disregarding connectionprobs something like a low impedanz "flattened" coaxial cable, "sandwiched" stripline a.s.o would be best. Paralelling will help to bring inductans further down. A cable with twisted wires alternately connected +-+- a.s.o. and the thinnest possible isolation should be good enough in most audioapplication. In low voltage applications the best "cables" can be made up of magnetwire. Pay attention to providing the smallest possible looparea at the caps connetion because this inductans can easely swamp low a otherwise low cableinductanc. In a PS with high current high-C input the looparea transformer-rectifier-first cap can induce significant strayfield. Keep it as short as possible. How critical the loop thereafter is depends mostly on load requirements. Pay attention to possible ringing and make sure that sufficient damping and "load-sided" C is provided. A "C" of 0.1uF wont necessarely cut it.
gootee, I am all with you on your last post, and for me in DIY there is no such thing as overkill, lol.
Geez, I am working on a practically zero-impedanc tube power amp to current induced OPT distortion minimized without the otherwise needed nasty feedback from the output.
I am about to sim a totally overkill amp giving pre-transformer thd in the ppm range. If I want in reality get anything even close to what I simmed I will need first of all a totally overkill powersupply. In the process of designing such a beast I "invented" a new type of powersupply wich I will hopefully be able to load up on Duncans PSU-calculator
side for public discussion. In the limited currentrange of a tube class-B amp this PS
is capable of giving better regulation than what is possible with L-input (without ringing)
using the same caps. It has also the advantage of not producing overvoltage at low load. Furthermore it has good pf and remarkable good efficience as compared to C-input and maybe even L or 100Hz resonated L (because of the smaller resistans po.
But there are also downsides: it needs really big caps,has fairly high resonant currents and need a electrically small but mechanically only a bit smaller than L-input choke with a critical and almost dc-undepended inductanc. This means big airgap and lozza electromagnetic strays wich will need shielding. The choke is also the bottleneck and makes a industrial maufacuring process very expensiv. Thats why I decided on making it public instead of patenting. It should be well suited for certain DIY projets. Simmed
with Duncan PSU designer I was able to get a dc-regulation of around 2-max2.5 % for 100-400mA at 250V (this includes extensiv filtering to get full load ripple output to only a few hundred uV).
Overkill?
Offcourse, but why bother with DIY if you could buy something like it
Geez, I am working on a practically zero-impedanc tube power amp to current induced OPT distortion minimized without the otherwise needed nasty feedback from the output.
I am about to sim a totally overkill amp giving pre-transformer thd in the ppm range. If I want in reality get anything even close to what I simmed I will need first of all a totally overkill powersupply. In the process of designing such a beast I "invented" a new type of powersupply wich I will hopefully be able to load up on Duncans PSU-calculator
side for public discussion. In the limited currentrange of a tube class-B amp this PS
is capable of giving better regulation than what is possible with L-input (without ringing)
using the same caps. It has also the advantage of not producing overvoltage at low load. Furthermore it has good pf and remarkable good efficience as compared to C-input and maybe even L or 100Hz resonated L (because of the smaller resistans po.
But there are also downsides: it needs really big caps,has fairly high resonant currents and need a electrically small but mechanically only a bit smaller than L-input choke with a critical and almost dc-undepended inductanc. This means big airgap and lozza electromagnetic strays wich will need shielding. The choke is also the bottleneck and makes a industrial maufacuring process very expensiv. Thats why I decided on making it public instead of patenting. It should be well suited for certain DIY projets. Simmed
with Duncan PSU designer I was able to get a dc-regulation of around 2-max2.5 % for 100-400mA at 250V (this includes extensiv filtering to get full load ripple output to only a few hundred uV).
Overkill?
Offcourse, but why bother with DIY if you could buy something like it
McCormick Audio amplifiers featured (don't know if they still do) smallish power supply filter capacitors at each output transistor. The trace is a few centimetres long, if that, so inductance is minimized. The only problem would be IR drop from rectifier pulses going through the wires from the rectifier to the filter caps.
gootee, I am all with you on your last post, and for me in DIY there is no such thing as overkill, lol.
