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Old 16th November 2011, 11:54 AM   #181
marce is online now marce  United Kingdom
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This is one reason why all the major PCB design software companies are adding Power Delivery Integrity software to their list of add ons. Went to a seminar on the subject of PDS recently,was very informative. The main conclusion is that decouplers are guesed at and generaly overcompensated for (ie to many of them).
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Old 16th November 2011, 12:20 PM   #182
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Hi, I'll give you results of what I hear (it's the only important thing!) and don't care about the measure!

Parralleling a PSU cap is only good in a CLC or CRC PSU and at its output only: parralleling the input cap will help noise disturbance wich is going out of the rectifiers to cross the PSU and you will hear it!
But in the end after the resistor or better the inductor it will help to open the bandwith in the highs but for the best result you have to use big MKP capacitor about 20 or 22uf is an optimum and there you will hear better highs with more air around. Don't use lilttle values most of the time you'll hear nothing

Have a good day: David
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Old 16th November 2011, 12:36 PM   #183
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by qusp View Post
to simplify the question, given the 100:1 rule is adhered to, is it still best to avoid additional decoupling capacitors on the load line between the regulator and the load; with only minimum output capacitance and let the local decoupling caps do their job? will additional parallel bypass caps add up with the localised caps to trigger unwanted resonance even given the correct ratio using low inductance parts and routing, or will they actually help?
Capacitors are useful at the point of load, where they provide a low impedance return path; placing additional ones at intermediate points is therefore superfluous, and can aggravate resonance problems.
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Old 16th November 2011, 08:36 PM   #184
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A lot of linear power supply PCBs have small film onboard film "decoupling" caps close to the output pins of the board, which is said to improve transient response of the regulators.

Wouldn't these be entirely useless and aggravate resonance problems once run to another amplifier board with (relatively) long wires?

I am thinking that these output bypass should most likely be removed since they wouldn't be doing anything for the load.
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Old 17th November 2011, 02:26 AM   #185
qusp is offline qusp  Australia
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thanks Elvee, probably my specific question would be better illustrated with a picture of the board. i'll try and rustle one up, youve pretty much answered my question though so thanks. i didnt place a heap of different places on the board, just the reference bypass and regulator output caps called for in the datasheet (a polymer and np0, although the DS calls for a slightly higher ESR of ~12mOhm) but i also put optional 1206 size pads at the output pins for each regulator in case i wanted to power something that didnt have its own decoupling and thus would have a cap closer to the point of load. nothing is very far away in this build though, as its contained in a 120mm x 30mm x 90mm area

all devices that are actually on the pcb that need power just have local decoupling and are only 20-30mm from the regulator

Last edited by qusp; 17th November 2011 at 02:31 AM.
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Old 17th November 2011, 07:07 AM   #186
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by nereis View Post
A lot of linear power supply PCBs have small film onboard film "decoupling" caps close to the output pins of the board, which is said to improve transient response of the regulators.

Wouldn't these be entirely useless and aggravate resonance problems once run to another amplifier board with (relatively) long wires?
If there is a substantial wiring downstream they are indeed useless.
If the wiring is clean, with the supply and return wires tied or twisted together, the resistance will dominate and they will be harmless.
If the wiring is cobweb style, as it is advised by some, the effect will be disastrous.


Quote:
I am thinking that these output bypass should most likely be removed since they wouldn't be doing anything for the load.
Indeed, and in addtion they will stress the stability of the regulator.
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Old 17th November 2011, 11:29 AM   #187
marce is online now marce  United Kingdom
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Hi, I'll give you results of what I hear (it's the only important thing!) and don't care about the measure!
Thats a scientific aproach to design and improving audio, hope you dont design real world products.
Both are improtant, measurements being the more important as they give us data and results that are non ambigous, repeatable for diferrent circuitry etc.
I'll go even firther, a power supply is there to create a stable DC voltage, you cant hear DC, its DC... If you can hear your power supply then its a BAD design.

