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regiregi22 26th December 2012 08:36 AM

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

Best regards

KatieandDad 26th December 2012 08:57 AM

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.

Robert Kesh 26th December 2012 10:13 AM

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.

regiregi22 26th December 2012 10:14 AM

That's what I thought, we are talking about audio frecuencies...

Yvesm 26th December 2012 10:21 AM

. . . 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.

yagoolar 26th December 2012 12:14 PM

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.

12E1 26th December 2012 12:39 PM

Quote:

Originally Posted by Yvesm (Post 3299338)
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.

regiregi22 30th December 2012 01:31 PM

Thank you guys, that's what I thought but wanted to confirm with you for a second opinion.

Best regards!

oshifis 30th December 2012 02:25 PM

Don't remove the glass bulb like depicted on the circuit diagram. Vacuum evaporates quickly ;)

audiodesign 6th January 2013 09:16 PM

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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