Elso is right, Justcallmedad
But he should just have said you that another N-Channel Jfet with the gate attached to te source could just replace the resistor feeding the led chain...
Far better constant current through the leds... and not as expensive as some integrated ones. For such a purpose, long channel Jfets are the best (2N4338 and the like... Just have a look on some Siliconix data books).
Seems too that Richard Marsh used a very similar circuit in early or mid-80s... Will try to find it out and put it on the forum if the thread just not collapse before...
jbaudiophile
But he should just have said you that another N-Channel Jfet with the gate attached to te source could just replace the resistor feeding the led chain...
Far better constant current through the leds... and not as expensive as some integrated ones. For such a purpose, long channel Jfets are the best (2N4338 and the like... Just have a look on some Siliconix data books).
Seems too that Richard Marsh used a very similar circuit in early or mid-80s... Will try to find it out and put it on the forum if the thread just not collapse before...
jbaudiophile
Hi Elso, Hi lineup,
“The LEDs should have a constant current source.”
Yes for PSRR a CCS will be better, but not sure for the sound, especially if I use a Pre Reg, but it's something that could be tested.
I just intended to draw a simplified last stage PSU.
“Your circuit has poor load regualtion as there is no feedback from the output”
I don’t like feedback even in PSU (at least for the last stage), in the case of this thread the PSU is intended for a complementary symmetrical balanced input balanced output class A preamplifier, so load regulation is not a problem.
“There are better references than a few LEDs and also way more expensive.”
I got best results with LEDs than with TL431 or LM336 but I have not tried other ones from AD LT etc.
“The LEDs should have a constant current source.”
Yes for PSRR a CCS will be better, but not sure for the sound, especially if I use a Pre Reg, but it's something that could be tested.
I just intended to draw a simplified last stage PSU.
“Your circuit has poor load regualtion as there is no feedback from the output”
I don’t like feedback even in PSU (at least for the last stage), in the case of this thread the PSU is intended for a complementary symmetrical balanced input balanced output class A preamplifier, so load regulation is not a problem.
“There are better references than a few LEDs and also way more expensive.”
I got best results with LEDs than with TL431 or LM336 but I have not tried other ones from AD LT etc.
Justcallmedad, thanks for showing a schematic. Personally I like your design, AND you avoided many oversights often made by others.
Your approach is truly low noise. The output transistor is driven by low impedance and the output is 'shorted' at audio by the large cap at the output. Your DC stability is OK, but could be improved, IF you felt it necessary by using a current source instead of a resistor, but it will still work well enough and it will be very quiet at audio frequencies.
Now, why don't I do this? Well, as I said in a previous comment, I can hear the 'sound contribution' of the output electrolytic cap when it powered my folded cascode circuit. As an engineer, I would not have thought it possible, but I heard it in a direct AB test with a large value film cap, that sounded better. This forced me to use another approach, still very similar to yours:
I just used the FET driver directly and removed the output transistor and the large output cap. Now what is the tradeoff? Well the output impedance WILL go up, BUT if I use a regulator for each individual circuit that is running class A at all times, then the 5-20 ohm output impedance might be OK, because the change in Gm will be very small, because the power supply current load will be essentially constant. Then I don't need the final large cap. There won't be any added X-talk either, because each channel uses separate regulators, in fact each gain stage has its own regulators. That is why I use so many regulators in my circuits. In the picture of the CTC there are 8 visible, and 12 total, in that box alone. With the power supply box added, there are a total of 28 active regulators to drive the audio circuits in this box.
Now, what about DC regulation? Well in the actual power supply box, I use conventional 3 terminal regulators, to remove hum and ultra low frequency (breathing) of the power line. I have found that 2 regulators in series is better than one 'super' regulator. I hope that this makes sense to you.
Your approach is truly low noise. The output transistor is driven by low impedance and the output is 'shorted' at audio by the large cap at the output. Your DC stability is OK, but could be improved, IF you felt it necessary by using a current source instead of a resistor, but it will still work well enough and it will be very quiet at audio frequencies.
