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Old 10th January 2013, 01:09 PM   #41
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Not that it matters but series should halve the both effective temperature and voltage coefficients whereas parallel will only halve the temperature coefficient (assuming the coefficients are somewhat matched, and I'm referring to self heating effects not absolute temperature which parallel connections wont halve).
Inductance will increase with series connections (but I dont think that matters either) so again your left having to choose which "problem" you think needs the most fixing.

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Old 10th January 2013, 03:16 PM   #42
GoatGuy is offline GoatGuy  United States
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Quote:
Originally Posted by Robert Kesh View Post
10% was just an example.

CLT is for the arithmetic mean of many samples, and so works for their sum too, which is why it works for series resistors, hence the 1/sqrt(2) in my first post on this, sd will reduced by a factor of 1/sqrt(n) for n similar resistors.

Paralleling resistors is related to the harmonic mean. I am not convinced it gives a similar result to the CLT. Though I confess I did the numbers when I was very tired.
Did the Monte Carlo version of the analysis (ab initio, theory-wise)... using bounded-normal distribution for 400 resistor values in a 10% range, where variance of columns 1 thru 4 were 8.5%, 11.5%, 9.2%, 10.3% (i.e. about right for 10% variance), and then used the values 3 ways: geometric mean [(a*b*c*d)^(0.25)], additive (sum(a:d)) and parallel resistor formula [1/(1/a+1/b+1/c+1/d)], and took the standard deviation divided by mean of those columns... 5.1%, 5.2%, 4.9% respectively.

Point is... the standard deviation of values becomes smaller, whether resistors are placed in series, or in parallel. The curious thing (which not being much of a statistician, is probably not curious at all!) is that it doesn't matter whether the values are series, parallel, or "geometric mean" averaged, it all works out the same. Net precision increase.

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Old 10th January 2013, 03:30 PM   #43
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I think its great to see these Snake Oil vendors trying to steal your money.

Have a look at 95% of all the High End makes out there. I haven't found a single one that employs this twaddle.
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Old 10th January 2013, 03:42 PM   #44
GoatGuy is offline GoatGuy  United States
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Quote:
Originally Posted by KatieandDad View Post
I think its great to see these Snake Oil vendors trying to steal your money.

Have a look at 95% of all the High End makes out there. I haven't found a single one that employs this twaddle.
Oh, by no means am I suggesting that one SHOULD employ a pair (or trio, or quartet, etc) of resistors, especially in a reversed-polarity (for laser-cut spiral thin-film). The discussion has become more of an analysis of the EFFECT of placing multiple resistors in series/parallel, and to whether there is any benefits that aren't "twaddle".

The simple answer is yes. There are benefits.

I was particularly amused (and tweaked my learning curve) on hearing that the inductance, if anything significant, would actually be a benefit in pushing UP the high-frequency response of the stage. Maybe just enough to counter Miller capacitance negative-feedback from plate-to-grid, without using a cascode stage? That'd be nice. But again, not likely ...

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Old 10th January 2013, 04:27 PM   #45
DF96 is online now DF96  England
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You would need a lot of inductance in a small resistor to affect audio HF. In most valve circuits the stray capacitance is more likely to be an issue - but even then a very tiny issue.

I am always amused when 'high end' people 'discover' some effect which is entirely irrelevant and promote it as a 'must have', while at the same time ignoring quite basic design errors in some of their circuits.

"It doesn't matter what resistor value you use (as I don't know how to calculate them anyway) but make sure you use a parallel pair of MingFord resistors and Bayshag capacitors. To do otherwise shows that you are entirely deaf and/or poor."
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Old 10th January 2013, 05:00 PM   #46
GoatGuy is offline GoatGuy  United States
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LOL, DF96 ... I love it.

Personally, I think the same thing about builders/users of massively overcompensated audio systems [from needle to tweeter] who on every occasion wax eloquent about the "increased detail of the sound-stage" and "degree of precision that, to my ear, sounded as if there were no 'system' at all".