Geez, I am working on a practically zero-impedanc tube power amp to current induced OPT distortion minimized without the otherwise needed nasty feedback from the output.
I am about to sim a totally overkill amp giving pre-transformer thd in the ppm range. If I want in reality get anything even close to what I simmed I will need first of all a totally overkill powersupply. In the process of designing such a beast I "invented" a new type of powersupply wich I will hopefully be able to load up on Duncans PSU-calculator
side for public discussion. In the limited currentrange of a tube class-B amp this PS
is capable of giving better regulation than what is possible with L-input (without ringing)
using the same caps. It has also the advantage of not producing overvoltage at low load. Furthermore it has good pf and remarkable good efficience as compared to C-input and maybe even L or 100Hz resonated L (because of the smaller resistans po.
But there are also downsides: it needs really big caps,has fairly high resonant currents and need a electrically small but mechanically only a bit smaller than L-input choke with a critical and almost dc-undepended inductanc. This means big airgap and lozza electromagnetic strays wich will need shielding. The choke is also the bottleneck and makes a industrial maufacuring process very expensiv. Thats why I decided on making it public instead of patenting. It should be well suited for certain DIY projets. Simmed
with Duncan PSU designer I was able to get a dc-regulation of around 2-max2.5 % for 100-400mA at 250V (this includes extensiv filtering to get full load ripple output to only a few hundred uV).
Overkill?
Offcourse, but why bother with DIY if you could buy something like it
Wow. Coool. I can hardly wait to see all of that!
Concur. Faraday's Law (and Maxwell's Equations) can be a bitch.
It also applies to emitting stray fields (as you alluded-to somewhere else, regarding power supply front ends' wiring, I think).
The two things that I probably repeat the most, on diyaudio.com, are to minimize ALL enclosed loop areas and to not share ground conductors.
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Sorry. No (unless I didn't model what you said). I added L and R for an inch of trace between the caps' connections to the rails (two in power rail and two in ground rail), for the un-paralleled model, and at high frequencies (1 MHz to 1 GHz), the filtering stays 0.4 dB worse than the original un-paralleled model, and 9.6 dB worse that the paralleled model. At low frequencies (up to somewhere between 20 and 100 kHz), it is 1.8 dB worse than the original un-paralleled model and 4.8 dB worse than the paralleled model.
I really don't even like to think of them as "filter caps", any more. They are "current reservoirs".
And remember that the inductances you wanted to add would get voltages induced across them, by any time-varying current that flows through them, and other voltages (which would sum with the inductive ones) induced across them because of their resistances.
It now seems that "voltage filtering" in a linear power supply is just not the best way to think about what the caps do. It's as unenlightening as thinking about the voltage, at all, in a linear PSU. The voltage is almost constant. The signal we hear is the CURRENT, from the PSU. The current is where the action is. The PSU rail voltage dips are directly controlled by the transient load current flows and the decoupling and reservoir capacitor sizes, ideally, but in reality are also significantly affected by the inductances of the conductors and the inductances of the capacitor sizes/geometries (there may be basically no inductance in most capacitors, except that which is due to conductor lengths, i.e. basically pin spacing).
We can probably also usually think that the rectifier output current just charges the capacitors, and the load current all comes from the capacitors. Yes, some of the 100 Hz or 120 Hz voltage ripple gets past the reservoir caps. But that is probably a small effect, usually, or can be made to be small, compared to the voltage fluctuations that are caused by the load's current draws across the inductance (and resistance) of the rails.
