Hi Mad_K
Why do you do not use the minus rail as input ground?
The way you have , the input ground is referenced to the the positive rail and the source of the mosfet is referenced to the minus rail, but the voltage that the mosfet "see" and amplifies , is the voltage between gate and source...
With your grounding arrangement the PSRR will be very poor...
Why do you do not use the minus rail as input ground?
The way you have , the input ground is referenced to the the positive rail and the source of the mosfet is referenced to the minus rail, but the voltage that the mosfet "see" and amplifies , is the voltage between gate and source...
With your grounding arrangement the PSRR will be very poor...
Mad_K said:
Do some home work, please:
http://www.eie.polyu.edu.hk/~ensurya/lect_notes/commun_cir/Ch2/Fig2-18.jpg
http://www.ee.bilkent.edu.tr/~aytur/courses/ee313/labs/exp6.pdf
Dear Yan, this can also be true.
In Greek we have different words for ‘simple but probably effective’, and for ‘dangerously simplified’, but unfortunately the English translation is the same: ‘Simple’.
In my opinion many of these little circuits are simple and effective if someone has the right speaker: sensitive and of smooth impedance (which two quantities are regarded as speaker qualities, in my way of thinking, btw). Then they can prove to be sonically even better from more complicated, respected, and well measuring designs. As we all know, there are many people who have such experiences, and such simplicity can be considered as a certain ‘philosophy’ in sound reproduction. All these people have the right to experiment, listen, like what they listen, post their findings without having to deal with questions like “how can this play good music, so simple as it is, with such a distortion figure etc.?” again and again. In the same time and as I have seen, all these don’t get into other forum discussions (regarding more complicated designs) protesting or demonstrating their different point of view, saying for instance ‘why do you build such a 4 stage circuitry, why not cut 2 stages’, or ‘how can this work with so many parts?’.
In general, I presume that these people know better that Hi-Fi isn’t a one-way street, nor is it determined from specific specs, so I (again) presume they perhaps know better how to choose an appropriate way (since they don’t know of only one) to satisfy their needs.
Now, about simplicity and complication: Even for this simple matter, of someone’s right and pleasure to post here his findings and have a conversation (given his simplistic approach and likings) and get on-topic comments and disagreements like tube-dude’s and lohk’s, and nothing else, we people have to complicate things enough to loose our motives.
In Greek we have different words for ‘simple but probably effective’, and for ‘dangerously simplified’, but unfortunately the English translation is the same: ‘Simple’.
In my opinion many of these little circuits are simple and effective if someone has the right speaker: sensitive and of smooth impedance (which two quantities are regarded as speaker qualities, in my way of thinking, btw). Then they can prove to be sonically even better from more complicated, respected, and well measuring designs. As we all know, there are many people who have such experiences, and such simplicity can be considered as a certain ‘philosophy’ in sound reproduction. All these people have the right to experiment, listen, like what they listen, post their findings without having to deal with questions like “how can this play good music, so simple as it is, with such a distortion figure etc.?” again and again. In the same time and as I have seen, all these don’t get into other forum discussions (regarding more complicated designs) protesting or demonstrating their different point of view, saying for instance ‘why do you build such a 4 stage circuitry, why not cut 2 stages’, or ‘how can this work with so many parts?’.
In general, I presume that these people know better that Hi-Fi isn’t a one-way street, nor is it determined from specific specs, so I (again) presume they perhaps know better how to choose an appropriate way (since they don’t know of only one) to satisfy their needs.
Now, about simplicity and complication: Even for this simple matter, of someone’s right and pleasure to post here his findings and have a conversation (given his simplistic approach and likings) and get on-topic comments and disagreements like tube-dude’s and lohk’s, and nothing else, we people have to complicate things enough to loose our motives.
Tube_Dude said:
Yes, I'm well aware that's the normal way to connect it. I was thinking of the sentence I posted earlier, as this is the way it is descibed in my book "Microelectric Circuits". I would very much appreciate a lesson in how this affects the PSRR, and AC signal current loop, in the mean time I will redraw the schematic to comply with the normal way of thinking.
hi. on the sewa amp that this thread spawned from the is a circuit with a light bulb instead of a resistor. Does any one know what type to use?http://www.diyaudio.com/forums/showthread.php?s=&threadid=66822&highlight=
Tube_Dude said:
Please , don't take me wrong, but if you breadboard the circuit with the grounding arrangement you have, certainly you will ear some hum and ripple noise.
Want you try?
I'm listening to it (with an active load) right now (and have been for a few months) and there is absolutely no hum, but I haven't measured the two configurations.
Mad_K said:
An easy way to see if PSRR is not so good:
Say you increase your supply voltage with 1 Volt.
Will this change the voltage across the output?
Yes, if you take your output across the transistor.
No, if you take your output across the resistor.
Yes, to BOTH, if the Gate operation point changes with supply voltage.
This is the case if a simple resistor divider sets working point.
Using an electrolytic filter of this input divider,
will filter away AC voltage changes in supply from effect Gate voltage.
In your first circuit here, any AC voltage changes in supply
will result in AC voltage change across load.
Even if Gate operation point voltage level stays the same,
and the voltage across power resistor is constant.
This is poor PSRR - power supply rejection.
--------------------------------
Can an amp be good and have very low PSRR?
YES!
Condition is that you have a very clean power supply.
When almost no ripple can reach amplifier.
For example some of Nelson Pass amplifiers have low supply rejection.
But his power supplies are very well filtered.
Using Cap-Inductor-Cap filter with very high filter values.
So called CLC filter.
In addition very big 'overdimensioned' transformers are used, which also gives lower ripple.
darkfenriz said:Jorge
what do you mean?
I think that with proper star ground it can have acceptable psrr.
Think that the mosfet sees and amplifies , the difference in voltage between gate and source.
The voltage at the gate is referenced to the positive rail and the source is referenced to the negative rail, so the mosfet input will be the desired input signal , plus the voltage difference between the positive and negative rail...capisce...
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