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Old 26th December 2011, 10:37 PM   #311
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fits what you would expect, the higher the frequency the more the impedanz will be dictated by L
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Old 27th December 2011, 03:07 AM   #312
gootee is offline gootee  United States
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Yes.

And at the load, a current source going from 0 to 3 amps in 1 s causes a 186 mV spike, with the shared-trace version, and only a 65 mV spike in the one with paralleled traces.

V = L(di/dt) and di/dt was the same in both cases. So the effective inductance really was lowered by almost ⅔, as expected.

Last edited by gootee; 27th December 2011 at 03:31 AM.
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Old 27th December 2011, 03:31 AM   #313
gootee is offline gootee  United States
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So, if not using power or ground planes, then paralleled capacitors for smoothing or decoupling should each use separate sets of parallel traces all the way to where their effect is desired, if possible.

It should therefore be a pretty good idea to use multiple parallel copies of each power rail (and the ground rail), maybe starting at the recifier diodes (or right after the regulator if one is used), with separate smoothing caps (in the PSU) and separate bypass/decoupling caps (at the load) for each parallel copy of each power rail. No?

Last edited by gootee; 27th December 2011 at 03:35 AM.
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Old 27th December 2011, 04:19 AM   #314
gootee is offline gootee  United States
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Couldn't we make the power supply impedance appear to be arbitrarily low, to the load, with this technique, i.e. just by adding more parallel power and ground rail conductors, each with another decoupling capacitance? (within the limits of the available PCB real-estate, at least) I believe that we could.

And therefore we could also make the power and ground rails' ripple and spikes' voltages arbirarily small, as well, as seen by the load, since the rail voltages induced by load currents should be almost divided by the number of parallel copies of the rails.

For board-to-board power supply cabling (for simple boards without planes), I would now have to recommend using something like a ribbon cable, with many conductors, with many alternating V+ and Gnd pairs (if single supply), or many V+/Gnd/V- triples (if dual supply), and the same number of small traces on the PCBs, all the way to the load (and from the rectifier bridge or regulator), with a separate decoupling cap near the load for each power trace (either to corresponding gnd or opposite rail, depending on the circuit).

Obviously, also, the size of each conductor (and trace) and the number of conductors (and traces) would have to be calculated to be sufficient for the maximum total average current, etc. But with lots of traces, each trace could be relatively narrow (and each capacitor could be relatively small), and performance would still be greatly enhanced.

Or would the conductors need to be separated, more, so that mutual inductance could be avoided, so that the inductance reduction due to paralleling would be retained? Or would alternating V+/Gnd or V+/Gnd/V- tend to prevent that problem? Also, could the increased inductance and/or resistance of smaller conductors tend to outweigh the advantage of paralleling, by too much? The conductors might need to be as large as is practical, to try to avoid those tendencies.

Cheers,

Tom

Last edited by gootee; 27th December 2011 at 04:34 AM.
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Old 28th December 2011, 04:34 AM   #315
gootee is offline gootee  United States
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The silence is deafening.

Has anyone used this type of technique? Or can someone please try to shoot some holes in it?
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Old 28th December 2011, 05:26 AM   #316
benb is offline benb  United States
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The silence is the sound of the residual noise of your amplifier being powered by this idea.

I think it's just fine, except that it may be getting into overkill range and diminishing returns. How much would an average audio power amplifier actually benefit from a power supply like this?

Maybe a class D amp would significantly benefit from this.
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Old 28th December 2011, 08:49 AM   #317
AndrewT is offline AndrewT  Scotland
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I would like to think about it from a slightly different direction.
The capacitor filter not only filters the 50Hz and it's harmonics, it also filters the HF trash that comes in along with the distorted sinewave power signal.

Little bits of carefully placed parasitic inductance and capacitance can enhance the HF filtering action.

I'll try to describe an example.
Take the first, high Zo, layout.
Reduce the inductance of the input and output cables slightly by adopting twisted wiring as close to the end capacitors as physically possible.
Place the 3 parallel caps alongside each other. Couple them together with a straight linking wire across the 3 +ve terminals and another straight wire across the 3 -ve terminals. The wiring from cap1 to 2 has a little inductance. The wiring from cap2 to cap3 has a little inductance. Add this inductance to the model.

I would expect the overall LF filtering to be similar to Gootee's first model. I would expect the HF filtering to be markedly improved compared to either of Gootee's models.

I have a 10cap bank for a KSA100. that makes up a +-75mF /channel. The 4 cap to cap links must have some effect.

Further, the effect of the first cap will have less to nothing of an influence on the sound quality coming from the speakers. The last cap in the string will have a greater influence on final sound quality. Effective decoupling at the amplifier and particularly at the output devices and VAS stage may completely dominate the sound quality now that real DC is emanating from the 10cap smoothing bank.
I think that a more accurate model of the smoothing bank will reveal advantages that Gottee's first model misses.
__________________
regards Andrew T.

Last edited by AndrewT; 28th December 2011 at 08:51 AM.
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Old 28th December 2011, 09:25 AM   #318
mjf is offline mjf  Austria
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quote:For board-to-board power supply cabling (for simple boards without planes), I would now have to recommend using something like a ribbon cable, with many conductors, with many alternating V+ and Gnd pairs (if single supply), or many V+/Gnd/V- triples (if dual supply)

here is a foto. it shows a small pa - amp, the psu board (+v 0 -v) is connected with a "ribbon cable" to the poweramp boards (the +-15v are made with res and z-diodes on the preamp board).
Attached Images
File Type: jpg lukas pa.JPG (175.8 KB, 344 views)
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Old 28th December 2011, 10:03 PM   #319
gootee is offline gootee  United States
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Default Do things that would otherwise be impossible (without a multilayer PCB)!