-----
Something that occurred to me, earlier today, about the 100/120Hz ripple voltage in a linear power supply: It seems like maybe we could just disconnect (or shunt-away) the rectifier output, whenever the capacitors are "full", i.e. when the voltage is already at the desired level. And then when the voltage dips, slightly, due to the load drawing some current, we could allow the rectifier to provide JUST enough current to recharge the reservoir caps. That way, NO 100/120Hz ripple voltage should EVER get past the reservoir caps. And knowing the sizes of the caps in advance and sensing the voltage differential to be corrected, as it occurs, we should be able to precisely meter-in the correct number of electrons, with the correct speed profile, exactly when needed. Of course, a good implementation would start to crack open the current valve whenever the voltage just started to dip, and voila, perfect constant DC voltage should result (AT the caps, at least). Maybe that means using a smart preregulator of some sort. We could probably also sense the voltage farther downstream (at the load), with a pair of conductors that didn't carry much current (so their sensing wouldn't be affected much by their parasitic inductances and resistances), and anticipate the effects of the inductances and resistances of the main current-carrying rails, and adjust the cap-recharge valve's dynamic response accordingly. It seems like a fairly-straightforward control-system problem, if a decent basic hardware control mechanism could be implemented. [Are there any 3rd or 4th year BSEE students lurking, who are taking (or have just taken) classical feedback control theory? A closed-form mathematical expression of the problem and solution would be nice.] Then again, who cares about anything but what happens at the point of load (and also, nothing interesting is happening when the caps are staying full, anyway)? So maybe the preceding idea should be applied at the decoupling caps or the point of load, instead of worrying about the ripple at the main caps. Or, we could do both. <smile>
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gootee, tnx for pointing out the emmitting field.
By "strays" I thincking of the emmitting field. Sorry, I was a bit sloppy. When I use a foreign language I often pick the first word that comes into my mind.
It also came to my mind that running a STRAIGTH RUN unshielded conductors to and from a shunt cap emmit and pick up AFTER your "perfect" cap. So, a 90deg bend nearest after the cap connection may be a good thing. Is it of importance in audio? Depends....
Anyway, I find it good to be aware of that too. I was not, until I nosedived into industrial heater equippement. There about everything needs more attention the higher
the power times frequency product gets. Alltough losses are mostly easier to "see" or measure than at low power/low frequency and other things arent, but results wont stay unnoticed if things are not done the rigth way. Paralleling stuff can be a very "enligthning" expirience as is a "bent" coppertube when the manetic field gets squeezed
to much
By "strays" I thincking of the emmitting field. Sorry, I was a bit sloppy. When I use a foreign language I often pick the first word that comes into my mind.
It also came to my mind that running a STRAIGTH RUN unshielded conductors to and from a shunt cap emmit and pick up AFTER your "perfect" cap. So, a 90deg bend nearest after the cap connection may be a good thing. Is it of importance in audio? Depends....
Anyway, I find it good to be aware of that too. I was not, until I nosedived into industrial heater equippement. There about everything needs more attention the higher
the power times frequency product gets. Alltough losses are mostly easier to "see" or measure than at low power/low frequency and other things arent, but results wont stay unnoticed if things are not done the rigth way. Paralleling stuff can be a very "enligthning" expirience as is a "bent" coppertube when the manetic field gets squeezed
to much
CORRECTION!
AndrewT was correct.
I made a rather-egregious error, here. Instead of looking at the Load Voltage vs Frequency plot with an AC voltage source at the input, I mistakenly looked at the plot of Impedance vs Frequency as seen by the load (with a AC current source at the load).
As AndrewT asserted, adding impedance models between the capacitors does, of course, increase the effective filtering of input voltages as seen by the load. If one inch of conductor is modeled between the capacitors, with 15 nH and 1 mOhm, then at 100 kHz there is an additional 6.7 dB of voltage attenuation between input and load, and the difference increases as frequency increases.
Attached are ltspice schematics and some saved plot-settings files, so that anyone can play around with the simulations.
I too worried about parallel resonances of power capacitors.
As newbie, I was given a design to cleanup hahah. Actually the senior guys
wanted me to learn about parallel-cap resonances. Twas a pulse
amplifier, for Sandia, to be "flat" from 100KHz to 100MHz (I think).
Using some HP spectrumAnalyzer+TrackingGenerator, a dip appeared
at 47MHz. I had not a clue.
The senior guys gently suggested I examine the 100UF and the 0.001UF
on the +15volt line. LO and BEHOLD, 10nH inductance (of the 100UF)
and 1,000 pF do indeed resonate near 47MHz. I got enlightened a bit.
