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Old 28th January 2006, 09:40 AM   #11
AndrewT is offline AndrewT  Scotland
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Hi Bora,
that piggy back layout on the unetched board looks really clever.
Well done.
It's one I may copy, since I bought 1000 1r0 some months ago but put off using them due to board space issues.

Does the back to back layout help cancel the small inductance?
Is it the parallel combination that reduces the small inductance?
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Old 28th January 2006, 12:51 PM   #12
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Hi AndrewT,

>Does the back to back layout help cancel the small inductance?<
No, they are positioned that way mostly for saving space. In most cases this arrangement occupy less space than standard single resistor of comparable wattage.
>Is it the parallel combination that reduces the small inductance?<
Exactly! As you know, inductances are behaving like resistors for that matter, hence 10 equal inductances in parallel results in total inductance of 1/10 of any single one. Good quality MF 1% resistors already have very low inductance and with this arrangement total will be 10 times lower! I tried many times to compare this arrangement with commercial Hi-End resistors, but neither instruments nor my ears were able to detect any difference in amplifier performances or characteristics worth mentioning (and spending money).
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Old 28th January 2006, 01:53 PM   #13
AndrewT is offline AndrewT  Scotland
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Thanks Bora
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Old 28th January 2006, 02:18 PM   #14
anatech is offline anatech  Canada
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Hi Bora,
This arrangement would also cure the very positive temperature coefficient I have measured in many low value resistors. Another problem solved.

-Chris
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Old 29th January 2006, 04:20 AM   #15
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Quote:
What would be a good choice for emitter resistors in a 50W-100W design?
Kind has been discussed.

As to value 0.1 to 0.47 was suggested - somewhere else on this forum this was discussed (good reading, sorry I do not have the link at my finger tips) and John Curl suggested a voltage of 15 to 25 mV (better double check that number) across the resistor and various references to why (Gilbert I think and Doug Self and others if memory serves, Blomley (sp?) maybe). So rather than ask with a power we should be asking what bias current you will be using, or pick a R value and then set the current.

This value will give the best linearity in a class ab design, use a bigger resistor with more voltage drop and it should give you better temperature stability all other things being equal - but go for the linearity.

Bill
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Old 29th January 2006, 05:28 AM   #16
lineup is offline lineup  Sweden
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My choice of emitter resistors.

I do not want more drop than like 0.6-0.7 Volt at maximal Current output.
This has advantage you can easily put a Current limit,
that is activated at 0.6-0.7 Volt drop across this resistor.
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