Now, why don't I do this? Well, as I said in a previous comment, I can hear the 'sound contribution' of the output electrolytic cap when it powered my folded cascode circuit. As an engineer, I would not have thought it possible, but I heard it in a direct AB test with a large value film cap, that sounded better. This forced me to use another approach, still very similar to yours:
I just used the FET driver directly and removed the output transistor and the large output cap. Now what is the tradeoff? Well the output impedance WILL go up, BUT if I use a regulator for each individual circuit that is running class A at all times, then the 5-20 ohm output impedance might be OK, because the change in Gm will be very small, because the power supply current load will be essentially constant. Then I don't need the final large cap. There won't be any added X-talk either, because each channel uses separate regulators, in fact each gain stage has its own regulators. That is why I use so many regulators in my circuits. In the picture of the CTC there are 8 visible, and 12 total, in that box alone. With the power supply box added, there are a total of 28 active regulators to drive the audio circuits in this box.
Now, what about DC regulation? Well in the actual power supply box, I use conventional 3 terminal regulators, to remove hum and ultra low frequency (breathing) of the power line. I have found that 2 regulators in series is better than one 'super' regulator. I hope that this makes sense to you.
Seems to me an output cap is ghosting any AC due to its dielectric absorption, DA being high for an electrolytic. Also seems to me uncontroversial that such ghosting could be audible (as IME it is), and that its audibility is an engineering consideration that may hard-limit a regulator's actual audio performance.
serengetiplains said:
What do you mean by "ghosting"? It seems to imply some "second" signal that's basically a time-delayed version of the original signal. I've seen similar notions before, usually by those who are somewhat familiar with the DC-based test for DA and draw erroneous conclusions from it, i.e. that of a time-delayed "second" signal, or "ghost."
se
Call it what you will, capacitors muck up AC signals in a way that seems tightly correlated with their DA rating. Beyond stating that correlation, who really knows how capacitors *actually* muck up AC signals? Steve, your use of the word "erroneous" suggests you're one who does know. Care to share?
Mr. Curl,
You say:
""""Well in the actual power supply box, I use conventional 3 terminal regulators.""""
You use them like voltage regulator or as current regulator (current regulator for to pilot your shunt regulator). Maybe the 2 in series, voltage regulator then current regulator.
Darry
You say:
""""Well in the actual power supply box, I use conventional 3 terminal regulators.""""
You use them like voltage regulator or as current regulator (current regulator for to pilot your shunt regulator). Maybe the 2 in series, voltage regulator then current regulator.
Darry
serengetiplains said:
Ok, but DA is also rather tightly correlated to dielectric constant as well as other parameters such as dissipation factor. So which comes first? The chicken or the egg?
I dunno, I think we know quite a lot about capacitors and how they affect AC signals.
But you seemed to be saying rather matter of factly that DA causes "ghosting." I was just trying to figure out exactly what you meant by it.
No, I was simply speaking of those who reach erroneous conclusions due to misunderstanding basic energy storage, conclusions which if true would mean there must be second "ghost" signals even with ideal capacitance and inductance, which of course there isn't.
se
Steve Eddy said:
Chicken, egg, DA, DC, DF, doesn't really matter so long as the correlation exists which, if it exists, can be used as a guide for classifying, and even designing, capacitors on a scale of better to worse.
Re ghosting, ever see the U2 video for "Vertigo" with the outline of Bono et all streaming into the distance? I mean something like that. What goes into a capacitor does not come out all at the same time. I'm assuming all comes out eventually, either as heat or as electricity, mostly electricity.
jam said:
When ghost is present, if you amplify the signal you amplify the ghost too.
That's why it's better to have a weak, grainy signal reception, with no reflections (ghosts) which is easy to solve with an amplifier.
Btw, on the NTSC system the ghost also has colour, it blurs the contours, a complete mess.
On the PAL system the ghost is transparent.
That's one of the reasons why the PAL system is better for (terrestrial) air transmission.
