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Old 30th March 2004, 06:44 PM   #1
PsykoK is offline PsykoK  France
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Default Bias Resistor for AX

I search some good 0.33R 3W resistor to build an AX.
I found this:
http://www.caddock.com/Online_catalo...000_Series.pdf
www.distrelec.ch ref: 721705 or 720703

What do you think about these parts?
With 1% tolerance must I match them?

Tanks in advance.

Alex
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Old 30th March 2004, 06:49 PM   #2
jwb is offline jwb  United States
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Seems like a very nice resistor. I wouldn't bother matching them at 1% quoted tolerance.

Personally, I just used four 1.3Ω 1W BC Components metal film resistors in parallel to get 0.33Ω. Only costs US$0.34.
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Old 31st March 2004, 05:08 PM   #3
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Default Parrallel Resistors

In my AX, I needed .4ohms. In order to do that I found .82 ohm 2watt MOX resistors. Used two per device. Since they were 5% tol, I measured them.

What was interesting was looking at the actual tolerence. Out of 200 resistors, only 4 were over 1% deviation. Infact the general population of the the groups was better than 0.5%. This supports not needing to measure 1% tol resistors. Of course we are DIY, why not measure them.

I used a method I saw on the forum of attaching 10 in series and passing 1 amp of current through them. The voltage drop across each device is equiv to the resistance in ohms. I was able to measure all of them in about 4 hours.

By selecting the resistors to use, the effective tolerence for the resistors is theoretically 0.01%. In reality, I think my meter has more error than that.

I did a similar thing for the current sense resistors and the ground resistors as seen in the photo

Scott
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Old 31st March 2004, 05:40 PM   #4
jwb is offline jwb  United States
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I love the half-circle terminals you built on those capacitors. Bravo.
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Old 31st March 2004, 05:59 PM   #5
PsykoK is offline PsykoK  France
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SGregory> Nice work!
Thanks for your information!


Alex
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Old 31st March 2004, 06:10 PM   #6
jam is offline jam  United States
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Scott,

I like the way your construction looks. How about more close up photographs.

Regards,
Jam
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