Am still getting enlightened, decades later.
Since the larger capacitor does not set the resonant frequency, we may
instead view it as a source of losses. And ESR of 1 ohm at 47MHz has what
dampening? Impedance of 1,000pF at 50MHz == 0.128 ohm. Thus even
0.1 ohm resistive losses would have killed that 6dB notch in the frequency
response. That 100UF sealed tantalum electrolytic was rather low loss!
Hmmm a way to measure HF losses? use an RF sweep generator, with 50 OHM
Rout, into two paralleled caps, and measure (with scope?) the signal across
the smaller cap? or across the bigger cap?
As newbie, I was given a design to cleanup hahah. Actually the senior guys
wanted me to learn about parallel-cap resonances. Twas a pulse
amplifier, for Sandia, to be "flat" from 100KHz to 100MHz (I think).
Using some HP spectrumAnalyzer+TrackingGenerator, a dip appeared
at 47MHz. I had not a clue.
The senior guys gently suggested I examine the 100UF and the 0.001UF
on the +15volt line. LO and BEHOLD, 10nH inductance (of the 100UF)
and 1,000 pF do indeed resonate near 47MHz. I got enlightened a bit.
Am still getting enlightened, decades later.
Since the larger capacitor does not set the resonant frequency, we may
instead view it as a source of losses. And ESR of 1 ohm at 47MHz has what
dampening? Impedance of 1,000pF at 50MHz == 0.128 ohm. Thus even
0.1 ohm resistive losses would have killed that 6dB notch in the frequency
response. That 100UF sealed tantalum electrolytic was rather low loss!
Hmmm a way to measure HF losses? use an RF sweep generator, with 50 OHM
Rout, into two paralleled caps, and measure (with scope?) the signal across
the smaller cap? or across the bigger cap?
Consider adding a SNUBBER (dampener).
The goal: ensure some lossy behavior at all frequencies,
regardless of capacitor internal losses (or lack of losses).
Thus compute what dampening R you want (0.1 ohm ?)
and include that in series with 1,000UF and with another 10UF
and with a third 0.1UF cap.
Ah. Alternative. Cute. I'd forgotten. PCB resistance may be adequate.
At 1/2,000 ohm per square, a 10mil by 500 mil trace has 50 squares
and thus 50/2,000 = 1/40 = 0.025 ohm. {this for standard 1-ounce foil}
tank
The goal: ensure some lossy behavior at all frequencies,
regardless of capacitor internal losses (or lack of losses).
Thus compute what dampening R you want (0.1 ohm ?)
and include that in series with 1,000UF and with another 10UF
and with a third 0.1UF cap.
Ah. Alternative. Cute. I'd forgotten. PCB resistance may be adequate.
At 1/2,000 ohm per square, a 10mil by 500 mil trace has 50 squares
and thus 50/2,000 = 1/40 = 0.025 ohm. {this for standard 1-ounce foil}
tank
"Any capacitor would (within reason) do the job if it was just capacitance that was to be considered, but the series ESL is the problem. That is why small physical lower value packages are placed next to the device pins, as the parasitic inductance is low they can supply the almost instantaneous requirement for current, then moving further away from the device power pins the larger reservoir caps, supply the next current requirements, then the power supply output cap(s), then finaly the voltage regulator, this being the slowest to react."
A perspective on inductance. 1nanoHenry at 1GegaHertz (I used to
do RFIC design) is j6.3 ohms. That is a problem for many designs.
1nH at 1MHz is 0.0063ohm
10nH at 0.1MHz is 0.0063ohm
10nH at 0.02MHz is 0.0012ohm.
Pulling 5 amps at 20KHz thru 0.0012ohm
is only 0.006 volts drop.
Thus with a 60 volt rail, we have -100dB effect (10^-5).
I expect the resonances {this thread is very valuable for that}
are more the problem, than the remaining small Ls.
tank
A perspective on inductance. 1nanoHenry at 1GegaHertz (I used to
do RFIC design) is j6.3 ohms. That is a problem for many designs.
