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Old 24th March 2014, 04:22 PM   #1
alibear is offline alibear  United Kingdom
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Default CRC Filter resistors

Hi all, could you please tell me the reason why the resistance in a CRC supply is usually made by putting resistors in parallel and not just using one resistor. The Pass type of supply seems to use 4 x 0.47 ohm. Could this be substituted for a 0.1ohm of a higher wattage, or are there other reasons why parallel resistors are better.
Thanks for your help
Alan
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Old 24th March 2014, 04:33 PM   #2
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Yes, you can use a single resistor of higher, it's just a matter of watts. The
parallel resistors are just handy and usually cheaper.

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Old 24th March 2014, 04:35 PM   #3
Zen Mod is offline Zen Mod  Serbia
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-wattage
-stock
-temperature spread

just few reasons

edit - Pa was faster
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Old 24th March 2014, 05:05 PM   #4
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Quote:
Originally Posted by Nelson Pass View Post
Yes, you can use a single resistor of higher, it's just a matter of watts. The
parallel resistors are just handy and usually cheaper.

I see time at the beach did well by you.
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Old 24th March 2014, 05:27 PM   #5
alibear is offline alibear  United Kingdom
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Thanks for your replies, much appreciated. Forgive me for being so stupid, I have been doing some calculations regarding the wattage of the resistor and I have as follows:
1.5 amp current draw ( bias current ) through a 0.1 ohm resistor gives a volts drop of 0.15V and a power dissipation of 0.225W Where have I gone wrong please?
Alan
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Old 24th March 2014, 05:40 PM   #6
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and if this is a push-pull amp driving 2ohm you have a peak current of 12A. Thats a voltage drop of 1.2V, wich means 14.4W. And then there is charging of the caps.

Last edited by AudioSan; 24th March 2014 at 05:43 PM.
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Old 24th March 2014, 06:55 PM   #7
alibear is offline alibear  United Kingdom
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Thanks for the help, I now understand
Alan
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Old 24th March 2014, 11:45 PM   #8
ZUM911 is offline ZUM911  Australia
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Follow on from this, can you use an umbilical lead as the resistance in the CRC? I plan to build a power supply in a separate enclosure to power my growing stable of FW clones and I'm thinking that a lead of about a meter or so from the power supply to the amp. I will have capacitor banks in both enclosures.
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Old 25th March 2014, 12:44 AM   #9
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yup
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Old 25th March 2014, 10:48 AM   #10
AndrewT is offline AndrewT  Scotland
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yup

Just watch the AVERAGE current, because that is where the main heating (softened insulation) of the umbilical will come from. P=IČR
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