Quote:
Originally Posted by benb View Post
The silence is the sound of the residual noise of your amplifier being powered by this idea.

I think it's just fine, except that it may be getting into overkill range and diminishing returns. How much would an average audio power amplifier actually benefit from a power supply like this?

Maybe a class D amp would significantly benefit from this.
Thanks.

That seems like a pretty difficult question for me to try to answer, for the general case (or for "the average audio power amplifier"). So I'll give it a try.

[Below is what I think, so far, but I do still need to examine the algebra and physics a little more closely to see if there are any major "gotchas".]

Competently using multiple parallel copies of power and ground rails in an audio power amplifier design should be able to result in (at least) lower Distortion and better Stability, plus better Transient Response characteristics. I can't think of any less-than-favorable effects that might occur. "How much better?", you might wish you could ask. It depends! But I'm guessing that it would at least be "significant", as in "not negligible".

You are asking something like the equivalent of, "What are the benefits of having smaller power-rail voltage fluctuations and lower power supply impedance and better decoupling/bypassing?".

The answer, in general, is, "It depends.".

But in at least some cases the benefits would probably seem relatively large compared to the benefits of many of the things to which a lot of diyaudio people devote much time, effort, and money.

For example, do you question why people worry about designing or using super-regulators, or why AndewT uses 75,000 uF (75 mF) of capacitance on each rail? (OK. maybe you do.)

I guess the typical answer is something like, "It might improve the sound.".

Most of the time, the improvement is not quantified, and sometimes its mechanism is not even well-defined or not known at all, and often the question of whether "might improve" actually did or did not improve is never even resolved.

I am trying to (eventually) actually quantify certain things, in this part of this thread. But even if I did eventually post all of the equations that could answer your question(s), the answer(s) would still depend on how (and how well) the techniques were applied, and would depend on in exactly what contexts they were used.

I thought about the possible "overkill" aspects, too. But the improvements in the example I gave seem quite dramatic for what are essentially trivial circuit-layout changes, requiring no additional components in most similar cases (and possibly fewer or cheaper components, in other cases).

So in some cases it might be overkill while in others it would be essential to make them even possible.

But the cost-benefit ratio should usually be favorable, since the cost would typically be low.

And "audiophile" stuff is basically all overkill, anyway, in one way or another, to somebody.

I would probably have to question why one _wouldn't_ use multiple parallel copies of power rail and power ground conductors, rather than why they would.

Its use should have significant good effects for a circuit designer to take advantage of, for most or all new power amplifier and preamplifier designs, and for many digital circuits (and for many other types of circuits).

Anyway, you might want to remember this technique, if/when you start designing decoupling networks mathematically, for example, or if you need the highest performance from decoupling capacitors and/or a power supply.

Without this paralleling technique, it can be literally impossible to hit the needed worst-case target impedance (as seen by the active device power pins) over the entire desired frequency range, even just as is required for relatively-slow devices such as chipamps.

That's probably the type of situation that would cause most commercial PCB layout designers to switch to using a multi-layer PCB with power and ground planes, if they weren't already using them. (But unless they know enough to distribute the power or ground feed through multiple connection points to each plane, for example, and distribute the capacitors in certain ways, then the multiple capacitor currents might still tend to all flow on top of each other, at least part of the time, negating some or all of the ESL reduction from paralleling. And in that case the discrete multi-parallel-conductor method being discussed here could actually be superior (in terms of capacitor and PCB trace ESL reduction), since by its very nature it basically _guarantees_ that parasitic inductances will be reduced by being paralleled, whereas when using planes that would still depend on using a correct layout to prevent the formation of mutual inductances among the parasitics, which wreck the algebra for the reduction that paralleling would otherwise induce.)

BUT, for our simple, cheap, home-made one-sided and two-sided DIY printed circuit boards (PCBs), and even for point-to-point wiring, we can gain at least ONE of the main benefits (of PCB planes) by using multiple parallel copies of power and ground rails, which will enable us to do things that would otherwise be impossible without a mutli-layer circuit board with power and ground planes and surface-mount components.

Well, let me start over and try again to answer your question:

Basically, the benefits are configurable. :-) So everyone's mileage will vary.

It (multi-paralleling) can enable design of a better and/or easier-to-implement bypass and decoupling capacitor configuration, making it much easier and/or cheaper to meet a design target for, for example, (a low) maximum load-induced voltage-rail disturbance amplitude.

It can enable meeting a design target for, for example, a "maximum available instantaneous transient current slew rate", at all, or, with fewer or smaller decoupling capacitors.

It can enable more-easily/cheaply meeting a design target for, for example, (a low) maximum power supply impedance, over a specified frequency band.

In layman's (marketing) terms, "Like magic, it will convert your old dented six-cylinder van into an agile shiny new high-performance race car!". (Vroom! Vroom!) <grin>
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Old 28th December 2011, 10:06 PM   #320
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Any means that force the loopcurrent-induced magnetic flux to travel ALL THE WAY through the smallest possible looparea will reduce inductance, stray and pickup of external fields. Reducing the loop area is the most efficient thing to do. Unluckely most caps are seldom built the way to accomplish that the best possible way.
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