All of which is a load of horsephlegm. EVERY speaker system is a massive box of coloration. EVERY microphone and/or pickup used to record the original stuff ... is a coloration device. EVERY wiggle of vinyl gradually wears down, coloring the signal further. We're just incredibly lucky that our ears do such a good job converting the time-domain to the frequency-domain, with such disregard for phase precision (all the audiophiles by this time are getting their hackles up).

And yes - the "MingFord + BayShag" R:C combo {paraphrased} is the epitome of the mania. Thanks for the humor.

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Old 21st January 2013, 06:00 PM   #47
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Quote:
Originally Posted by regiregi22 View Post
Thank you guys, that's what I thought but wanted to confirm with you for a second opinion.

Best regards!
Sorry OT, regiregi22 your pm box is full.
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Old 21st January 2013, 11:57 PM   #48
ilimzn is offline ilimzn  Croatia
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Quote:
Originally Posted by DF96 View Post
You would need a lot of inductance in a small resistor to affect audio HF. In most valve circuits the stray capacitance is more likely to be an issue - but even then a very tiny issue.

I am always amused when 'high end' people 'discover' some effect which is entirely irrelevant and promote it as a 'must have', while at the same time ignoring quite basic design errors in some of their circuits.
Sadly, this tends to apply to the aforementioned author, and I knew exactly which one it was as soon as I saw the title of the thread. For example, one of the designs waxes poetic abut using speciffic tyoes of resistors but COMPLETELY fails to address thermal stability of a MOSFET design. Problems arising from that will easily overwhelm any 'effect' of said resitor by, oh, say, 100dB or so... and I know I'll get a 'I built it and it works' from someone, somewhere. Well, consider yourself lucky, it could just as well have burnt down your house, so why not just keep it working and wait for it.
Not to mention that 'I was told this trick by a high-end audio designer' is abut as good a technical argument as 'it's written in the holly book'. I have had experiences with at least two very well known and established Italian high-end companies (and therefore their designers) which lead me to think they would have been better off playing cards or drinking coffee for a living.
Fortunately there are others that are excellent at their job, even if not as well known and established.

Quote:
"It doesn't matter what resistor value you use (as I don't know how to calculate them anyway) but make sure you use a parallel pair of MingFord resistors and Bayshag capacitors. To do otherwise shows that you are entirely deaf and/or poor."


Anyway, to the subject:
Two film equal resitors in parallel closely mechanically located (also in parallel) will have SLIGHTLY less inductance than half of each resitor, due to magnetic field coupling. Two in series also mechanically in series, will have SLIGHTLY more than double. Someone mentioned that a typical resitor has very little added inductance due to it's helical cut film, compared to a straight cut or 'wire'. This in fact is usually insignificant compared to the inductance that happens by bending the wires to mount a resitor into a through-hole PCB - the leads and resistor make half a winding. Even that can be insignifficant if the resitor has ferromagnetic parts (and some do!) like leads or endcaps. In other words unless you really screw up by using a badly constructed part, any benefit you hope to gain by this 'trick' will likely be undome by a huge factor by other more important concerns such as mechanical positioning in relation to other parts (possibly ferromagnetic), routing, etc. Unfortunately, we can be sure to get this question again, soon enough (this sort of meme is so hard to kill...), hopefully not as often as 'can I replace lateral MOSFETs with HEXFETS'
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Old 22nd January 2013, 02:31 AM   #49
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Quote:
Originally Posted by regiregi22 View Post
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.
It's nonsense. The only reason to put resistors in parallel is to increase the power handling capability. It doesn't cancel any inductance because the coefficient of coupling will be well below 100%. Modern metal film resistors aren't that inductive, and the few extra nanohenries that might make a difference at 400MHz aren't going to make any difference at 400Hz.

All this will do is double the expense for resistors for your project.
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Old 22nd January 2013, 07:13 AM   #50
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For using the output transformer at a lower Z; Quads in the 1960's did exactly this to cancel some transformer induced harmonics. Rest of the inductance created by resistors is peanuts at the standard audio level is complete sales flannel.
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