several opamps, like AD797, are better, regarding voltage noise, but nothing to call home about in current noise. You know your current noise, Bob?
PMA said:
No, I don't know the current noise. I'm assuming it is pretty low because the inputs are JFETs instead of bipolars, but it is true that these are fairly large-area JFETs.
Cheers,
Bob
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