Back to audio mode...
Folks, there are many imperfections in capacitors. DA is related to the material in the dielectric. Aluminum electrolytic caps tend to have the worst DA. Dissipation factor is only slightly related to DA, but is most concerned with heating of the cap, due to its losses. This includes DA, but also connection resistance and lead resistance. DF is important in switching supplies so that the filter cap does not overheat and explode.
ESR is again related, but is mostly concerned with the 'short-circuit' aspects of the cap, and how well it will pass signals without any drop across it.
These are approximations, and you all can quibble with me about them, but it is important to understand that they are not all the same thing.
DA was found to be important, first, in analog computers, popular in the 1950's. It was known to effect calculations, and was difficult to compensate for. It is also very important in sample and hold circuit operations.
Tantalum and ceramic caps can have lots of nonlinear distortion as well. Aluminum caps are better, but not perfect in this respect.
ESR is again related, but is mostly concerned with the 'short-circuit' aspects of the cap, and how well it will pass signals without any drop across it.
These are approximations, and you all can quibble with me about them, but it is important to understand that they are not all the same thing.
DA was found to be important, first, in analog computers, popular in the 1950's. It was known to effect calculations, and was difficult to compensate for. It is also very important in sample and hold circuit operations.
Tantalum and ceramic caps can have lots of nonlinear distortion as well. Aluminum caps are better, but not perfect in this respect.
Folks, there are many imperfections in capacitors. DA is related to the material in the dielectric. Aluminum electrolytic caps tend to have the worst DA. Dissipation factor is only slightly related to DA, but is most concerned with heating of the cap, due to its losses. This includes DA, but also connection resistance and lead resistance. DF is important in switching supplies so that the filter cap does not overheat and explode.
ESR is again related, but is mostly concerned with the 'short-circuit' aspects of the cap, and how well it will pass signals without any drop across it.
These are approximations, and you all can quibble with me about them, but it is important to understand that they are not all the same thing.
DA was found to be important, first, in analog computers, popular in the 1950's. It was known to effect calculations, and was difficult to compensate for. It is also very important in sample and hold circuit operations.
Tantalum and ceramic caps can have lots of nonlinear distortion as well. Aluminum caps are better, but not perfect in this respect.
ESR is again related, but is mostly concerned with the 'short-circuit' aspects of the cap, and how well it will pass signals without any drop across it.
These are approximations, and you all can quibble with me about them, but it is important to understand that they are not all the same thing.
DA was found to be important, first, in analog computers, popular in the 1950's. It was known to effect calculations, and was difficult to compensate for. It is also very important in sample and hold circuit operations.
Tantalum and ceramic caps can have lots of nonlinear distortion as well. Aluminum caps are better, but not perfect in this respect.
Steve Eddy said:
How do you know what you assert? Not anything like ... ? Show me a picture or do your best to describe in words, then we can compare.
DA, or something to which DA corresponds or correlates---for simplicity's sake, what I'll call DA---smears and/or ghosts and/or adds to and/or subtracts from an audio signal. I hear DA's effects as a form of veiling and grunge, among other descriptions I could throw at it; veiling because DA disrupts my ability to hear clearly into instruments, spaces and dynamics, and grunge because I feel a sense of subtle relaxation or relief when DA is removed as if an irritation has been removed.
The effects of DA will not manifest themselves as reverberation, echo, or ghosting. These are reflections or repititions of complex AC waveforms. DA's mechanism is that of charge retention, and while the effects are not clearly understood... there is little if no potential for DA to store anything other than a decaying DC potential (not that this is good for audio... after all... DC relative to what?).
I do not argue with the fact that DA, and an as yet undescribed (but obvious) property of it, is probably the prime explaination for the percieve difference in capacitor sound... provided these differences do indeed exist.
I do not argue with the fact that DA, and an as yet undescribed (but obvious) property of it, is probably the prime explaination for the percieve difference in capacitor sound... provided these differences do indeed exist.
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