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Old 26th December 2012, 07:36 AM   #1
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Default Pairs of resistors in opposite directions

Hello,
I am just about to start building this amplifier. The circuit calls for using pairs of resistors in opposite polarities (If we could call it polarity being a resistor), from what I've read that may reduce/cancel inductance. I have never done that in any of my previous amplifier designs, and neither seems to be a common practice. Is that really necessary or did the designer done that the same way he could have used silver wire or isolation feet?
Does it really make a difference to make it worth it to implement that way?

PP2012 - KT88 Hi-End Push Pull Amplifier

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Last edited by regiregi22; 12th January 2013 at 08:46 PM.
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Old 26th December 2012, 07:57 AM   #2
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Complete snake oil.

All the resistors shown in parallel are available in film type which are completely non-inductive. Even wire-wound resistors have so little inductance that at audio frequencies the inductance is irrelevant.

Last edited by KatieandDad; 26th December 2012 at 08:00 AM.
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Old 26th December 2012, 09:13 AM   #3
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turning a winding the other way around does not reverse the winding's orientation.

to reverse a winding's magnetic field you either have to mirror image the winding or reverse the current.

doubling resistors is a good way to have twice the wattage though. perhaps they are doing that. i'm too tired to read the article closely.

Last edited by Robert Kesh; 26th December 2012 at 09:16 AM.
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Old 26th December 2012, 09:14 AM   #4
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That's what I thought, we are talking about audio frecuencies...
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Old 26th December 2012, 09:21 AM   #5
Yvesm is offline Yvesm  France
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. . . and there is NO guaranty that marking orientation has something to do with an improbable building assymetry . . .
I mean, how many operations beetween the metalisation and the marking processes and how many times the resistor "could have" been flipped ?

But yes, if they are inductive, putting two of them in parallel will halve the inductance this does not mean the 2 * 100K becomes less inductive than a single 50K was.
Anyway, the capacitance is always doubled

Yves.
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Old 26th December 2012, 11:14 AM   #6
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Andrea Ciuffoli is a member of the Forum, so he is the best person to answer your question.

Second thought.
You have 2 identical coils in parallel. (resistors). If you rotate one coil 180 degrees (as on the photo) you simply get the same circuit! To cancel magnetic field one coil should be wound clockwise and the other - anticlockwise.

I think leads inductance has greater effect than resistor ones.

Last edited by yagoolar; 26th December 2012 at 11:36 AM.
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Old 26th December 2012, 11:39 AM   #7
12E1 is offline 12E1  United Kingdom
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Quote:
Originally Posted by Yvesm View Post
I mean, how many operations beetween the metalisation and the marking processes and how many times the resistor "could have" been flipped ?
As already pointed out, flipping a helical coil end to end does nothing to change the coil's twist. So even if where is a magnetic property of such a resistor, it is not reversed by flipping the device end to end. You would literally have to unwind the coil and rewind with the opposite twist it to create the opposite magnetic effect - and that is not practical or possible unless you want to start winding your own resistors.
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Old 30th December 2012, 12:31 PM   #8
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Thank you guys, that's what I thought but wanted to confirm with you for a second opinion.

Best regards!
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Old 30th December 2012, 01:25 PM   #9
oshifis is offline oshifis  Hungary
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Don't remove the glass bulb like depicted on the circuit diagram. Vacuum evaporates quickly
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Old 6th January 2013, 08:16 PM   #10
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Both Yagoolar and Yvesm have given the two answer.

The my reference as resistor is a Caddock MK132.

Using a normal 1% metal film resistors and this solution you have the same sound of a MK132 Caddock.

I learned this trick 15 years ago by the owner of a famous company that makes high-end amplifiers.

He uses the same technique also on the capacitors.
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