Yes I have read his ariticles in headwize and those in his own site.

And yes Andrea does recommend various brands of resistors on his other designs. BUT not on the amp I linked.

your opinion vs andrea's opinion in relation to audio DIY...

let us not forget that the recommendation was for "paralleled resistors"

Quote:



The recommendation in question is to situate the parallel resistors in opposite directions in reference to the printed labels. The construction of a resistor should be symmetrical, as opposed to say an electrolytic capacitor which has a decided difference in its construction between the two leads. Even if there is a slight, systematic, and reproducible difference in the construction as seen from each lead, I doubt that the printing of the label on the resistor is done consistently in regards to this directionality.

The idea of putting them in parallel to reduce inductance is a sound idea. All linear circuit elements in real life will have minute parasitic capacitances or inductances. Putting capacitance in series reduces the total capacitance. Placing inductors in parallel reduces inductance (provided that the mutual inductance between the two inductors is not significant in regards to their respective self-inductance, which is a very reasonable assumption here). Resistors are generally inductive because of how they are constructed. For example, they can be long resistive wire loops which lend towards inductive parasitics. For the most part though, with audio frequencies, the frequency is so low that the impact of the parasitics should be fairly insignificant. But there is no harm in using these tricks. Nothing wrong with going that extra mile.

EDIT: Actually, there is another practical reason why you may want to do the parallelized resistors given that you can replace them with a single resistor of equivalent value. By using two resistors in parallel, the error in your final resistance value will be less than the error in the individual resistors provided that the two resistors are the same. Working it out real quickly, if the error in resistor 1 is E1 and the error in resistor 2 is E2, then the total error will be (1/E1+1/E2)^{-1}. So if you have a positive 10% error in your value for both resistors where both of them are supposed to be the same resistance, then the resulting error in your parallel configuration will be a positive 5%.

Quote:



But how does that make it directional ?

It was my understanding two resistors in series will give the same resistance in whatever orientation and order. Same I'd imagine goes for a single flawed resistor. Overall it still provides a resistance that isn't directional. A less resistive side as far as I can imagine would only put the resistor slightly out of spec.

If the order and orientation of those resistors make a difference I stand corrected.

here's a thread I created in diyaudio:

http://www.diyaudio.com/forums/showt...threadid=84819

more mature discussion IMO (not to say that every discussion there is mature)

C'mon guys!

I don't like how everyone dispels snake oil like it doesn't do anything!

Quote:



And what do you know, they are saying the same things. Parallel resistors will reduce the total inductance in comparison to a single resistor (ignoring the added inductance of the additional traces). However, this introduces mutual inductance in addition to their self-inductance. But since the magnetic moment of the resistors are the same in either orientation, reversing the resistors has no effect on this. But we can make the safe assumption that the mutual inductance is negligible. In addition, there is no way to assume that the resistors are banded in a consistent orientation at the factory.

Quote:



Take it a step further.... if the manufacturers had a reason to make it consistent they would talk about it in their datasheets. It is probably a safe assumption that if they don't have a specific reason to maintain the orientation then if they do it is an accident of the specific manufacturing process. That could change with the next tweak or upgrade to the process.

I find it amusing that someone would put something in a schematic such as polarized resistors without a very complete explanation. Kind of goes along with the old saying "extraordinary claims require extraordinary evidence".

Quote:



Other than making people sick if consumed.

Reducing whatever inductance exists in a resistor by paralleling two of them works because a paralleled pair of identical inductors will reduce the inductance by half (which I think is what born2bwire is trying to explain). Assuming the inductance of the two resistors is indentical, their combined inductance would then be halved.

There's nothing really mentioned about directionality in Andrea's article from what I can see. He marks the "orientation" of the resistors with the dot, but there's no explanation as to why, other than trying to reduce the inductance of the metal oxide resistors in his circuit. I have no idea how this has anything to do on the discussion of whether or not resistors are directional.

My thought on it is similar to Neil's: If directionality in resistors actually existed and affected anything in a circuit, the manufacturers would spec it in the resistor's datasheet. We also would have probably heard about what circuits could be affected by said directionality.

I always put resistors in with the bands describing the first value "up" because it looks so cool... you guys should try snake oil on west indian manatee... it really softens up those endangered aquatic speedbump tags.

As do I, Vixr.. I generally try to make the look of the amp consistent for purely aesthetic reasons (i.e. bending the pins on the vishay/dale resistors so that you can read their value, and the text is oriented in the same direction on all parallel resistors).t

I'd recommend finding out for youself. Take your DMM and measure the resistor in both directions. If the value is the same on both readings, it's not directional. I've done this now and then... still have yet to find a "directional" resistor.

...........................

Quote:



You have the right idea here, but the explanation could use some additional info. It's possible that 2 resistors in parallel will achieve a final resistance closer to the desired value, but the errors need to cancel out each other. That is, one resistor having a higher reading, and the other having a lower reading. If they are both higher, or lower, then the total resistance can still be off as much as a single resistor. Here's the math --

Desired resistance - 50 ohms

Circuit 1: 100 ohm (measures 110 ohms) & 100 ohm (measures 110 ohms) in parallel = 55 ohms. Resistors off by 10%, circuit off by 10% also.

Circuit 2: 100 ohm (measures 110 ohms) & 100 ohm (measures 90 ohms) in parallel = 50 ohms. Resistors off by 10%, circuit achieves desired resistance because the offsetting differences cancel each other out.

As for resistors being polarity sensitive, I haven't seen one yet.