1nH at 1MHz is 0.0063ohm
10nH at 0.1MHz is 0.0063ohm
10nH at 0.02MHz is 0.0012ohm.
Pulling 5 amps at 20KHz thru 0.0012ohm
is only 0.006 volts drop.
Thus with a 60 volt rail, we have -100dB effect (10^-5).
I expect the resonances {this thread is very valuable for that}
are more the problem, than the remaining small Ls.
tank
What you are describing is the collector to collector (of an EF pair) that are connected together via pair of series connected low value low inductance decoupling caps. The cap junction is effectively power ground for the VHF pulses.
That route: collector to cap to VHF Power Ground to cap to collector must be very short to minimise inductance.
This is the battery that Gootee uses as an analogy.
Assume that no speaker current comes from the PSU nor does any VHF current come from the on board electrolytics. All the VHF current comes from those two decoupling caps. Think of them as VHF batteries. Design the layout and the routing to maximise the VHF current available to flow around that tiny figure of 8 PSU.
As an aside, I believe the output Zobel that is required to help with HF stability must also couple into that VHF current route. I think that locating the Zobel further away than necessary, reduces the effectiveness of the stability enhancing duty of the Zobel.
That route: collector to cap to VHF Power Ground to cap to collector must be very short to minimise inductance.
This is the battery that Gootee uses as an analogy.
Assume that no speaker current comes from the PSU nor does any VHF current come from the on board electrolytics. All the VHF current comes from those two decoupling caps. Think of them as VHF batteries. Design the layout and the routing to maximise the VHF current available to flow around that tiny figure of 8 PSU.
As an aside, I believe the output Zobel that is required to help with HF stability must also couple into that VHF current route. I think that locating the Zobel further away than necessary, reduces the effectiveness of the stability enhancing duty of the Zobel.
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Dear Gootee wrote:
If I understood well, this circuit, created by -ECdesigns- for low power uses but adapted by myself also for higher power, goes on that direction on a different aproach and could also be able to get rid of the HF noise from the rectifiers...
https://picasaweb.google.com/lh/photo/rOgiSl8IVgPdqOcKLPkbNNMTjNZETYmyPJy0liipFm0?feat=directlink
It works very well on my Class AB and UCD power amps...
https://picasaweb.google.com/lh/photo/if0Yt3ku1R4vGDMHNErStNMTjNZETYmyPJy0liipFm0?feat=directlink
Cheers,
M.
If I understood well, this circuit, created by -ECdesigns- for low power uses but adapted by myself also for higher power, goes on that direction on a different aproach and could also be able to get rid of the HF noise from the rectifiers...
https://picasaweb.google.com/lh/photo/rOgiSl8IVgPdqOcKLPkbNNMTjNZETYmyPJy0liipFm0?feat=directlink
It works very well on my Class AB and UCD power amps...
https://picasaweb.google.com/lh/photo/if0Yt3ku1R4vGDMHNErStNMTjNZETYmyPJy0liipFm0?feat=directlink
Cheers,
M.
We can exploit the skin-depth of PCBs, to ensure high dampening
at high frequencies. Somewhere around 5MHz, standard-thickness
foil begins to increase in resistance because the "self-inductance"
(view the foil as having myriad internal threads of current, all
generating Hfields) begins to crowd the current toward the surface.
And surface-roughness only increases the resistance.
At 50MHz, foil is 1.5milliOhm per square.
At 500MHz, foil is 5 milliOhm per square.
Then we can wonder about the HF losses (our friend) of
the solder-plated capacitor leads.
at high frequencies. Somewhere around 5MHz, standard-thickness
foil begins to increase in resistance because the "self-inductance"
(view the foil as having myriad internal threads of current, all
generating Hfields) begins to crowd the current toward the surface.
And surface-roughness only increases the resistance.
At 50MHz, foil is 1.5milliOhm per square.
At 500MHz, foil is 5 milliOhm per square.
Then we can wonder about the HF losses (our friend) of
the solder-plated capacitor leads.
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