Last edited by marce; 17th November 2011 at 11:31 AM.
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Old 18th November 2011, 03:46 AM   #188
gootee is offline gootee  United States
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Quote:
Originally Posted by qusp View Post
<snipped>

I donmt yet have the skill to provide the desired series R by way of trace resistance

<snipped>
Ah, that's easy:

For simple conductor geometries (e.g. rectangular, circular, or other shapes of cylinders):

R = rho x L / A

where

L is length in meters (m),

A is cross-sectional area in m^2 (square meters, i.e. meters squared),

rho is the Resistivity of the conductor material in Ohm-meters (There are tables, on the web, with the resistivities of lots of different materials). Note that rho will vary with temperature.

At room temperature, rho of copper is 1.7 x 10^-8 Ohm meters.
At room temperature, rho of aluminum is 2.6 x 10^-8 Ohm meters.

From the equation for R, it is obvious that to get a higher resistance you could use a smaller cross-sectional area or a larger length, or change the conductor material. Knowing rho and the length, for example, you would calculate the cross-sectional area needed to give a desired resistance. Then, knowing the copper thickness of your PCB layer, you can calculate the trace-width that would give the desired cross-sectional area and thus the desired resistance for the given length. Alternatively, you could solve for the length and adjust that instead.

You will probably also want to google "trace inductance calculat*".

Cheers,

Tom

Last edited by gootee; 18th November 2011 at 03:53 AM.
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Old 18th November 2011, 05:40 AM   #189
gootee is offline gootee  United States
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Originally Posted by marce View Post
Thats a scientific aproach to design and improving audio, hope you dont design real world products.
Both are improtant, measurements being the more important as they give us data and results that are non ambigous, repeatable for diferrent circuitry etc.
I'll go even firther, a power supply is there to create a stable DC voltage, you cant hear DC, its DC... If you can hear your power supply then its a BAD design.
Well, even though the power supply VOLTAGE is "DC" (actually, we often hope for a "FIXED" DC voltage, i.e. unchanging), the power supply CURRENT should be almost exactly the music signal(!), if the load impedance is a fixed value (no, it's usually not, but my point remains valid).

With that in mind, everyone can see that the primary "signal path" for what you hear from your speakers is the current through the power supply, then through the active power devices in the amplifier, then through the speakers and back through the ground returns to the power supply. It's all about the current. The power supply voltages are only there to enable the current to flow whenever and however commanded/allowed.

At the same time, we can see that the input "signal path" ENDS at the active power amplification devices. It just stops, there! It controls the active power devices (e.g. power transistors, chipamps, etc), which can be thought of as current-modulating "valves", which allow precise currents to be pushed or pulled through them, because of the existence of the power supply voltages.

The signal that actually makes the sound is the large currents that go through the power supply, the active power amplification devices, and the speakers.

So yes, every component in the power supply is in the main sound-signal path, and could possibly affect the sound quality even more-directly than the components in the input "signal path".

And I'll go further: (This is just one of my "pet peeves" but I'm "on a roll", now: ) Forget the myth that shunt components are "not in the signal path" like series components are. That's simplistic nonsense.

Sorry to have blathered-on about all of that, for so long!

Cheers,

Tom

Last edited by gootee; 18th November 2011 at 05:51 AM.
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Old 18th November 2011, 10:04 AM   #190
AndrewT is online now AndrewT  Scotland
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Quote:
Originally Posted by gootee View Post
L is length in meters (m), A is cross-sectional area in m^2 (square meters, i.e. meters squared),
Quote:
Originally Posted by gootee View Post
..................everyone can see that the primary "signal path" for what you hear from your speakers is the current through the power supply, then through the active power devices in the amplifier, then through the speakers and back through the ground returns to the power supply. It's all about the current. The power supply voltages are only there to enable the current to flow whenever and however commanded/allowed. At the same time, we can see that the input "signal path" ENDS at the active power amplification devices. It just stops, there!
Sorry Tom, we usually agree on everything, but here I draw a line.
metre is a unit of Length. eg. kilometre is 1000 metres.
meter is an instrument that measures an effect. eg, voltmeter measures voltage.

Input signal does not just stop !!! The input signal circuit has the same rules as all other circuits. Where your power current circuit example listed the route out (flow) and back (return) to the power supply, she source similarly has a flow route and a return route. For current to flow in the signal circuit there must be a return route. This is usually the signal ground. Current must return all the way back to the source.

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Last edited by AndrewT; 18th November 2011 at 10:10 AM.
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