Negative Effects of external power supply? - diyAudio
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Old 30th May 2007, 06:30 PM   #1
pjpoes is offline pjpoes  United States
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Default Negative Effects of external power supply?

I designed a very over the top CLC power supply for my HT amp project. I was messing around with layout the other day, and given the chassis I have, feel that an external power supply is necassary. As is the power supply is huge, each channel taking up most of an 8" by 19" by 10" chassis. Having decided that for now I don't want three massive chassis in my house, I am scaling back the power supply to be two squeezed into the same box with slightly less capacitance. I was starting to think about mounting the second set of capacitors in the main amp chassis, but wondered if it added any benefit. When thinking about how it might react with the power supply, I realized it would be like having very low value resistors in series between the inductor and second set of capacitors. My first thought is that it would increase ripple, but then I remembered not if its in series.

To Model this, should I try and increase the inductors resistance the amount the wire adds, and see how that effects things? I plan on using a shielded chord I will make for this purpose, so hopefully picking up noise won't be an issue. Also, it will only be at most 2-3 feet long. More than likely less than that, I'm shooting for 1.5 feet. I'm also going to use either XLR or Powercon connectors, depending on how cheap I can get the powercons.

Any thoughts here would be appreciated. I now know why manufacturers don't build better power supplies into their amps, packaging and cost. I also can now tell why some of the really big amps from big name companies get to be as big and expensive as they do. Anyway, I have thought about paralleling some smaller value caps with the 22mf caps, such as say some 600uf and 47uf's of higher quality, like Panasonic FC's. I even thought about going as large as 1500uf or so. They deal with higher frequencies better, lower the esr some, and charge faster.
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Old 30th May 2007, 09:39 PM   #2
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Old 31st May 2007, 12:26 AM   #3
pjpoes is offline pjpoes  United States
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That was very useful, looks like there is a preferance to having the second stage of capacitance in with the power amps themselve's and not in the power supply case. I thought it might be a good way to go. Since I need to have the voltage increase of a CLC over an LC, I will go with just two capacitors in the power supply case, and the rest will be in the power amp case. Thank you.

Can anyone comment on any potential problems having a long power cord between the inductor and capacitor can cause. My only thoughts is that it could create its own capacitance, inductance, and resistance. Resistance and Inductance in series is a good thing, and I think the capacitance will be a minor issue. I think it all will be a minor issue, but was curious.
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Old 31st May 2007, 07:01 AM   #4
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Quote:
Originally posted by pjpoes

Can anyone comment on any potential problems having a long power cord between the inductor and capacitor can cause. My only thoughts is that it could create its own capacitance, inductance, and resistance. Resistance and Inductance in series is a good thing, and I think the capacitance will be a minor issue. I think it all will be a minor issue, but was curious.
The PSU resistance and capacitance should be a non issue if you use reasonable cable. You live in NYC, a terrible RF environment, so you might want to shield the cable to keep over-the-air RF crud from getting into the power supply lines.
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Old 31st May 2007, 08:35 AM   #5
AndrewT is offline AndrewT  Scotland
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Hi,
RCRC and RCLC are very good at keeping mains ripple at a low level.
A split supply/amplifier should work just as well and maybe better than an integrated, if the downsides are avoided.

The first R is the resistance/impedance of the transformer and the first stage cabling/connectors.
The first C is the smoothing cap just after the rectifier.
The second R/L is the cabling/added resistor between first stage smoothing and second stage capacitors.
The final C is the main capacitance that meets peak current demand into the amplifier.

I believe that the first RC should be in the PSU box and that the C MUST be selected to survive the very high ripple current that this system imposes.
The last C MUST be next to the amplifier, otherwise the inductance of the connecting cables will ruin the high frequency performance of the amplifier. The last C MUST also be scaled to allow all intended signals to be reproduced properly. That means big and fast (some builders will not agree with my big requirement).

The middle R can be an added R or just the resistance of the connecting cables. If there is significant inductance in the connecting cables then it simply changes the single pole filter to a two pole filter and helps attenuate the mains ripple. This additional two pole effect allows a lower R value. This philosophy will allow smaller diameter cables to be used that have a significant spacing between the conductors. One may find that added resistance is of little benefit if the cables length and diameter are optimised with the selected capacitor values.

Any conductor to conductor capacitance will act as a very small high frequency cap from line to ground or line to line. This is a benefit, not a downside. It helps attenuate very high frequency spikes coming into the PSU. It should not be considered as
Quote:
capacitance should be a non issue
it is very much an issue without any downsides.
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Old 31st May 2007, 09:48 AM   #6
nikwal is offline nikwal  Sweden
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Hmmm when I read this, suddenly I think it was worth it using 4 vicor modules in my amp, they work very nicely..
( Just a tip, keep lookout for vicor dcdc on for example ebay, sometimes it happens the corrent voltage drops by for a reasonable price)..
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Old 31st May 2007, 11:30 AM   #7
flg is offline flg  United States
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My concern with the remote supply arrangement would be the grounding
Would a power gnd and a signal gnd be wired back to the remote supply seperately to a central point
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Old 31st May 2007, 11:37 AM   #8
pjpoes is offline pjpoes  United States
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I intended to ground the signal ground all to one star point in the amp chassis. The Mains ground will connect to a star point in the amp chassis, and then back to the power supply as well. I also thought about having the Signal ground connect back to the mains via a resistor. Grounding is something I will come to when things are more together.
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